CBSE Class 10

HOTS Questions for Class 10 Science Chapter 2 Acids, Bases and Salts

These Solutions are part of HOTS Questions for Class 10 Science. Here we have given HOTS Questions for Class 10 Science Chapter 2 Acids, Bases and Salts

Question 1.
A student working in the laboratory added some water to a syrupy liquid taken in a tube. The tube immediately cracked and the liquid which escaped out of it, produced blisters on the skin of the student. What actually happened ?
Answer:
The syrupy liquid in the tube was concentrated sulphuric acid. Since it has great affinity for water, the energy released was in the form of heat. That is why the tube cracked and the vapours of the escaping acid produced blisters on the skin.

More Resources

• HOTS Questions for Class 10 Science
• NCERT Solutions for Class 10 Science
• Value Based Questions in Science for Class 10
• NCERT Exemplar Solutions for Class 10 Science
• Previous Year Question Papers for CBSE Class 10 Science

Question 2.
A baker found that the cake prepared by him is hard and small in size. Which ingredient has he forgotten to add that would have made the cake fluffy ? Give reason.
Answer:
The baker has forgotten to add baking powder while making the dough for the cake. Actually, sodium hydrogen carbonate present in baking powder releases carbon dioxide on baking. The bubbles of the gas evolved leave behind pores which make the cake soft and fluffy.

Question 3.
A substance X is used as a building material and is insoluble in water. When reacted with dilute HCl, it produces a gas which turns lime water milky. Predict the substance. Write the chemical equations involved.
Answer:
The substance is probably calcium carbonate (CaCO₃). also called lime stone or marble. It is used as a building material. On reacting with dilute HCl, it evolves CO₂ gas which turns lime water milky.

Question 4.
Dry pellets of base ‘X’ when kept in open absorb moisture and turn sticky. The compound is also formed by chlor-alkali process. Write chemical name and formula of X. Describe chlor-alkali process with balanced chemical equation. Name the type of reaction that occurs when X is treated with dilute hydrochloric acid. Write the chemical equation. While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid ?
Answer:
The base ‘X’ is NaOH. It is of deliquescent nature and absorbs moisture from air and becomes wet. It is manufactured by chlor-alkali process.  The reaction of NaOH with dilute HCl is known as neutralisation reaction.

Pure HCl is highly concentrated. In case, it is to be diluted, the acid should be added drop-by-drop to water taken in a glass beaker with constant stirring. Actually, the acid has a strong affinity for water and the process of dissolution is highly exothermic. If water is added to acid so much heat is evolved that the glass beaker is likely to crack and the acid will spill.

Question 5.
What will you observe when :

1. Red litmus paper is introduced into a solution of sodium carbonate.
2. A methyl orange drop is added to dilute hydrochloric acid.
3. A drop of phenolphthalein is added to the solution of lime water.
4. Blue litmus is introduced into a solution of ferric chloride.

Answer:

1. The colour of the litmus paper will change to blue. Sodium carbonate (Na₂CO₃) dissolves in water to form sodium hydroxide and carbonic acid (H₂O and CO₂). The solution is of basic nature since sodium hydroxide is a strong bases and carbonic acid is a weak acid.
   
2. In the acidic solution, the colour of methyl orange will change to reddish.
3. Lime water contains traces of calcium hydroxide, Ca(OH)₂. It is therefore, basic in nature. The colour of phenolphthalein will become pink.
4. Ferric chloride (FeCl₃) solution on reacting with water will form ferric hydroxide and hydrochloric acid. Since the acid is strong, the solution will be acidic. Therefore, the colour of blue litmus will change to red.
   

Hope given HOTS Questions for Class 10 Science Chapter 2 Acids, Bases and Salts are helpful to complete your science homework.

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NCERT Exemplar Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations

These Solutions are part of NCERT Exemplar Solutions for Class 10 Science. Here we have given NCERT Exemplar Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations

NCERT Exemplar Solutions for Class 10 Science Chapter 1 Multiple Choice Questions

Question 1.
Which of the following is not a physical change ?
(a) Boiling of water to give water vapours
(b) Melting of ice to give water
(c) Dissolution of salt in water
(d) Combustion of Liquefied Petroleum Gas (LPG)
Answer:
(d). LPG is a mixture of gases like propane (C₃Hg) and butane (C₄H₁₀) in liquefied form. These are chemical substances and undergo combustion upon heating with air or oxygen. It is therefore, a chemical change.

More Resources

• NCERT Exemplar Solutions for Class 10 Science
• NCERT Solutions for Class 10 Science
• Value Based Questions in Science for Class 10
• HOTS Questions for Class 10 Science
• Previous Year Question Papers for CBSE Class 10 Science

Question 2.
The following reaction is an example of a
4NH₃(g) + SO₂(g) ————-> 4NO(g) + 6H₂O(g)
(i) displacement reaction
(ii) combustion reaction
(iii) redox reaction
(iv) neutralisation reaction
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (ii)
(d) (iii) and (iv)
Answer:
(c). Oxygen has displaced hydrogen from NH₃. It is also a combustion reaction.

Question 3.
Which of the following statements about the given reaction are correct ?
3Fe(s) + 4H₂O(g) ———-> Fe₃O₄(s) + 4H₂(g)
(i) Iron metal is getting oxidised
(ii) Water is getting reduced
(iii) Water is acting as reducing agent
(iv) Water is acting as oxidising agent
(a) (i), (ii) and (iii)
(b) (iii) and (iv)
(c) (i), (ii) and (iv)
(d) (ii) and (iv).
Answer:
(c). Statements (i), (ii) and (iv) are all correct.

Question 4.
Which of the following are exothermic processes ?
(i) Reaction of water with quick lime
(ii) Dilution of an acid
(iii) Evaporation of water
(iv) Sublimation of camphor (crystals)
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (iii) and (iv)
Answer:
(a).
(i) Reaction of quick lime with ; water and (ii) dilution of an acid are both exothermic processes. The other two processes (iii) and (iv) are of endothermic nature.

Question 5.
Three beakers labelled as A, B and C each containing 25 mL of water were taken. A small amount of NaOH, anhydrous CuS04 and NaCl were added to the beakers A, B and C respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas in case of beaker C, the temperature of the solution fell. Which one of the following statement(s) is(are) correct ?
(i) In beakers A and B, exothermic process has occurred.
(ii) In beakers A and B, endothermic process has occurred.
(iii) In beaker C exothermic process has occurred.
(iv) In beaker C endothermic process has occurred.
(a) (i) only
(b) (ii) only
(c) (i) and (iv)
(d) (ii) and (iii)
Answer:
(c).

Question 6.
A dilute ferrous sulphate solution is gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation ?
(a) KMnO₄ is an oxidising agent and it oxidises FeSO₄
(b) FeSO₄ acts as an oxidising agent and it oxidises KMnO₄
(c) The colour disappears due to dilution; no reaction is involved
(d) KMnO₄ is an unstable compound and decomposes in presence of FeSO₄ to a colourless compound.
Answer:
(a). Potassium permanganate (KMnO₄) is an oxidising agent. It oxidises ferrous sulphate to ferric sulphate in the presence of dilute
H₂SO₄.

By taking part in the reaction, the light purple colour of the solution slowly fades and finally disappears.

Question 7.
Which among the following is(are) double displacement reaction(s) ?
(i) Pb + CuCl₂ ————> PbCl₂ + Cu
(ii) Na₂SO₄ + BaCl₂ ———-> BaSO₄ + 2NaCl
(iii) C + O₂  ———–> CO₂
(iv) CH₄ + 2O₂  ———> CO₂ + 2H₂O
(a) (i) and (iv)
(b) (ii) only
(c) (i) and (ii)
(d) (iii) and (iv)
Answer:
(b). Only reaction (ii) is double displacement in nature.

Question 8.
Which among the following statement(s) is(are) true ? ‘Exposure of silver chloride to sunlight for a long duration turns grey due to
(i) the formation of silver by decomposition of silver chloride
(ii) sublimation of silver chloride
(iii) decomposition of chlorine gas from silver chloride
(iv) oxidation of silver chloride
(a) (i) only
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (iv) only
Answer:
(a). Silver chloride is sensitive to sun light and decomposes slowly to give silver which is grey in colour and chlorine.

Question 9.
Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form a solution called lime water. Which among the following is (are) true about slaking of lime and the solution formed ?
(i) It is an endothermic reaction
(ii) It is an exothermic reaction
(iii) The pH of the resulting solution will be more than seven
(iv) The pH of the resulting solution will be less than seven
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (iii) and (iv).
Answer:
(b). Slaking of lime is an exothermic process. Lime (CaO) dissolves in water to form calcium hydroxide called slaked lime Ca(OH)₂. Since it is a base, the pH of solution will become more than seven (7).

Question 10.
Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved ?
(i) Displacement reaction
(ii) Precipitation reaction
(iii) Combination reaction
(iv) Double displacement reaction
(a) (i) only
(b) (ii) only
(c) (iv) only
(d) (ii) and (iv).
Answer:
(d). A white precipitate of BaSO₄ is formed. The reaction is double displacement in nature.

Question 11.
Electrolysis of water is a decomposition reaction. The mole ratio of hydrogen and oxygen gases liberated during electrolysis of water is
(a) 1:1
(b) 2:1
(c) 4:1
(d) 1:2.
Answer:
(b).

Question 12.
Which of the following is(are) an endothermic process (es) ?
(i) Dilution of sulphuric acid
(ii) Sublimation of dry ice
(iii) Condensation of water vapours
(iv) Evaporation of water
(a) (i) and (iii)
(b) (ii) only
(c) (iii) only
(d) (ii) and (iv)
Answer:
(d). Both sublimation of dry ice (ii) and evaporation of water (iv) are of endothermic nature.

Question 13.
In the double displacement reaction between aqueous potassium iodide .and aqueous lead nitrate, a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available, which of the following can be used in place of lead nitrate ?
(a) Lead sulphate (insoluble)
(b) Lead acetate
(c) Ammonium nitrate
(d) Potassium sulphate.
Answer:
(b). Lead sulphate being insoluble in water will not react. However, lead acetate can be used since it is water soluble in nature.

Question 14.
Which of the following gases can be used for storage of fresh sample of an oil for a long time ?
(a) Carbon dioxide or oxygen
(b) Nitrogen or oxygen
(c) Carbon dioxide or helium
(d) Helium or nitrogen.
Answer:
(d). Both helium (He) and nitrogen (N₂) can be used. In their presence, rancidity of fresh sample of an oil will not take place.

Question 15.
The following reaction is used for the preparation of oxygen gas in the laboratory

Which of the following statement(s) is(are) correct about the reaction ?
(a) It is a decomposition reaction and is endothermic in nature
(b) It is a combination reaction
(c) It is a decomposition reaction and is accompanied by release of heat
(d) It is a photochemical decomposition reaction and exothermic in nature
Answer:
(a).

Question 16.
Which one of the following processes involve chemical reactions ?
(a) Storing of oxygen gas under pressure in a gas cylinder
(b) Liquefaction of air
(c) Keeping petrol in a china dish in the open
(d) Heating copper wire in the presence of air at high temperature.
Answer:
(d). Copper will react with oxygen present in air upon strong heating to form copper (II) oxide or cupric oxide.

Question 17.
In which of the following chemical equations, the abbreviations represent the correct states of the reactants and products involved at reaction temperature ?
(a) H₂(l) + O₂(l) ———–> 2H₂O(g)
(b) H₂(g) + O₂(l) ———>2H₂O(l)
(c) 2H₂(g) + O₂(g) ———> 2H₂O(l)
(d) 2H₂(0) + O₂(g) ——–> 2H₂O(g)
Answer:
(d). The reaction is carried upon strong heating. At this temperature, H₂O formed is in gaseous state.

Question 18.
Which of the following are combination reactions ?
(i)  2KClO₃  ———-> 2KCl + 3O
(ii) MgO + H₂O ———–> Mg(OH)₂
(iii) 4Al + 3O₂ ———–> 2Al₂O₃
(iv) Zn + FeSO₄ ———-> ZnSO₄ + Fe
(a) (i) and (iii)
(b) (iii) and (iv)
(c) (ii) and (iv)
(d) (ii) and (iii).
Answer:
(d). Both the reactions (ii) and (iii) are the examples of combination reactions.

NCERT Exemplar Solutions for Class 10 Science Chapter 1 Short Answer Questions

Question 19.
Write the balanced chemical equations for the following reactions and identify the type of reaction in each
(a) Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773 K to form ammonia gas.
(b) Potassium hydroxide solution is treated with acetic acid to form potassium acetate and water.
(c) Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H₂SO₄.
(d) Ethene is burnt in the presence of oxygen to form carbon dioxide, water and to release heat and light. Catalyst (Pt)
Answer:

Question 20.
Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(a) Iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide. (CBSE 2012)
(b) Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.
(c) Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.
(d) Ethanol is burnt in air to form carbon dioxide, water and releases heat. (CBSE 2013)
Answer:

Question 21.
Complete the missing components/variables given as x and y in the following reactions
(a) Pb(NO₃)₂ (aq) + 2KI(aq) ———>PbI₂(x) + 2KNO₃(y)
(b) Cu(s) + 2AgNO₃(aq) ————> Cu(NO₃)₂(aq) + x(s)
(c) Zn(s) + H₂SO₄(aq) ———–> ZnSO₄(x) + H₂(g)
(d) CaCO₃(s)  ————>  CaO(s) + CO₂(g)
Answer:
(a) x = yellow precipitate, y = (aq)
(b) x = 2Ag(s)
(c) x = (aq) ; y = (g)
(d) x = heat.

Question 22.
Which among the following changes are exothermic or endothermic in nature ?
(a) Decomposition of ferrous sulphate
(b) Dilution of sulphuric acid
(c) Dissolution of sodium hydroxide in water
(d) Dissolution of ammonium chloride in water
Answer:
(a) Endothermic
(b) Exothermic
(c) Exothermic
(d) Endothermic.

Question 23.
Identify the reducing agent in the following reactions
Ammonia (NH₃) is the reducing agent. It has reduced oxygen (O₂) which acts as oxidising agent.
(b) Water (H₂O) is the reducing agent. It has reduced fluorine (F₂) which acts as oxidising agent.
(c) Carbon monoxide (CO) is the reducing agent. It has reduced ferric oxide (Fe₂O₃) which acts as oxidising agent.
(d) Hydrogen (H₂) is the reducing agent. It has reduced oxygen (O₂) which acts as oxidising agent.
Answer:

Question 24.
Identify the oxidising agent (oxidant) in the following reactions
(a) Pb₃O₄ + 8HCl ———-> 3PbCl₂ + Cl₂ + 4H₂O
(b) 2Ca + O₂ ———-> 2CaO
(c) CuSO₄ + Zn ———-> Cu + ZnSO₄
(d) V₂O₅ + 5Ca ————> 2V + 5Ca
(e) 3Fe + 4H₂O ———–> Fe₃O₄ + 4H₂
(f) ZnO + H₂ ———–> Zn + H₂O
Answer:
(a) Pb₃O₄
(b) O₂
(c) CuSO₄
(d) V₂O₅
(e) H₂O
(f) ZnO

Question 25.
Write the balanced chemical equations for the following reactions
(a) Sodium carbonate on reaction with hydrochloric acid in equal molar concentrations gives sodium chloride and sodium hydrogen carbonate.
(b) Sodium hydrogen carbonate on reaction with hydrochloric acid gives sodium chloride, water and liberates carbon dioxide.
(c) Copper sulphate on treatment with potassium iodide precipitates cuprous iodide (Cu₂I₂), liberates iodine gas and also forms potassium sulphate.
Identify the reducing agent in the following reactions
Answer:
(a) Na₂CO₃ (s) + HCl (aq) ———–> NaCl(aq) + NaHCO₃ (aq)
(b) NaHCO₃ (s) + HCl (aq) ———–> NaCl(aq) + H₂O (aq) + CO₂(g)
(c) 2CuSO₄ (s) + 4KI (aq) ———–> Cu₂I₂ (s) + 2K₂SO₄ (aq) + I₂ (g)

Question 26.
A solution of potassium chloride when mixed with silver nitrate solution, an insoluble substance is formed.
Write the chemical reaction involved and mention the type of the chemical reaction.
Answer:
The chemical reaction is :

It is an example of the double displacement reaction.

Question 27.
Ferrous sulphate decomposes with the evolution of a gas having a characteristic smell of burning sulphur. Write the chemical reaction involved and identify the type of reaction.
Answer:
The chemical reaction is an example of thermal decomposition reaction.

The gases evolved are a mixture of sulphur dioxide and sulphur trioxide. Both have the smell of burning sulphur.

Question 28.
Why do fire flies glow at night ?
Answer:
Fire flies are associated with certain protein. In the presence of a enzyme, the protein undergoes aerial oxidation. The reaction is accompanied by emission of light. As a result, fire flies glow at night.

Question 29.
Grapes hanging on the plants do not ferment but after being plucked from the plant, can be fermented. Under what conditions do these grapes ferment ? Is it a chemical or a physical change ?
Answer:
Grapes hanging on the plants are living in nature. Their immune system does not allow any fermentation.
However, when these are plucked, they are no longer living. They undergo fermentation under aerobic conditions (in the absence of air or oxygen). The other factors which favour fermentation are enzyme and temperature between 25°C to 30°C. The fermentation is a chemical change.

Question 30.
Which among the following are physical or chemical changes ?
(a) Evaporation of petrol
(b) Burning of Liquefied Petroleum Gas (LPG)
(c) Heating of an iron rod to red hot.
(d) Curding of milk
(e) Sublimation of solid ammonium chloride.
Answer:
(a) Physical
(b) Chemical
(c) Physical
(d) Chemical
(e) Physical.

Question 31.
During the reaction of some metals with dilute hydrochloric acid, following observations are made.
(a) Silver metal does not show any change
(b) The temperature of the reaction mixture rises when aluminium (Al) is added.
(c) The reaction of sodium metal is found to be highly explosive
(d) Some bubbles of a gas are seen when lead (Pb) is reacted with the acid.
Explain these observations giving suitable reasons.
Answer:
(a) Silver (Ag) is placed below hydrogen in the activity series. It cannot replace hydrogen from dilute HCl and no chemical reaction is possible.
(b) The reaction of aluminium (Al) with dilute HCl is of exothermic nature. Therefore the temperature rises.
(c) Hydrogen gas is evolved when sodium metal (Na) is reacted with dilute HCl. The reaction is of exothermic nature. Therefore, hydrogen catches fire accompanied by explosion.
2Na (s) + 2HCl(aq) ———-> 2NaCl(aq) + H₂(g)
Remember : Sodium metal as such does not catch fire. It is the hydrogen gas evolved which burns since the reaction is highly exothermic in nature.
(d) Lead (Pb) reacts with dilute HCl to evolve hydrogen gas accompanied by bubbles.
Pb(s) + 2HCl (aq) ———-> PbCl₂(aq) + H₂(g).

Question 32.
A substance ‘A’, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water it forms a solution which turns red litmus blue. Identify A’ and also write the chemical reactions involved.
Answer:
The available information suggests that the substance A’ is oxide of the element calcium (Ca) which is present in group 2 of the periodic table. Calcium is also a constituent of our bones in the form of calcium phosphate. . Calcium oxide (CaO) reacts with water to form calcium hydroxide (basic in nature). It forms a basic solution which turns red litmus blue.

Question 33.
Write a balanced chemical equation for each of the following reactions and also classify them.
(a) Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.
(b) A piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.
(c) Iron (III) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.
(d) Hydrogen sulphide gas reacts with oxygen gas to form solid sulphur and liquid water. (CBSE 2014)
Answer:

Question 34.
Why do we store silver chloride in a dark coloured bottle ?
Answer:
Silver chloride is a white solid. However, it is very senstive to sun light and decomposes in the presence of light to form silver (grey in colour) and chlorine.

In order to avoid action by sun light, it is kept in a coloured bottle.

Question 35.
Balance the following chemical equations and identify the type of chemical reaction.

Answer:
The chemical equations in their balanced form may be written as follows :

Question 36.
A magnesium ribbon is burnt in oxygen to give a white compound ‘X’ accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound ‘Y’.
(a) Write the chemical formulae of X and Y.
(b) Write a balanced chemical equations when X and Y are dissolved in water.
Answer:
(a) The Compound ‘X’ is magnesium oxide (MgO). The compound ‘Y’ is magnesium nitride (Mg₃N₂)

Question 37.
Zinc liberates hydrogen gas when reacted with dilute hydrochloric acid whereas copper does not. Explain why ?
Answer:
Zinc (Zn) is placed above hydrogen in the activity series. It therefore, displaces hydrogen from dilute HCl.
Zn (s) + 2HCl (aq) ————-> ZnCl₂ (aq) + H₂(g)
Copper is placed below hydrogen and therefore, does not react with dilute HCl.
Cu (s) + HCl (aq) ———–> No action.

Question 38.
A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining.
(a) Why do silver articles turn black when kept in the open for a few days ? Name the phenomenon involved.
(b) Name the black substance formed and give its chemical formula.
Answer:
(a) Air contains traces of hydrogen sulphide (H₂S) gas. It slowly reacts with silver present in the silver article to form silver sulphide (black in colour). A coating of silver sulphide (Ag₂S) gets deposited on the surface of the metal. The phenomenon is known as corrosion. Tooth pastes generally contain traces of hydrogen peroxide as one of the constitutents. It reacts with silver sulphide to form silver sulphate which is white in colour. Therefore, whiteness is restored to the article.
(b)

NCERT Exemplar Solutions for Class 10 Science Chapter 1 Long Answer Questions

Question 39.
On heating blue coloured powder of copper (II) nitrate, in a boiling tube, copper oxide (black), oxygen gas and a brown gas X is formed
(a) Write a balanced chemical equation of the reaction.
(b) Identify the brown gas X evolved.
(c) Identify the type of reaction.
(d) What could be the pH range of aqueous solution of the gas X ?
Answer:

(b) Brown gas (X) is nitrogen dioxide.
(c) It is an example of decomposition reaction.
(d) Nitrogen dioxide is an acidic oxide. Therefore, it dissolves in water to form an acidic solution. The pH of the solution is expected to be less than 7.

Question 40.
Give the characteristic tests for the following gases :
(a) CO₂
(b) SO₂
(c) O₂
(d) H₂
Answer:
(a) CO₂ gas : It is a colourless and odourless gas. When passed through lime water, it will initially become milky.

(b) SO₂ gas : It is a colourless but a pungent smelling gas. The gas when passed through an acidified solution of potassium permanganate (pink) will decolourise it.

Similarly the gas when passed through an acidified solution of potassium dichromate (orange) will make it light green.

(c) Oxygen gas : The gas is a supporter of combustion. It can be tested by bringing a burning or smouldering match-stick near the mouth of the test tube from which the gas escapes. The match-stick will burn more brightly.
(d) Hydrogen gas : The gas itself is combustible. It will burn with a pop sound when a burning candle or match- stick is brought near it.
2H₂ (g) + O₂ (g) ———-> 2H₂O (g)

Question 41.
What happens when a piece of
(a) zinc metal is added to copper sulphate solution ?
(b) aluminium metal is added to dilute hydrochloric acid ?
(c) silver metal is added to copper sulphate solution ?
Also write the balanced chemical equation if the reaction occurs.
Answer:
(a) Metal zinc displaces hydrogen component on reacting with dilute sulphuric acid (H₂SO₄) as H₂ gas which is evolved
Zn(s) + H₂SO₂(aq) ———-> ZnSO₄(aq) + H₂(g)
(b) Ammonia and hydrogen chloride gas. When vapours of ammonia and hydrogen chloride gas are mixed, the compound formed is ammonium chloride. It is a white solid.
NH₃(g) ₊ HCl(g) ———-> NH₄Cl (s)
(c) Copper displaces silver from the aqueous solution of silver nitrate.
Cu(s) + 2AgNO₃(aq) ——–> Cu(NO₃)₂(aq) + 2Ag(s)

Question 42.
What happens when zinc granules are treated with dilute solution of H₂SO₄, HCl, HNO₃, NaCl and NaOH ? Also write the chemical equations if reaction oçcurs.
Answer:
With dilute H₂SO₄ : Hydrogen gas evolves
Zn (s) + H₂SO₄ (dil.) ————> ZnSO₄ (aq) + H₂(g)
with dilute HCl : Hydrogen gas evolves
Zn (s) + 2HCl (dil.) ———–> ZnCl₂(aq) + H₂(g)
with dilute HNO₃ : Nitrous oxide gas evolves. It is colourless.
4Zn (s) + 10HNO₃ (aq) ———->  4Zn(NO₃)₂ (aq) + 5H₂O (l) + N₂O(g)
with NaCl : There is no chemical reaction, with NaOH : Hydrogen gas evolves :

Question 43.
On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite, white precipitate is obtained :
(a) Write a balanced chemical equation for the reaction involved.
(b) What other name can be given to this precipitation reaction ?
(c) On adding dilute hydrochloric acid to the reaction mixture, white precipitate disappears. Why ?
Answer:

(b) The precipitation reaction is also called double displacement reaction.
(c) White precipitate of barium sulphite reacts with dilute hydrochloric to form barium chloride and sulphur dioxide gas. Since barium chloride is water soluble, the white precipitate will slowly disappear.

Question 44.
You are provided with two containers made up of copper and aluminium. You are also provided with solutions of dilute HCl, dilute HNO₃, ZnCl₂ and water. In which of the above containers, can these solutions be kept ?
Answer:
Solutions to be kept in copper container :

1. Dilute HCl can be kept since no chemical reaction is expected. Copper is placed below hydrogen in the activity series.
2. Dilute HNO₃ cannot be kept since a chemical reaction is expected. Nitric acid is a strong oxidising agent.
   3Cu (s) + 8HNO₃ (dit) ———–> 3 CU(NO₃)₂ (aq) + 2NO (g) + 4H₂O (aq)
3. ZnCl₂ solution can be kept since copper is placed below zinc in the activity series and no chemical reaction is possible.
4. Water can be kept since no chemical reaction is expected.

Solutions to be kept in aluminium container:

1. Dilute HCl cannot be kept since aluminium reacts with acid to evolve hydrogen gas.
   2Al (s) + 6HCl (aq) ———-> 2AlCl₃ (aq) + 3H₂ (g)
2. Dilute HNO₃ can be kept. Actually, aluminium is initially oxidised by the acid to aluminium oxide (Al₂O₃). A coating of aluminium oxide gets deposited on the surface of the metal and makes it passive towards reaction with the acid.
3. ZnCl₂ solution cannot be kept since a chemical reaction will take place as aluminium is placed above zinc in the activity series.
   2Al (s) + 3ZnCl₂ (aq) ———-> 2AlCl₃ (aq) + 3Zn (s)
4. Water as such can be kept in the container. However, we cannot keep steam since a chemical reaction is likely to take place.
   

Hope given NCERT Exemplar Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations are helpful to complete your science homework.

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Value Based Questions in Science for Class 10 Chapter 1 Chemical Reactions and Equations

These Solutions are part of Value Based Questions in Science for Class 10. Here we have given Value Based Questions in Science for Class 10 Chapter 1 Chemical Reactions and Equations

Question 1.
A lady wanted to give a coating of white wash to her room. She purchased quick lime from the market and dissolved it in water and immediately applied the same on the wall. In this process, she spoiled her hands and even suffered minor burns. Her friend advised her not be in haste and keep the container overnight before applying a coating on the wall. She followed her advice and there was now no problem.

1. What mistake was committed by the lady ?
2. Why did she suffer from burns ?
3. Why was so much heat evolved ?
4. What values are exhibited by her friend in this episode ?

Answer:

1. The lady should have waited for a few hours because when quick lime is dissolved in water, slaked lime is formed and this process is highly exothermic.
2. The solution might have become very hot and that is why the lady suffered from burns.
3. Quick lime is CaO and it reacts with water to form Ca(OH)₂ which is known as slaked lime. The dissolution process is highly exothermic. That is why so much heat was evolved. By keeping container overnight, the chemical reaction subsided and now there was no problem to apply the coating of white wash on the wall. In this way, she rendered service to the lady.
4. Her friend had the knowledge of chemistry.

More Resources

• Value Based Questions in Science for Class 10
• HOTS Questions for Class 10 Science
• NCERT Solutions for Class 10 Science
• NCERT Exemplar Solutions for Class 10 Science
• Previous Year Question Papers for CBSE Class 10 Science

Question 2.
Mohan was working in a factory. He purchased a new cycle but kept it in the open. After two months he found that the cycle chain and even the handles got rusted. His friend advised him to apply a coating of rust proof paint to the cycle and not to keep it in the open in future.

1. Why was the cycle rusted ?
2. What is the role of rust proof paint ?
3. What values are associated with this gesture ?

Answer:

1. Air contains both oxygen and moisture. In their presence iron slowly got rusted
   
2. The coating of rust proof paint checked further corrosion. Similarly, by keeping the cycle under a covered shed, rusting can be avoided.
3. He played the role of a sincere friend and gave a very sincere advice to Mohan.

Question 3.
A student working in the laboratory prepared an aqueous solution of silver nitrate and kept it in a glass beaker overnight. Next morning, he found that the beaker has developed black turbidity.

1. Why did the solution develop black turbidity ?
2. In your opinion, what precaution he should have taken ?

Answer:

1. The silver salts are sensitive to light. When kept exposed to light for a few hours silver nitrate decomposes and a black turbidity appears.
2. The student should have covered the beaker from outside with the help of a brown paper to avoid direct action of sun light.

Question 4.
Sonia purchased a packet of potato chips from the shop. She opened the packet and ate some of the chips and left the packet as such in one comer of her study room. After a gap of about two weeks, she saw the packet and wanted to do so munching again. At that time, her elder sister Pallavi, a science student of class eleven was present in her room. She found that a foul smell was coming out from the packet. She immediately threw it in the dustbin and did not allow her sister to eat the chips.

1. Why did potato chips develop foul smell ?
2. What was the cause of the spoilage of the chips ?
3. What is the nature of the chemical reaction involved in it ?
4. Why do not sealed packets develop foul smell even if kept for months ?
5. What values are displaced by Pallavi ?

Answer:

1. Potato chips developed foul smell due to rancidity.
2. Potato chips contain some oil as well as fat. These were slowly oxidised since they were exposed to air and therefore, developed foul smell.
3. It is an oxidation reaction
4. The bags or packets containing chips or other such etables are filled with nitrogen and then sealed. This checks rancidity.
5. The knowledge of science came to the help of Pallavi. She was aware of the consequences if one eats rancid food material. She therefore, did not allow her sister to eat the chips and thus, saved her from getting sick.

Hope given Value Based Questions in Science for Class 10 Chapter 1 Chemical Reactions and Equations are helpful to complete your science homework.

If you have any doubts, please comment below. Learn Insta try to provide online science tutoring for you.

HOTS Questions for Class 10 Science Chapter 1 Chemical Reactions and Equations

These Solutions are part of HOTS Questions for Class 10 Science. Here we have given HOTS Questions for Class 10 Science Chapter 1 Chemical Reactions and Equations

Question 1.
Study the given diagram and answer the following questions :
(a) Write the chemical reaction involved in the process.
(b) Mention the colour of :

1. copper powder and
2. the substance formed after heating it.

(c) How can we reverse the above reaction ? Write the equation for the reverse reaction and state the substance that undergoes oxidation and the substance that undergoes reduction.
(CBSE 2015)

Answer:
(a) Copper powder upon heating reacts with oxygen (present in air) to form cupric oxide or copper (II) oxide.

(b)

1. Copper powder is brownish in colour.
2. The substance formed after heating is cupric oxide. It has black colour.

(c) The reaction can be reversed by heating cupric oxide in a current of hydrogen.
CuO(s) + H₂(g) ———–> Cu (s) + H₂O(g)
In this reaction, H₂ undergoes oxidation to H₂O and CuO is reduced to Cu.

More Resources

• HOTS Questions for Class 10 Science
• NCERT Solutions for Class 10 Science
• Value Based Questions in Science for Class 10
• NCERT Exemplar Solutions for Class 10 Science
• Previous Year Question Papers for CBSE Class 10 Science

Question 2.
The gases hydrogen and chlorine do not react with each other even if kept together for a long time. However, in the presence of sun light, they readily combine. What does actually happen ?
Answer:
We know that in chemical reactions, energy is needed to break the bonds present in the reacting molecules so that they may combine to form the products. In the present case, sun light is the source of energy in the form of photons. The energy made available helps in breaking the bonds present in the reactant molecules and the chemical reaction leading to hydrogen chloride gas takes place.

Question 3.
A water insoluble substance ‘X’ on reacting with dilute H₂SO₄ released a colourless and odourless gas accompanied by brisk effervescence. When the gas was passed through water, the solution obtained turned blue litmus red. On bubbling the gas through lime water, it initially became milky and the milkiness disappeared when the gas was passed in excess. Identify the substance ‘X’ and write the chemical equations of the reactions involved.
Answer:
The water in soluble substance ‘X’ is most probably some metal carbonate (CaCO₃). The chemical equations that are involved are given.

Question 4.
(a) Based on the reactions given below, arrange the metals involved in these reactions in decreasing order of reactivity. Give suitable explanation.

1. Zn + CuSO₄ ———> ZnSO₄ + Cu
2. Cu + 2AgNO₃ ———> Cu(NO₃)₂ + 2Ag
3. Zn + FeSO₄ ———-> ZnSO₄ + Fe
4. Fe + CuSO₄ ———-> FeSO₄ + Cu

(b) What is the nature of the reactions ?
Answer:
(a)

1. Since Zn displaces Cu from CuSO₄ solution, it is more reactive than Cu.
2. Since Cu displaces Ag from AgNO₃ solution, it is more reactive than Ag.
3. Since Zn displaces Fe from FeSO₄ solution, it is more reactive than Fe.
4. Since Fe displaces Cu from CuSO₄ solution, it is more reactive than Cu.
   The decreasing order of reactivity of the metals is :
   Zn > Fe> Cu> Ag

(b) All these reactions are the examples of displacement reactions.

Question 5.
A, B and C are three elements which undergo chemical reactions according to following equations.
A₂O₃ + 2B ———-> B₂O₃ + 2A
3CSO₄ + 2B ———-> B₂(SO₄)₃ + 3C
3CO + 2A ———> A₂O₃ + 3C
Answer the following questions :
(a) Which element is the most reactive ?
(b) Which element is the least reactive ?
Answer:
(a) The most reactive element is ‘B’ as it has displaced both A’ and ‘C’ from their compounds.
(b) The least reactive element is ‘C’ as it has been replaced by both A’ and ‘B’.

Question 6.
You are given the following materials

1. Marble chips
2. Dilute hydrochloric acid
3. Zinc granules

Identify the type of reaction when marble chips and zinc granules are added separately to acid taken in two tubes. Write chemical equations in each case.
Answer:

1. Marble chips react with dilute hydrochloric acid to form calcium chloride and carbonic acid. The acid changes to CO₂ and H₂O. It is a double displacement reaction.
   CaCO₃(s) + 2HCl (aq) ———–> CaCl₂(aq) + H₂CO₃(aq) (CO₂+H₂O)
2. Zinc granules react with hydrochloric acid to form zinc chloride accompanied by hydrogen gas. It is a displacement reaction.
   Zn(r) + 2HCl(aq) ———–> ZnCl₂(aq) + H₂(g)

Question 7.
A strip of a metal X is immersed in the aqueous solution of salt YSO₄ blue in colour. After sometime, a layer the metal Y from the salt solution is deposited on the strip of the metal X. Whereas the metal X is used for galvanisation, the metal Y is employed in making electric cables.

1. Predict the metal X.
2. What could be the metal Y ?
3. Can yon name the salt YSO₄ ?
4. What is the nature of the chemical reaction taking place ?

Answer:

1. Since the metal X is used for galvanisation, it is most probably Zn.
2. Since the metal Y is used in electric cable, it is likely to be Cu.
3. The salt is CuSO₄.
4. It is an example of metal displacement reaction. Zn lies above Cu in the activity series and has therefore, displaced Cu from the blue CuSO₄ solution.
   

Hope given HOTS Questions for Class 10 Science Chapter 1 Chemical Reactions and Equations are helpful to complete your science homework.

If you have any doubts, please comment below. Learn Insta try to provide online science tutoring for you.

NCERT Exemplar Solutions for Class 10 Science Chapter 11 Human Eye and Colourful World

These Solutions are part of NCERT Exemplar Solutions for Class 10 Science. Here we have given NCERT Exemplar Solutions for Class 10 Science Chapter 11 Human Eye and Colourful World

Question 1.
A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power
(a) +0.5 D
(b) -0.5 D
(c) +0.2 D
(d) -0.2 D
Answer:
(b).
Explanation : Person is suffering from myopia. Focal length of the lens used to correct the defect, f = – d = – 2 m

More Resources

• NCERT Exemplar Solutions for Class 10 Science
• NCERT Solutions for Class 10 Science
• Value Based Questions in Science for Class 10
• HOTS Questions for Class 10 Science
• Previous Year Question Papers for CBSE Class 10 Science

Question 2.
A student sitting on the last bench can read the letters written on the black board but is not able to read the letters written in his test book. Which of the following statements is correct ?
(a) The near point of his eyes has receded away
(b) The near point of his eyes has come closer to him
(c) The far point of his eyes has receded away
(d) The far point of his eyes has come closer to him.
Answer:
(a).
Explanation : Student suffers from hypermetropia. In this case, the near point of the eye recedes away.

Question 3.
A student wants to have third colour from the top corresponds to the colour of the sky after the dispersion of white light through a glass prism. He placed prism ABC with BC as base as shown in figures P, Q, R and S. Which position of the prism is correct ?

(a) P
(b) Q
(c) R
(d) S.
Answer:
(b).
Explanation : Colour of sky is blue.

Question 4.
At noon, the sun appears white as
(a) light is least scattered
(b) all the colours of the white light are scattered away.
(c) blue colour is scattered the most
(d) red colour is scattered the most
Answer:
(a).
Explanation : At noon, scattering of all colours is almost same.

Question 5.
Which of the following phenomena of light are involved in the formation of a rainbow ?
(a) Reflection, refraction and dispersion
(b) Refraction, dispersion and total internal reflection.
(c) Refraction, dispersion and internal reflection.
(d) Dispersion, scattering and total internal reflection
Answer:
(c).
Explanation : When light falls on a droplet, refraction of light takes place. This refracted light suffers dispersion. Then the light suffer total internal reflection from other surface of the droplet.

Question 6.
Twinkling of stars is due to atmospheric
(a) dispersion of light by water droplets
(b) refraction of light by different layers of varying refractive indices.
(c) scattering of light by dust particles
(d) internal reflection of light by clouds.
Answer:
(b).
Explanation : When sun light enters the earth’s atmosphere, it continuously goes from rarer to the denser medium and hence refraction of light takes place. The refraction of light taking place in the atmosphere is known as atmospheric refraction.

Question 7.
The clear sky appears blue because
(a) blue light gets absorbed in the atmosphere
(b) ultraviolet radiations are absorbed in the atmosphere.
(c) violet and blue lights get scattered more than lights of all other colours by the atmosphere.
(d) light of all other colours is scattered more than the violet and blue colour lights by the atmosphere.
Answer:
(c).
Explanation : Intensity of scattered light,  I ∝ 1/λ⁴ . The wavelength of blue and violet light is smaller than the wavelengths of other colours.

Question 8.
Which of the following statements is correct regarding the propagation of light of different colours of white light in air ?
(a) Red light travels fastest.
(b) Blue light moves faster than green light.
(c) All the colours of white light move with the same speed.
(d) Yellow light moves with the mean speed as that of the red and the violet light.
Answer:
(c).
Explanation : There is no dispersion of white light in air. So all colours travel with the same speed.

Question 9.
The clanger signals installed at the top of tall building are red in colour. These can be seen from a distance because among all other colours, the red light
(a) is scattered the most by smoke or fog
(b) is scattered the least by smoke or fog
(c) is absorbed the most by smoke or fog
(d) moves fastest in air
Answer:
(b).
Explanation : Intensity of scattered light, I ∝ 1/λ⁴ . Since the wavelengths of red light is greater than the wavelengths of all other lights, therefore, red colour can be seen from a distance.

Question 10.
Which of the following phenomena contributes significantly to the reddish appearance of the sun at sunrise or sunset ?
(a) Dispersion of light
(b) Scattering of light
(c) Total internal reflection of light
(d) Reflection of light from the earth.
Answer:
(b).
Explanation : Intensity of scattered light, I ∝ 1/λ⁴. Since the wavelength of red light is greater than the wavelengths of all other lights, therefore, red colour is scattered least and confined around the sun.

Question 11.
Water in deep sea is bluish in colour due to
(a) absorption of light by the sea
(b) reflection of sky in water
(c) scattering of light
(d) presence of plants in the sea.
Answer:
(c).

Question 12.
When light rays enter the eye, most of the refraction occurs at the
(a) crystalline lens
(b) outer surface of the cornea
(c) iris
(d) pupil
Answer:
(b).

Question 13.
The focal length of the eye lens increases when eye muscles
(a) are relaxed and lens becomes thinner
(b) contracts and lens becomes thicker
(c) are relaxed and lens becomes thicker
(d) contract and lens becomes thinner
Answer:
(a).
Explanation : Focal length of thin lens is greater than the focal length of thick glass.

Question 14.
Which of the following statement is correct ?
(a) A person with myopia can see distant objects clearly.
(b) A person with hypermetropia can see nearby objects clearly.
(c) A person with myopia can see nearly objects clearly.
(d) A person with hypermetropia cannot see distant objects clearly.
Answer:
(c).
Explanation : Hypermetropia : A person suffering from this defect can see far off objects clearly but cannot see nearby objects clearly.
Myopia : A person suffering from this defect can see nearby objects clearly but cannot see far off objects clearly.

Question 15.
Draw ray diagrams each showing
(i) myopic eye and
(ii) hypermetropic eye.
Answer:
(i)

(ii)

Question 16.
A student sitting at the back of the classroom cannot read clearly the letters written on the black board. What advice will a doctor give to her ? Draw ray diagram for the correction of this defect.
Answer:
Doctor will advice the student to wear spectacles havi ng con¬cave lens of suitable focal length or power as she is suffering from myopia.
For diagram,

Question 17.
How are we able to see nearby and also the distant objects clearly? (CBSE 2012)
Answer:
Human eye is able to see nearby and also the distant objects clearly using its power of accommodation.

Question 18.
A person needs a lens of power -4.5 D for correction of her vision.
(a) What kind of defect is she suffering from ?
(b) What is the focal length of the corrective lens ?
(c) What is the nature of the corrective lens ?
(CBSE Sample Paper 2017-18)
Answer:
(a) She is suffering from myopia

(c) Concave lens.

Question 19.
How will you use two identical prisms so that a narrow beam of white light incident on one prism emerges out of the sec¬ond prism as white light ? Draw the diagram.
Answer:
Perform an activity to show that the colours of white light splitted by a glass prism can be recombined to get white light by another glass prism.
Apparatus required. Two glass prisms made of same kind of glass, a card board having a fine hole at its centre, a white screen.
Procedure:

1. Place a card board in front of a prism A. A ray of white light coming from the hole in the card board falls on the prism A (Figure 11).
   
2. White light splits into seven colours by prism A is made to fall on another glass prism B placed with its base upward. Since prism A disperses white light, so it is known as dispersing prism.
3. The prism B deviates colours of light towards its base. The various colours recombines at the opposite lace of glass prism B.
4. This activity was initially performed by the great scientist Issac Newton.
   The light received on the white screen placed in front of prism B is white. Since the prism B recombines the colours of light to produce white light, so glass prism B is known as recombination prism.

Question 20.
Draw a ray diagram showing the dispersion through a prism when a narrow beam of white light is incident on one of its refracting surfaces. Also indicate the order of the colours of the spectrum obtained.
Answer:

Question 21.
Is the position of a star as seen by us its true position. Justify your answer.
Answer:
No.
Light emitted by distant stars (act as point sources of light) passes through the atmosphere of the earth before reaching our eyes. The atmosphere of the earth is not uniform but consists of many layers of different densities. The layers close to the surface of the earth are optically denser. As we go higher and higher, the density of layers and refractive index decreases progressively. As the light from a star enters the upper­most layer of the atmosphere, it bends towards the normal as it enters the next layer. This process continues till the light enters our eyes. So due to refraction of light, the apparent position of the star is different from the actual position of the star (Figure 13).

Question 22.
Why do we see a rainbow in the sky only after rainfall ?
Answer:
Rainbow is the example of dispersion of sunlight. In sky, prism like objects are needed for the dispersion of light. After rainfall, tiny water drops suspended in air act as prisms. Hence, we see a rainbow in the sky only after rainfall.

Question 23.
Why is the colour of clear sky blue ?
Answer:
When sunlight enters the earth’s atmosphere, the atoms or molecules of the gases present in the atmosphere scatter this light. Since wavelength of red colour is larger than the wavelengths of other colours in sunlight, so red colour is scattered least. Violet colour is scattered the most followed by blue, green, yellow, orange and red colours respectively. Our eye is more sensitive to the blue light than the violet light. Therefore, scattered light in the sky contains blue colour in plenty and hence the clear sky appears blue.
Note : Sky appears greyish over cities having industrial units. The smoke and dust particles in the atmosphere over such cities scatter red, orange and yellow colours more than other colours of small wavelengths. Hence, the sky appears greyish.

Question 24.
What is the difference in colours of the sun observed during sunrise/sunset and noon ? Give explanation for each.
Answer:
At the time of sunrise or sunset, the position of the sun is very far away from us (Figure 16).

The sunlight travels longer distance through the atmosphere of the earth before reaching our eyes. Scattering of blue light is more than the scattering of red light. As a result of this, more red light reaches our eyes than any other colour. Hence sunset and sunrise appear red.
During noon, the sun is overhead and sunlight travels less distance through the earth’s atmosphere to reach our eyes. In this case, the scattering of almost all colours is very small. Hence, the sun appears white.

Hope given NCERT Exemplar Solutions for Class 10 Science Chapter 11 Human Eye and Colourful World are helpful to complete your science homework.

If you have any doubts, please comment below. Learn Insta try to provide online science tutoring for you.