Hello students, and welcome to class 10. Chapter 1 Chemical Reactions and Equations is a fundamental and very important chapter and you will have to learn it thoroughly. We’ve gathered all the solutions to in-text questions, exercises, and activities in one convenient spot for your benefit. These solutions are crafted to spark your interest in the subject, making learning enjoyable and engaging. Plus, we’ve added an extra set of problems to help you ace your exams! You’ll also love the illustrations we’ve included. Dive in and enjoy the journey!
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Solutions to In Text Questions of NCERT Class 10 Science Chapter 1 Chemical Reactions and Equations
Page 6:
1. Why should a magnesium ribbon be cleaned before burning in air?
Answer:
The magnesium ribbon be cleaned before burning in air because magnesium by itself reacts with oxygen in the atmosphere to form a layer of magnesium oxide which is a very stable compound. This layer of magnesium oxide prevents further reaction of oxygen and hence needs to be removed.
2. Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine → Hydrogen chloride
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
Answer:
(i) H2 + Cl2 → 2HCl
(ii) 3BaCl2 + Al2(SO4)3 →3BaSO4 + 2AlCl3
(iii) 2Na + 2H2O → 2NaOH + H2
3. Write a balanced chemical equation with state symbols for the following reactions.
(i) Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
(ii) Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
Answer:
(i) BaCl2 + Na2SO4 → BaSO4 + 2NaCl
(ii) NaOH + HCl → NaCl + H2O
Page 10:
1. A solution of a substance ‘X’ is used for whitewashing.
(i) Name the substance ‘X’ and write its formula.
(ii) Write the reaction of the substance ‘X’ named in (i) above with water.
Answer:
(i) The substance ‘X’ which used in whitewashing is quick lime or Calcium Oxide and the formula is CaO.
(ii) The reaction of CaO with water is: CaO + H2O → Ca(OH)2
2. Why is the amount of gas collected in one of the test tubes in Activity 1.7 double of the amount collected in the other? Name this gas.
Answer:
During electrolysis of water, water splits into hydrogen and oxygen gas. 2 molecules of hydrogen are formed for every one molecule of oxygen. The balanced reaction is shown below:
2H2O → 2H2 + O2
Hence, the amount of hydrogen collected is twice the amount of oxygen collected.
Page 13:
1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Answer:
When an iron nail is dipped in copper sulphate solution, iron displaces copper from copper sulphate to form iron sulphate. Therefore, the colour of copper sulphate solution changes. The displacement reaction is shown below:
Fe + CuSO4 → FeSO4 + Cu
2. Give an example of a double displacement reaction other than the one given in Activity 1.10.
Answer:
Another example of a double displacement reaction is the reaction of Sodium Chloride and Calcium Sulphate to form Sodium Sulphate and Calcium Chloride. The reaction is shown below:
2NaCl + CaSO4 → Na2SO4 + CaCl2
3. Identify the substances that are oxidised and the substances that are reduced in the following reactions.
(i) 4Na(s) + O2 (g) → 2Na2O(s)
(ii) CuO(s) + H2 (g) → Cu(s) + H2O(l)
Answer:
(i) In this reaction, sodium is oxidised because sodium gains oxygen.
(ii) In this reaction, copper loses oxygen and hence it is reduced.
Solutions to Exercises (Page No 14) of NCERT Class 10 Science Chapter 1 Chemical Reaction and Equations
1. Which of the statements about the reaction below are incorrect?
2PbO(s) + C(s) → 2Pb(s) + CO2 (g)
(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.
(i) (a) and (b)
(ii) (a) and (c)
(iii) (a), (b) and (c)
(iv) all
Answer: (i) (a) and (b)
In the above reaction, carbon is getting oxidised due to addition of oxygen and Lead oxide (PbO) is reduced due to removal of oxygen.
2. Fe2O3 + 2Al → Al2O3 + 2Fe
The above reaction is an example of a
(a) combination reaction.
(b) double displacement reaction.
(c) decomposition reaction.
(d) displacement reaction.
Answer: (d) displacement reaction.
In the above reaction, Aluminium has displaced iron from ferrous oxide (Fe2O3) to form aluminium oxide (Al2O3). Hence, it is displacement reaction.
3. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.
(a) Hydrogen gas and iron chloride are produced.
(b) Chlorine gas and iron hydroxide are produced.
(c) No reaction takes place.
(d) Iron salt and water are produced.
Answer: (a) Hydrogen gas and iron chloride are produced.
When dilute hydrochloric acid is added to iron fillings, the following reaction takes place:
Fe + 2HCl → FeCl2 + H2
Iron displaces hydrogen from hydrochloric acid to form iron chloride (FeCl2).
4. What is a balanced chemical equation? Why should chemical equations be balanced?
Answer:
A balanced chemical equation in one in which the number of atoms of each element are the same both on the reactant side and on the product side. Chemical equations should be balanced to uphold the law od conservations of mass, which states that the total mass of the elements in the products must be equal to the total mass of elements in the reactants. In other words, the number of atoms of each element remains the same before and after a chemical reaction.
5. Translate the following statements into chemical equations and then balance them.
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
Answer:
(a) Hydrogen gas combines with nitrogen to form ammonia.
The statement is translated into a chemical equation as follows:
N2 + H2 → NH3
The balanced chemical equation is:
N2 + 3H2 → 2NH3
(b) Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
The statement is translated into a chemical equation as follows:
H2S + O2 → H2O + SO2
The balanced chemical equation is:
2H2S + 3O2 → 2H2O + 2SO2
(c) Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
The statement is translated into a chemical equation as follows:
BaCl2 + Al2(SO4)3 → AlCl3 + BaSO4
The balanced chemical equation is:
3BaCl2 + Al2(SO4)3 → 2AlCl3 + 3BaSO4
(d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.
The statement is translated into a chemical equation as follows:
K + H2O → KOH + H2
The balanced chemical equation is:
2K + 2H2O → 2KOH + H2
6. Balance the following chemical equations.
(a) HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
(b) NaOH + H2SO4 → Na2SO4 + H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + HCl
Answer:
(a) HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
Step 1: Write down the given equation.
HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
Step 2: List the number of atoms of different elements present in the unbalanced reaction.
| Element | Number of atoms in reactants (LHS) | Number of atoms in products (RHS) |
| H | 3 | 2 |
| N | 1 | 2 |
| O | 5 | 7 |
| Ca | 1 | 1 |
Step 3: We note thatthe Calcium atoms are balanced.
Step 4: We now balance the nitrogen atoms. The equation becomes:
2HNO3 + Ca(OH)2 → Ca(NO3)2 + H2O
Step 5: We now balance the hydrogen atoms. The equations becomes:
2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
Step 6: We note that the oxygen atoms are balanced.
Step 7: To confirm whether the equation is balanced we count the number of atoms of each element on both sides of the equations to make sure they are equal. The final balanced equation is:
2HNO3 + Ca(OH)2 → Ca(NO3)2 + 2H2O
(b) NaOH + H2SO4 → Na2SO4 + H2O
Step 1: Write down the given equation.
NaOH + H2SO4 → Na2SO4 + H2O
Step 2: List the number of atoms of different elements present in the unbalanced reaction.
| Element | Number of atoms in reactants (LHS) | Number of atoms in products (RHS) |
| Na | 1 | 2 |
| O | 5 | 5 |
| H | 3 | 2 |
| S | 1 | 1 |
Step 3: We balance the sodium atoms first. The equation becomes:
2NaOH + H2SO4 → Na2SO4 + H2O
Step 4: We balance the oxygen atoms next. The equation becomes:
2NaOH + H2SO4 → Na2SO4 + 2H2O
Step 5: We note the hydrogen atoms are balanced.
Step 6: To confirm whether the equation is balanced we count the number of atoms of each element on both sides of the equations to make sure they are equal. The final balanced equation is:
2NaOH + H2SO4 → Na2SO4 + 2H2O
(c) NaCl + AgNO3 → AgCl + NaNO3
Step 1: Write down the given equation.
NaCl + AgNO3 → AgCl + NaNO3
| Element | Number of atoms in reactants (LHS) | Number of atoms in products (RHS) |
| Na | 1 | 1 |
| Cl | 1 | 1 |
| Ag | 1 | 1 |
| N | 1 | 1 |
| O | 3 | 3 |
Step 2: We note the number of atoms of each element in LHS and RHS are equal. Therefore, it does not require further balancing. The final balanced equation is:
NaCl + AgNO3 → AgCl + NaNO3
(d) BaCl2 + H2SO4 → BaSO4 + HCl
Step 1: Write down the given equation.
BaCl2 + H2SO4 → BaSO4 + HCl
| Element | Number of atoms in reactants (LHS) | Number of atoms in products (RHS) |
| Ba | 1 | 1 |
| Cl | 2 | 1 |
| H | 2 | 1 |
| S | 1 | 1 |
| O | 4 | 4 |
Step 2: We balance the Cl atoms. The equation becomes:
BaCl2 + H2SO4 → BaSO4 + 2HCl
Step 3: We now note that the number of atoms of each element in LHS and RHS have become equal. Therefore, it does not require further balancing. The final balanced equation is:
BaCl2 + H2SO4 → BaSO4 + 2HCl
7. Write the balanced chemical equation for the following reactions.
(a) Calcium hydroxide + Carbon dioxide —> Calcium carbonate + Water
(b) Zinc + Silver nitrate —> Zinc nitrate + Silver
(c) Aluminium + Copper chloride —> Aluminium chloride + Copper
(d) Barium chloride + Potassium sulphate —> Barium sulphate + Potassium chloride
Answers:
(a) Calcium hydroxide + Carbon dioxide —> Calcium carbonate + Water
The balanced equation is:
Ca(OH)2 + CO2 → CaCO3 + H2O
(b) Zinc + Silver nitrate —> Zinc nitrate + Silver
The balanced equation is:
Zn + 2AgNO3 → Zn(NO3)2 + 2Ag
(c) Aluminium + Copper chloride —> Aluminium chloride + Copper
The balanced equation is:
2Al + 3CuCl2 → 2AlCl3 + 3Cu
(d) Barium chloride + Potassium sulphate —> Barium sulphate + Potassium chloride
The balanced equation is:
BaCl2 + K2SO4 → BaSO4 + 2KCl
8. Write the balanced chemical equation for the following and identify the type of reaction in each case.
(a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)
Answer:
(a) Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)
The unbalanced chemical equation is:
KBr (aq) + BaI2 (aq) → KI (aq) + BaBr2 (s)
The balanced chemical equation is as follows:
2KBr (aq) + BaI2 (aq) → 2KI (aq) + BaBr2 (s)
The reaction is a double displacement reaction.
(b) Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
The balanced chemical equation is as follows:
ZnCO3 (s) → ZnO (s) + CO2 (g)
The reaction is a decomposition reaction since a single reactant breaks down to give simpler products.
(c) Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
The unbalanced chemical equation is:
H2 (g) + Cl2 (g) → HCl (g)
The balanced chemical equation is as follows:
H2 (g) + Cl2 (g) → 2HCl (g)
The reaction is a combination reaction since a single product is formed fro/m two reactants.
(d) Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)
The unbalanced chemical equation is:
Mg (s) + HCl (aq) → MgCl2 (aq) + H2 (g)
The balanced chemical equation is as follows:
Mg (s) + 2HCl (aq) → MgCl2 (aq) + 2H2 (g)
9. What does one mean by exothermic and endothermic reactions? Give examples.
Answer:
Reactions in which heat is given out along with the products are called exothermic reactions. An example is the burning of natural gas:
CH4 (g) + 2O2 (g) → CO2 (g) + 2H20 (g) + heat
Reactions in which energy is absorbed are known as endothermic reactions. An example is photosynthesis where leaves of plants absorb heat energy from the sun to convert carbon dioxide and water into glucose and oxygen.
10. Why is respiration considered an exothermic reaction? Explain.
Answer:
During digestion carbohydrates are broken down into glucose. During respiration this glucose combines with oxygen in the cells of our body and releases energy which our body uses to function. Since energy is released during respiration, respiration is considered an exothermic reaction:
C6H12O6 (aq) + 6O2 (aq) → 6CO2 (aq) + 6H2O (l) + energy
11. Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Answer:
Combination reactions involve the combination of two or more substances to form a single product whereas decomposition reactions involve breaking down of a single reactant into two or more simpler products. Hence, decomposition reactions are called the opposite of combination reactions.
Reaction for combination reaction:
C (s) + O2 (g) → CO2 (g)
Reaction for decomposition reaction:
CaCO3 (s) + Heat → CaO (s) + CO2 (g)
12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Answer:
Find the reactions for each case below:
(a) Thermal decomposition reaction:
Decomposition of calcium carbonate to calcium oxide and carbon dioxide on heating is an example of a thermal decomposition reaction.
CaCO3 (s) + Heat → CaO (s) + CO2 (g)
(b) Electrolysis:
Electrolysis of water involves decomposition of water into hydrogen gas and oxygen gas.
2H2O (l) → 2H2 (g) + O2 (g)
(c) Decomposition by Light:
White silver chloride decomposes into grey silver and chlorine in the presence of sunlight.
2AgCl(s) + Sunlight → 2Ag(s) + Cl2(g)
13. What is the difference between displacement and double displacement reactions? Write relevant equations for the above.
Answer:
In a displacement reaction, a more reactive element displaces a less element from its compound whereas in a double displacement reaction there is a mutual exchange of ion between the reactants. In a displacement reaction, there is a single displacement whereas in a double displacement reaction two displacement two displacements occur.
Example of Displacement reaction:
Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu
Example of Double Displacement reaction:
2KBr (aq) + BaI2 (aq) → 2KI (aq) + BaBr2 (s)
14. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.
Answer:
The reaction involved is:
Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)
15. What do you mean by a precipitation reaction? Explain by giving examples.
Answer:
When a reaction occurs in which a solid substance is formed as a product which is insoluble in water, the reaction is called a precipitation reaction. The insoluble solid is known as the precipitate.
An example of a precipitation reaction is given below:
Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)
In the above reaction a white precipitate BaSO4 is formed which in insoluble in water while sodium chloride (NaCl) remains in the solutions.
16. Explain the following in terms of gain or loss of oxygen with two examples each.
(a) Oxidation
(b) Reduction
Answer:
(a) Oxidation
If a substance gains oxygen during a reaction it is oxidised.
Examples:
2Cu + O2 + heat → 2CuO
In the above reaction Copper (Cu) is oxidised to copper oxide (CuO).
4Na(s) + O2(g) → 2Na2O(s)
In the above reaction sodium is oxidised to sodium oxide.
(b) Reduction
If a substance loses oxygen during a reaction it is reduced.
Examples:
CuO(s) + H2(g) → Cu(s) + H2O(l)
In the above reaction copper oxide is reduced to copper.
ZnO + C → Zn + CO
In the above reaction Zinc oxide is reduced to Zinc.
17. A shiny brown coloured element ‘X’ on heating in the air becomes black in colour. Name the element ‘X’ and the black-coloured compound formed.
Answer:
The shiny brown coloured substance ‘X’ is copper metal. On heating in air, it reacts with oxygen to form the black-coloured compound copper oxide.
2Cu + O2 + heat → 2CuO
18. Why do we apply paint on iron articles?
Answer:
We apply paint on iron articles to prevent them from rusting. Without the protective coating of paint, iron forms reddish-brown ferric oxide (Fe2O3) on contact with atmospheric oxygen. This is known as rusting and iron gets damaged due to this process.
19. Oil and fat containing food items are flushed with nitrogen. Why?
Answer:
Oil and fat containing food items are flushed with nitrogen to prevent oxidation. Nitrogen is inert and does not react. Hence food items are flushed with nitrogen to remove the oxygen and hence prevent oxidation.
20. Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity
Answer:
(a) Corrosion
When a metal is attacked by substances around it such as oxygen, moisture, acids etc it is said to undergo corrosion. For example, iron corrodes and forms reddish-brown rust on contact with atmospheric oxygen and moisture. Corrosion causes damage to objects made of metal, specially those of iron.
(b) Rancidity
Rancidity is the process by which fats and oils in foods are oxidised and their smell and taste change. For example, potato chips give out an unpleasant smell due to rancidity if kept open in the air for too long.
Solutions to Group Activity of NCERT Class 10 Science Chapter 1 Chemical Reactions and Equations
Perform the following activity.
- Take four beakers and label them as A, B, C and D.
- Put 25 mL of water in A, B and C beakers and copper sulphate solution in beaker D.
- Measure and record the temperature of each liquid contained in the beakers above.
- Add two spatulas of potassium sulphate, ammonium nitrate, anhydrous copper sulphate and fine iron fillings to beakers A, B, C and D respectively and stir.
- Finally measure and record the temperature of each of the mixture above. Find out which reactions are exothermic and which ones are endothermic in nature.
Answer:
Solutions to All In-text Activities of NCERT Class 10 Science Chapter 1 Chemical Reactions and Equations
1. Complete Activity 1.1 (Page 1).
CAUTION: This Activity needs the teacher’s assistance. It would be better if students wear suitable eyeglasses.
- Clean a magnesium ribbon about 3-4 cm long by rubbing it with sandpaper.
- Hold it with a pair of tongs. Burn it using a spirit lamp or burner and collect the ash so formed in a watch-glass as shown in Fig. 1.1. Burn the magnesium ribbon keeping it away as far as possible from your eyes.
- What do you observe?
Answer:
2. Complete Activity 1.2 (Page 2).
- Take lead nitrate solution in a test tube.
- Add potassium iodide solution to this.
- What do you observe?
Answer:
3. Complete Activity 1.3 (Page 2).
- Take a few zinc granules in a conical flask or a test tube.
- Add dilute hydrochloric acid or sulphuric acid to this (Fig. 1.2). CAUTION: Handle the acid with care.
- Do you observe anything happening around the zinc granules?
- Touch the conical flask or test tube. Is there any change in its temperature?
Answer:
4. Complete Activity 1.4 (Page 6).
- Take a small amount of calcium oxide or quick lime in a beaker.
- Slowly add water to this.
- Touch the beaker as shown in Fig. 1.3.
- Do you feel any change in temperature?
Answer:
5. Complete Activity 1.5 (Page 8).
- Take about 2 g ferrous sulphate crystals in a dry boiling tube.
- Note the colour of the ferrous sulphate crystals.
- Heat the boiling tube over the flame of a burner or spirit lamp as shown in Fig. 1.4.
- Observe the colour of the crystals after heating.
Answer:
6. Complete Activity 1.6 (Page 8).
- Take about 2 g lead nitrate powder in a boiling tube.
- Hold the boiling tube with a pair of tongs and heat it over a flame, as shown in Fig. 1.5.
- What do you observe? Note down the change, if any.
Answer:
7. Complete Activity 1.7 (Page 9).
- Take a plastic mug. Drill two holes at its base and fit rubber stoppers in these holes. Insert carbon electrodes in these rubber stoppers as shown in Fig. 1.6.
- Connect these electrodes to a 6 volt battery.
- Fill the mug with water such that the electrodes are immersed. Add a few drops of dilute sulphuric acid to the water.
- Take two test tubes filled with water and invert them over the two carbon electrodes.
- Switch on the current and leave the apparatus undisturbed for some time.
- You will observe the formation of bubbles at both the electrodes. These bubbles displace water in the test tubes.
- Is the volume of the gas collected the same in both the test tubes?
- Once the test tubes are filled with the respective gases, remove them carefully.
- Test these gases one by one by bringing a burning candle close to the mouth of the test tubes. CAUTION: This step must be performed carefully by the teacher.
- What happens in each case?
- Which gas is present in each test tube?
Answer:
8. Complete Activity 1.8 (Page 9).
- Take about 2 g silver chloride in a china dish.
- What is its colour?
- Place this china dish in sunlight for some time (Fig. 1.7).
- Observe the colour of the silver chloride after some time.
Answer:
9. Carry out the following Activity (Page 10):Take about 2 g barium hydroxide in a test tube. Add 1 g of ammonium chloride and mix with the help of a glass rod. Touch the bottom of the test tube with your palm. What do you feel? Is this an exothermic or endothermic reaction?
Answer:
10. Complete Activity 1.9 (Page 10).
- Take three iron nails and clean them by rubbing with sand paper.
- Take two test tubes marked as (A) and (B). In each test tube, take about 10 mL copper sulphate solution.
- Tie two iron nails with a thread and immerse them carefully in the copper sulphate solution in test tube B for about 20 minutes [Fig. 1.8 (a)]. Keep one iron nail aside for comparison.
- After 20 minutes, take out the iron nails from the copper sulphate solution.
- Compare the intensity of the blue colour of copper sulphate solutions in test tubes (A) and (B) [Fig. 1.8 (b)].
- Also, compare the colour of the iron nails dipped in the copper sulphate solution with the one kept aside [Fig. 1.8 (b)].
Answer:
11. Complete Activity 1.10 (Page 11).
- Take about 3 mL of sodium sulphate solution in a test tube.
- In another test tube, take about 3 mL of barium chloride solution.
- Mix the two solutions (Fig. 1.9).
- What do you observe?
Answer:
12. Complete Activity 1.11 (Page 12).
- Heat a china dish containing about 1 g copper powder (Fig. 1.10).
- What do you observe?
Answer:
Extra Questions to Complement Solutions to NCERT Class 10 Science Chapter 1 Chemical Reactions and Equations
Very Short Answer Type:
1. Is burning of natural gas an exothermic process or endothermic process?
Answer:
Exothermic process.
2. Name a phenomenon which happens inside our bodies which is an exothermic process.
Answer:
Respiration.
3. Name the gas that is evolved at the anode during electrolysis of water.
Answer:
Oxygen.
4. Burning of natural gas gives which two products?
Answer:
Carbon dioxide and water.
5. An iron nail in copper sulphate turns brown while the copper sulphate solution turns from blue to green. What kind of a reaction is this?
Answer:
Displacement reaction.
6. Which law requires you to balance chemical equations?
Answer:
Law of conservation of mass.
7. On decomposition of a substance containing lead, nitrogen dioxide gas is produced. Write the formula of the substance.
Answer:
Pb(NO3)2
8. Describe the visual change when lead nitrate reacts with potassium iodide.
Answer:
Yellow precipitate of lead iodide forms.
9. What happens when CO2 is passed through lime water?
Answer:
Lime water turns milky.
10. What is a solution of a substance in water called?
Answer:
Aqueous solution.
Multiple Choice Questions (MCQ):
1. Which reaction is an example of an exothermic reaction?
(A) Electrolysis of water
(B) Dissolution of ammonium chloride in water
(C) Reaction of calcium oxide with water
(D) Melting of ice
Answer: (C) Reaction of calcium oxide with water
Calcium oxide reacts vigorously with water to produce slaked lime and releases a large amount of heat.
CaO + H2O à Ca(OH)2 + Heat
Hence, the reaction is exothermic.
2. Which of the following is NOT an indication of a chemical reaction?
(A) Change in state
(B) Change in colour
(C) Evolution of a gas
(D) Dissolution in water
Answer: (D) Dissolution in water
3. The reaction of calcium oxide with water is an example of a:
(A) Combination reaction
(B) Displacement reaction
(C) Double displacement reaction
(D) Decomposition reaction
Answer: (A) Combination reaction
4. What colour change is observed when ferrous sulphate is heated?
(A) Green to blue
(B) Green to brown
(C) Green to yellow
(D) Green to red
Answer: (B) Green to brown
5. Which of the following is an example of a redox reaction? (
(A) Dissolution of sugar in water
(B) Combustion of methane
(C) Dissociation of salt in water
(D) Photosynthesis in plants
Answer: (B) Combustion of methane
In combustion of methane:
CH4(g) + 2O2(g) à CO2(g) + 2H2O(g)
Methane is oxidised to carbon by addition of oxygen and oxygen is reduced to water by addition of hydrogen.
Short Answer Type:
1. Name the gas which burns with a popping sound. Write an equation in which this gas is evolved as a product.
Answer:
The gas which burns with a popping sound is hydrogen. An equation in which this gas is evolved is :
Zn + H2SO4 à ZnSO4 + H2
2. What kind of a reaction is burning of coal? Give the reaction equation.
Answer:
The burning of coal is a combination reaction. The reaction equation is: C(s) + O2(g) à CO2(g)
3. When ferrous sulphate crystals are heated two gases are produced. Name the two gases and write the balanced equation involved.
Answer:
Sulphur dioxide (SO2) and sulphur trioxide (SO3) gases are produced. The equation involved is:
2FeSO4(s) + Heat à Fe2O3(s) + SO2(g) + SO3(g)
4. Complete the missing components/variables given as x in the following reactions:
(a) 2AgCl(s) + Sunlight à 2Ag(s) + Cl2(x)
(b) Pb(s) + CuCl2(aq) à PbCl2(x) + Cu(s)
(c) Na2SO4(aq) + BaCl2 à BaSO4(x) + 2Nacl(aq)
(d) CaCO3 + x à CaO(s) + CO2(g)
Answers:
(a) 2AgCl(s) + Sunlight à 2Ag(s) + Cl2(g)
(b) Pb(s) + CuCl2(aq) à PbCl2(aq) + Cu(s)
(c) Na2SO4(aq) + BaCl2 à BaSO4(s) + 2Nacl(aq)
(d) CaCO3 + Heat à CaO(s) + CO2(g)
5. Describe two reactions which are used in black and white photography.
Answer:
The below reactions are used in black and white photography:
Reaction 1: White silver chloride decomposes into grey silver and chlorine by light.
2AgCl(s) + Light à 2Ag(s) + Cl2(g)
Reaction 2: Silver bromide decomposes into grey silver and bromine by light.
2AgBr(s) + Light à 2Ag(s) + Br2(g)
6. Is electrolysis of water an exothermic or endothermic reaction? Why?
Answer:
Electrolysis of water is an endothermic reaction because it requires energy in the form of electricity to occur.
7. List four signs that indicate a chemical reaction has taken place.
Answer:
The following indicates that a chemical reaction has taken place:
- Change in state
- Change in colour
- Evolution of a gas
- Change in temperature
8. Identify the reducing agent in the following reactions:
(A) ZnO + C à Zn + CO
(B) 2Al + 3CuO à Al2O3 + 3Cu
(C) H2S + Cl2 à 2HCl + S
(D) CuO + H2 à Cu + H2O
Answer:
(A) ZnO + C à Zn + CO
ZnO loses oxygen and is reduced. Therefore, carbon (C) is the reducing agent.
(B) 2Al + 3CuO à Al2O3 + 3Cu
CuO loses oxygen and is reduced. Therefore, Aluminium (Al) is the reducing agent.
(C) H2S + Cl2 à 2HCl + S
Cl2 gains hydrogen and is reduced to HCl. Therefore, H2S is the reducing agent.
(D) CuO + H2 à Cu + H2O
CuO loses oxygen and get reduced to copper. Therefore, H2 is the reducing agent.
9. Identify the oxidising agent in the following reactions:
(A) H2O2 + 2KI à I2 + 2KOH
(B) 2MnO2 + 4HCl à MnCl2 + Cl2 + 2H2O
(C) Fe2O3 + 3CO à 2Fe + 3CO2
(D) 2K + H2O à 2KOH + H2
Answer:
(A) H2O2 + 2KI à I2 + 2KOH
Here KI gains oxygen and gets oxidised. Hence, the oxidising agent is H2O2.
(B) 2MnO2 + 4HCl à MnCl2 + Cl2 + 2H2O
HCl loses hydrogen and gets oxidised to Cl2. Hence, MnO2 is oxidising agent.
(C) Fe2O3 + 3CO à 2Fe + 3CO2
CO gains oxygen and gets oxidised to CO2. Hence, Fe2O3 is the oxidising agent.
(D) 2K + H2O à 2KOH + H2
K gains oxygen and is oxidised to KOH. Hence, H2O is the oxidising agent.
10. What steps can you take to prevent rancidity?
Answer:
Antioxidants can be added to oily and fatty foods. These foods can be kept in airtight containers to help slow down oxidation. Bags containing these foods can be flushed with non-reactive gases like nitrogen which displaces the oxygen and helps to prevent oxidation.
Long Answer Type:
1. A chemistry student carried out an experiment to determine the reactivity of different metals with hydrochloric acid (HCl). The student added small pieces of various metals to separate test tubes containing HCl solution. Each metal reacted differently with the acid. The following observations were noted:
Test Tube 1: Zinc (Zn) pieces were added to HCl solution. Bubbles of gas were observed, and the solution turned cloudy.
Test Tube 2: Copper (Cu) pieces were added to HCl solution. No visible reaction was observed.
Test Tube 3: Magnesium (Mg) pieces were added to HCl solution. Bubbles of gas were observed, and the solution turned colourless.
Test Tube 4: Iron (Fe) pieces were added to HCl solution. Bubbles of gas were observed, and the solution turned pale green.
Based on the observations:
(A) Identify the metals that react with HCl and those that do not.
(B) Explain why some metals react with HCl while others do not.
(C) Describe the observations made in each test tube and explain the chemical reactions that occurred.
(d) Suggest a method to determine the identity of the gas evolved in each reaction.
Answer:
(A) Zinc (Zn), Magnesium (Mg) and Iron (Fe) reacted with HCl because bubbles of gas observed and the colour of the solution changed. Copper (Cu) did not react with HCl because no permanent changes were observed.
(B) Zinc (Zn), Magnesium (Mg) and Iron (Fe) are more reactive elements than copper (Cu), hence they reacted with HCl, while copper did not.
(C) Test Tube 1: Bubbles of hydrogen gas were observed, and the solution turned cloudy due to the formation of zinc chloride (ZnCl2):
Zn(s) + 2HCl(aq) à ZnCl2(aq) + H2(g)
Test Tube 2: No reaction happened.
Test Tube 3: Bubbles of hydrogen gas were observed, and the solution turned colourless due to the formation of magnesium chloride (MgCl2):
Mg(s) + 2HCl(aq) à MgCl2(aq) + H2(g)
Test Tube 4: Bubbles of hydrogen gas were observed, and the solution turned pale green due to the formation of Iron Chloride (FeCl2):
Fe(s) + 2HCl(aq) à FeCl2(aq) + H2(g)
(D) If a burning candle or matchstick is held in front of test tubes 1, 3 and 4, a popping sound is heard. This indicates that hydrogen is produced. Test tube 2 does not produce any hydrogen and hence will not produce a popping sound on contact with the candle.
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Frequently Asked Questions (FAQs) on NCERT Solutions to Class 10 Science Chapter 1 Chemical Reactions and Equations
Our experts have answered all in-text questions, exercise problems, group activity and in-text activities comprehensively in one convenient spot. Plus, we offer an exclusive set of extra practice problems to elevate your learning experience. And here’s the best part – you can download our PDF solutions for free, anytime you need them! Dive in and supercharge your studies with us!
The following topics are covered:
1.1 Chemical Equations
– 1.1.1 Writing a Chemical Equation
– 1.1.2 Balanced Chemical Equations
1.2 Types of Chemical Reactions
– 1.2.1 Combination Reaction
– 1.2.2 Decomposition Reaction
– 1.2.3 Displacement Reaction
– 1.2.4 Double Displacement Reaction
– 1.2.5 Oxidation and Reduction
1.3 Have You Observed the Effects of Oxidation Reactions in Everyday Life
– 1.3.1 Corrosion
– 1.3.2 Rancidity
Here are the number of questions for the chapter:
(i) 3 Multiple Choice Questions (1, 2, 3)
(ii) 13 Short Answer Type Questions (4, 9 – 20)
(iii) 4 Long Questions (Questions 5, 6, 7, 8)
It is of utmost importance that you know how to balance chemical equations. Make sure you get plenty of practise balancing chemical equations because you will definitely see questions in the exam. Next, understand the different types of reactions – combination reaction, decomposition reaction, displacement reaction, double displacement reaction, oxidation and reduction and the differences between them. Understand and memorise the reactions given in the book as they are important for your exams.
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