NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations includes all the important topics with detailed explanation that aims to help students to understand the concepts better. Students who are preparing for their Class 10 exams must go through NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations. All Chapter 1 – Chemical Reactions and Equations Exercise Questions with Solutions to help you to revise complete Syllabus and Score More marks.
NCERT Solution for Class 10 Science Ch 1 Chemistry : Chemical Reactions & Equations
Intext Questions, Page no - 6
1. Why should a magensium ribbon be cleaned before burning in air ?
Answer :
A magnesium ribbon is cleaned to remove the protective layer of basic magnesium carbonate from its surface so that it may readily combine with the oxygen of air (on heating).
2. Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine → Hydrogen Chloride
(ii) Barium Chloride + Aluminium Sulphate → Barium Sulphate + Aluminium Chloride
(iii) Sodium + Water → Sodium hydroxide + Hydrogen
Answers :
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.
Answers :
Intext Questions, Page - 10
1. A solution of 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.
Answers :
(i) The substance whose solution in water we use for white - washing is calcium oxide (lime, choona). So, the substance X is calcium oxide. Its formula is CaO.
(ii)
2. Why 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 :
The gas which is collected in double the amount in the electrolysis of water experiment is hydrogen. This is because water (H2O) contains 2 parts of hydrogen element (as compared to only 1 part of oxygen element).
Intext Questions, 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, then the blue colour of copper sulphate solution changes because iron displaces copper from copper sulphate solution to form a light green solution of iron sulphate.
2. Give an example of a double displacement reaction other than the one given in activity 1.10
Answer :
When silver nitrate solution is added to sodium chloride solution, then a double displacement reaction takes place in which a white precipitate of silver chloride is formed alongwith sodium nitrate solution.
3. Identify the substances that are oxidised and the substances that are reduced in the following reactions.
Answers :
(i) Substance oxidised : Na ; Substance reduced : O2
(ii) Substance oxidised : H2 ; Substance reduced : CuO
EXERCISES, Page - 14, 15 & 16
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)
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
3. What happens when dilute hydrochloric acid is added to iron fillings ? Tick the correct answers.
(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
4. What is a balanced chemical equation ? Why should chemical equations be balanced ?
Answer :
A chemical equation having an equal number of atoms of different elements in the reactants and products is called a balanced chemical equation. Here is an example. Zinc reacts with dilute sulphuric acid to form zinc sulphate and hydrogen :
Now, this equation has an equal number of Zn atoms (1 each), H atoms (2 each), S atoms (1 each), and O atoms (4 each) in reactants and products, so it is a balanced chemical equation.
The chemical equations are balanced to satisfy the law of conservation of mass which says that 'matter (or atoms) can neither be created nor destroyed in a chemical reaction'. So, the total mass of all the elements present in the products of a chemical reaction should be equal to the total mass of all the elements present in the reactants. In other words, the number of atoms of each element in the products must be equal to the number of atoms of these elements in the reactants.
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.
Answers :
6. Balance the following chemical equations.
7. Write the balanced chemical equations 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 :
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)
Answers :
9. What does one mean by exothermic and endothermic reactions ? Give examples.
Answer :
Those reactions in which heat is evolved are known as exothermic reactions. For example, when carbon burns in oxygen to form carbon dioxide, a lot of heat is produced in this reaction :
C (s) + O2 (g) → CO2 (g) + Heat
Those reactions in which heat is absorbed are known as endothermic reactions. For example, when nitrogen and oxygen are heated to a very high temperature (of about 3000℃) they combine to form nitrogen monoxide, and a lot of heat is absorbed in this reaction :
N2 (g) + O2 (g) + Heat → 2NO (g)
10. Why is respiration considered an exothermic reaction ? Explain.
Answer :
Respiration is considered an exothermic reaction because energy is released in this process. During respiration, glucose (obtained from the digestion of food) combines with oxygen of air in the cells of our body to form carbon dioxide and water, and energy is released :
C6H12O6 (aq) + 6O2 (g) → 6CO2 (g) + 6H2O (l) + Energy
11. Why are decomposition reactions called the opposite of combination reactions ? Write equations for these reactions.
Answer :
The decomposition reactions are called the opposite of combination reactions because in a combination reaction two or more substances combine to form a single substance whereas in a decomposition reaction, a single substance splits up to form two or more simpler substances.
(a) When hydrogen burns in oxygen, it forms water :
2H2 (g) + O2 (g) → 2H2O (l)
In this reaction, two substances hydrogen and oxygen combine to form a single substance water, so this is a combination reaction.
(b) When acidified water is eletrolysed, hydrogen and oxygen are formed :
Here a single substance water breaks up into two simpler substances, hydrogen and oxygen. So, this is a decomposition reaction. We can see from the above examples that a decomposition reaction is opposite of a combination reaction.
12. Write one equation each for decomposition reactions where energy is supplied in the form of (a) heat (b) light, and (c) electricity.
Answers :
13. What is the difference between displacement and double displacement reactions ? Write equations for these reactions.
Answer :
In a displacement reaction, a more reactive element displaces a less reactive element from its compound whereas in a double displacement reaction, two compounds combine by an exchange of ions to form two new compounds.
(i) A displacement reaction takes place between copper sulphate solution and zinc to form zinc sulphate solution and copper :
CuSO4 (aq) + Zn (s) → ZnSO4 (aq) + Cu (s)
(ii) A double displacement reaction takes place between barium chloride solution and sodium sulphate solution to form a white precipitate of barium sulphate and sodium chloride solution :
BaCl2 (aq) + Na2SO4 (aq) → BaSO4 (s) + 2NaCl (aq)
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 :
15. What do you mean by a precipitation reaction ? Explain by giving examples.
Answer :
Any reaction in which an insoluble solid (called precipitate) is formed that suddenly separates from the solution, is called a precipitation reaction. The reaction between silver nitrate solution and sodium chloride solution to form silver chloride precipitate is an example of a precipitation reaction :
In this reaction, silver chloride is formed as a white, insoluble solid (called precipitate) which separates out suddenly from the solution.
16. Explain the following in terms of gain or loss of oxygen with two examples each.
(a) Oxidation (b) Reduction
Answers :
(a) Oxidation : The gain of oxygen by a substance in a reaction is called oxidation. For example,
- When magnesium is burned in air, then magnesium oxide is formed :
- When copper oxide is heated with hydrogen, then copper metal and water are formed :
(b) Reduction : The loss of oxygen by a substance in a reaction, is called reduction.
- When zinc oxide is heated with carbon, then zinc metal and carbon monoxide are formed :
In this reaction, Zinc oxide (ZnO) is losing oxygen to form zinc metal (Zn), therefore, zinc oxide is reduced to zinc.
- When iron (III) oxide is heated with aluminium powder, then aluminium oxide and iron metal are formed :
In this case, iron (III) oxide (Fe2O3) is losing oxygen to form iron metal (Fe), therefore, iron (III) oxide is reduced to iron.
17. A shiny brown coloured element 'X' on heating air becomes black in colour. Name the element 'X' and the black coloured compound formed.
Answer :
The shiny brown coloured element 'X' is copper metal (Cu).
When copper metal is heated in air, it forms a black coloured compound copper oxide. So, the black coloured compound is copper oxide or copper (II) oxide, CuO.
18. Why do we apply paint on iron articles ?
Answer :
Paint is applied on iron articles to prevent their rusting. When a coat of paint is applied to the surface of an iron article, then air and moisture can't come in contact with the iron metal of the article and hence no rusting takes place.
19. Oil and fat containing food items are flushed with nitrogen. Why ?
Answer :
The plastic bags containing oil and fat containing food items (such as potato chips) are flushed with an unreactive gas nitrogen so as to prevent them from getting oxidised and turn rancid. This is because in the presence of oxygen of air, the fats and oils present in food items get oxidised forming products having unpleasant smell and taste which turn the foods rancid (making them unfit for eating). When air containing oxygen is replaced by unreactive nitrogen gas, the packed food items do not get spoiled. They remain fresh for a much longer time.
20. Explain the following terms with one example each.
(a) Corrosion
(b) Rancidity
Answers :
(a) Corrosion : The process in which metals are eaten up gradually by the action of air, moisture or a chemical (such as an acid) on their surface, is called corrosion. Rusting of iron is the most common example of corrosion. Rusting involves unwanted oxidation of iron metal which occurs in nature on its own. When an iron object is left in damp air for a considerable time, it gets covered with a red - brown flaky substance called 'rust'. The corrosion (or rusting) of iron is a continuous process which, if not prevented in time, eats up the whole iron object.
(b) Rancidity : Oxidation has damaging effect on foods containg fats and oils. When the food materials prepared in fats and oil are kept for a long time, they start giving unpleasant smell and taste. The condition produced by the aerial oxidation of fats and oil in foods marked by unpleasant smell and taste is called rancidity. Rancidity spoils the food materials prepared in fats and oil which have been kept for a considerable time and makes them unfit for eating. For example, if potato chips prepared in oil are kept exposed to air for a long time, they start giving unpleasant smell and taste due to the oxidation of oil present in them. The potato chips turn rancid and become unfit for eating.