RBSE Class 10 Science Solutions Chapter 1 Chemical Reactions and Equations

RBSE Class 10 Science Solutions Chapter 1 Chemical Reactions and Equations

RBSE Class 10 Science Chapter 1 Chemical Reactions and Equations InText Questions and Answers

Page 6.

Question 1.
Why should a magnesium ribbon be cleaned before burning in air?
Answer:
Magnesium ribbon is cleaned with sand paper before burning in air because combustion of it is not easy due to impurities present on it. The surface of it beomes rough due to cleaning with sand paper so rate of reaction increases and pure magnesium is obtained.

Question 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.
Answer:

Question 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:

Page 10.

Question 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.
Answer:
(i) The substance ‘X’ used for whitewashing is quicklime (calcium oxide), the chemical formulae of this is CaO.

Question 2.
Why is the amount of gas collected in one of the test tubes in Activity 1.7 (See in text book) double of the amount collected in the other? Name this gas.
Answer:
In activity 1.7 the reaction of electrolysis of water occurs as follows:

On completion of reaction hydrogen and oxygen are obtained in the ratio of 2 : 1 by volume.
According to law of mass action, when two molecules of water (H₂O) are decomposed then amount of Hydrogen produced in double than amount of oxygen. So in the above activity amount of gas (Hydrogen) collected in one of the test tubes is double of the amount collected in the other.

Page 13.

Question 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 reaction given below takes place. In this reaction iron displaces copper from copper sulphate solution.

In this, the blue colour of copper of copper sulphate solution fades and Iron nails becomes brown.

Question 2.
Give an example of a double displacement reaction other than the one given in activity 1.10 (See in textbook).
Ans.
Double displacement reaction:
The reaction in which there is an exchange of ions between the reactants are called double displacement reaction

Question 3.
Identify the substances that are oxidised and 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) 4Na(s) + O₂(g) → 2Na₂O(s)
In this reaction sodium (Na) is oxidised and oxygen (O₂) is reduced.

(ii) CuO(s) + H₂(g) → Cu(s) + H₂O(l)
In this reaction CuO is reduced and H₂ is oxidised.

RBSE Class 10 Science Chapter 1 Chemical Reactions and Equations Textbook Questions and Answers

Question 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)

Question 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:
Displacement reaction.

Question 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:
Hydrogen gas and iron chloride are produced.

Question 4.
What is a balanced chemical equation? Why should chemical equations be balanced?
Answer:
The chemical equation in which the number of atoms of each element on both sides (reactants and products) of the equation are equal is called balanced chemical equation. Importance of balancing chemical equation – According to the law of conservation of mass : Mass can neither be created nor be destroyed. In a chemical reaction the total mass of elements of products must be equal to the total mass of the elements of reactants. In other words, the number of atoms of each element of the reactants must be equal to the number of atoms of each element of the products. So the skeleton equation must be balanced.
For example:

In the above reaction, Fe reacts with water vapours and gives Iron oxide and Hydrogen gas.

Question 5.
Translate the following statements into chemical equations and then balance them:
(a) Hydrogen gas combines with nitrogen to form ammonia.
(b) Hydrogen sulphate gas bums in air to give water and sulphur dioxide.
(c) Barium chloride reacts with alumni – nium 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) N₂(g) + H₂(g) → NH₃(g)
Balanced equation:
N₂(g)+3H₂ (g) → 2NH₃ (g)

(b) H₂S(g) + O₂(g) → H₂O(D + SO₂(g)
Balanced equation:
2H₂S(g) + 3O₂(g) 2H₂O(l) + 2SO₂ (g)

(c) Al₂(SO₄)₃(aq) + BaCl₂(aq) → AlCl₃(aq) + BaSO₄(s)
Balanced equation:
Al₂(SO₄)₃(aq) + 3BaCl₂(aq) → 2AlCl₃(aq) + 3BaSO₄(s)↑

(d) K(s) + H₂O(l) → KOH(aq) + H₂(g)
Balanced equation:
2K(s) + 2H₂O(l) → 2KOH(aq) + H₂ (g)

Question 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:
Balanced chemical equation:
(a) 2HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + 2H₂O
(b) 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O
(c) NaCl + AgNO₃ → AgCl +NaNO₃
(d) BaCl₂ + H₂SO₄→ BaSO₄ + 2HCl

Question 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.
Answer:
Balanced chemical equation:
(a) Ca(OH)₂(aq) + CO₂(g) CaCO₃(s) + H₂O(l)
(b) Zn(s) + 2AgNO₃(aq) → Zn(NO₃)₂(aq) + 2Ag(s)
(c) 2Al(s) + 3CuCl₂(aq)→ 2AlCl₃(aq) + 3Cu(s)
(d) BaCl₂(aq) + K₂SO₄(aq) → BaSO₄(s) + 2KCl(aq)

Question 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:

Question 9.
What does one mean by exo – thermic and endothermic reactions? Give examples.
Answer:
Exothermic reactions: The reactions in which energy or heat is evolved with products are called exothermic reactions.
Example:
(1) Combustion of Natural gas CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g) + Energy
(2) Respiration is also exothermic reaction.
(3) Formation of compost by the decomposition of vegetable matter is also exothermic reaction.
Endothermic reactions – The reactions in which heat is absorbed are called endothermic reactions.
Example:

Question 10.
Why is respiration considered an exothermic reaction? Explain.
Answer:
All the living organisms requires energy for survival which is obtained from food. During digestion, the food material is broken down into small pieces. Some substances like rice, potato and bread have carbohydrate which are broken down into glucose. The glucose combines with oxygen present in the cells of our body and provides energy. This oxygen is obtained by respiration. So, the respiration is exothermic reaction.
The reaction for respiration from which energy is obtained is as follows:

Question 11.
Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Answer:
Decomposition reaction is opposite of combination reaction because in the decomposition reaction a single substance decomposes to give two or more substances whereas in combination reaction two or more substances (element or compounds) combine to form a new single substance.
Combination reaction:  Formation of water from H₂(g) and O₂(g).
2H₂(g)+O₂(g) → 2H₂O(l)
Decomposition reaction:

On heating crystals of ferrous sulphate (FeSO₄ – 7H ₂O) gives water so colour of crystal is changed. After that this is decomposed in ferric oxide (Fe₂O₃), sulphur dioxide (SO₂) and sulphur trioxide (SO₂). So it is clear that decomposition reactions are opposite of combination reactions.

Question 12.
Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.
Answer:
(i) Decomposition reaction involving absorption of heat: On heating calcium carbonate it gives calcium oxide and carbon dioxide.

(ii) Decomposition reaction involving absorption of light: In the presence of sunlight, silver chloride splits into silver and chlorine

(iii) Decomposition reaction involving absorption of electricity: When electrolysis is done on distilled water, then it decompose to form hydrogen and oxygen.

Question 13.
What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Answer:
Equations for these reactions:

Question 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:
In the purification of silver metal, to obtain silver from silver nitrate solution it is displaced by copper metal because copper is more reactive than silver. The reaction occurs in the following manner:

Quesation 15.
What do you mean by a precipitation reaction? Explain by giving examples.
Answer:
When an insoluble material is formed as a product in a reaction, the insoluble substance settles down in the solution and is called ‘precipitate’. The reaction in which a precipitate is formed is called a precipitation reaction.
Example:

Question 16.
Explain the following in terms of gain or loss of oxygen with two examples each:
(a) Oxidation
(b) Reduction.
Answer:
(a) Oxidation: A reaction in which addition of oxygen to a substance or removal of hydrogen from a substance takes place is called oxidation reaction.
Examples of Oxidation:

(b) Reduction:  A reaction in which a substance gains hydrogen or losses oxygen is called reduction reaction.
Examples of Reduction:

Question 17.
A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.
Answer:
Element X is copper and the black coloured compound formed is copper (II) oxide. Copper is brown coloured shiny element, which converts in black coloured copper (II) oxide on heating in the presence of air.

Question 18.
Why do we apply paint on iron articles?
Answer:
Corrosion of articles of iron starts when they comes in contact with acid, moisture etc. and a reddish brown layer is formed on it. This is called rusting of iron. Due to this reason iron articles start destroying. So we apply paint on these to stop this because paint covers the surface of the iron articles and they do not come in direct contact of air so rusting do not occurs.

Question 19.
Oil and fat containing food items are flushed with nitrogen. Why?
Answer:
Oil and fat containing food items are flushed with less reactive gas nitrogen so that they cannot oxidise. Otherwise due to oxidation, these becomes rancid and taste and odour are changed.

Question 20.
Explain the following terms with one example each:
(a) Corrosion
(b) Rancidity.
Answer:
(a) Corrosion: When a metal comes in contact with acid, humidity, etc. then this reacts with O₂, moisture etc. and forms oxides and hydroxides; due to which metals starts destroying. This process is called corrosion. The shining of articles is destroyed.

Example:
Rusting of iron, formation of black layer on silver, formation of green layer on copper.

(b) Rancidity:  When the food materials having oil and fat are kept for long time then they gives bad taste due to oxidation. This is called rancidity. So to stop the oxidation of these substances antioxidants are mixed and these are kept in airtight container.

Example:
When potato chips are packed, these are flushed with nitrogen to control the oxidation.