Class 10 Science Chapter 1 Intext Questions

In-text questions set 1 Page number – 6
1. Why should a magnesium ribbon be cleaned before burning in air?
Solution:
Magnesium ribbon should be cleaned before burning in air because Magnesium metal reacts with the atmospheric oxygen and forms Magnesium Oxide (MgO) layer which is a very stable compound. In order to prevent further reactions with Oxygen, it is therefore necessary to clean the ribbon by to remove the layer of MgO.
2. Write a balanced equation for the following chemical reactions.
i) Hydrogen + Chloride —-> Hydrogen chloride
ii) Barium chloride + Aluminium sulphate —-> Barium sulphate + Aluminium chloride
iii) Sodium + Water —-> Sodium hydroxide + Hydrogen
Solution:
i) H+ Cl→ 2HCl
ii) 3BaCl+ Al2(SO4)→3BaSO+ 2AlCl
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 solution of Sodium chloride.
ii) Sodium hydroxide solution in water reacts with hydrochloric acid solution to produce Sodium chloride solution and water.
Solution:
i) BaCl+ Na2SO→ BaSO+ 2NaCl
ii) NaOH + HCl → NaCl + H2O
In-text questions set 2 Page number – 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.
Solution:
i) The substance ‘X’ which is used in whitewashing is quick lime or Calcium Oxide and its formula is CaO.
ii) 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
Solution:
In activity 1.7, gas collected in one of the test tubes is double of the amount collected in the other because water gets hydrolysed to release H2 and O2 gas. Here, after electrolysis two molecules of Hydrogen and one molecule of oxygen gas is released, hence the amount of Hydrogen collected would be double than that of oxygen.
In-text questions set 3 Page number – 13
1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Solution:
When an iron nail dipped in the copper sulphate solution, iron displaces copper from the copper sulphate because iron is more reactive than copper. Therefore the colour of the copper sulphate solution changes. The reaction is:
Fe + CuSO4 → FeSO4 + Cu
2. Give an example of a double displacement reaction other than the one given in Activity 1.10.
 Solution:
Reaction Between silver nitrate (AgNO3) and Sodium chloride (NaCl) is an example of double displacement reaction. During the reaction negative and positive ions trade positions as a result in the formation of white silver chloride precipitate. The chemical reaction is given below.
Ag+ + NO3 + Na+ + Cl– → AgCl + Na+ + NO3
3. Identify the substances that are oxidized and that are reduced in the following equation.
i) 4Na(s) + O2(g) → 2Na2O(s)
ii) CuO(s) + H2(g) → Cu(s) + H2O(l)
Solution:
The Sodium (Na) in the first equation is getting oxidized with the addition of Oxygen (O2) and the Copper (Cu) in the second equation is reduced due to the addition of Hydrogen (H2)
Exercise Questions Page number – 14-16
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
Solution:
(i) (a) and (b)
Explanation: (a) because Oxygen is being removed and (b) because the removed oxygen from Lead is added to the elemental Carbon.
2.  Fe2O+ 2Al → Al2O+ 2Fe
The above reaction is an example of a
  1. Combination reaction.
  1. Double displacement reaction.
  1. Decomposition reaction.
  1. Displacement reaction.
Solution:
Answer is 4. Displacement reaction.
Explanation: The Oxygen from the Ferrous oxide is getting displaced to the Aluminium metal to form Aluminium Oxide. In this reaction Aluminum is more reactive metal than Fe. Therefore Al will displace Fe from its oxide. This type of chemical reactions in which one of the elements displace another is called displacement reaction. Here less reactive metal is displaced by more reactive metal. Since one-time displacement is occurring, therefore, it is called a single displacement reaction.
3. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.
  1. Hydrogen gas and Iron chloride are produced.
  1. Chlorine gas and Iron hydroxide are produced.
  1. No reaction takes place.
  1. Iron salt and water are produced.
Solution:
  1. Hydrogen gas and Iron chloride are produced.
Explanation: The Chlorine from Hydrogen chloride is displaced by the Iron fillings to undergo the following reaction.
2HCl + Fe → FeCl+ H2
4. What is a balanced chemical equation? Why should a chemical equation be balanced?
Solution:
A balanced equation is the one in which number of different atoms on both the reactant and product sides are equal. Balancing chemical equation is necessary for the reaction should obey The Law of Conservation of mass. Balancing the chemical equation has no defined method and is purely a trial and error attempt.
Question 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) 3H2 (g) + N2 (g) → 2NH3 (g)
(b) H2S (g) + 3O2 (g) → SO2 (g) + 2H2O(l)
(c) 3BaCl2 (aq) + Al2(SO4)3 (aq) → 2AlCl3 (aq) + 3BaSO4 ↓(s)
(d) 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:
(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:
(a) Ca (OH)2 + CO2 → CaCO3 + H2O
(b) Zn + 2AgNO3 → Zn(NO3)2 + 2 Ag
(c) 2Al + 3 CuCl2 → 2AlCl3 + 3 Cu
(d) BaCl2 + K2SO4 → BaSO4 + 2KClQuestion 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
(b) Zinc carbonate(s) → Zinc oxide (s) + Carbon dioxide (g) bromide(s)
(c) Hydrogen (g) + Chloride (g) → Hydrogen chloride (g)
(d) Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen (g)
Answer:
(a) 2KBr (aq) + Bal2(aq) → 2Kl(aq) + BaBr2(s)
Type : Double displacement reaction
(b) ZnCO3 (s) → ZnO (s) + CO2 (g)
Type : Decomposition reaction
(c) H2 (g) + Cl2 (g) → 2HCl(g)
Type : Combination reaction
(d) Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)
Type : Displacement reaction
Question 9
What does one mean by exothermic and endothermic reactions ? Give examples.
Answer:
Exothermic reactions : Those reactions in which heat is evolved are known as exothermic reactions. An exothermic reaction is indicated by writing “+ Heat”on the products side of an equation.
Example :
(i) C (s) + O2 (g) → CO2 (g) + Heat
(ii) N2 (g) + 3H2 (g) → 2NH3 (g) + Heat
Endothermic reactions : Those reactions in which heat is absorbed are known as endothermic reactions. An endothermic reaction is usually indicated by writing “Heat” on the product side of a chemical equation.
Examples :
(i) C (s) + 2S (s) → CS2 (l) – Heat
(ii) N2 (g) + O2 (g) → 2NO(g) – Heat
Question 10
Why is respiration considered an exothermic reaction ? Explain.
Answer:
Respiration is an exothermic process because during respiration glucose combines with oxygen in the cells of our body to form carbon dioxide and water along with the production of energy.
NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations Chapter End Questions Q10
Question 11
Why are decomposition reactions called the opposite of combination reactions? Write equations for these reactions.
Answer:
In a decomposition reaction, a single compound breaks down to produce two or more simpler substances.
For example:
NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations Chapter End Questions Q11
While, in a combination reaction, two or more substances simply combine to form a new substance.
For example:
NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations Chapter End Questions Q11.1
Question 12
Write one equation each for the decomposition reactions where energy is supplied in the form of heat, light or electricity.
OR
Decomposition reactions require energy either in the form of heat or light or electricity for breaking down the reactants. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light and electricity. [CBSE 2015 (Delhi)]
Answer:
NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations Chapter End Questions Q12
Question 13
What is the difference between displacement and double displacement reactions? Write equations for these reactions.
Answer:
In displacement reactions, a more reactive metal displaces a less reactive metal from its solution. For example,
Fe(s) + CuSO4(aq) → Cu(s) + FeSO4(aq)
This is a displacement reaction where iron displaces copper from its solution.
In double displacement reactions, two reactants in solution exchange their ions. For example,
AgNO3(aq) + NaCl (aq) → AgCl(s) + NaNO3 (aq)
This is a double displacement reaction where silver nitrate and sodium chloride exchange Cl and NO3 ions between them.
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:
NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations Chapter End Questions Q14
Question 15
What do you mean by a precipitation reaction ? Explain by giving examples.
Answer:
A reaction in which an insoluble solid called precipitate is formed that separates from the solution is called a precipitation reaction.
Example : When a solution of iron (III) chloride and ammonium hydroxide are mixed, a brown precipitate of iron (III) hydroxide is formed.
NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations Chapter End Questions Q15
Question 16
Explain the following in terms of gain or loss of oxygen with two examples each:
(a) Oxidation and
(b) Reduction.
Answer:
(a) Oxidation : The addition of oxygen to a substance is called oxidation.
Example :
(i) S(s) + O2(g) → SO2(g) (Addition of oxygen to sulphur)
(ii) 2Mg(s) + O2 (g) → 2MgO(s) (Addition of oxygen to magnesium)
(b) Reduction : The removal of oxygen from a substance is called reduction.
Example: (i) CuO + H2 Heat


Cu + H2O
Here, copper oxide is being reduced to copper because oxygen gets removed from copper oxide.
(ii) ZnO + C → Zn + CO
Here, zinc oxide is being reduced to zinc because oxygen gets removed from zinc oxide.
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 (Cu).
The black coloured compound is copper oxide (CuO). The reaction involved is
NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations Chapter End Questions Q17
Question 18
Why do we apply paint on iron articles ?
Answer:
Paint does not allow iron articles to come in contact with air, water and saves iron articles from damage due to rusting.
Question 19
Oil and fat containing food items are flushed with nitrogen. Why ?
Answer:
To keep food items fresh and save from getting oxidised, food items are flushed with nitrogen.
Question 20
Explain the following terms with one example each (a) Corrosion, (b) Rancidity.
Answer:
(a) Corrosion : It is 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.
Example : When iron is exposed to moist air for a long period of time, its surface acquires a coating of a brown, flaky substance called rust. Rust is mainly hydrated iron (III) oxide [Fe2O3.xH20].
NCERT Solutions for Class 10 Science Chapter 1 Chemical Reactions and Equations Chapter End Questions Q20
(b) Rancidity : The condition produced by aerial oxidation of fats and oils in foods marked by unpleasant smell and taste is called rancidity.

Rancidity spoils the food materials prepared in fats and oils which have been kept for a considerable time and makes them unfit for eating.
Rancidity can be prevented by adding anti-oxidants to foods containing fats and oils. It can also be prevented by flushing fat and oil containing foods with nitrogen before sealing.



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