Class 10 Science (Chemistry) Chapter 1-- Chemical Reactions and Equations
Solutions for Class 10th Science Chapter -1
Chemical Reactions and Equations
Q 1.Which of the given statements about the reaction below are incorrect?
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
Ans- (i) (a) and (b)
Explanation- (a) Because Oxygen is being removed.
(b) Because the removed oxygen from lead is added to the carbon.
Q2.
The above reaction is an example of a
(i). Combination reaction
(ii). Double displacement reaction
(iii). Decomposition reaction
(iv). Displacement reaction
Ans -(iv) Displacement reaction
Explanation- The Oxygen from the Ferrous Oxide is getting displaced form Aluminium Oxide. In this reaction Al is more reactive than Fe.
Q 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
Ans:-Hydrogen gas and iron chloride are produced.
Q 4. What is a balanced chemical equation? Why should chemical equations be balanced?
Ans:-An equation for a chemical reaction is an equation in which the number of atoms for each element in the reaction and the total charge is the same for both the reactants and the products. In other words, the mass and the charge are balanced on both sides of the reaction.
Question 5
Translate the following statements into chemical equations and then balance them.
a. Hydrogen gas combines with nitrogen to form ammonia
b. Hydrogen sulfide gas burns in air to give water and sulfur dioxide
c. Barium chloride reacts with Aluminium sulfate to give Aluminium chloride and a precipitate of barium sulphate
d. Potassium metal reacts with water to give a potassium hydroxide and hydrogen gas
Ans:-
a. 3H2 + N2 → 2NH3
b. 2H2S + 3O2 → 2H2O + 2SO2
c. 3BaCl2 + Al2(SO4)3 → 2AlCl3 + 3BaSO4
d. 2K + 2H2O → 2KOH + H2
Q 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
Ans:-
a. 2HNO3 + 2Ca(OH)2 → Ca(NO3)2 + 2H2O
b. 6NaOH + 3H2SO4 → 3Na2SO4 + 6H2O
C. NaCl + AgNO3 → AgCI + NaNO3
d. BaCl2 + H2SO4 → BaSO4 + 2HCl
Q 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
Ans:- (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 + 2KCl
Q 8. Write the balanced chemical equation for the following and identify the type of reaction of each case.
Ans:-
a. Double Displacement reaction
b. Decomposition reaction
c. Combination reaction
d. Displacement reaction
Q 9. What is meant by exothermic and endothermic reactions? Give examples.
Ans:- An endothermic reaction occurs when energy is absorbed from the surrounding in the form of heat.
example- Photosynthesis, melting of ice, evaporation.
An exothermic reaction is one in which energy is released from the system into the surrounding.
example- Explosions, concrete setting, nuclear fission and fusion.
Q 10- Why is respiration considered an exothermic reaction?
Ans:- During respiration, glucose combines with oxygen in the cells of our body to form carbon dioxide and water along with the production of energy.
Glucose + oxygen → carbon dioxide + water + energy
It is an exothermic reaction, because energy is produced during this process.
Q 11- Why are decomposition reactions called the opposite of combination reactions? Write equations for decomposition reactions.
Ans:- Essentially, decomposition reactions are the opposite of combination reactions. A compound decomposes into two or more compounds and/or elements.
For example, mercury (II) oxide will, decompose into mercury metal and oxygen, upon heating:
2HgO → 2Hg + O2
Since heat had to be added to make this reaction occur, it is an endothermic reaction. Most decomposition reactions are endothermic. Another example of decomposition reaction is the heating of calcium carbonate (sea shells, chalk):-
Q 12- Write one equation each for decomposition reactions in which energy is supplied in the form of heat, light or electricity?
Ans:- When calcium carbonate is heated, it decomposes to give calcium oxide and carbon dioxide:
Q 13- What is the difference between displacement and double displacement reactions? Write relevant equations for the above?
Ans:- 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.
This is a double displacement reaction where silver nitrate and sodium chloride exchange Cl– and NO3– ions between them.
Q 14- In the refining of silver, the recovery of silver from silver nitrate solution involves displacement by copper metal. Write down the reaction involved.
Ans:
Q 15- What do you mean by a precipitation reaction? Explain by giving examples:
Ans:- A precipitation reaction is a reaction in which soluble ions in separate solutions are mixed together to form an insoluble compound that settles out of solution as a solid. This insoluble compound is called a precipitate.
An example of a precipitation reaction
AgNO3 (aq) + KCl(aq) → AgCl(s) + KNO3(aq)
The silver chloride (AgCl) has formed a solid, which is observed as a precipitate.
Q 16- A shiny brown colored element ‘X’ on heating in the air becomes black in color. Name the element ‘X’ and the black coloured compound formed.
Ans:- Element ‘X’ is copper (Cu).
Q 17- Why do we apply paint on iron articles?
Ans:- Rust is a soft and porous substance, which gradually falls from the surface of an iron object, and then the iron below starts rusting. Thus, rusting of iron (or corrosion of iron) is a continuous process which, if not prevented in time, eats up the whole iron object. So, when we apply paint on iron articles it reduces the rusting of iron.
Q 18- Oil and fat containing food items are flushed with nitrogen. Why?
Ans:- Packaging fat and oil containing foods in nitrogen gas can prevent rancidity. When the fat and oil present in food materials gets oxidised (in air), their oxidation products have an unpleasant smell and taste. When it is surrounded by unreactive gas, nitrogen, there is no oxygen (of air) to cause its oxidation and make it rancid.
Q 19- Explain the following terms with one example each-
a. Corrosion b. Rancidity
Ans:- a. Corrosion is the process in which metals are eaten up gradually by the action of air, moisture or a chemical on their surface. Corrosion is caused mainly by the oxidation of metals by the oxygen of air.
Example: Rusting of iron is the most common form of corrosion. When an iron object is left in damp air for a considerable period of time, it gets covered with a red-brown flaky substance called ‘rust’. This is called rusting of iron.
b. The condition produced by aerial oxidation of fat and oil in food which is marked by an unpleasant smell and taste is called rancidity.
Example: Rancidity can be retarded by keeping food in a refrigerator.
The refrigerator has a low temperature inside it. When the food is kept in a refrigerator, the oxidation of fat and oil in it is slowed down due to low temperature. So, the development of rancidity due to oxidation is retarded.
Q 20- Why should a magnesium ribbon be cleaned before burning in air?
Ans:- To remove the oxide layer and facilitates rapid burning.
Q 21- Write the 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
Ans:
i. H2 + Cl2 → 2HCl
ii. 3BaCl2 + Al2(SO4)3 → 3BaSO4 + 2AlCl3
iii. 2Na + 2H2O → 2NaOH + H2
Q 22- Write a balanced chemical equation and state symbols for the following reactions.
a. Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride
b. Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
Ans:-
Q 23- A solution of a substance ‘X’ is used for white washing.
Name the substance ‘X’ and write its formula.
(i) Write the reaction of the substance ‘X; named in (ii) above with water
Ans:-
Q 24- Why does the colour of copper sulphate solution change when an iron nail is dipped into it?
Ans:- In this reaction, iron displaces copper from copper sulphate solution. The deep blue colour of copper sulphate solution fades due to the formation of light green solution of iron sulphate. A red-brown coating of copper metal is formed on the surface of the iron metal. This displacement reaction occurs because iron is more reactive than copper.
Q 25- 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)
Ans:-
i. 4Na(s) + O2 (g) → 2Na2O(s)
Here oxygen is added to sodium. The addition of oxygen is Called oxidation. So the substance that is oxidized is sodium Na.
ii. CuO(s) + H2(g) → Cu(s) + H2O(l)
In this reaction, copper oxide (CuO) gives the oxygen required for the oxidation of hydrogen; therefore, copper oxide is the oxidizing agent. Hydrogen is responsible for removing oxygen from copper oxide; therefore, hydrogen is the reducing agent here.
Comments
Post a Comment
please let me know if you have any questions .
please do not enter any spam link in the comment box ..