10th Science - Book Back Answers - Chemistry Unit 10 - English Medium Guides

 

1. I. Choose the correct Answer
2. II. Fill in the blanks
3. III. match the following
4. IV.  True or False (If false give the correct staement)
5. V.  Short answer questions
6. VI. Short in detail
7. VII. HOT questions
8. VIII. Solve the following Problems

SSLC / 10th - Science - Book Back Answers - Chemistry Unit 10 - English Medium

Tamil Nadu Board 10th Standard  Science - Chemistry Unit 10: Book Back Answers and Solutions

    This post covers the book back answers and solutions for Unit 10 – Chemistry from the Tamil Nadu State Board 10th Standard  Science textbook. These detailed answers have been carefully prepared by our expert teachers at KalviTips.com.

    We have explained each answer in a simple, easy-to-understand format, highlighting important points step by step under the relevant subtopics. Students are advised to read and memorize these subtopics thoroughly. Once you understand the main concepts, you’ll be able to connect other related points with real-life examples and confidently present them in your tests and exams.

    By going through this material, you’ll gain a strong understanding of Chemistry Unit 10 along with the corresponding book back questions and answers (PDF format).

Question Types Covered:

• 1 Mark Questions: Choose the correct answer, Fill in the blanks, Identify the correct statement, Match the following 
• 2 Mark Questions: Answer briefly 
• 3, 4, and 5 Mark Questions: Answer in detail

All answers are presented in a clear and student-friendly manner, focusing on key points to help you score full marks.

All the best, Class 10 students! Prepare well and aim for top scores. Thank you!

Topic: Types of Chemical Reactions

I. Choose the correct Answer

1. H_2(g) + Cl_29(g) → 2HCl_(g)
(a) Decomposition Reaction
(b) Combination Reaction
(c) Single Displacement Reaction
(d) Double Displacement Reaction
Answer Key:
(a) Decomposition Reaction

2. Photolysis is a decomposition reaction caused by ______.
(a) heat
(b) electricity
(c) light
(d) mechanical energy
Answer Key:
(c) light
 
3. A reaction between carbon and oxygen is represented by C_(s) + O_2(g) → CO_2(g) + Heat. In which of the type(s), the above reaction can be classified?
(i) Combination Reaction
(ii) Combustion Reaction
(iii) Decomposition Reaction
(iv) Irreversible Reaction
(a) (i) and (ii)
(b) (i) and (iv)
(c) (i), (ii) and (iii)
(d) (i), (ii) and (iv)
Answer Key:
(d) (i), (ii) and (iv)

4. The chemical equation Na2SO4(aq)+BaCl2(aq)→BaSO4(s)↓+2NaCl(aq represents which of the following types of reaction?
(a) Neutralisation
(b) Combustion
(c) Precipitation
(d) Single displacement.
Answer Key:
(c) Precipitation

5. Which of the following statements are correct about a chemical equilibrium?
(i) It is dynamic in nature
(ii) The rate of the forward and backward reactions are equal at equilibrium
(iii) Irreversible reactions do not attain chemical equilibrium
(iv) The concentration of reactants and products may be different
(a) (i), (ii) and (iii)
(b) (i), (ii) and (iv)
(c) (ii), (iii) and (iv)
(d) (i), (iii) and (iv)
Answer Key:
(a) (i), (ii) and (iii)

6. A single displacement reaction is represented by X(s)+2HCl(aq)→XCl2(aq)+H2(g). the following(s) could be X?
(i) Zn
(ii) Ag
(iii) Cu
(iv) Mg.
Choose the best pair.
(a) i and ii
(b) ii and iii
(c) iii and iv
(d) i and iv.
Answer Key:
(d) i and iv

7. Which of the following is not an “element + element → compound” type reaction?
(a) C_(s) + O_2(g) → CO_2(g)
(b) 2K_(s) + Br_2(l) → 2KBr_(s)
(c) 2CO_(g) + O_2(g) → 2CO_2(g)
(d) 4Fe_(s) + 3O_2(g) → 2Fe₂O_3(s)
Answer Key:
(c) 2CO_(g) + O_2(g) → 2CO_2(g)

8. Which of the following represents a precipitation reaction?
(a) A_(s) + B_(s) → C_(s) + D_(s)
(b) A_(s) + B_(aq) → C_(aq) + D_(l)
(c) A_(aq) + B_(aq) → C_(s) + D_(aq)
(d) A_(aq) + B_(s) → C_(aq) + D_(l)
Answer Key:
(c) A_(aq) + B_(aq) → C_(s) + D_(aq)

9. The pH of a solution is 3. Its [OH–] concentration is ______.
(a) 1 × 10^-3 M
(b) 3 M
(c) 1 × 10^-11 M
(d) 11 M.
Answer Key:
(c) 1 × 10^-11 M

10. Powdered CaCO₃ reacts more rapidly than flaky CaCO₃ because of :
(a) large surface area
(b) high pressure
(c) high concentration
(d) high temperature
Answer Key:
(a) large surface area

II. Fill in the blanks

1. A reaction between an acid and a base is called ………..
2. When zinc metal is placed in hydrochloric acid, ………. gas is evolved.
3. The equilibrium attained during the meiting of ice is known as ………..
4. The pH of a fruit juice is 5.6. If you add slaked lime to this juice, its pH ……….
5. The value of ionic product of water at 25 °C is ………..
6. The normal pH of human blood is …………
7. Electrolysis is type of ……….. reaction.
8. The number of products formed in a synthesis reaction is ………..
9. Chemical volcano is an example for ……….. type of reaction.
10. The ion formed by dissolution of H+ in water is called …………
Answer Key:
1. neutralization
2. H₂
3. physical equilibrium
4. increases to ‘7’
5. 1 × 10^-14 mol² dm^-6
6. 7.4
7. decomposition
8. 1
9. decomposition
10. hydronium ion

III. match the following

REACTION		TYPE
1	NH4OH(aq) + CH3COOH(aq) → CH3COONH4(aq) + H2O(l)	i	Single Displacement
2	Zn(s) + CuSO4(aq)  → ZnSO4(aq) + Cu(s)	ii	Combustion
3	ZnCO3(s) + Heat → ZnO(s) + CO2(g)	iii	Neutralisation
4	C2H4(g) + 4O2(g) → 2CO2(g) + 2H2O(g) + Heat	iv	Thermal decomposition

Answer Key:

REACTION		TYPE
1	NH4OH(aq) + CH3COOH(aq) → CH3COONH4(aq) + H2O(l)	iii	Neutralisation
2	Zn(s) + CuSO4(aq)  → ZnSO4(aq) + Cu(s)	i	Single Displacement
3	ZnCO3(s) + Heat → ZnO(s) + CO2(g)	iv	Thermal decomposition
4	C2H4(g) + 4O2(g) → 2CO2(g) + 2H2O(g) + Heat	ii	Combustion

IV.  True or False (If false give the correct staement)

1. Silver metal can replace hydrogen gas from nitric acid.
2. The pH of rain water containing dissolved gases like SO3, CO2, NO2 will be less than 7.
3. At the equilibrium of a reversible reaction, the concentration of the reactants and the products will be equal.
4. Periodical removal of one of the products of a reversible reaction increases the yield.
5. On dipping a pH paper in a solution, it turns into yellow. Then the solution is basic.
Answer Key:
1. False – Silver cannot displace H2 from HNO3 acid, since it is placed below hydrogen in the activity series.
2. True
3. False – At equilibrium the concentration of the reactants and products do not change it remains constant, but the concentration of the reactants and the products will not be equal.
4. True
5. False – The solution is neutral if the solution is basic it will be green in colour.

V.  Short answer questions

1. When an aqueous solution of potassium chloride is added to an aqueous solution of silver nitrate, a white precipitate is formed. Give the chemical equation of this reaction.
Answer Key:

${\mathrm{KCl}}_{\left(\mathrm{aq}\right)}+{\mathrm{AgNO}}_{3\left(\mathrm{aq}\right)}\to {\mathrm{AgCl}}_{\left(\mathrm{s}\right)}\downarrow +{\mathrm{KNO}}_3$

${\mathrm{ \; \; \; \; \; \; \; \; \; \; \; Silver\; chloride}}_{}$

${\mathrm{ \; \; \; \; \; \; \; \; Curdy\; white\; precipiate}}_{}$

2. Why does the reaction rate of a reaction increase in raising the temperature?
Answer Key:
On increasing temperature heat is supplied to the reactant. This energy breaks more bonds and thus speed up the chemical reaction. Foods kept at room temperature spoils faster than that kept in the refrigerator.
 
3. Define combination reaction. Give one example for an exothermic combination reaction.
Answer Key:
A combination reaction is a reaction in which two or more reactants combine to form a compound.
Eg: C(s) + O2(g) → CO2(g) + heat

4. Differentiate reversible and irreversible reactions.
Answer Key:

REVERSIBLE REACTION	IRREVERSIBLE REACTION
It can be reversed under suitable conditions.	It cannot be reversed.
Both forward and backward reactions take place simultaneously.	It is unidirectional. It proceeds only in forward direction.
It attains equilibrium.	Equilibrium is not attained.
The reactants cannot be converted completely into products.	The reactants can be completely converted into products.
It is relatively slow.	It is fast.

VI. Short in detail

1. What are called thermolysis reactions?
Answer Key:
Thermal decomposition reactions are called ‘thermolysis’ reaction. In this type of reaction, the reactant is decomposed by applying heat. There are two types of thermolysis reactions. They are:
(i) Compound to element / element decomposition:
A compound is decomposed into two elements.
Eg:
$\mathbf{2}\mathbf{H}\mathbf{g}{\mathbf{O}}_{\mathbf{s}}\stackrel{\mathbf{h}\mathbf{e}\mathbf{a}\mathbf{t}}{\mathbf{\to }}\mathbf{2}{\mathbf{Hg}}_{\mathbf{1}}\mathbf{+}{\mathbf{O}}_{\mathbf{2}\mathbf{\left(}\mathbf{g}\mathbf{\right)}}$
(ii) Compound to compound / compound decomposition:
A compound is decomposed into two compounds.
Eg:

$\mathbf{C}\mathbf{a}\mathbf{C}{\mathbf{O}}_{\mathbf{3}\mathbf{\left(}\mathbf{s}\mathbf{\right)}}\stackrel{\mathbf{heat}}{\mathbf{\to }}\mathbf{Ca}{\mathbf{O}}_{\mathbf{\left(}\mathbf{s}\mathbf{\right)}}\mathbf{+}\mathbf{C}{\mathbf{O}}_{\mathbf{2}\left(\mathbf{g}\right)}$
 
2. Explain the types of double displacement reactions with examples.
Answer Key:
There are two major classes of double displacement reactions. They are,
(i) Precipitation Reactions: When aqueous solutions of two compounds are mixed, if they react to form an insoluble compound and a soluble compound, then it is called precipitation reaction.
$\mathbf{P}\mathbf{b}\mathbf{(}\mathbf{N}{\mathbf{O}}_{\mathbf{3}}{\mathbf{)}}_{\mathbf{2}\mathbf{\left(}\mathbf{a}\mathbf{q}\mathbf{\right)}}\mathbf{+}\mathbf{2}\mathbf{K}{\mathbf{I}}_{\mathbf{\left(}\mathbf{a}\mathbf{q}\mathbf{\right)}}\mathbf{\downarrow }\mathbf{+}\mathbf{2}\mathbf{K}{\mathbf{NO}}_{\mathbf{3}\mathbf{\left(}\mathbf{a}\mathbf{q}\mathbf{\right)}}$
(ii) Neutralisation Reactions: Another type of displacement reaction in which the acid reacts with the base to form a salt and water. It is called ‘neutralisation reaction’ as both acid and base neutralize each other.
$\mathbf{N}\mathbf{a}\mathbf{O}{\mathbf{H}}_{\mathbf{a}\mathbf{q}}\mathbf{+}\mathbf{H}\mathbf{C}{\mathbf{l}}_{\mathbf{\left(}\mathbf{a}\mathbf{q}\mathbf{\right)}}\mathbf{\to }\mathbf{N}\mathbf{a}\mathbf{c}{\mathbf{l}}_{\mathbf{\left(}\mathbf{a}\mathbf{q}\mathbf{\right)}}\mathbf{+}{\mathbf{H}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{\left(}\mathbf{1}\mathbf{\right)}}\mathbf{.}$
 
3. Explain the factors influencing the rate of a reaction.
Answer Key:

 
Important factors that affect rate of a reaction are:
1. Nature of the reactants
2. Concentration of the reactants
3. Temperature
4. Catalyst
5. Pressure
6. Surface area of the reactants
1. Nature of the reactants : The reaction of sodium with hydrochloric acid is faster than that with acetic acid, because Hydrochloric acid is a stronger acid than acetic acid and thus more reactive. So, the nature of the reactants influence the reaction rate.
2Na_(s) + 2HCl_(aq) → 2NaCl_(aq) + H_2(g) (fast)
2Na_(s) + 2CH₃COOH_(aq) → 2CH₃COONa_(aq) + H_2(g) (slow)
2. Concentration of the reactants : Changing the amount of the reactants also increases the reaction rate. More the concentration, more particles per volume exist in it and hence faster the reaction. Granulated zinc reacts faster with 2M hydrochloric acid than 1M hydrochloric acid.
3. Temperature : Most of the reactions go faster at higher temperature. Because adding heat to the reactants provides energy to break more bonds and thus speed up the reaction. Calcium carbonate reacts slowly with hydrochloric acid at room temperature. When the reaction mixture is heated the reaction rate increases.
4. Pressure : If the reactants are gases, increasing their pressure increases the reaction rate. This is because, on increasing the pressure the reacting particles come closer and collide frequently.
5. Catalyst : A catalyst is a substance which increases the reaction rate without being consumed in the reaction. In certain reactions, adding a substance as catalyst speeds up the reaction. For example, on heating potassium chlorate, it decomposes into potassium chloride and oxygen gas, but at a slower rate. If manganese dioxide is added, it increases the reaction rate.
6. Surface area of the reactants : Powdered calcium carbonate reacts more readily with hydrochloric acid than marble chips. Because, powdering of the reactants increases the surface area and more energy is available on collision of the reactant particles. Thus, the reaction rate is increased.
 
4. How does pH play an important role in everyday life?
Answer Key:
• The pH of blood is almost 7.4. Any increase or decrease in this value leads to diseases
• Citrus fruits require slightly alkaline soil, while rice requires acidic soil and sugarcane requires neutral soil.
• If the pH of rainwater becomes less than 7, it becomes acid rain which is harmful in day-to-day life.
• pH changes cause tooth decay.
• During indigestion, the stomach produces too much acid and this causes pain and irritation.

5. What is chemical equilibrium? What are its characteristics?
Answer Key:
Chemical equilibrium is a state of a reversible chemical reaction where the,
Rate of forward reaction = Rate of backward reaction.
No change in the amount of the reactants and products takes place.
Characteristics of equilibrium:
1. In a chemical equilibrium, the rates of the forward and backward reactions are equal.
2. The observable properties such as pressure, concentration, colour, density, viscosity etc., of the system remain unchanged with time.
3. The chemical equilibrium is a dynamic equilibrium, because both the forward and backward reactions continue to occur even though it appears static externally.
4. In physical equilibrium, the volume of all the phases remain constant.

VII. HOT questions

1. A solid compound ‘A’ decomposes on heating into ‘B’ and a gas ‘C’ On passing the gas ‘C’ through water, it becomes acidic. Identify A, B and C.
Answer Key:
A – CaCO₃, solid compound
‘A’ decomposes on heating into ‘B’ and a gas ‘C’.
 asas
On passing the gas CO₂ through water, it becomes acidic.
asas
A – CaCO₃, Calcium carbonate
B – CaO, Calcium oxide
C – CO₂, Carbondioxide gas
 
2. Can a nickel spatula be used to stir copper sulphate solution? Justify your answer.
Answer Key:
No, nickel spatula cannot be used to stir the copper sulphate solution. Actually, on the basis of activity series, nickel is more reactive than copper, so nickel will displace copper from its solution and copper will be deposited on nickel spatula.

VIII. Solve the following Problems

1. Lemon juice has a pH 2, what is the concentration of H+ ions?
Answer Key:
pH = – log [H⁺]
[H+] = antilog of [-pH]
= antilog [-2]
[H⁺] = 10^-2 M
[OR]
PH = – log [H⁺]
[H⁺] = 10^-pH
[H⁺] = 10^-2M
 
2. Calculate the pH of 1.0 × 10-4 molar solution of HNO3.
Answer Key:
pH = – log [H+]
HNO3 → H⁺ + NO₃^–
pH = -log [1 × 10^-4]
= -(-4)log₁₀ 10 = 4
pH = 4

3. What is the pH of 1.0 x 10-5 molar solution of KOH?
Answer Key:
KOH → K+ + OH–
pOH = -log[OH–]
= -log [1 × 10^-5]
pOH = 5
pH + pOH = 14
∴ pH of KOH = 14 – 5 = 9
pH = 9

4. Laundry detergent has a pH 8.5, What is the concentration of H+ ions?
Answer Key:
pH = 8.5
pH = – log [H⁺]
[H⁺] = 10^-pH
[H⁺] = 10^-8.5
[H⁺] = 3.16 × 10^-9 M

5. The hydroxide ion concentration of a solution is 1 × 10^-11M. What is the pH of the solution?
Answer Key:
[OH–] = 1 × 10^-11 M
pOH = – log[OH–]
= – log[1 × 10^-11]
= -log₁₀1 – log₁₀10^-11
= -(-11) log₁₀10 = 11
pOH = 11
pH + pOH = 14
pH = 14 – 11
pH = 3
.