Q1: A chemical reaction involves in
a. Only breaking of bonds
b. Only formation of bonds
c. Both breaking and formation of bonds
d. None of these
Answer: (c) Both breaking and formation of bonds
Q2: A balanced chemical equation always obeys
a. Law of conservation of mass
b. Law of thermal equilibrium
c. Law of conservation of energy
d. All of the above
Answer: (a) law of conservation of mass.
Q3: Single displacement reaction involves:
a. Oxidation
b. Reduction
c. Redox
d. Heating
Answer: (c) redox
Q4: String of ants, bees contain
a. Formic acid
b. Vinegar
c. Succinic acid
d. Common Salt (NaCl)
Answer: (a) Formic acid
Q5: Some stale food gives a bad taste and a bad
smell because of:
a. Corrosion
b. Displacement
c. Heating
d. Rancidity
Answer: (d) rancidity
Q6: A red brown gas is released on heating lead
nitrate. It is an example of
a. Combination reaction
b. Oxidation reaction
c. Decomposition reaction
d. Reduction reaction
Answer: (c) Decomposition
Q7: The sign ↓ indicates
a. release of gas
b. dissolution of gas
c. formation of a precipitate
d. lowering of temperature
Answer: (c) formation of a precipitate
Q8: Why do gold and silver do not corrode?
Answer:It is because they are less reactive.
Q9: What do you mean by balanced chemical
equation?
Answer: An equation that has equal number of atoms of
each element on both the sides of equation is called
balanced chemical equation, i.e., mass of the reactants
is equal to mass of the products.
e.g., 2Mg + O2 → 2MgO
Q10: Define rancidity.
Answer: When fats and oils are oxidized, they become
rancid and their smell and taste
change. This process is known as rancidity.
Q11 (CBSE 2007): Write the type of reactions in the
following:
i. Reaction between an acid and a base
ii. Rusting of iron
Answer: i. Neutralization reaction
ii. Oxidation reaction
Q12: Give an example of decomposition reaction
where energy is supplied in form of light.
Answer:
sunlight
2AgBr(s) ------------------------> 2Ag (s) + Br2 (g)
(Silver Bromide)
Q13: Why does copper vessel acquire green coating
in rainy season?
Answer: It reacts with CO2 in the atmosphere and
forms a layer of basic Copper Carbonate.
Q14: What is the name of the gas which burns with
a pop sound?
Answer: Hydrogen gas.
Q15: Why is Hydrogen peroxide stored in coloured
bottles?
Answer: It is done to prevent photolytic decomposition
of hydrogen peroxide.
Q16: Name the oxidizing agent and reducing agent
in the following equation.
3MnO 2 (s) + 4Al(s) → 3Mn(s) + 2Al 2O 3 (s)
OR
Name a reducing agent that may be used to obtain
manganese from manganese dioxide.
Answer: Reducing agent : Al
Oxidation Agent : MnO2
Q17: Give two example from everyday life
situations where redox reactions are taking place.
Answer: Corrosion and Rancidity
Q18: In electrolysis of water, why is the volume of
gas collected over one electrode double that of gas
collected over the other electrode ?
Answer: In water (H2O), hydrogen and oxygen are
present in the raito of 2:1 by volume.
Q19: Why should a magnesium ribbon be cleaned
before burning in air?
Answer: Magnesium is a reactive metal. It combines
with oxygen of air to form a layer of magnesium oxide
on its surface. Hence, it should be cleaned with a sand
paper before burning to remove the oxide layer formed
on its surface.
Q20: Explain how respiration is an exothermic
reaction.
Answer: During digestion, food is broken down into
simpler substances. For example, rice, potatoes and
bread contain carbohydrates. These carbohydrates are
broken down to form glucose. This glucose combines
with oxygen in the cells of our body and provides
energy. Hence, respiration is an exothermic process.
C6 H 12O 6 (aq) + 6O 2(aq) → 6CO 2 (aq) + 6H 2O
(l) + energy
(Glucouse)
Q21: What factors influence the rate of chemical
reaction?
Answer: Following are the factors that can influence the
rate of reaction:
Nature of Reactants. e.g. Mg reacts faster in HCl than in
acetic acid.
Concentration of reactants
Surface Area of reactants. E.g. Powdered CaCO3 reacts
quickly than marble chips.
Temperature
Catalyst
Q22: Define Endothermic reaction.
Answer: The reactions in which heat is absorbed are
called endothermic reactions. In such reactions heat is
shown as one of the reactants. If exact amount of heat
absorbed is known then this amount is written
otherwise simply the word heat is written.
E.g. N 2(g) + 2O 2(g) + heat → 2NO(g)
nitric oxide
Q23: A silver ware is kept in a solution of CuSO 4
(aq). What change do you expect?
Answer: No reaction. because Silver is less reactive than
copper.
Q24(CBSE exam): Name one metal when placed in
ferrous sulphate solution will discharge its green
colour. Write a chemical equation and state the
reasons also.
Answer: Potassium(K) is one example. K is more
reactive than iron and will replace it.
2K + FeSO4 → K2 SO 4 + Fe
Potassium + Iron Sulphate → Potassium
Sulphate + Iron
Q25: Why do we apply paint on iron articles?
Answer: Iron articles are painted to prevent them from
rusting. Rusting is oxidation of iron in the presence of
air and moisture. The paint layer cuts off the the
contact of iron articles from moisture and air.
Q26(CBSE): A solution of a substance ''X'' is used
for white washing
(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 white washing is quick
lime (calcium oxide). Its formula is CaO.
(ii) When quick lime is mixed with water, the following
reaction takes place:
CaO (s) + H 2O(l) → Ca(OH) 2 (aq)
Quick Lime Water Slaked Lime
(Calcium Oxide) (Calcium Hydroxide)
The white suspension of slaked lime when applied on
the walls, combines with carbon dioxide (in air) forming
a thin shining layer of calcium carbonate.
Ca(OH) 2 (aq) + CO 2 (g) → CaCO 3 (s) + H 2 O(l)
Slaked Lime Calcium
Carbonate
Q27(CBSE): Why is it important to balance a
chemical equation?
Answer: The balancing of chemical equation is done to
satisfy the law of conservation of mass, i.e. "total mass
of all the products of reaction in a chemical reaction is
equal the total mass of all the reactants ".
Q28: What are the coefficients of the correctly
balanced equation?
? Fe2 O 3 + ? CO → ? Fe + ? CO2
(a) 0, 2, 2, 3
(b) 1, 3, 2, 3
(c) 1, 2, 2, 2
(d) 2, 6, 4, 3
Answer: (b) Ferric Oxide + Carbon Mono-oxide → Iron
+ Carbon DiOxide
Q29: What are the coefficients of the correctly
balanced equation?
? BaCl 2 + ? Al 2(SO 4 )3 → ? BaSO 4 + ? AlCl3
(aq)
(a) 1, 1, 1, 2
(b) 3, 2, 3, 2
(c) 3, 1, 3,2
(d) 2, 1, 1, 2
Answer: (c) 3 BaCl 2 + 1 Al 2(SO 4 )3 → 3 BaSO 4 + 2
AlCl3 (aq)
Barium Chloride + Aluminium Sulphate → Barium
Sulphate + Aluminium Chloride
Q30(CBSE2011): What is the colour of FeSO 4.7H 2 O
crystals ? How does this colour change upon
heating ? Give balanced chemical equation for the
changes.
Answer: Hydrated ferrous sulphate crystals are green in
colour. On heating, single reactant breaks down to give
simpler products. This is a decomposition reaction.
Ferrous sulphate crystals (FeSO 4 .7H 2 O) lose water
when heated and the colour of the crystals changes. It
then decomposes to ferric oxide (Fe2O3), sulphur
dioxide (SO 2 ) and sulphur trioxide (SO 3 ). Ferric oxide
is a solid, while SO 2 and SO3 are gases.
You may use Wolfram Chemical Reaction Calculator E.g.
Type lime + Water --> Calcium Hydroxide
Q31: Quick like (CaO - Calcium Oxide) reaction with
water is regarded as exothermic. A student mixes
these two products in a test tube and touches its
side surface. Which of the following statement
correctly describes the student's observation?
(a) The test tube becomes cold due to release of heat
energy.
(b) The test tube becomes hot due to release of heat
energy.
(c) The test tube becomes hot due to absorption of heat
energy.
(d) The test tube becomes cold due to absorption of
heat energy.
Answer: (b) The test tube becomes hot due to release
of heat energy.
Q32: The decomposition of vegetable matter into
compost is an example of _____.
(Choose the correct option).
(a) endothermic reaction.
(b) exothermic reaction.
Answer: (b) exothermic.
Q33(CBSE): Write a balanced chemical equation to
represent the following reaction:
Iron reacts with steam to form Iron(II,III) oxide
and hydrogen gas.
Answer:
3Fe(s) + 4H 2 O(l) ▬▬▬▬▬▶ Fe 3O 4 (s) + 4H
2(g)
Iron Water Iron Oxide Hydrogen
Q34(CBSE): Identify the substance oxidized,
substance reduced, oxidising agent and reducing
agent.
MnO 2 + 4HCl → MnCl 2 + 2H 2O + Cl 2
Answer:
Substance Oxidised: HCl
Substance reduced: MnO2
Reducing Agent: HCl
Oxidising Agent: MnO2
Q35: Bromine gas (Br 2 ) reacts with Sodium
Carbonate (Na 2 CO 3) in aqueous solution and gives
sodium bromide (NaBr), sodium bromate (NaBrO 3)
and carbon-dioxide gas. How many number of
sodium bromide molecules obtained in the
balanced chemical equation.
Answer: From the question, we infer the unbalanced
chemical equation is:
Br2 + Na 2CO 3 → NaBr + NaBrO 3 + CO2
Balanced equation is:
3 Br2 + 3 Na2 CO 3 → 5 NaaBr + NaBrO3 + 3
CO2
It means 5 molecules of NaBr are obtained.
Q36: A numismatist (coin collector) has been
collecting gold coins, silver coins and copper coins
for a long time. One day he observed a black
coating on silver coins and green coating on copper
coins. What chemical process is responsible for
these coatings. Also name the chemical formula of
the black and green coatings.
Answer: The coating occurred due to a chemical
process called corrosion. Black coating is due to
deposit of Silver Sulphide (Ag 2 S). Green coating is due
to formation of Copper Carbonate (CuCO 3)
(✪ Note: Silver usually is corrosion resistant and does
not oxidize. However presence of sulphur gases in
atmosphere can react and cause sulphur-corrosion. Tkn hlp cbse note
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