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1. Chemical reactions and equations Activity Based Question 10th
Chemistry
Q. A student added a few pieces of zinc into dil.H₂SO₄ taken in a test tube. Suddenly,
evolution
of gas occurs. What gas is evolved?
Answer: Hydrogen gas
Q. Why do copper sulphate crystals change colour from blue to white on heating?
Answer: Due to lose of water of crystallization which can also be called as dehydration
Q. What happens when a small piece of iron is kept in copper sulphate solution?
Answer: Simple displacement reaction results in the Formation of a brown coating of copper
on
the surface of iron nail. The green colour of the solution is due to the displaced Fe2⁺ ions
from
the Iron nail
Q. While performing an experiment, a student adds sodium sulphate solution to a colourless
solution. A white precipitate is immediately formed and is insoluble in dil. HCl. The colourless
solution is …………………………… and the precipitate formed is……………………
Answer: Barium chloride reacts with sodium sulphate to form a white precipitate of barium
sulphate[BaCl₂ and BaSO₄]
Q. When NaOH is added to zinc sulphate solution, a precipitate is formed which is soluble in
excess of NaOH. The precipitate obtained is……………………. & the colour of the
precipitate
is……………….
Answer: A white gelatinous precipitate of zinc hydroxide is formed Zn(OH)₂ & white
gelatinous
Q. On heating Pb(NO₃)₂, what is observed during the reaction?
Answer: Lead nitrate decomposes on strong heating with a crackling sound. It produces NO₂
(g), O₂ (g) and PbO (s)
Q. Take dilute sulphuric acid in a test tube and put a few zinc granules into the test tube.
What
will you observe?
Answer: Since Zn and dil H₂SO₄ react with each other liberating H₂ gas, the size of zinc
granules
keep on decreasing
Q. When magnesium combines with oxygen, it produces magnesium oxide that appears to
be
like:
Answer:int: Mg combines with O₂ to form a white ash of MgO
Q. 100 ml of a saturated copper sulphate solution was taken in a beaker. A small amount of
iron
filings was added to the beaker and left undisturbed overnight. The mixture was then filtered
to
obtain the residue. The residue was found to be what colour?
Answer: In this reaction copper particles are obtained which appears as reddish brown
residue.
Q. When you place an iron nail in copper sulphate solution, the reddish brown coating
formed
on the nail is _______.
Answer: The reddish brown coating is a soft and dull coating of copper
Q. What is observed when dilute sulphuric acid is added to zinc granules?
Answer: Zn reacts with dil. H₂SO₄ to liberate H₂ gas and bubbles start coming from the
surface
of the Zinc granules.

2. Q. Why is magnesium ribbon held with a pair of tongs and not with bare hands, when it is
burnt
in air?
Answer: Magnesium metal is a good conductor of heat, so it gets very hot when it is held in
the
flame.
ASSIGNMENT : FIRST TERM (2012-2013) X SUBJECT : CHEMISTRY
CHAPTER : CHEMICAL REACTIONS AND EQUATIONS Max Marks: 55
A. Very short answer questions: (1 mark each) (1x 14= 14 marks)
1. What are reactants ?
2. What are products ?
3. What is the term used for symbolic representation of a chemical reaction ?
4. What does the + sign between the reactants indicate ?
5. How is the salt solution in water indicated in a chemical reaction /
6. Aluminium burns in chlorine to form aluminum chloride. Write a balanced equation for this
reaction ?
7. Balance the following equation and add the state symbols :
Zn(s) + 2HCl(aq) → ZnCl2 + H2
8. Name the following reaction.
AB + CD → AD + BC
9. Aluminium metal displaces iron from ferric oxide (Fe2O2) giving aluminium oxide and iron.
Which is more reactive, aluminium or iron ?
10. Identify from the following reaction : H2S + Cl2 → 2HCl + S
a. Component oxidized
b. Oxidizing agent
11. Give one example of a redox reaction which is also a combination reaction.
12. Which atom is reduced on burning an element in air.
13. When SO2 gas is passed through saturated solution of H2S, the following reaction
occurs
SO2 + 2H2S → 2 H2O + 3S
In this reaction, which substance is oxidized and which one is reduced.
14. In the following reaction between lead sulphide and hydrogen peroxide
PbS(s) + 4H2O(aq) → PbSO4(s) + 4H2O(l)
a. Which substance is reduced ?
b. Which substance is oxidized ?
B. Short answer questions: (2 marks each) (2x4=8)
1. Write a chemical equation for each of the following reactions :
a. Zinc metal reacts with aqueous solution of hydrochloric acid to form zinc chloride solution
and
hydrogen gas.
b. When solid mercury (II) oxide is heated, liquid mercury and oxygen gas are produced.
2. H2 + O → H2O is a balanced chemical equation. It is considered to be incorrect. Why? 3.
Write balance chemical equations to represent the following statements :
a. Carbon (coke) burns in air to form carbon dioxide gas.
b. A piece of sodium metal on putting in water forms caustic soda and hydrogen gas.
3. Write the balanced chemical equations for the following chemical reactions :
a. Aqueous solutions of sulphuric acid and sodium hydroxide react to form aqueous sodium
sulphate and water.
b. Phosphorus burns in chlorine gas to form phosphorus penta chloride.
4. Magnesium is more reactive than copper or iron but iron is more reactive than copper.
a. A solution of magnesium sulphate is put into a copper pot.
b. A solution of copper sulphate is put into a iron pot.
c. A solution of magnesium sulphate is put into a iron pot.
Which of the above pots will get damaged? Why? What is this reaction called?

3. C. Short answer questions: (3 marks each)(3x 4= 12)
1. What are the three essentials of a chemical equation ?
2. Explain the term reduction with examples.
3.A colourless lead salt, when heated, produces a yellow residue and brown fumes.
a. Name the lead salt.
b. Name the brown fumes.
c. Write a chemical equation of the reaction involved.
4. When a green iron salt is heated strongly, its colour finally changes to black and colour of
burning sulphur is given out.
a. Name the iron salt.
b. Name the type of reaction that takes place during the heating of iron salt.
c. Write a chemical equation for the reaction involved.
D. Balance the following skeleton equation by hit and trial method : (2x6=12)
a. C2H4 + O2 → CO2 +H2O
b. C2H2 + O2 → CO2 +H2O
c. CH4 + O2 → CO2 +H2O
d. Al2(SO4)3 + NaOH → Al(OH)3 + Na2SO4
e. Cu2S + O2 → Cu2O +S2O
f. AlN + H2O → Al(OH)3 + NH3
E Define: (1x9=9)
1. Rancidity 2. Combination reactions 3. Decomposition reactions 4. Double displacement
reaction 5. Displacement reaction 6. Redox reaction 7. Corrosion 8. Oxidising agent 9.
Reducing agent
Questions/ Answers
1. What happens when magnesium ribbon burns in air?
Ans. When magnesium ribbon burns in air, it combines with the oxygen to form magnesium
oxide.
2Mg(s) + O2(g)→ 2MgO(s)
2. Name the gas evolved when zinc reacts with dil. HCl.
Ans. Hydrogen gas is evolved.
3. What is a chemical equation?
Ans. A chemical equation is a symbolic notation that uses formulae instead of words to
represent a chemical equation.
4. On what chemical law, balancing of chemical equation is based?
Ans. Balancing of a chemical equation is based on the law of conservation of mass.
5. Represent decomposition of ferrous sulphate with the help of balanced chemical equation.
Ans. 2FeSO4(s)→ Fe2O3(s) + SO2(g) + SO3(g)
6. When carbon dioxide is passed through lime water, it turns milky, why?
Ans. Lime water (calcium hydroxide) combines with carbon dioxide to form a suspension of
calcium carbonate which makes lime water milky. Ca(OH)2 + CO2→ CaCO3 + H2O
7. A zinc rod is left for nearly 20 minutes in a copper sulphate solution. What change would
you
observe in zinc rod?
Ans. Zinc rod will change into zinc sulphate.
8. What type of reaction is this: Na2SO4 + BaCl2 → BaSO4 + 2NaCl
Ans. It is a double displacement reaction.
9. Identify the compound oxidized in the following reaction. H2S (g) + Cl2 → S(s) + 2HCl (g)
Ans. H2S is oxidized.
10. What is rust? Ans. Rust is mainly hydrated iron (III) oxide, Fe2O3.xH2O.
11. How does the food become rancid?
Ans. Food becomes rancid when fat and oils present in the food are oxidized.
2-marks Questions/ Answers

4. Q.1. An iron knife kept dipped in a blue copper sulphate solution turns the blue solution light
green. Why?
Ans. As we know iron is more reactive than copper. So, it displaces Cu from CuSO4 solution
and forms ferrous sulphate which is of Light Green Colour.
CuSO4 (aq) + Fe (s) → FeSO4(aq) + Cu(s)
Blue colour light green colour
Q.2. A copper coin is kept in a solution of silver nitrate for some time. What will happen to
the
coin and the colour of the solution?
Ans. We know that copper is more reactive than silver, so it will displace silver from its salt
solution:
Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq) + 2Ag(s)
So the solution will turn blue due to the formation of copper nitrate.
Q.3. What do you understand by precipitation reaction? Explain with suitable examples.
Ans. Precipitate. When two reactants react and product formed remains insoluble and settles
as a solid it is called a precipitate. Such reactions in which precipitate is formed are called
precipitation reactions. For example,(i) when aqueous solution of sodium sulphate is mixed
with
the aqueous solution or barium chloride, barium sulphate comes in the form of white
precipitate
Na2SO4(aq) + BaCl2(aq) → BaSO4(↓) + 2NaCl(aq)
(ii) When aqueous solution of sodium chloride is mixed with the aqueous solution of silver
nitrate, silver chloride comes in the form of white precipitate.
Q.4. What is lime-water test for the detection of carbon dioxide?
Ans. When carbon dioxide gas is passed through lime water ,it turns milky due to the
formation
of milky suspension (precipitate) of calcium carbonate. Carbon dioxide is produced by the
action
of dilute HCl on sodium carbonate.
Na2CO3(s) + 2HCl(aq) → 2NaCl + H2O(l) + CO2
Carbon dioxide gas produced in this reaction is passed through lime water that changes to
milky
colour due to the formation of calcium carbonate.
Ca(OH)2(aq) + CO2(g) → Caco3 + CO2(g)
3 Marks Questions/ Answers
Q.5. What is corrosion? State the conditions necessary for rusting of iron. How rusting is
harmful?
Ans: Corrosion. The process of eating away of the metal by the action of atmospheric
reagents
changing the metal into its compound is called corrosion.
Rusting of Iron. When iron and iron objects are exposed to atmosphere, they are attacked by
air
and moisture (water) of the atmosphere and a brown and orange coloured layer is formed on
the surface. It is called rust which is mainly hydrated iron (iii) oxide Fe2O3.xH2O.
Harmful Effect of Rusting. Hydrated iron (iii) oxide is brittle substance and moves away from
the
surface thus the object is damaged. The objects get holes, cavities and rough surface.
Conditions necessary for rusting :
(i) Open surfaces of the metal. (ii) Presence of air (Oxygen). (iii) Presence of moisture
(water).
Q.6. What is rancidity? Write the common method to prevent it.
Ans. When food item are kept unprotected for some time, they give some unpleasant smell
and

5. taste and become rancid. This process is called rancidity. Actually, the micro organisms
oxidise
the fat and oils present in them. So oxidation of food items need to be prevented to protect
them.
Common methods to Prevent Rancidity of Food item:
(i) Keeping the food at low temperature (ii) Keeping food item in air tight containers
(iii) By filling nitrogen in the food storage bags.
5 Marks Questions/ Answers
1. a. Why cannot a chemical change be normally reversed?
b. why is it always essential to balance a chemical equation?
c. what happens when CO2 gas is passed through lime water and why does it disappear on
passing excess CO2?
d. Can rusting of iron takes place in distilled water?
Ans: a. In a chemical change some bonds are broken and some bonds are formed. The
products are quite different from the reactants. Therefore it normally can’t be reversed.
b. A chemical equation has to be balanced to satisfy the law of conservation of mass.
c. On passing CO2 gas through lime water, it turns milky due to formation of insoluble
calcium
carbonate which dissolves on passing excess CO2 due to formation of soluble calcium
bicarbonate.
Ca(OH)2 + CO2(g) --------------→ CaCO3(s) + H2O(l)
CaCO3(s) + H2O(l) + CO2 (g) ---------------→ Ca(HCO3)2(soluble)
d. No, rusting of iron cannot take place in distilled water because it neither contains
dissolved
oxygen nor CO2 both are essential for rusting of iron.
Hots Questions
Q 1 . The marble statues often slowly get corroded when kept in open for a long time .Assign
a
suitable explanation
Ans-SO2,NO2 gases are released into the atmosphere from various sources. These
dissolve in
rain water to give acid which corrodes marble statues
2SO2+O2 --------------→ 2SO3
H2O+SO3 --------------→ H2SO4
2NO2+H2O 2HNO3 CaCO3+H2SO4--------------→ CaSO 4 +H2O+CO2
CaCO3+2HNO3 --------------→Ca(NO3)2+H2O+CO2
Q 2. You are given the following materials
(1) marble chips (2)dilute hydrochloric acid (3)Zinc granules ,identify the type of reaction
when
marble chips and Zinc granules are added separately to acid taken in two test tubes
Ans-(i) marble chips react with dilute hydrochloric acid to form calcium chloride and carbon
dioxide .it is a double displacement reaction
CaCO3+2HCl → CaCl2 + H2O +CO2
(ii)Zinc granules react with dilute hydrochloric acid to give hydrogen gas. it is a displacement
reaction
Zn(s)+2HCl → ZnCl2(aq)+H2(g)
Q3. The gases hydrogen & chlorine do not react with each other even if kept together for a
long
time . However , in the presence of sunlight , they readily combine . What does actually
happen ?
Ans-In Chemical reactions , energy is needed to break the bonds present in the reacting
molecules so that they may combine to form the products . In this reaction , sunlight is the
source of energy in the form of photons . The energy made available by sunlight helps in
breaking the bonds & this leads to chemical reaction between hydrogen & chlorine.

6. H2 (g) + Cl2(g) sunlight→ 2HCl (g)
Q 4. A,B&C are three elements which undergo chemical reactions in the following way
A2O3 + 2B®B2O3 + 2A 3CSO4 + 2B -® B2(SO4)3 + 3C 3CO+
2A→A2O3 +3C
Answer the following
(A) Which element is most reactive ? (B) Which element is least reactive ?
Ans: a) The most reactive element is ‘B’. It has displaced both ‘A’ and ‘c’ from their
compounds.
b) The least reactive element is ‘C’ as it has been displaced by both ‘A’ and ‘B’ .
Q. A water insoluble substance ‗X‘ on reacting with dilute H2SO4 released a colourless and
odourless gas accompanied by brisk effervescence. When the gas was passed through
water ,
the solution obtained turn blue litmus red . On bubbling the gas through lime water , it initially
became milky and the milkiness disappeared when the gas was passed in excess . Identify
the
substance ‗X‘ and write the chemical equations of the reaction involved
ANS: the water insoluble substance ‘X’ is most probably metal carbonate ( CaCO3 ). The
chemical reaction that involved are given below
CaCO3 (s) + H2SO4 (aq) →CaSO4 ( aq) + H2O (aq) + CO2 (g)
Ca(OH)2 (s) + CO2 (g) → CaCO3 (s) ( milky) + H2O (l)
CaCO3 (s) + CO2 (g) + H2O (aq) →Ca(HCO3)2 ( milkiness)
Extra score questions:
Q 1. If you collect silver coins and copper coins. After some day a black coating on silver
coins
and a green coating on copper coins. Which chemical phenomenon is responsible for these
coatings? Write the chemical name of black and green coatings
Ans: Corrosion is responsible for this coating. Black coating is due to formation of Ag2S and
green coating is due to formation of CuCO3.Cu (OH)2
Q.2. An aqueous solution of metal nitrate P reacts with sodium bromide solution to form
yellow
ppt of compound Q which is used in photography. Q on exposure to sunlight undergoes
decomposition reaction to form metal present in P along with reddish brown gas. Identify
P&Q .
Write the chemical reaction & type of chemical reaction.
Ans: P = Ag NO3 , Q = AgBr 2 A gBr (s)→ 2Ag(s) + B r2(g) Photochemical
decomposition
Q.3. A substance X used for coating iron articles is added to a blue solution of a reddish
brown
metal Y, the color of the solution gets discharged Identify X and Y & also the type of
reaction.
Ans. 6 X= Fe, Y = Cu, Displacement reaction.
Q.4. A student burnt a metal A found in the form of ribbon. The ribbon burnt with a dazzling
flame & a white powder B is formed which is basic in nature. Identify A &B. Write the
balanced
chemical equation.
Ans.11 X = Mg, Y = MgO, Mg + O2® 2 MgO
Q.5. why magnesium ribbon cleaned before burning?
Ans: The magnesium ribbon is always found with a white layer of MgO due attack of moist
air.
So, magnesium ribbon cleaned before burning.
Q.6. During electrolysis of water gas collected in one test tube is double than other why?
Ans: On electrolysis water decompose into hydrogen and oxygen in ratio 2:1 by volume
so,H2
gas collected in one test tube is double than O2

7. Evaluation Assignment
Very short answer questions (V.S.A) : X Chemical reactions and Chemical
Equation:FA
1. Arrange the following metals in the decreasing under of reactivity or electro positive
character.
K Zn Na Fe Pb Cu
2. Which of them will be a reducing agent a metal or non metal?
3. Balance the chemical equation Na(s) + H2O → NaOH + H2
4. Select the combination reaction from following
(i)KClO3→ KCl + 3 O2 (ii) S + O2→ SO2
5. Select the decomposition reaction from following
(i) 2H2O + O2 → 2H2 O
(ii) CaCO3 ------Heat------® CaO + CO2
6. Select the double displacement reaction
(i) BaCl2 + H2SO4 ---® Ba SO4 + H2
(ii) 2KBv + Cl2 → K Cl2 + Bv2
7. Fill in the following about reactivity series of metal
(a) the …………………. Metal replaces the ………………. Metal from its salt solution.
8. Which of the following is not the necessary condition for rusting
(i) Presence of oxygen (ii) Presence of catalyst (iii) Presence of moisture
9. Which of the following is required for prevention of corrosion?
(i) coating of less electropositive metal
(ii) coating of move electropositive metal
10. Choose the correct about rancidity
(i) Rancidity is a reduction process (ii) Rancidity is an oxidation process
Answers
1. K > Na > Zn > Fe > Pb > Cu
2. Non metal
3. 2 Na(s) +2 H2O → 2NaOH + 2H2
4. S + O2→ SO2
5. CaCO3 ------Heat® CaO + CO2
6. BaCl2 + H2SO4→ Ba SO4 + H2
7. Strong, Weak
8. Presence of catalyst
9. Coating with move electropositive metal
10. Rancidity is an oxidation process
See some questions: Short Answer type Question (2 marks)
1. (i) What happens when aqueous solution of barium chloride is added to aqueous sodium
sulphate solution?
(ii) When silver colored metal (A) is added to dilute sulphuric acid, solution (B) is formed
which
is colorless solution and a gas (c) is evolved which is colorless name ‘A’, ‘B’ and ‘C’ and
write
the equation?
(iii) An ‘A’ blue colored crystalline salt on heating decomposes to ‘B’ white substance. W hen
in
blue salt solution, a metal (Zinc) is added, its gives rise to colorless solution ‘C’ wth leaving
behind ‘D’ reddish brown metal.
2. Name the compounds ‘A’, ‘B’, ‘C’ and ‘D’
(iv) A reaction mixture of chromium Oxide is heated with aluminum powder on strong heating
3. a. Write the reaction?
b. Give one application of this reaction?

8. (v) Define Rusting?
4. Give two methods of protection of metal trans rusting.
5. (i) Rusting is a slow electrochemical process in which hydrated oxide of metal in formed
from
metal when it comes in with air moisture (ii) By Painting, by galvanization, by tinning
6. (i) Explains the term ‘corrosion’?
(ii) Write the chemical reaction of corrosion of Iron?
(iii) Name two metals which corrodes easily?
(iv) Aluminum corrodes in moist air but is widely used is making utensils.
(v) what is galvanization and why do we use Zn for it?
7. (i) What is rancidity? Where does it happen
(ii) what are anti oxidants? Why are they added fat and oil containing food to prevent from
rancidity?
(iii) why do most items puffed with nitrogen.
Solution:
1. White precipitate of BaSO4 is obtained. Reaction will be as
Na2SO4 + BACl2 ----------------BaSO4 + 2NaCl
2. A is Zinc, B is ZnSO4 solutions C is H2gas and reactions will be
Zn (s) + H2SO4 (d) ------------Zn SO4 (aq) + H2 (g)
3. A, B, C, and D are respectively-
CuSO4, 5 H2O, CuSO4, ZnSO4 (aq), Cu (s)
4. (i)Cr2O3 + 2Al ------Al2O3 + 2 Cr
(ii) This reaction is used in termite welding
5. (i) The process of slow destruction of metals when exposed to air, moisture and pollutant
gases , in called as corrosion.
(ii) Fe + 3H2 + 2H2O ------------ Fe2O3 x H2O
(iii) Formation of green coating on copper and formation of thin layer of oxide on aluminum
are
example of corrosion.
(iv) Aluminum forms oxide layer on exposure to air, this oxide layer further checks corrosion.
(v) Galvanization is a process in which Zinc layer is applied on Iron. It is used to protect iron
from rusting.
6. (i) The oxidative deterioration of oils and fats leading to stinking smell or stale taste is
known
as rancidity.
(ii) Anti Oxidants are those chemicals which an addition to fat and oil checks it from
rancidityan
addition of anti oxidants fatty food is protected from stale.
(iii) Nitrogen is filled in potato chips & other food to create anaerobic (air free atmosphere)
which
avoids rancidity.
X Formative assessment Chemical reactions and
equations
Q1. The given equation represents the reaction of sodium metal with water.
Sodium + Water Sodium hydroxide + Hydrogen
Which of the following chemical equations represents a complete balanced chemical
equation
for the given word equation?
A. 2Na(s) + H2O → 2NaOH(aq) + H2(g)
B. Na(s) + 2H2O → NaOH(aq) +2H2(g)
C. 2Na(s) + 2H3O → 2NaOH(aq) + 2H2(g)
D. 2Na(s) + 2H2O → 2NaOH(aq) + H2(g)
Q2. Identify the chemical equation which represents a complete balanced equation for the

9. reaction of barium chloride with sodium sulphate to produce barium sulphate and sodium
chloride.
A. BaCl2(aq) + Na2SO4 (aq) → BaSO4(s) + 2NaCl(aq)v
B. BaCl2(aq) + Na2SO4 (aq) → 2BaSO4(s) + 2NaCl(aq)
C. 2BaCl2(aq) + Na2 → SO4 (aq) 2BaSO4(s) + NaCl(aq)
D. BaCl2(aq) + Na2 → SO4 (aq) BaSO4(s) + NaCl(aq)
Q3. Ferric oxide reacts with aluminum to produce aluminum oxide and iron. The balanced
chemical equation for the given reaction is
Fe2O3 + 2Al → Al2O3 + 2Fe
Which of the following substances is oxidized in the given reaction?
A. Al2O3
B. Fe2O3
C. A1
D. Fe
Q4. White silver chloride changes to grey in sunlight because of the formation of silver metal
along with the evolution of chlorine gas. Identify the chemical equation that gives a correct
representation of the process.
A. 2AgCl → 2Ag + Cl2
B. AgCl → Ag + Cl2
C. 2Ag + Cl2 → 2AgCl
D. Ag + Cl2 → 2AgCl
Q5. When copper oxide is treated with hydrogen gas copper is produced along with water.
The
balanced chemical equation for the given reaction is CuO + H2 → Cu + H2O Which
substance
is oxidized in the given reaction?
A. H2
B. Cu
C. H2O
D. CuO
Q6. The balanced chemical equation for the reaction of nitrogen with hydrogen to produce
Ammonia gas is-
A. N2(g) + H2(g) → 2NH3(g)
B. 2N2(g) + H2(g) → 2NH3(g)
C. N2(g) + 3H2(g) → 2NH3(g)
D. 2N2(g) + H2(g) → 2NH3(g)
Q7. Identify the chemical equation that correctly represents production of magnesium
nitrideby
burning magnesium metal in a pure nitrogen atmosphere from the following–
A. Mg3N2(s)→ Mg(g) + N2(g) B. Mg + N2→ Mg3N2
C. 3Mg(g)N2(g) →Mg3N2(g) D. Mg3N2→ 3Mg + N2
Q8. Which of the following reactions represents a combination reaction?
A. CaO(s) + H2O(g)→ Ca(OH)2(aq) B. CaCO3(s)→ CaO(s) + CO2(g)
C. Zn + CuSO4(aq)→ ZnSO4(aq) + Cu(s) D. 2FeSO4(s)→ Fe2O3(s) +
SO2(g) + SO3(g)
Q9. Which of the following reactions represents a double displacement reaction?
A. BaCl2(aq) + Na2SO4(aq)→ BaSO4(s) + 2NaCl(aq)
B. 2FeSO4(s)→ Fe2O3(s) + SO2(g) + SO3(g)
C. 2Pb(NO3)2(g)→ 2PbO(s) + 4NO2(g) + O2(g)
D. Zn(s) + 2AgNO3(aq)→Zn(NO3)2(aq) + 2Ag(s)
Q10. The reaction: Fe2O3(s) + 2Al(s)→Al2O3(s) + 2Fe(s) is an example of a–
A. combination reaction B. double displacement reaction

10. C. decomposition reaction D. displacement reaction
Q10. What happens when dilute hydrochloric acid is added to iron fillings?
A. Hydrogen gas and iron chloride are produced B. Chlorine gas and hydroxide are
produced
C. heat is absorbed, i.e. test tube becomes cold. D. Iron salt and water are produced
Q. Write balanced chemical equations for the following word equations:
A. Calcium hydroxide + Carbon dioxide Calcium carbonate + Water
Skeletal equation:______________________________________
Balanced equation: ______________________________________
B. Zinc + Silver nitrate® Zinc nitrate + Silver
Skeletal equation:______________________________________
Balanced equation:______________________________________
C. Aluminium + Copper chloride→ Aluminium chloride + Copper
Skeletal equation:______________________________________
Balanced equation:______________________________________
D. Potassium bromide (aq) + Barium iodide (aq ) Potassium iodide (aq) +
Barium bromide(s)
Skeletal equation:______________________________________
Balanced equation:______________________________________
E. Zinc carbonate(s)→ Zinc oxide(s) + Carbon dioxide(g)
Skeletal equation:______________________________________
Balanced equation:______________________________________

11. CLASS X SCIENCE
CHEMICAL REACTIONS AND EQUATIONS
1 – Mark questions answer
1. What happens when magnesium ribbon burns in air?
Ans. When magnesium ribbon burns in air, it combines with the oxygen to form magnesium oxide.
2Mg(s) + O2(g) 2MgO(s)
2. Name the gas evolved when zinc reacts with dil. HCl.
Ans. Hydrogen gas is evolved.
3. What is a chemical equation?
Ans. A chemical equation is a symbolic notation that uses formulae instead of words to represent a
chemical equation.
4. On what chemical law, balancing of chemical equation is based?
Ans. Balancing of a chemical equation is based on the law of conservation of mass.
5. Represent decomposition of ferrous sulphate with the help of balanced chemical equation.
Ans. 2FeSO4(s) Fe2O3(s) + SO2(g) + SO3(g)
6. When carbon dioxide is passed through lime water, it turns milky, why?
Ans. Lime water (calcium hydroxide) combines with carbon dioxide to form a suspension of calcium
carbonate which
makes lime water milky. Ca(OH)2(aq) + CO2(g) CaCO3( ) + H2O(l)
7. A zinc rod is left for nearly 20 minutes in a copper sulphate solution. What change would you
observe in zinc rod?
Ans. Zinc rod will change into zinc sulphate.
8. What type of reaction is this: Na2SO4 + BaCl2 BaSO4 +2NaCl
Ans. It is a double displacement reaction.
9. Identify the compound oxidized in the following reaction. H2S (g) + Cl2 S(s) + 2HCl (g)
Ans. H2S is oxidized.
10. What is rust?
Ans. Rust is mainly hydrated iron (III) oxide, Fe2O3.xH2O.
11. How does the food become rancid?
Ans. Food becomes rancid when fat and oils present in the food are oxidized.

12. 2-marks Questions/ Answers
Q.1. An iron knife kept dipped in a blue copper sulphate solution turns the blue solution light green.
Why? [2]
Ans. As we know iron is more reactive than copper. So, it displaces Cu from CuSO4 solution and
forms ferrous
sulphate which is of Light Green Colour.
CuSO4 (aq)+Fe (s) → FeSO4(aq) + Cu(s)
Blue colour light green colour
Q.2. A copper coin is kept in a solution of silver nitrate for some time. What will happen to the coin
and the colour of the
solution? [2]
Ans: We know that copper is more reactive than silver,
so it will displace silver from its salt solution: Cu(s) + 2AgNO3(aq) → Cu(NO3)2(aq)+2Ag(s)
So the solution will turn blue due to the formation of copper nitrate.
Q.3. what do you understand by precipitation reaction? Explain with suitable examples. [2]
Ans. Precipitate. When two reactants react and product formed remains insoluble and settles as a
solid it is called a
precipitate. Such reactions in which precipitate is formed are called precipitation reactions. For
example,
(i) When aqueous solution of sodium sulphate is mixed with the aqueous solution or barium
chloride, barium sulphate
comes in the form of white precipitate
Na2SO4(aq)+BaCl2(aq) → BaSO4(↓)+2NaCl(aq)
(ii) When aqueous solution of sodium chloride is mixed with the aqueous solution of silver nitrate,
silver chloride comes
in the form of white precipitate.
Q.4. What is lime-water test for the detection of carbon dioxide? [2]
Ans. When carbon dioxide gas is passed through lime water, it turns milky due to the formation of
milky suspension
(precipitate) of calcium carbonate. Carbon dioxide is produced by the action of dilute HCl on sodium
carbonate.
Na2CO3(s)+2HCl(aq) →2NaCl+H2O(l)+CO2
Carbon dioxide gas produced in this reaction is passed through lime water it changes to milky colour
due to the

13. formation of calcium carbonate.
Ca(OH)2(aq)+CO2(g) → CacO3+ CO2(g)
3 Marks Questions/ Answers
Q.5. what is corrosion? State the conditions necessary for rusting of iron. How rusting is harmful? [3]
Ans: Corrosion. The process of eating away of the metal by the action of atmospheric reagents
changing the metal into
its compound is called corrosion.
Rusting of Iron. : When iron and iron objects are exposed to atmosphere, they are attacked by air
and moisture
(water) of the atmosphere and a brown and orange colored layer is formed on the surface. It is
called rust which is
mainly hydrated iron (iii) oxide Fe2O3.xH2O.
Harmful Effect of Rusting. : Hydrated iron (iii) oxide is brittle substance and moves away from the
surface thus the
object is damaged. The objects get holes, cavities and rough surface.
Conditions necessary for rusting:
(i) Open surfaces of the metal.
(ii) Presence of air (Oxygen).
(iii) Presence of moisture (water).
Q.6. what is rancidity? Write the common method to prevent it. [3]
Ans. When food item are kept unprotected for some time, they give some unpleasant smell and
taste and become
rancid. This process is called rancidity. Actually, the micro organisms oxidize the fat and oils present
in them. So,
oxidation of food items need to be prevented to protect them.
Common methods to Prevent Rancidity of Food item:
(i) Keeping the food at low temperature
(ii) Keeping food item in air tight containers
(iii) By filling nitrogen in the food storage bags.
Q.6. a. Why cannot a chemical change be normally reversed? b. why is it always essential to balance
a chemical
equation? c. what happens when CO2 gas is passed through lime water and why does it disappear
on passing excess
CO2? d. Can rusting of iron takes place in distilled water?

14. Ans: a. In a chemical change some bonds are broken and some bonds are formed. The products are
quite different
from the reactants. Therefore it normally can’t be reversed.
b. A chemical equation has to be balanced to satisfy the law of conservation of mass.
c. On passing CO2 gas through lime water, it turns milky due to formation of insoluble calcium
carbonate which
dissolves on passing excess CO2 due to formation of soluble calcium bicarbonate.
Ca(OH)2 + CO2(g) -----→ CaCO3(s) + H2O(l)
CaCO3(s) + H2O(l) + CO2 (g) ---------------→ Ca(HCO3)2(soluble)
No, rusting of iron cannot take place in distilled water because it neither contains dissolved oxygen
nor CO2 both are
essential for rusting of iron.
HOTS QUESTIONS (Chemical Reactions and Equations)
Q. The marble statues often slowly get corroded when kept in open for a long time .Assign a suitable
explanation
Ans-SO2, NO2 gases are released into the atmosphere from various sources. These dissolve in rain
water to give acid
which corrodes marble statues
2SO2+O2 2SO3
H2O+SO3 H2SO4
2NO2+H2O 2HNO3
CaCO3+H2SO4→ CaSO4 +H2O+CO2
CaCO3+2HNO3 → Ca(NO3)2+H2O+CO2
Q. You are given the following materials (a) marble chips (b)dilute hydrochloric acid (c)Zinc granules
,identify the type
of reaction when marble chips and Zinc granules are added separately to acid taken in two test tubes
Ans-(a) marble chips react with dilute hydrochloric acid to form calcium chloride and carbon dioxide
.it is a double
displacement reaction
CaCO3+2HCl → CaCl2 + H2O +CO2
(b)Zinc granules react with dilute hydrochloric acid to give hydrogen gas. it is a displacement
reaction Zn(s)+2HCl →
ZnCl2(aq)+H2(g)
Q. The gases hydrogen & chlorine do not react with

15. each other even if kept together for a long time . However, in the presence of sunlight, they readily
combine. What
does actually happen? Ans-In Chemical reactions, energy is needed to break the bonds present in
the reacting
molecules so that they may combine to form the products. In this reaction, sunlight is the source of
energy in the form
of photons. The energy made available by sunlight helps in breaking the bonds & this leads to
chemical reaction
between hydrogen & chlorine. H2(g) + Cl2(g) sunlight→ 2HCl (g)
Q. A,B and C are three elements which undergo chemical reactions in the following way
A2O3 + 2B B2O3 + 2A
3CSO4 + 2B B2(SO4)3 + 3C
3CO+ 2A A2O3 +3C
Answer the following
(A) Which element is most reactive? (B) Which element is least reactive ?
Ans: a) The most reactive element is ‘B’. It has displaced both ‘A’ and ‘c’ from their compounds.
b) The least reactive element is ‘C’ as it has been displaced by both ‘A’ and ‘B’ .
Q. A water insoluble substance ‗X‘ on reacting with dilute H2SO4 released a colourless and
odourless gas
accompanied by brisk effervescence. When the gas was passed through water, the solution obtained
turn blue litmus
red . On bubbling the gas through lime water, it initially became milky and the milkiness disappeared
when the gas was
passed in excess. Identify the substance ‗X‘ and write the chemical equations of the reaction
involved .
Ans: the water insoluble substance ‘X’ is most probably metal carbonate ( CaCO3 ). The chemical
reaction that
involved are given below
CaCO3 (s) + H2SO4 (aq) →CaSO4 ( aq) + H2O (aq) + CO2 (g)
Ca(OH)2 (s) + CO2 (g) → CaCO3 (s) + H2O (l) ( milky)
CaCO3 (s) + CO2 (g) + H2O (aq) →Ca(HCO3)2 ( milkiness)
Q. Ahmad took a magnesium ribbon (cleaned) and burned it on a flame. The white powder formed
was taken in a test
tube and water was added to it. He then tested the solution formed with red and blue litmus paper.
What change was

16. seen? Why?
Ans. Red litmus paper turned blue. Blue litmus paper remained blue.
This is because the magnesium ribbon on burning in air forms the white magnesium oxide. Which
dissolved in water, it
forms magnesium hydroxide, which is Basic in nature.
Q. Give one example of a combination reaction in which an element combines with a compound to
give you a new
compound.
Ans. O2 + 2SO2 2SO3
8NH3 + 3Cl2 6NH4Cl