Page 1 - HA

SAI International School
Lesson Notes

Subject-Chemistry
Ch-Is Atoms and molecules?
Topic-Concept mapping of chapter-3

HOME ASSIGNMENT
Concept- Laws of Chemical Combination
Q1 Assertion: When 58.5 g of NaCl is decomposed, 35.5 g chlorine is formed and 1
. 23 g of Sodium is formed.
Reason: Law of conservation of energy states that energy can neither be
created nor be destroyed.

Q2 Assertion: Hydrogen sulphide prepared by different methods was found to 1
contain Hydrogen and Sulphur combined in the ratio 1:16 by mass.
Reason: Mass can neither be created nor be destroyed
Q3 Assertion:When10gofCaCO isdecomposed,5.6gofresidueisleftand4.4gofCO escape
3
2
s.
Reason:Lawofconservationofmassisfollowed.
Q. Assertion : Pure water obtained from different sources such as river, well,
4 spring, sea etc. always contains hydrogen and oxygen combined in the ratio of
1 : 8 by mass.
Reason : A chemical compound always contains same elements combined in
same fixed proportion by mass.
Q3 In a chemical reaction the mass is destroyed. (True or false) 1

Q4 Which of the following reactions is not suitable for the verification of law of 1
conservation of mass?
a) Mixing HCl with NaOH solution
b) Thermal decomposition of ferrous sulphate
c) Mixing Copper sulphate and Barium sulphate solutions
d) Mixing Lead nitrate and Potassium iodide solutions.
Q5 While verifying the law of conservation of mass Subham added 3.5 g of 1
magnesium metal into 13.7 g of hydrochloric acid. What is the mass of
eliminated hydrogen gas along with 10 g of magnesium chloride if the
law of conservation mass is correct?
a) 7.2 g b) 3.4 g
c) 4.3 g d) 5 g

Q6 To identify the law of conservation of mass a student added 10 mL of 1
5% barium chloride solution into 10 mL of 5% Sodium sulphate solution.
Which of the following is correct observation?
a) A clear solution is obtained
b) The solution turns to red colour.
c) A yellow precipitate is formed.
d) A white precipitate is formed.