TAGORE INTERNATIONAL SCHOOL
VASANT VIHAR, NEW DELHI
ASSIGNMENT (2025-26)
CHEMISTRY
(Basic Concepts in Chemistry)
CLASS: XI
Name ____________________
Sec __________
Date ____________
LAWS OF CHEMICAL COMBINATION
1. Calculate the molecular mass of KCl and Calcium carbonate
2. What is the value of Avogadro number?
3. State and explain the laws with a suitable example.
a. Law of conservation of mass
b. Law of definite or constant proportion
c. Law of multiple proportion
Conservation of Mass
1. If 10g of substance A reacts with 15g of substance B to produce substance C, what is the mass of
substance C?
2. In a chemical reaction, 100g of reactant A decomposed to give 55g of product B and some amount of
product C. What is the mass of product C?
3. In the formation of iron II sulphide by heating iron and sulphur, 56 parts of Fe and 32 parts of sulphur
chemically combine to form 88 parts of FeS. Verify the law of conservation of mass. (Write the balanced
equation first)
Definite Proportions
4. A compound is formed when 7g of element X combines with 8g of element Y. What is the percentage
composition of X and Y in the compound?
5. If 5g of calcium combines with 2g of oxygen to form calcium oxide, what mass of oxygen is required to
combine with 20g of calcium?
6. 5.18g of copper metal is first converted to copper nitrate and subsequently to 6.45g CuO. In another
experiment 1.10g copper gave 1.37g CuO on combustion. Show that the above data verify the law of
definite proportion.
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Law of Multiple Proportions
7. In three experiments silver was converted to silver iodide. Samples of silver weighing 9.896, 10.440
and 9.528 were converted to 21.537g, 22.723g and 20.737g of silver iodide respectively. Show that
these data illustrate the law of definite proportions.
8. Two different compounds are formed by the elements carbon and oxygen. The first compound contains
42.9% by mass carbon and 57.1% by mass oxygen. The second compound contains 27.3% by mass
carbon and 72.7% by mass oxygen. Show that the data are consistent with the law of multiple
proportions.
Gay-Lussac's Law
9. 2 litres of hydrogen gas react with 1 litre of oxygen gas to produce water vapor. If the reaction is carried
out at the same temperature and pressure, what volume of water vapor will be formed?
10. 100 mL of methane is combusted with 200mL of oxygen. What is the volume of CO 2 formed?
CH4+2O2 ⟶ CO2+ 2H2O
EMPIRICAL AND MOLECULAR FORMULA
Molecular formula – a formula showing the types and numbers of atoms combined in a single
molecule of a molecular compound. It is a whole number multiple of the empirical formula.
The relationship between a compounds’ empirical and molecular formula can be written as:
x (empirical formula) = molecular formula
Also
x (empirical formula mass) = molecular formula mass
4. To determine the molecular formula of a compound, you must know the compound’s molar mass.
5.
Divide the molecular mass by the empirical formula mass to determine the whole number multiple
(x). You may have to find the empirical formula in order to obtain the empirical formula mass.
6. Determine the molecular formula of the compound with an empirical formula of CH and a molar mass of
78.110 g/mol.
7. A sample with a molar mass of 34.00 g/ mol is found to consist of 0.44g H2 and 6.92 g O2. Find its
molecular formula.
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8. The molar mass of a compound is 92 g/mol. Analysis of a sample of the compound indicates that it
contains 0.606g N2 and 1.390g O2. Find its molecular formula.
LIMITING REAGENT
9. Given the following equation: 2 KClO3 ---> 2 KCl + 3 O2
How many moles of O2 can be produced by letting 12.00 moles of KClO3 react?
10. NO2 is formed when 0.740 g of O3 reacts with 0.670 g of NO. Identify the limiting reagent and the excess
reagent?
11. What is the greatest amount of MgO (i moles) that can be made with 7.8 moles of Mg and 4.7 moles of
O2? Which is the limiting reagent?
12. Given the following equation: 2 K + Cl2 ---> 2 KCl
How many grams of KCl is produced from 2.50 g of K and excess Cl2.
(K=39 Cl=35.5)
13. Given the following equation: 8 Fe + S8 ---> 8 FeS (Fe= 56, S=32)
a) What mass of iron is needed to react with 16.0 grams of sulphur?
b) How many grams of FeS are produced?
14. If 15 grams of copper (II) chloride react with 20 grams of sodium nitrate, how much sodium chloride can
be formed? CuCl2 + 2 NaNO3
Cu (NO3)2 + 2 NaCl (Cu= 63.5)
How much of the non-limiting reagent is left over in this reaction?
15. Read the given passage and answer the questions that follow:
Stoichiometry is a section of chemistry that involves a calculation based on chemical equations. Chemical
equations are governed by laws of chemical combination. The mass of reactants is equal to the mass of
products. The compound obtained from different methods contains the same elements in the fixed ratio by
mass. A mole is a counting unit, equal to 6.022 × 1023 particles. One mole is also equal to molar mass
expressed in grams. One mole of every gas at STP has a volume equal to 22.4 L. The reacting species
which are consumed in the reaction completely is called limiting reagent which decides the amount of
products formed. The concentration of the solution is expressed in terms of molarity, morality, and mole
fraction.
(a) Calculate the number of moles of NH3 formed by the reaction of 2 moles of N2 and 2 moles of H2,
N2(g) + 3H2(g) → 2NH3(g).
(b) Calculate number of electrons in 18 g of H2O. [Atomic mass of H = 1, O = 16]
(c) Calculate the molality of 1 M NaCl solution having density 1.10 g cm–3. (Molar mass = 58.5 g mol–1)
(d) Define mole fraction.
(e) In aqueous solution of glucose x glucose = 0.1, what is x H2O = ?
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Molarity And Molality
16. The density of 1 M solution of HCl is 1.0585 g/mL. The molality of the solution is:
a)
b)
c)
d)
1.0585
1
0.10
0.0585
17. The mole fraction of a solute in an aqueous solution is 0.2. The molality of the solution will be:
a)
b)
c)
d)
13.88
1.388
0.138
0.0138
18. measure the molality of 34.5g of sugar dissolved in 215 g of water.
a)
b)
c)
d)
0.559 m
0.613 m
0.603 m
0.554 m
19. Which of the following is the correct formula for molality?
a)
b)
c)
d)
Molality = kilograms of solute ÷ litres of solvent
Molality = moles of solute ÷ kilograms of solvent
Molality = kilograms of solute ÷ kilograms of solution
Molality = moles of solute ÷ moles of solution
20. Assertion: Equal moles of different substances contain same number of constituent particles.
Reason: Equal weights of different substances contain the same number of constituent particles.
a)
b)
c)
d)
Assertion is correct, reason is correct; reason is a correct explanation for assertion.
Assertion is correct, reason is correct; reason is not a correct explanation for assertion
Assertion is correct, reason is incorrect
Assertion is incorrect, reason is correct statement.
21 Assertion: Molarity of a solution in liquid state changes with temperature.
Reason: The volume of a solution changes with change in temperature.
a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
c) Assertion is correct, reason is incorrect
d) Assertion is incorrect, reason is correct statement
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