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Class 11 Some Basic Concepts of Chemistry worksheet
CBSE Chemistry. Moles, molar mass, empirical formulas, concentration, limiting reagent. Every sheet has 20 questions in three sections and an answer key, and the numbers change every time.
Sample questions
Real questions from this chapter, as the app sets them. Tap Answer to see the answer and working.
Section A · multiple choice
- 1.
One mole of a substance contains:
- 22.7 particles
- 1 gram of particles
- 6.022 × 10²² particles
- 6.022 × 10²³ particles
Answer
(d) 6.022 × 10²³ particles
the Avogadro constant
- 2.
How many significant figures are there in 90007?
- 5
- 6
- 4
- 7
Answer
(a) 5
non-zero digits and zeros between them count; leading zeros never count; trailing zeros count after a decimal point
- 3.
How many moles are there in 18.5 g of Ca(OH)₂? (Atomic masses: H = 1 u, O = 16 u, Ca = 40 u)
- 0.125 mol
- 0.5 mol
- 1 mol
- 0.25 mol
Answer
(d) 0.25 mol
n = mass ÷ molar mass = 18.5 ÷ 74
Section B · short answer
- 4.
State the law of multiple proportions with an example.
Answer
When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in a simple whole-number ratio. Example: 12 g of carbon combines with 16 g of oxygen in CO and 32 g in CO₂, a ratio of 1 : 2.
- 5.
How many moles and how many atoms are there in 310.5 g of lead? (Pb = 207 u; N_A = 6.022 × 10²³ mol⁻¹)
Answer
1.5 mol; 9.033 × 10²³ atoms
n = mass ÷ molar mass; atoms = n × N_A
Section C · long answer
- 6.
State the laws of chemical combination. Explain the law of definite proportions with an example.
Answer
Laws: conservation of mass; definite proportions; multiple proportions; Gay-Lussac’s law of gaseous volumes; Avogadro’s law. Definite proportions: a compound always contains the same elements combined in the same proportion by mass, whatever its source. Example: pure water from any source has hydrogen and oxygen in the ratio 1 : 8 by mass.
Fresh sheets for your child
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