Chemistry

Mole Concept and Stoichiometry

365 Questions

The mole concept is a core area of chemistry focusing on the quantitative relationships between reactants and products in chemical reactions. Questions cover molecular mass calculations, stoichiometric conversions, and determining the number of molecules. This topic is essential for most science entrance and competitive examinations.

molecular mass calculationsstoichiometric conversionsmole fraction problemsheavy water reactionsoxidation calculations

Mole Concept and Stoichiometry Questions

Multiple choice

What is the correct number of hydrogen atoms in 0.25 moles of water?

  1. 2

  2. 12.05 x 1023

  3. 0.18 x 1023

  4. 3.01 x 1023

  5. 0.75 x 1023

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

1 mole of H2O atoms contains 2 moles of H atoms. = 2 X 6.023 X 1023 hydrogen atoms So, 0.25 moles of H2O contains 2 x 6.023 X 1023 X 0.25 H atoms. = 3.01 X 1023 H atoms. Thus, this is the correct answer.

Multiple choice

What is the mass of one molecule of water?

  1. 0.33 X 10-23

  2. 2.66 X 10 -23

  3. 6.02 X 1023

  4. 1.99 X 10 -23

  5. 2.99 X 10 -23
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

 Molecular mass of water = 2 + 16 = 18 g 1 mole of water (6.023 X 1023 molecules) weighs 18 g. Weight of 1 molecule of water = 18 / 6.023 X 1023 = 2.99 X 10 -23

Thus, this is correct.

Multiple choice

What is the number of grams of Cr in 85 grams of Cr2S3?

  1. 200 grams

  2. 104 grams

  3. 244.7 grams

  4. 163.4 grams

  5. 44.2 grams
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Molecular mass of Cr2S3 = 52 x 2 + 32 x 3 = 200 200 g Cr2S3 has Cr = 104 g 85 g of Cr = 104 / 200 x 85 = 44.2 g

Thus, this is the correct answer.

 

Multiple choice

Which of the following statements is/are correct?

(a). The word “mole” was introduced in 1896 by Wilhelm Ostwald. (b). The mass of 1 mole of a substance is equal to its relative atomic or molecular mass in grams. (c). The quantity of a substance can be characterised by the valency of its molecules.

  1. (a) only

  2. (b) only

  3. (c) only

  4. (a) and (b)

  5. (a), (b) and (c)
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

This is the correct answer. Both the statements (a) and (b) are correct.

Multiple choice

What is the molecular formula of butane?

  1. C4H8

  2. C4H9

  3. C4H10

  4. C5H12
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Butane is a 4-carbon alkane with the formula C4H10 following the CnH2n+2 pattern for alkanes. Substituting n=4 gives C4H(2×4+2) = C4H10.

Multiple choice

Formula for diborane is

  1. B2H3

  2. B2H4

  3. B2H6

  4. B2H8
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Diborane has the chemical formula B2H6. It is the simplest boron hydride and consists of two boron atoms connected by hydrogen bridges, with each boron also bonded to two terminal hydrogen atoms.

Multiple choice

The general formula for alkane is

  1. CnH2n+2

  2. CnHn

  3. CnH2n

  4. C2nH2n
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Alkanes are saturated hydrocarbons where each carbon forms four single bonds. The formula CnH2n+2 ensures all carbons are fully saturated with hydrogens, unlike alkenes (CnH2n) or alkynes.

Multiple choice

Formula for hydrazine is

  1. H2NNH2

  2. NH2NH2

  3. NHNH

  4. NH3
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Hydrazine is N2H4, which is properly written as NH2NH2 showing the N-N single bond with each nitrogen bonded to two hydrogens. It is a powerful reducing agent used in rocket fuels and as a precursor to polymers.

Multiple choice

How many oxygen atoms are present in an ozone molecule?

  1. 1

  2. 2

  3. 3

  4. 4
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Ozone is a molecule made of three oxygen atoms, giving it the chemical formula O3. This distinguishes it from regular oxygen which has only two oxygen atoms (O2). Ozone forms the ozone layer in the upper atmosphere.