IB · IB Chemistry

IB Chemistry: How much? The amount of chemical change — Practice Questions & Answers

352 practice questions available for this topic — here are 10 with full answers and explanations.

Start an interactive quiz on How much? The amount of chemical change →

Practice questions with answers

1 Multiple choice · Easy

In a balanced chemical equation, the coefficients give the ratio of the:

Tap an answer to check it.

WhyThe stoichiometric coefficients give the mole ratio in which substances react and are formed.
2 Multiple choice · Medium

In a reaction the limiting reagent is the reactant that:

Tap an answer to check it.

WhyThe limiting reagent is completely used up first and therefore determines the maximum amount of product formed.
3 Multiple choice · Medium

How is percentage yield calculated?

Tap an answer to check it.

WhyPercentage yield $= \dfrac{\text{actual yield}}{\text{theoretical yield}} \times 100\%$.
4 Multiple choice · Medium

Atom economy is a measure of:

Tap an answer to check it.

WhyAtom economy is the percentage of the total mass of reactants that ends up in the desired product, a measure of the efficient use of atoms.
5 Multiple choice · Medium

In the reaction $\text{N}_{2} + 3\text{H}_{2} \rightarrow 2\text{NH}_{3}$, how many moles of $\text{H}_{2}$ react completely with $2\,\text{mol}$ of $\text{N}_{2}$?

Tap an answer to check it.

WhyThe mole ratio of $\text{N}_{2}:\text{H}_{2}$ is $1:3$, so $2\,\text{mol}$ of $\text{N}_{2}$ needs $2 \times 3 = 6\,\text{mol}$ of $\text{H}_{2}$.
6 Multiple choice · Hard

$0.50\,\text{mol}$ of $\text{Mg}$ reacts completely in $\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_{2} + \text{H}_{2}$. What mass of $\text{H}_{2}$ ($M = 2\,\text{g mol}^{-1}$) is produced?

Tap an answer to check it.

WhyMole ratio $\text{Mg}:\text{H}_{2} = 1:1$, so $0.50\,\text{mol}$ of $\text{H}_{2}$ forms. Mass $= n \times M = 0.50 \times 2 = 1.0\,\text{g}$.
7 Fill in the blank · Easy

In $2\text{H}_{2} + \text{O}_{2} \rightarrow 2\text{H}_{2}\text{O}$, the number of moles of water formed from $2\,\text{mol}$ of $\text{H}_{2}$ is .

Answer: 2 / two

WhyThe mole ratio $\text{H}_{2}:\text{H}_{2}\text{O}$ is $2:2 = 1:1$, so $2\,\text{mol}$ of $\text{H}_{2}$ gives $2\,\text{mol}$ of water.
8 Fill in the blank · Medium

A reaction has a theoretical yield of $8.0\,\text{g}$ but only $6.0\,\text{g}$ is obtained. The percentage yield is %.

Answer: 75 / 75%

Why$\%\text{ yield} = \dfrac{6.0}{8.0} \times 100 = 75\%$.
9 Multiple choice · Medium

For AlCl3 -> Al + 3 Cl, what mass of chlorine atoms forms from 1.25 mol AlCl3? (Ar Cl = 35.45)

Tap an answer to check it.

Whyn(Cl) = 3 x 1.25 = 3.75 mol; m = 3.75 x 35.45 = 133 g.
10 Multiple choice · Easy

The coefficients in a balanced equation give the ratio of amounts in

Tap an answer to check it.

WhyStoichiometric coefficients represent the ratio of amounts in moles.

Ready to test yourself?

Practise How much? The amount of chemical change with instant marking and per-topic score tracking.

Start the How much? The amount of chemical change quiz →

Practise other IB Chemistry topics

Topic S1.1 (SL/HL): Introduction to the particulate nature of matter Topic S1.2 (SL/HL): The nuclear atom Topic S1.2 (HL): The nuclear atom Topic S1.3 (SL/HL): Electron configurations Topic S1.3 (HL): Electron configurations Topic S1.4 (SL/HL): Counting particles by mass: the mole Topic S1.5 (SL/HL): Ideal gases Topic S2.1 (SL/HL): The ionic model Topic S2.1 (HL): The ionic model Topic S2.2 (SL/HL): The covalent model Topic S2.2 (HL): The covalent model Topic S2.3 (SL/HL): The metallic model Topic S2.3 (HL): The metallic model Topic S2.4 (SL/HL): From models to materials Topic S2.4 (HL): From models to materials Topic S3.1 (SL/HL): The periodic table: classification of elements Topic S3.1 (HL): The periodic table: classification of elements Topic S3.2 (SL/HL): Functional groups: classification of organic compounds Topic S3.2 (HL): Functional groups: classification of organic compounds Topic R1.1 (SL/HL): Measuring enthalpy changes Topic R1.2 (SL/HL): Energy cycles in reactions Topic R1.2 (HL): Energy cycles in reactions Topic R1.3 (SL/HL): Energy from fuels Topic R1.4 (HL): Entropy and spontaneity Topic R2.2 (SL/HL): How fast? The rate of chemical change Topic R2.2 (HL): How fast? The rate of chemical change Topic R2.3 (SL/HL): How far? The extent of chemical change Topic R2.3 (HL): How far? The extent of chemical change Topic R3.1 (SL/HL): Proton transfer reactions Topic R3.1 (HL): Proton transfer reactions Topic R3.2 (SL/HL): Electron transfer reactions Topic R3.2 (HL): Electron transfer reactions Topic R3.3 (SL/HL): Electron sharing reactions Topic R3.4 (SL/HL): Electron-pair sharing reactions Topic R3.4 (HL): Electron-pair sharing reactions