Edexcel A-Level Chemistry Arithmetic and Numerical Computation

Practise Edexcel A-Level Chemistry arithmetic and numerical computation through percentage composition, density, yield, molar-ratio and unit-conversion calculations.

Exam points

calculate percentage composition by mass from formulae, repeat units or molar masses
use density, volume and mass relationships across cm3, dm3, g and tonnes
work through yield, percentage error and molar-ratio calculations with correct rounding

Covered syllabus points

B.0.0—Units in calculations B.0.1—Decimal and standard form B.0.2—Ratios, fractions and percentages B.0.3—Estimating calculation results B.0.4—Powers, exponentials and logarithms B.0.P—SI unit prefixes

[Maximum number: 1]

A student investigated the kinetics of the reaction between bromide ions, $\mathrm{Br}^{-}$ , and bromate(V) ions, $\mathrm{BrO}_{3}^{-}$ , in aqueous acid.

5 \mathrm{Br}^{-}(\mathrm{aq})+\mathrm{BrO}_{3}^{-}(\mathrm{aq})+6 \mathrm{H}^{+}(\mathrm{aq}) \rightarrow 3 \mathrm{Br}_{2}(\mathrm{aq})+3 \mathrm{H}_{2} \mathrm{O}(\mathrm{l})

To determine the rate equation for the reaction, the student varied the concentration of bromide ions, bromate(V) ions and acid in turn.

The effect of the concentration of bromide ions was investigated first.

Procedure

Step 1 Add $10.0 \mathrm{~cm}^{3}$ of $0.0050 \mathrm{~mol} \mathrm{dm}^{-3}$ potassium bromate(V), $15.0 \mathrm{~cm}^{3}$ of acidified methyl orange indicator solution and $5.0 \mathrm{~cm}^{3}$ of $0.00010 \mathrm{~mol} \mathrm{dm}^{-3}$ aqueous phenol to a beaker labelled P.

Step 2 Prepare the contents of beaker Q for Run 1 as specified in the table.
Step 3 Pour the contents of beaker Q into beaker P and start a timer. Pour the contents of beaker P back into beaker Q and place beaker Q on a white tile.

Step 4 Stop the timer as soon as the mixture turns colourless. Record the time, along with the temperature of the solution.

Step 5 Repeat Steps 1 to 4 for the remaining runs.

Table for Question B.0 Arithmetic and numerical computation question 1 — Edexcel A-Level Chemistry A2

The student's results are shown.

Complete the table by calculating the remaining values of 1 / t.

table complete with both 1 / t values to 2 SF

Example of completed table:

Volume of $\mathrm{KBr} / \mathrm{cm}^{3}$ & 10.0 & 8.0 & 6.0 & 5.0 & 4.0 & 3.0

Time,t / s & 23 & 24 & 32 & 39 & 48 & 64

$(1 / t) / \mathrm{s}^{-1}$ & 0.043 & 0.042 & 0.031 & 0.026 & $\underline{\mathbf{0. 0 2 1}}$ & $\underline{\mathbf{0. 0 1 6}}$

Temperature $/{ }^{\circ} \mathrm{C}$ & 18 & 22 & 22 & 22 & 22 & 22

[Maximum number: 1]

The reaction shown is at equilibrium. The forward reaction is endothermic.

\mathrm{C}(\mathrm{~s})+\mathrm{CO}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{CO}(\mathrm{~g})

At $680^{\circ} \mathrm{C}$ and $1 \mathrm{~atm}, 52.6 \%$ of the molecules in the gas mixture are carbon monoxide. What is the partial pressure of carbon dioxide, in atmospheres?

0.237

0.263

0.474

0.526

All question bank results loaded

Covered syllabus points

B.0 Arithmetic and numerical computation question 1

B.0 Arithmetic and numerical computation question 2