Edexcel A-Level Chemistry Handling Data

Practise Edexcel A-Level Chemistry handling-data skills through concordant titre selection, mean calculations, uncertainty ranges and significant-figure decisions.

Exam points

select concordant titres from burette tables before calculating a valid mean titre
calculate percentage uncertainty from repeated readings and measured changes
complete data tables with reciprocal or equilibrium values to stated significant figures

Covered syllabus points

B.1.1—Significant figures B.1.2—Arithmetic and weighted means B.1.3—Measurement uncertainty

[Maximum number: 1]

Washing soda is hydrated sodium carbonate ( $\mathrm{Na}_{2} \mathrm{CO}_{3} \cdot \mathrm{nH}_{2} \mathrm{O}$ ). The value of n can be determined by titration.

A titration method was carried out using the following procedure.
Step 14.29 g of $\mathrm{Na}_{2} \mathrm{CO}_{3} \cdot \mathrm{nH}_{2} \mathrm{O}$ was weighed into a beaker.
Step 2 The $\mathrm{Na}_{2} \mathrm{CO}_{3} \cdot \mathrm{nH}_{2} \mathrm{O}$ was dissolved in $50 \mathrm{~cm}^{3}$ of deionised water.
Step 3 All of the solution was transferred to a $250 \mathrm{~cm}^{3}$ volumetric flask. The beaker was rinsed with deionised water and these washings were added to the volumetric flask.

Step 4 The volumetric flask was made up to the mark with deionised water. The flask was stoppered and inverted several times.

Step 5 A burette, pipette and conical flask were all rinsed with deionised water.
Step 6 The burette was rinsed and then filled with $0.125 \mathrm{~mol} \mathrm{dm}^{-3}$ hydrochloric acid solution. The pipette was rinsed with the sodium carbonate solution and then used to transfer $25.0 \mathrm{~cm}^{3}$ of the solution to the conical flask.

Step 7 A few drops of methyl orange were added to the conical flask. The sodium carbonate solution was titrated with the hydrochloric acid. This step was repeated until concordant titres were obtained.

The following results were obtained in the titration.

Table for Question B.1 Handling data question 2 — Edexcel A-Level Chemistry AS

Complete the table and calculate the mean titre, using all concordant values.

calculation of titre volumes and
mean

Example of calculation

Titration & Trial & 1 & 2 & 3

Final volume $/ \mathrm{cm}^{3}$ & 24.45 & 48.50 & 24.95 & 29.05

Initial volume $/ \mathrm{cm}^{3}$ & 0.15 & 24.45 & 1.00 & 5.05

Titre $/ \mathrm{cm}^{3}$ & 24.30 & 24.05 & 23.95 & 24.00
((24.05+23.95+24.00) / 3)=24.00

Allow just 24 for both titre 3 and the mean titre.
\end{tabular}

(1)

[Maximum number: 1]

Fuels

Fuels burn in oxygen to release a lot of energy.
Many hydrocarbons and alcohols are used as fuels. During complete combustion, they produce carbon dioxide and water.

Petrol contains 2,2,4-trimethylpentane, an isomer of octane, that promotes smooth combustion.

Figure for Question B.1 Handling data question 3 — Edexcel A-Level Chemistry AS

2,2,4-trimethylpentane

Alcohols, such as methanol and ethanol, can be used as fuels either on their own or as additives in petrol.

In an experiment to determine the enthalpy change of combustion of ethanol, $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}$ , a student used the apparatus shown.

Results:
Mass of water $=100.0 \mathrm{~g}$
Mass of ethanol used $=0.305 \mathrm{~g}$
Temperature rise of water $=13.2^{\circ} \mathrm{C}$

The uncertainty in each thermometer reading is $\pm 0.05^{\circ} \mathrm{C}$ .

Calculate the percentage uncertainty in the temperature rise in this experiment.

All question bank results loaded

Covered syllabus points

B.1 Handling data question 1

B.1 Handling data question 2

B.1 Handling data question 3