Edexcel IAL Chemistry 16.16 uncertainty in redox titration results

Use twice the burette reading uncertainty for a titre, add apparatus percentage uncertainties and compare the total uncertainty with the quoted significant figures.

Exam points

Calculate percentage uncertainty for titres, balances, pipettes and volumetric flasks.
Add apparatus uncertainties to estimate the total percentage uncertainty.
Judge whether a final percentage result is quoted to too many significant figures.

[Maximum number: 4]

This question is about manganese compounds. Some data are given below.

Table for Question 16.16—Discuss the uncertainty of measurements and their implications for the validity of the final results question 1 — Edexcel A-Level Chemistry A2

(a)

The uncertainties of the apparatus used in the experiment in (b) are shown.

Table for Question (a) — Edexcel A-Level Chemistry A2

[ 4 ]

(i)

Complete the table.

[ 2 ]

$\text { (Balance: } \frac{100 \times 0.005 \times 2}{1.53}=0.65 \text { ) }$

- burette: $\frac{100 \times 0.05 \times 2}{27.35}=0.37(\%)$

- pipette: $\frac{100 \times 0.06}{25}=0.24(\%)$

- volumetric flask: $\frac{100 \times 0.3}{250}=0.12(\%)$

(Total =1.38 )

All three percentages correct scores (2)

Any two percentages correct scores (1)

IGNORE SF

(ii)

A third student obtained a value of 95.863% for the proportion of iron in the wire. State whether or not this student has given their answer to an appropriate number of significant figures. Justify your answer in terms of the total percentage uncertainty of the experiment.

[ 2 ]

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16.16—Discuss the uncertainty of measurements and their implications for the validity of the final results question 1

Question (a)

Question (i)

Question (ii)