IB Chemistry HL 1.4.2 Relative Atomic and Formula Mass Question Bank

Practise IB Chemistry HL 1.4.2 with SL and HL questions on Ar, Mr, isotopic abundance and weighted averages.

[Maximum number: 1]

Two groups of students (Group A and Group B) carried out a project* on the chemistry of some group 7 elements (the halogens) and their compounds.

The students reacted ICl(l) with CsBr(s) to form a yellow solid, $\mathrm{CsICl}_{2}(\mathrm{~s})$ , as one of the products. $\mathrm{CsICl}_{2}(\mathrm{~s})$ has been found to produce very pure CsCl(s) which is used in cancer treatment.

To confirm the composition of the yellow solid, Group A determined the amount of iodine in 0.2015 g of $\mathrm{CsICl}_{2}(\mathrm{~s})$ by titrating it with $0.0500 \mathrm{moldm}^{-3} \mathrm{Na}_{2} \mathrm{~S}_{2} \mathrm{O}_{3}(\mathrm{aq})$ . The following data were recorded for the titration.

Table for Question 1.4.2—Relative atomic mass (Ar) and relative formula mass (Mr) question 1 — IB Chemistry HL

Calculate the percentage of iodine by mass in $\mathrm{CsICl}_{2}(\mathrm{~s})$ , correct to three significant figures.

$\left(\frac{126.90}{330.71} \times 100\right)=38.4 \%$ ;

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1.4.2—Relative atomic mass (Ar) and relative formula mass (Mr) question 1