An analytical chemist in a metallurgy laboratory is tasked with verifying the identity of an unknown Group 2 metal, M\text{M}M, which has been recovered from a scrap alloy sample.
To determine the identity, the chemist performs a 'back-titration' analysis:
Stage 1 The chemist reacts a 1.28 g1.28\text{ g}1.28 g sample of the metal M\text{M}M with 100.0 cm3100.0\text{ cm}^3100.0 cm3 of 1.20 mol dm−3 HCl(aq)1.20\text{ mol dm}^{-3}\ \text{HCl(aq)}1.20 mol dm−3 HCl(aq). An excess of acid is used to ensure all of metal M\text{M}M reacts completely. A redox reaction occurs, forming hydrogen gas and a solution containing M2+\text{M}^{2+}M2+ ions.
Stage 2 The entire mixture from Stage 1 is quantitatively transferred to a volumetric flask and diluted with deionised water to a total volume of 250.0 cm3250.0\text{ cm}^3250.0 cm3.
Stage 3 A 25.00 cm325.00\text{ cm}^325.00 cm3 sample of the diluted solution is titrated against 0.250 mol dm−3 NaOH(aq)0.250\text{ mol dm}^{-3}\ \text{NaOH(aq)}0.250 mol dm−3 NaOH(aq) to neutralise the excess hydrochloric acid:
HCl(aq)+NaOH(aq)→NaCl(aq)+H2O(l) \text{HCl(aq)} + \text{NaOH(aq)} \rightarrow \text{NaCl(aq)} + \text{H}_2\text{O(l)} HCl(aq)+NaOH(aq)→NaCl(aq)+H2O(l)The titration is repeated to obtain concordant results.
The burette readings have been recorded to the nearest 0.05 cm30.05\text{ cm}^30.05 cm3.
| 1 | 2 | 3 | |
|---|---|---|---|
| Final reading / cm3\text{cm}^3cm3 | 23.15 | 23.95 | 27.55 |
| Initial reading / cm3\text{cm}^3cm3 | 0.00 | 1.50 | 5.20 |
Analyse these results to identify metal M\text{M}M. Show all your working.
