An alkali metal weighing 6.65 grams was completely dissolved in water. 7.5 grams
September 28, 2021 | education
| An alkali metal weighing 6.65 grams was completely dissolved in water. 7.5 grams of alkali was isolated from the resulting solution by evaporation. Identify this metal.
Let’s write the reaction equation:
2M + 2H2O = 2MOH + H2 ↑, where M is an unknown alkali metal.
Amount of substance M:
v (M) = m (M) / M (M) = 6.65 / M (M) (mol).
Amount of substance MOH:
v (MOH) = m (MOH) / M (MOH) = 7.5 / (M (M) + 17) (mol).
According to the reaction equation, from 2 mol of M, 2 mol of MOH is formed, therefore:
v (M) = v (MOH),
6.65 / M (M) = 7.5 / (M (M) + 17),
M (M) = 133 (g / mol), which corresponds to the cesium metal (Cs).
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