Question

in percentage of water in hydrated salts experiment

1.How does the “percent-water in the hydrated salt” will be affected -?

a.If you handle the crucible with (oily) fingers before its mass measurements.

. b.If the hydrated salt is overheated and the anhydrous salt thermally

c.decomposes, one product being a gas d.If one student decided to skip the step of reheating the sample in the experimental procedure.

e.If the original sample is unknowingly contaminated with a second anhydrous salt.

2. What is the % mass of water present in a 4.63 g sample of FeCl3 ●6H2O?

Answer 1

Hydrated salts

1. Effect of following errors on percent water in th hydrated salt

a. If the crucible was handled with oily fingers, impurities will be added to the crucible which would increase the mass of salt before mass meaurement. Therefore, higher percent water in the hydrated salt would be obtained than the actual value.

b. If overheating of hydrated salt is done, leading to decomposition of salt. Lesser mass of water would be obtained, therefore, lower percent water would be calculated than actual value.

c. decomposed products have one gas, which leaves lowering down the percent water in the salt.

d. If student skips reheating the sample step, higher mass of original dehydrated salt is obtained. Therefore higher percent water is calculated in this case.

2. percent water in 4.63 g of FeCl3.6H2O

molar mass of FeCl3.6H2O = 270.3 g/mol

mass of 6H2O = 6 x 18.015 g/mol = 108.1 g/mol

percent water = 108.1 x 100/270.3 = 40%

So,

mass water in 4.63 g sample = 4.63 x 0.4 = 1.852 g

percent water = 40%