I am enrolled in analytical chemistry after a 4 year break from any chemistry. I was recently given a problem set and I need some help on the following:
A 0.899g sample containing epsom salt, MgSO4 & 7 H2O, and other non-hydrated materials was dehydrated completely in a stream of hot, dry nitrogen. The resulting air stream was passed through a tube containing the desiccant magnesium perchlorate. The original weight of the desiccant tube was 61.997g and, after the determination, the tube weighed 62.318g. What is the % epsom salt in the sample.
I would appreciate any help. Thanks!
The gain in weight of the perchlorate is the mass of H2O. Convert that to mols by mols = grams/molar mass H2O.
Convert mols H2O to mols MgSO4.7H2O using the coefficient in the balanced equation below.
MgSO4.7H2O+ heat ==> MgSO4 + 7 H2O
mols MgSO4.7H2O = mols H2O x (1 mol MgSO4.7H2O/7H2O). (note how the units that we don't want cancel and leaves the units we want to keep.)
Convert mols MgSO4.7H2O to grams.
g = mols x molar mass.
Finally,
%MgSO4.7H2O = [mass MgSO4.7H2O/mass sample]*100 = ??
Post your work if you get stuck.
To determine the percentage of epsom salt (MgSO4 · 7 H2O) in the given sample, we need to consider the weight loss of the sample during the dehydration process.
To solve this problem, we can follow the steps below:
Step 1: Calculate the weight loss of the sample during dehydration.
- Weight loss = Initial weight of the sample - Final weight of the sample
- Initial weight of the sample = 0.899g
- Final weight of the sample = Weight of the desiccant tube (after determination) - Weight of the desiccant tube (before determination)
- Weight of the desiccant tube (after determination) = 62.318g
- Weight of the desiccant tube (before determination) = 61.997g
Step 2: Calculate the weight of the water lost during the dehydration.
- The weight of water lost = Weight loss of the sample
Step 3: Calculate the weight of the epsom salt (MgSO4 · 7 H2O) remaining after dehydration.
- Weight of the remaining epsom salt = Initial weight of the sample - Weight of water lost
Step 4: Calculate the percentage of epsom salt in the sample.
- % epsom salt = (Weight of the remaining epsom salt / Initial weight of the sample) * 100
Now let's calculate the values:
Step 1: Calculate the weight loss of the sample during dehydration.
- Weight loss = 0.899g - (62.318g - 61.997g)
= 0.899g - 0.321g
= 0.578g
Step 2: Calculate the weight of the water lost during the dehydration.
- The weight of water lost = 0.578g
Step 3: Calculate the weight of the remaining epsom salt (MgSO4 · 7 H2O) after dehydration.
- Weight of the remaining epsom salt = 0.899g - 0.578g
= 0.321g
Step 4: Calculate the percentage of epsom salt in the sample.
- % epsom salt = (0.321g / 0.899g) * 100
≈ 35.7%
Therefore, the percentage of epsom salt in the sample is approximately 35.7%.