Chemistry URGENT
posted by jazz .
I am not good with math problems. I need help with these two problems. I'm not sure what equations to use. please help.
A student heated a hydrated salt sample with an initial mass of 4.9702 g. After the first heating, the mass had decreased to 3.0662g.
1. if the sample was heated to constant weight after reheating, what is the minimum mass that the sample can have after the second weighing? Show how you determined your answer.
2. the student determined that the mass lost by the sample was 1.8053. What was the percent in the original hydrated sample. Show calculation setup.
thanking you in advance

The answer to A depends upon what kind of accuracy/precision you are looking for. I think 0.2 to 0.3 mg is pretty standard. So I would go with 3.0662  0.0002 = ? or on a bad day 3.05520.0003 = ? Frankly, that is in the neighborhood of 7% error and that isn't great but it's tough to do better than about 0.2 mg with a top line balance that weighs to 0.2 mg. I would be interested in knowing what your prof considers constant weight and he s/he determines it.
2. % H2O = (mass lost/mass sample)*100 = ? 
I just looked at this old problem. 0.2 mg is 0.0002 g and that is closer to (0.0002/3.0662)*100 = not anywhere close to 7%. More like 0.007%.