# Homework Help: Basic stoichiometry question

1. Jul 11, 2006

### JEscribir

Can someone show me how to calculate the number of moles of a given compound's molecules when given the mass in grams of the compund sample?

I am kind of confused by this because at first I thought it just asked for me to convert the grams into moles, but that isnt exactly what is being asked.

2. Jul 11, 2006

### JEscribir

The actual problem that I dont understand says " how many moles of C2H3Cl3O2 molecules are in 100.0 g chloral hydrate (C2H3Cl3O2)?"

So thats to four sig figs and chloral hydrate has a molar mass of about 165.4 g/mol. I divided 100.0g / 165.4 g per mol to get about .6064 moles, but I'm getting that, it is incorrect.
So did I do something wrong or is it a mistake by the teacher?

3. Jul 11, 2006

### PPonte

Did you calculated the molar mass of $$C_2H_3Cl_3O_2$$ or it was given by your teacher? Anyway, the molar mass of $$C_2H_3Cl_3O_2$$ is 165.403 g.mol-1 which is the value you got.
Then, the number of moles is 0.6046.

Honestly, I do not see anything wrong in what you have done. You should ask your teacher to revise this exercise.

Last edited by a moderator: Jul 11, 2006
4. Jul 11, 2006

### JEscribir

Yeah I emailed my teacher because I was freaking out since I could have sworn I did it right.

Other people have already finished the assignment and no one has pointed out the supposed mistake to be revised that is why I am so skeptical.

5. Jul 11, 2006

### PPonte

Do you have the solution?

6. Jul 11, 2006

### JEscribir

what do you mean by solution?

7. Jul 11, 2006

### PPonte

You say that you are incorrect. Then, you should know the correct answer. That's what I am asking. Which is the correct answer to this problem?

8. Jul 11, 2006

### Cesium

I too get that as my answer.