# Homework Help: % mass by Vol problem

1. Dec 7, 2007

### MichaelXY

[SOLVED] % mass by Vol problem

1. The problem statement, all variables and given/known data
Concentrated Hydrochloric acid is 37% HCl by mass and has a density of 1.19 g/ml. What is the molarity of HCl.

2. Relevant equations
Mass = D(V)
1 mole HCl = 36.5g

3. The attempt at a solution
What has thrown me off on this problem is that volume is not given. So I assume 100ml.
With that I can compute mass = 1.19g/ml (100ml) = 119g
Where 36.5 is 1 mol HCl
So then I compute 119g/36.5g = 3.26 mole

Did I do that right? I really don't feel confident on this problem.

2. Dec 7, 2007

### symbolipoint

Remember, you started with 37% HCl.
(0.37)*(100 ml)*(1.19 grams)/(1 ml) = however many grams of HCl

Now, (HCl grams) / (36.5 grams/mole) = the moles of HCl

Take it from there...

3. Dec 7, 2007

### MichaelXY

Thanks so much, and Gadzooks, how did I miss the 37%. I think I got it. So I end up with 1.2 moles. Molarity = moles/liter, so I have 1.2mol/.1L = a molarity of 12.06
Again thanks. This chapter is is kicking my behind, and my teacher said this chapter is the core of Chemistry. I seem to have trouble seeing the whole picture. Is this just me?

4. Dec 7, 2007

### symbolipoint

This must be your first time either studying Elementary Chemistry, or General Chemistry and you never before studied Elementary Chemistry. You'll become accustomed to these calculations with practice.

5. Dec 7, 2007

### MichaelXY

I guess it shows, and your correct, I never had chem before, in fact I never finished the 10th grade, and now I am playing catch up in a JC. Sorry if my questions are elementary.
But thank you for the help.