Posted by **joe** on Friday, February 12, 2010 at 8:22pm.

1.) How much ethanol, C2H5OH, in liters (d=0.789g/ml) must be dissolved in water to produce 190.5 of 1.65 M C2H5OH? (Molarity problem.)

2.) How much concentrated hydrochloric acid solution (36.0% HCl by mass, d = 1.18g/mL}), in milliliters, is required to produce 11.0 L of 0.296 M HCl?

- chemistry -
**DrBob222**, Friday, February 12, 2010 at 8:32pm
1.) How much ethanol, C2H5OH, in liters (d=0.789g/ml) must be dissolved in water to produce 190.5 of 1.65 M C2H5OH? (Molarity problem.)

**
**

190.5 WHAT for crying out loud?barrels, freight cars, lakes, I will assume you meant mL. If not that, adjust values below to what you should have written.

M = moles/L and moles = grams/molar mass.

1.65M = moles/0.1905. Calculate moles.

moles = gram/molar mass.

You know moles and molar mass, calculate grams.

From the density, calculate volume of ethanol to use and convert to liters.

- chemistry -
**bobpursley**, Friday, February 12, 2010 at 8:35pm
molarity=mass/molmass*volumeinLiters

1) massEthanol=density*volumeEthanol

so volumeEthanol=molarity*molmass*Volumesolution/density

Watch units.

2)work out the similar steps for the HCL.

- chemistry -
**DrBob222**, Friday, February 12, 2010 at 8:45pm
2.) How much concentrated hydrochloric acid solution (36.0% HCl by mass, d = 1.18g/mL}), in milliliters, is required to produce 11.0 L of 0.296 M HCl?

**
**

First calculate the molarity of the concentrated HCl.

1.18 g/mL x 1000 mL - mass of 1 L = 1180 g.

How much of that is HCl? 36% so,

1180 x 0.36 = 424.8 g HCl.

How many moles is that?

424.8/36.5 = 11.6 M

Now use the dilution formula to determine what you want to prepare.

mL x M = mL x M

Check my work. I estimated the molar masses and rounded here and there so you need to go through the problem yourself and do those numbers right.

- chemistry -
**david**, Friday, February 12, 2010 at 9:01pm
The second one is correct. Regarding the first one though, I calculated the grams to 6.8 g of C2H5OH. I don't quite understand the next step (regarding the density, etc)

- chemistry -
**joe**, Friday, February 12, 2010 at 9:07pm
that was me who posted the comment above. my friend had the same question.

- chemistry -
**DrBob222**, Friday, February 12, 2010 at 9:40pm
I don't know how you obtained 6.8 g.

The part about the density:

The problem asks for VOLUME of ethanol to add to make ?? soln of ??M.

mass = volume x density

You calculate mass from above, substitute density here of 0.789, and solve for volume (in mL). Then convert to L. Look at your math. I don't get 6.18 grams (more like 15 g or so--in round numbers).

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