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.)
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.
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.
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.
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)
that was me who posted the comment above. my friend had the same question.
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).