Chemistryplease help
posted by anne on .
Please show me the calculation steps.
How do I prepare 10%w/w Hydrochloric acid from 37%w/w Hydrochloric acid?
The density of 37%w/w HCl is 1.19g/ml.
Thank you.

You can do this one of two ways.
Method 1 is the usual dilution formula but it works with percent as well as with molarity and normality. The problem doesn't give a volume needed so I've chosen 100 g soln.
%soln1 x mass soln1 = %soln2 x mass soln2.
37% x g soln 1 = 10% x 100 g soln 2
g soln 1 = 10*100/367 = 27.03 g soln 1 which i would round to 27 g.
The other way is to solve by volume since you know the density.
1.19 g/mL x 1000 mL x 0.37 = 440.3 g HCl in the 1000 mL volume (the other 559.7 mL is water).
To make a 10% soln we want 10 g HCl.
440.3 g HCl/1000 mL x ?mL = 10 g
?mL = 10/440.3 = 22.71 mL of the 37% soln. By the way that will have a mass of 22.71 mL x 1.19 g/mL = 27.02g which rounds to 27 g, then add water to make 100 g of solution.