Asked by j
Describe how to prepare 1 liter of 0.5N solution of HCl from concentrated HCl. H=1, Cl=35.5, spgr=1.19, 37.2%
Answers
Answered by
DrBob222
Find the normality (molarity of HCl is the same as normality).
mass HCl in 1 L soln = 1.19g/mL x 1000 mL x 0.372 = 442.68 g.
How many moles is that?
442.68/36.5 = 12.12 N
Then mL x N = mL x N
mL x 12.12 = 1000 mL x 0.5N
Solve for mL of the concd acid.
Problems stated like this usually have a trick to them and many students never realize it. Here is the trick part. You solve for the mL of the concd acid, place that # mL in a 1 L volumetric flask, then add water TO THE MARK OF THE FLASK. [Note: This is NOT the same as placing 41.25 mL of the concd acid in a container and adding 958.75 mL water.]
Second note: The problem as you wrote it has only one significant figure (in the 0.5 N solution) and you should round the answer to just one s.f. unless you omitted some zeros from the 0.5N figure.
mass HCl in 1 L soln = 1.19g/mL x 1000 mL x 0.372 = 442.68 g.
How many moles is that?
442.68/36.5 = 12.12 N
Then mL x N = mL x N
mL x 12.12 = 1000 mL x 0.5N
Solve for mL of the concd acid.
Problems stated like this usually have a trick to them and many students never realize it. Here is the trick part. You solve for the mL of the concd acid, place that # mL in a 1 L volumetric flask, then add water TO THE MARK OF THE FLASK. [Note: This is NOT the same as placing 41.25 mL of the concd acid in a container and adding 958.75 mL water.]
Second note: The problem as you wrote it has only one significant figure (in the 0.5 N solution) and you should round the answer to just one s.f. unless you omitted some zeros from the 0.5N figure.
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