Question #cd3b0

1 Answer
May 24, 2017

Answer:

  1. #12"mol"/"L"#

  2. #0.081 "L" = 81"mL"#

Explanation:

1.

Let's look at the problem: the #"HCl"# in solution is #38%# by mass. If we assume a #100 "g"# sample, then then the mass of #"HCl"# in solution is #38"g"#. The number of moles of the solute is thus

#38cancel("g HCl")((1 "mol HCl")/(36.46cancel( "g HCl"))) = 1.04 "mol HCl"#

Now, let's use the density of the solution (#1.19 "g"/"mL"#), and the fact that we assumed a #100 "g"# sample to calculate the volume, in #"L"#:

#100 cancel("g")((1cancel( "mL"))/(1.19 cancel("g")))((1 "L")/(10^3 cancel("mL"))) = 0.0840 "L soln"#

The molarity of the solution is thus

#M = "mol solute"/"L soln" = (1.04 "mol HCl")/(0.0840 "L soln") = color(red)(12"mol"/"L"#

2.

In #1000"mL"# (or #1 "L"#) of a #1 M# solution, the number of moles of #"HCl"# is

#1 "mol"/cancel("L")(1 cancel("L")) = 1 "mol HCl"#

We'll use this number and the fact that #1.04 "mol HCl"# occupies a volume of #0.0840 "L"# to find the volume of solution needed:

#1 cancel("mol HCl")((0.0840 "L soln")/(1.04 cancel("mol HCl"))) = color(blue)(0.081 "L")#, or #color(blue)(81 "mL"#