What is the percent by mass of #"12 M HCl"#?

1 Answer
Truong-Son N.
May 3, 2017

Knowing the concentration is about #"12 M"# (it's specifically about #"12.06 M"#), we can assume a volume of #"1 L"# to calculate the mass density.

#(12 cancel"mols HCl")/"L solution" xx "36.4609 g"/cancel"mol HCl" = "437.5308 g HCl"/"L solution"#

Based on the mass density, we can calculate the mass percent by converting the solution volume to its mass.

#("437.5308 g HCl")/cancel"L solution" xx cancel("1 cm"^(3))/("1.17 g solution") xx cancel"1 mL"/cancel("1 cm"^(3)) xx cancel"1 L"/(1000 cancel("mL")#

#= 0.374#

Or, about #color(blue)("37.4% w/w")#. Note that #37%# is actually reagent-grade, not commercial-grade, which is about #39%#.

See if you can calculate the concentration in #39%# commercial-grade HCl! HINT: Use a ratio of the molar concentrations of the #37%# to the #39%#, and assume the density is similar enough.

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