Question #c5ce9

1 Answer
Apr 7, 2016

Answer:

#"2 mol L"^(-1)#

Explanation:

Molar concentration essentially depends on two things

  • how many moles of solute you have present
  • the total volume of the solution, expressed in liters

You're dealing with a sample of hydrogen gas, #"H"_2#, so you're looking for the volume of the reaction vessel, not of the solution.

The problem provides you with the mass of hydrogen gas, so use its molar mass as a conversion factor to go figure out how many moles would be present here

#20 color(red)(cancel(color(black)("g"))) * "1 mole H"_2/(2.016color(red)(cancel(color(black)("g")))) = "9.921 moles H"_2#

Now, in order to find the molar concentration of the gas, you must figure out how many moles would occupy a volume of one liter. To do that, use the given fact that #9.921# moles occupy #"5 L"#

#1 color(red)(cancel(color(black)("L"))) * "9.921 moles H"_2/(5color(red)(cancel(color(black)("L")))) = "1.984 moles H"_2#

So, if one liter contains #1.984# moles of hydrogen gas, it follows that its molar concentration is #"1.984 mol L"^(-1)#.

Rounded to one significant figure, the answer will be

#["H"_2] = color(green)(|bar(ul(color(white)(a/a)"2 mol L"^(-1)color(white)(a/a)|)))#