# Question #c5ce9

##### 1 Answer

#### Explanation:

**Molar concentration** essentially depends on two things

how manymoles of soluteyou have presentthetotal volume of the solution, expressed inliters

You're dealing with a sample of hydrogen gas, **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

#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 **moles** of hydrogen gas, it follows that its molar concentration is

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)|)))#