Question

314.5g HBr (MMHBr = 80.91g/mol), is mixed into 4.50L solution. Find Molarity (M) of the

solution.

Answer 1

`\boxed {\boxed {\sf M \approx0.864 \ M \ HBr}}`

Step-by-step explanation:

The molarity of a solution is the moles per liter. It is found using this formula:

`M=\frac { moles \ of \ solute}{liters \ of \ solution}`

First we must calculate moles, since we are given grams. To convert from grams to moles, the molar mass is used. This is also given to us, it is 80.91 grams per mole. We can use it as a ratio.

`\frac {80.91 \ g \ HBr}{1 \ mol \ HBr}`

Multiply by the given number of grams.

`314.5 \ g \ HBr *\frac {80.91 \ g \ HBr}{1 \ mol \ HBr}`

Flip the fraction so the grams of HBr cancel.

`314.5 \ g \ HBr *\frac {1 \ mol \ HBr}{80.91 \ g \ HBr}`

`\frac {314.5 \ mol \ HBr}{80.91 }=3.88703497714 \ mol \ HBr`

Now we know the moles, and can calculate the molarity.

There are 3.88703497714 moles of solute and 4.50 Liters of solution.

`M= \frac {3.88703497714 \ mol }{ 4.50 \ L}`

`M= 0.863785550476 \ mol/ L`

The original measurements have 4 and 3 significant figures, so we use the lowest number of 3 for our answer. For the number we calculated, that is the thousandth place.

The 7 in the ten thousandth place tells us to round the 3 to a 4.

`M \approx 0.864 \ mol/ L`

`M \approx 0.864 \ M \ HBr`

The molarity of the solution is about 0.864 M HBr.