Percent solutions

Example 1

The process of solving problems like these can be simplified by following a series of steps.

The first step is to extract from the problem statement the information that has been provided and the information being asked for.

The information we are provided with is:

We have 21 grams of NaCl and 350 mL of water.

The information we are asked for is:

Percent concentration (w/v) resulting from dissolving NaCl in water.

The second step is to identify the formula to find out the information being asked for.

In this problem we are being asked to find percent concentration (w/v). Hence the formula to calculate percent concentration (w/v) is:

The third step is to match the information provided in the problem statement with the formula. As NaCl is dissolved in water, therefore NaCl is the solute i.e. 21 grams and water is the solution i.e. 350 millilitres. Hence, we have both pieces of information required to calculate percent concentration.

The fourth step is to check that the values being used are in the correct units. When calculating percent concentrations, the solute should always be in grams and the solution should always be in millilitres. In this case, both the solute and the solution are in the correct units.

Now we go ahead with the calculations. 21 grams divided by 350 mL gives 0.06.

0.06 multiplied by 100 is 6. Hence the percent concentration (w/v) when 21g of Sodium Chloride NaCl is dissolved in 350 mL of water is 6 %.