Percent concentrations

Percent concentrations

A percent concentration refers to the percent of solute that is dissolved in a specific quantity of solvent or solution. Percent means parts solute per hundred total parts (solute plus solvent) so 5% salt solution could also be reported as a five parts per hundred salt solution (5pph) but percent is more commonly used. When solutions contain very small quantities of a solute concentration units of parts per million (ppm) and parts per billion (ppb) are useful because instead of writing (for ppm) .0005 one can write 5 ppm.

How to calculate percent concentrations

Example problems:

1.A common salt water solution contains 30 grams of table salt and 60 grams of water what is the concentration of this solution expressed in percent by mass?

First one places 30g over 60 plus 30 (30g/60+30) then add 60 + 30 (30g/90g) then divide 30 by 90 and you will get .33 then you multiple .33 by 100 (.33x100) and you will get 33% of salt.

2. Lets say there is 33% of salt in 90gs of a salt-water solution how many grams of salt are there?

First you divide 33% by 100 and get .33 then you multiple .33 by 90 and get 30 grams of salt.

3. When transferring a number into parts per million or parts per billion you take the number (usually in decimal form) and move the decimals all the way to the right.

Examples:

.0005 = 5 ppm and .00005 = 5ppb.

4. In order to transfer a number back from when it is converted to ppm (for ppb one must divide by 1 billion) one must divide that number by 1,000,000 then multiply by the amount of g of solvent present

Example: Lets say there are 5ppm of salt in 100g of water how many grams of salt are there present in the water?

5ppm/1,000,000 = 0.000005 x 100 = 0.0005 grams of salt are present in 100 grams of water