Question 755d3

Jan 10, 2015

Percent means "out of 100." So percent composition refers to how many parts (grams, litres, moles, etc.) there are in 100 parts (grams, litres, moles, etc.) of a substance.

Chemists use four types of percent composition.

Percent by mass (m/m)

Mass percent is the mass of a component divided by the total mass of the sample, multiplied by 100%.

"Mass %" ="mass of component"/"total mass of sample" × 100%

Percent mass by volume (m/v)

Volume percent is the mass of a component divided by the volume of the sample, multiplied by 100%.

"m/v %" = "mass of component"/"volume of sample" × 100%

Example: What is the mass by volume percent of NaOH if you dissolve 5.00 g of NaOH in enough water to make 100 mL of solution?

"m/v %" = "mass of component"/"volume of sample" × 100% = "5.00 g"/"100 mL" × 100% = 5.00%

Percent by volume (v/v):

Volume percent is the volume of a component divided by the volume of the sample, multiplied by 100%

"Volume %" = "volume of component"/"total volume of sample" × 100%

Example: What is the volume percent of ethanol in a 750 mL bottle of wine that contains 94 mL of ethanol?

"Volume %" = "volume of component"/"total volume of sample" × 100% = "94 mL"/"750 mL" × 100% =

12.5%

Mole %

Mole percent is the moles of a component divided by the total moles of the sample, multiplied by 100%

"Mole %" = "moles of component"/"total moles in sample" × 100%

Example: A solution contains 1.00 mol of NaOH in 5.00 mol water. What is the mole percent of NaOH?

Total moles = 1.00 mol + 5.00 mol = 6.00 mol

"Mole %" = "moles of component"/"total moles in sample" × 100% = "1.00 mol"/"6.00 mol" × 100% = 16.7%#