Question

Question #755d3

Answer 1

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%`

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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%`

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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%`

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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%`