Solution Composition: Mass Percent

I. VIDEO ON MASS PERCENT

II. NOTES ON MASS PERCENT

Mass percent = mass of solute x 100%

mass of solution

= grams of solute x 100%

grams of solute + grams of solvent

III. EXERCISES ON MASS PERCENT

1. A solution is prepared by mixing 1.00 g of ethanol, C₂H₅OH, with 100.0 g of water. Calculate the mass percent of ethanol in this solution.

2. A 135-g sample of seawater is evaporated to dryness, leaving 4.73 g of solid residue (the salts formerly dissolved in the seawater). Calculate the mass percent of solute present in the original seawater.

3. Although, milk is not a true solution (it is really a suspension of tiny globules of fat, protein, and other substrates in water), it odes contain a dissolved sugar called lactose. Cow's milk typically contains 4.5% by mass of lactose C₁₂H₂₂O₁₁. Calculate the mass of lactose present in 175 g of milk.

4. What mass of water must be added to 425 g of formaldehyde to prepare a 40.0% (by mass) solution of formaldehyde? This solution is called formalin, is used to preserve biological specimens.

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