Describing Solution Composition

Notes 15.2Describing Solution CompositionMass PercentMass percent= mass of solute X 100 mass of solution

= grams of solute X 100grams of solute + grams of solventExampleA solution is prepared by mixing 1.00g of ethanol with 100.0g of water. Calculate the mass percent of ethanol in this solution.

Mass% = 1.00 g of ethanol x 100 100.0 g of water + 1.00 g ethanol

Mass % of ethanol = 0.99 %MolarityMolarity is the number of moles of solute per volume of solution in liters

M= molarity= moles of solute = mol Liters of solution L

exampleCalculate the molarity of a solution prepared by dissolving 11.5 g of solid NaOH in enough water to make 1.50 L of solution.

11.5 g NaOH x 1 mol NaOH = .288 mol NaOH 40 g NaOHMolarity= moles litersMolarity = .288 mol NaOH = 0.192 M NaOH 1.50 L NaOHMolarityLiters of solution x Molarity = moles of solute

L x M = mols

Concentration can also be expressed in g/L

exampleFormalin is an aqueous solution of formaldehyde, HCHO, used as a preservative for biological specimens. How many grams of formaldehyde must be used to prepare 2.5 L of 12.3M formalin?

Moles = Liters x MolarityMoles= 2.5 L x 12.3 M = 31 mols

31 mols HCHO x 30 g HCHO = 930 g HCHO 1 mol HCHO

molarityA standard solution is a solution whose concentrations is accurately known.

The process of adding more solvent to a solution is call dilution

M1 X V1 = M2 x V2exampleWhat volume of 16M sulfuric acid must be used to prepare 1.5 L of a 0.10M sulfuric acid solution?

M1 V1 = M2 V2 16 M (V1) = 0.10 M x 1.5 L V1 = 0.0094 L or 9.4 mL