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Solution Composition & Concentration

Solution Composition & Concentration. Mass Percent & Molarity!. Mass %. Describes the composition of a solution. a.k.a. weight percent Mass % = mass of solute x 100% mass of solution = grams of solute x 100%

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Solution Composition & Concentration

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  1. SolutionComposition & Concentration Mass Percent & Molarity!

  2. Mass % • Describes the composition of a solution. • a.k.a. weight percent • Mass % = mass of solute x 100% mass of solution = grams of solute x 100% grams of solute + grams of solvent

  3. Mass % example • A solution is prepared by dissolving 1.0g of sodium chloride in 48g of water. Calculate the percent mass of the solution! • 1.0 g of solute • Total mass of solution is 49g (1.0g of solute + 48g of solvent) 1.0g solute x 100% = 2.0% NaCl 49 g solution

  4. Try this one… • Cow’s milk typically contains 4.5% by mass of lactose (C12H22O11). Calculate the mass of lactose present in 175g of milk. 7.9g lactose 175 g milk X 0.045 =

  5. Molarity, M • Describes the solution concentration in terms of volume • rather than composition in terms of mass (it’s much more convenient to measure the volume of a liquid!) • M = Molarity = moles of solute = mol liters of solution L Ex/ a solution that contains 1.0 mol of solute per Liter of solution is 1.0M: “1.0 molar”

  6. Molarity example • A solution is prepared by dissolving 11.5g of solid NaOH in enough water to make a 1.50L solution. (The solute and solvent together have a volume of 1.50L) Calculate the Molarity. • Mass of solute = 11.5 g NaOH  convert to moles! • 11.5g NaOH x 1 mol NaOH = 0.288 mol NaOH 40.0g NaOH • Volume of solution = 1.50L Molarity = 0.288 mol NaOH = 1.92 M NaOH 1.50 L solution

  7. Try this one… • What mass of solid potassium dichromate (K2Cr2O7) must be weighed out to make 1.00 L of a 0.200 M solution? (molar mass = 294.2) 58.8 g potassium dichromate Algebra g = (molar mass)(molarity)(volume)

  8. Standard Solutions • A solution with an accurately known concentration • Prepared in a volumetric flask • Vol. flasks measure volume extremely accurately • Solute is weighed and completely added to vol. flask • Solvent is added to flask to bring volume up to exact volume line on neck of flask

  9. How to make a solution of a given molarity. 1. Calculate the grams needed g = (mm)(M)(L) • Measure out that exact amount. • Rinse into mL volumetric flask. • Fill 2/3’ s full with distilled water. • Swirl to dissolve. • Fill to line with distilled water. • Cap and flip 20 times. • Label: M(what it is), date: , who made it:

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