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Solution Problems

Solution Problems. A. Vocabulary. 1 Solution homogeneous mixture written NaCl (aq) which means NaCl dissolved in water 2 Solute the substance that is being dissolved in a solution. In chocolate milk, the chocolate is the solute. 3 Solvent

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Solution Problems

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  1. Solution Problems

  2. A. Vocabulary 1 Solution • homogeneous mixture • written NaCl(aq) which means NaCl dissolved in water 2 Solute • the substance that is being dissolved in a solution. • In chocolate milk, the chocolate is the solute. 3 Solvent • the substance that does the dissolving in a solution. • In NaCl(aq), water is the solvent. 4 Solubility • the amount of solute that dissolves in a given amount of solvent at a given temperature. • If a substance is soluble, it dissolves in water.

  3. B. Using the Reference Tables • Table F • Table F tells if a substance dissolves (soluble) or does not dissolve (insoluble) in water • Examples • (NH4)2O • All ammonium compounds are soluble • CaS • All sulfides are insoluble • AgBr • All halides are soluble except with Ag+ • Ba(OH)2 • All hydroxides are insoluble except Ba+2

  4. 2. Table G • Reference Table G shows how solubility changes with temperature • Each line represents a compound’s saturation point • On the line • Saturated—maximum solute that can dissolve • Below the line • Unsaturated—not saturated; can still hold more solute • Above the line “over saturated” • Supersaturated (dissolves anyway) • Precipitate (excess solute falls to the bottom of container)

  5. Example 30g KClO3 in 100g water at 70 ºC • Check mass of water • Locate g and temp • Locate compound • On/below/above the line • Under the line • Unsaturated

  6. Example 20g HCl is dissolved in 25g water at 30 ºC • Check mass of water • 25g water must be made into 100g • Multiply all masses by 4 • Locate g and temp • 20g →80g • 25g → 100g • Locate compound • On/below/above the line • Over the line • Supersaturated

  7. Example A saturated solution of KNO3 is made using 100g water at 60 ºC. What happens when the solution is cooled to 10 ºC • Identify amount to saturate at each temperature • 60ºC • 105 g • 10ºC • 25 g • Compare • 25g stays dissolved • 80g precipitates out

  8. C Expressions of Concentration Concentration represents the amount of solute dissolved in a solution 1. Vague Terms • Strong vs weak • Concentrated vs dilute 2. Measured values • Molarity • ppm (parts per million)

  9. 3. Molarity • Represents moles of solute per 1 liter of solution Ex. What is the molarity of a solution containing 1.2 moles NaCl in a 150 mL solution? • M = moles ÷ liters • 150 mL = 0.150 L • Move decimal 3 places • M = 1.2 ÷ 0.150 L • M = 8.0M • Means 8 moles NaCl in 1 liter of solution

  10. 4. Parts per Million (ppm) • ppm = grams solutex 1,000,000 grams solution Ex. 0.0043g of O2 can be dissolved in 100 g water at 20ºC. Express this in terms of parts per million. • ppm = grams solutex 1,000,000 grams solution • ppm = 0.0043x 1,000,000 = 43 ppm 100.0043

  11. Practice Problems • What is the molarity of a KF solution containing 0.32 moles in 200 mL of solution? • What is the molarity of a NaCl solution containing 1.02 moles in 125 mL of solution? • What is the molarity of a NaOH solution containing 12g NaOH in 50 mL of solution? • What is the ppm of a CO2 solution containing 0.032 grams in 200g of solution? • What is the ppm of a NH3 solution containing 0.0012 grams in 350g of solution?

  12. Dilution Problems • Addition of water to change the concentration • Two types • Dilute an amount of solution and determine the new molarity • Determine how much of a concentrated solution must be used to make a specific molarity

  13. Dilute an amount of solution and determine the new molarity ex. What is the concentration of a solution made if 35 mLs of 18M H2SO4 is diluted to 250 mLs? • Find the original mole value • Find new molarity 0.035 L x 18 moles = 1 L 0.63 moles = 0.250 L 0.63 moles H2SO4 2.52 M H2SO4

  14. Determine how much of a concentrated solution must be used to make a specific molarity ex. How would you make 100 mL of a 3.0M HCl using 12M HCl? • How many moles do you need? • Find the volume needed of the concentrated solution 0.100 L x 3.0 moles = 1 L 0.30 moles x 1 L = 12 moles Use 25 mLsHCl 0.30 moles HCl 0.025 L HCl

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