Solution Problems

A. Vocabulary 1Solution homogeneous mixture written NaCl(aq) which means NaCl dissolved in water 2Solute the substance that is being dissolved in a solution. In chocolate milk, the chocolate is the solute. 3Solvent the substance that does the dissolving in a solution. In NaCl(aq), water is the solvent. 4Solubility 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.

B. Using the Reference Tables 1. Table F Table F tells if a substance dissolves (soluble) or does not dissolve (insoluble) in water Examples  (NH 4 ) 2 O  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

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)

Example 30g KClO 3 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

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

Example A saturated solution of KNO 3 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

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)

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 = L  Move decimal 3 places M = 1.2 ÷ L M = 8.0M  Means 8 moles NaCl in 1 liter of solution

4. Parts per Million (ppm) ppm = grams solute x 1,000,000 grams solution Ex g of O 2 can be dissolved in 100 g water at 20ºC. Express this in terms of parts per million. ppm = grams solute x 1,000,000 grams solution ppm = x 1,000,000 = 43 ppm

Practice Problems 1. What is the molarity of a KF solution containing 0.32 moles in 200 mL of solution? 2. What is the molarity of a NaCl solution containing 1.02 moles in 125 mL of solution? 3. What is the molarity of a NaOH solution containing 12g NaOH in 50 mL of solution? 4. What is the ppm of a CO 2 solution containing grams in 200g of solution? 5. What is the ppm of a NH 3 solution containing grams in 350g of solution?

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

Dilute an amount of solution and determine the new molarity ex. What is the concentration of a solution made if 35 mLs of 18M H 2 SO 4 is diluted to 250 mLs? Find the original mole value Find new molarity L x 18 moles = 1 L 0.63 moles = L 0.63 moles H 2 SO M H 2 SO 4

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 L x 3.0 moles = 1 L 0.30 moles x 1 L = 12 moles Use 25 mLs HCl 0.30 moles HCl L HCl