Measures of Concentration Concentration The amount of solute
- Slides: 27
Measures of Concentration
Concentration • The amount of solute that is dissolved in a solvent • A precise quantitative measurement § Terms such as “diluted” and “concentrated” are too vague.
Concentration amount of solute amt. of solution (or solvent)
Percent by Mass g solute × 100% g solution v. Useful only when comparing different concentrations of the same solution
Sample Problem 1 If 5. 81 g of salt is dissolved in water to make 56. 3 g of solution, what is the percent by mass? 5. 81 g solute × 100% = 10. 3% 56. 3 g solution
Question If 10 grams of sugar is added to 90 grams of water, what is the percent by mass? 1. 2. 3. 4. 10% 11% 5% 20%
Question If 10 grams of sugar is added to 90 grams of water, what is the percent by mass? 1. 10% 10 g sugar = 10% sugar soln 100 g total
Question When 25 g of salt is dissolved to make 125 g solution, what is the percent by mass? 1. 2. 3. 4. 10% 20% 16. 7% 25%
Question When 25 g of salt is dissolved to make 125 g solution, what is the percent by mass? 2. 20% 25 g salt = 20% solution 125 g total
Percent by Volume volume of solute × 100% volume of solution
Molarity molarity (M) = mol solute L solution
Sample Problem 2 Dissolving 345 g of HCl to make 3. 75 L of solution results in what molarity? 345 g HCl 1 mol HCl 3. 75 L soln 36. 5 g HCl = 2. 52 M HCl
Question If 2. 9 moles Na. Cl is dissolved to make 3. 8 L of solution, what is the M? 1. 2. 3. 4. 2. 5 M Na. Cl 5. 8 M Na. Cl 1. 3 M Na. Cl 0. 76 M Na. Cl
Question If 2. 9 moles Na. Cl is dissolved to make 3. 8 L of solution, what is the M? 2. 9 mol Na. Cl = 0. 76 M Na. Cl 3. 8 L soln 4. 0. 76 M Na. Cl
Question If 200 g Na 2 SO 4 is added to make 3. 5 L of solution, what is the M? 1. 2. 3. 4. 1. 8 M Na 2 SO 4 0. 40 M Na 2 SO 4 2. 6 M Na 2 SO 4 2. 2 M Na 2 SO 4
Question If 200 g Na 2 SO 4 is added to make 3. 5 L of solution, what is the M? 2. 0. 40 M Na 2 SO 4 200 g Na 2 SO 4 1 mol Na 2 SO 4 3. 5 L soln 142 g Na 2 SO 4 = 0. 40 M Na 2 SO 4 soln
Sample Problem 3 You have 0. 6 L of a 0. 5 M HCl solution. How many moles of HCl does this solution contain? Solution: The M value gives you the number of mol that are in 1 L of soln. You can use this ratio as a conversion factor.
Sample Problem 3 0. 6 L soln 0. 5 mol HCl 1 L soln = 0. 3 mol HCl
Sample Problem 4 A chemical reaction requires 0. 180 mol of silver nitrate (Ag. NO 3). How many m. L of a 0. 800 M solution should be added to the reaction vessel to provide this amount?
Sample Problem 4 Solution: Since M means moles of solute per liter of solution, we can rewrite the concentration as 0. 800 mol Ag. NO 3/1 L of solution and use its inverse as a conversion factor.
Sample Problem 4 0. 180 mol Ag. NO 3 1 L soln 1000 m. L 0. 800 mol Ag. NO 3 1 L = 225 m. L soln
Molality molality (m) = mol solute kg solvent
Sample Problem 5 If 271 g of H 2 SO 4 is added to 724 g of water, what is the molality of the solution? 271 g acid 1 mol acid 0. 724 kg H 2 O 98 g acid = 3. 82 m acid
Question What is the molality of a solution formed by adding 1. 25 mol of Li. Cl to 2. 8 kg of water? 1. 2. 24 m Li. Cl 2. 4. 05 m Li. Cl 3. 0. 45 m Li. Cl 4. 1. 55 m Li. Cl 5. 9. 87 m Li. Cl
Question What is the molality of a solution formed by adding 1. 25 mol of Li. Cl to 2. 8 kg of water? 3. 0. 45 m Li. Cl 1. 25 mol Li. Cl = 0. 45 m Li. Cl soln 2. 8 kg H 2 O
Question When 136 g of Na. Cl is added to 780 g of water, what is the molality? 1. 0. 17 m Na. Cl 2. 2. 99 m Na. Cl 3. 0. 00298 m Na. Cl 4. 5. 73 m Na. Cl 5. 8. 13 m Na. Cl
Question When 136 g of Na. Cl is added to 780 g of water, what is the molality? 2. 2. 99 m Na. Cl 136 g Na. Cl 1 mol Na. Cl. 780 kg H 2 O 58. 4 g Na. Cl = 2. 99 m Na. Cl soln
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