12-3: Concentration of Solutions Chapter 12 - Solutions 12-3: Concentration of Solutions

The concentration of a solution is a measure of the amount of solute in a given amount of solvent of solution. Sometimes solutions are called “dilute” or “concentrated”, but these are not definite terms. Dilute means that there is a relatively small amount of solute in a solvent Concentrated means that there is a relatively large amount of solute. Neither of these terms has anything to do with saturation

Measures of Concentration Molarity – the number of moles of solute in one liter of solution Symbol is M Molality – the number of moles of solute in one kg of solvent Symbol is m

Molarity A 3.0 M solution of HCl has 3.0 moles of HCl in a liter of solution. This is NOT the same as 3.0 moles added to 1 liter of water. The total amount of the solution AFTER adding the 3.0 moles of HCl is 1 liter.

Molarity To make a solution of a particular molarity: Calculate the amount of solute needed in grams Add the solute to an amount of solvent that is LESS than the total amount of solution desired. Dissolve Add enough solvent to bring the total amount of solution to the desired volume.

Molarity You want to make a 3.50 M solution of NaCl and you need a total of 500. mL of the solution. How many grams of NaCl do you need?

Molarity You have 1.20 L of solution and you know that it contains 43.5 g of NaCl. What is the molarity of the solution?

Molarity You have 1.2 L of a 0.75 M HCl solution. How many moles of HCl does the solution contain?

Molarity To produce 40.0 g of silver chromate, you will need at least 24.3 g of potassium chromate in solution as a reactant. All you have on hand in the stock room is 5 L of a 6.0M K2CrO4 solution. What volume of the solution is needed to give you the 24.3 g of K2CrO4 needed for the reaction?

Molarity What is the molarity of a solution that is composed of 5.85 g of potassium iodide dissolved in enough water to make 0.125 L of solution?

Molarity How many moles of H2SO4 are present in 0.500 L of a 0.150 M H2SO4 solution?

Molarity What volume of 3.00 M NaCl is needed for a reaction that requires 146.3 g of NaCl?

Molality A 0.500 m solution of sodium hydroxide is a mixture of 0.500 moles of NaOH mixed with 1 kg of water. Note that molality does not tell us anything about the total amount of the solution

Molality To make a solution of a particular molality: Measure out the necessary mass of the solute Add to exactly 1 kg of solvent For water, 1 kg equals 1000 mL

Molality A solution was prepared by dissolving 26.4 g of sucrose in 250. g of water. What is the molal concentration of the solution? Sucrose is C12H22O11, and its molar mass is 342.34 g/mol

Molality What is the molality of a solution composed of 255 g of acetone, (CH3)2CO, dissolved in 200. g of water?

Molality What quantity, in grams, of methanol (CH3OH), is required to prepare a 0.244 m solution in 400. g of water?

Molality How many grams of AgNO3 are needed to prepare a 0.125 m solution in 250. g of water?

Molality What is the molality of a solution containing 18.2 g HCl and 250. g of water?