Solution Concentration Section 14.2

Solution Concentration Solution Concentration is the measure of how much solute is dissolved in a specific amount of solvent. Solutions can be described qualitatively using words concentrated and dilute. -A concentrated solution would have a lot of solute compared to the amount of solvent. -A dilute solution would have very little solute compared to the amount of solvent.

Expressing Concentration Concentration can be expressed in many different ways. Three that we will use are percent by mass, percent by volume and molarity. Percent by mass and volume both use the familiar phrase “part over whole times a hundred” to obtain the answer. Concentration is expressed as a percent in a ratio of measured amount of solute to a measured amount of solution. - Percent by mass = solid dissolved in a liquid - Ratio of solute’s mass to the solution’s mass - Mass of solution = masses of solute + mass of solvent Percent by mass = mass of solute x 100 mass of solution Molarity takes into account the number of particles (atoms and molecules) present in the solution. mass of solute + mass of solvent

Percent by Mass Examples What is the % concentration by mass of 8.3 g of NaCl dissolved in 300 g of water? 2. What is the % concentration by mass of 65 g of C6H12O6 dissolved in 500 g of water? 3. You have a 1000 g bleach solution. The % concentration by mass of the solute NaOCl is 6.02 % . How many grams of the NaOCl are in the solution? 4. How many grams of water would you have to add to 50 g of NaCl to produce a solution concentration of 5%? 5. What is the solution concentration by mass of 12 grams of NaCl dissolved in 300 grams of water? 6. If you need to produce 500 grams of an 8.3% saline solution, how many grams of salt and how many grams of water would you use to form the solution?

Same thing as % by mass, only we’re working with liquids instead of solids Percent by Volume What is the percent by volume of ethanol in a solution that contains 35 mL of ethanol dissolved in 115 mL of water? If you have 100 mL of a 30% aqueous solution of ethanol, what volumes of ethanol and water are in the solution? What is the percent by volume of isopropyl alcohol in a solution that contains 24 mL of isopropyl alcohol in 1.1 L of water? What is the percent by volume of 140 mL of isopropyl alcohol dissolved in 60 mL of water?

Diluting Solutions M1V1 = M2V2 Where ‘M’ = Molarity Where ‘V’ = Volume In the laboratory, I purchase concentrated stock solutions of chemicals because they are much more economical to buy. To use these solutions I have to dilute them to concentrations that are required by the labs we perform in class. To properly dilute these solutions I use the following equation: M1V1 = M2V2 Where ‘M’ = Molarity Where ‘V’ = Volume Molarity is measured in mol/L (M) Volume is measured in mL or L

Diluting Solutions What volume of a 3M KI solution would you use to make .3 L of a 1.25M KI solution? How many milliliters of a 5M H2SO4 solution would you need to prepare 100 mL of .25M H2SO4? If you dilute 20 mL of a 3.5M solution to make 100 mL of solution, what is the molarity of the dilute solution?

Molarity = moles of solute liters of solution When chemists are working with a reaction in an aqueous solution, they must know the number of particles (atoms, molecules) that are present. Since we count the number of particles present using moles, then the number of moles of solute dissolved per liter of solution is referred to as MOLARITY (M) or molar concentration, The unit M is read as molar and a liter of solution containing one mole of solute as a 1M solution. To calculate the molarity of a solution, we utilize the following formula: Molarity = moles of solute liters of solution Remember: grams/mm = moles Hint: 100 mL = 1 L

Molarity Practice 58 g NaCl in 1L = 1 Molar Solution

Molarity This is a typical molarity problem: What is the molarity of a solution containing 58 grams of salt in 1 Liter of solution? What is the molarity of a glucose solution containing 12.8 g of glucose in 1.5 liters of an aqueous soluton? Calculate the molarity of 100 mL of a solution containing 50 g of H2SO4. What is the molarity of 500 mL of a solution containing 125 g of MgSO4? 5. What is the solution concentration of 45 g of NaCl in 350 mL of water?

Molarity How many grams of salt would be dissolved in 1.0 L of a 0.5M solution of NaCl? If the solubility of O2 is 8.3 g/L at 3 atm, how many g/L will dissolve at 10 atm? How many grams of CaCO3 are contained in one liter of a 4M CaCO3 solution? How many grams of Na3PO4 should be dissolved in 800 mL of water to make a .3M solution of Na3PO4? 10. How many grams of LiCl are in 750 mL of a 4.0M LiCl solution?

Molarity If the solubility of N2 is 2.3 g/L at 3 psi, how much pressure is needed to dissolve 8.0 g/L? How many grams of water must be added to 12 grams of salt to make a 15% solution concentration? How many grams of C6H12O6 are needed to make a 600 mL of .3M aqueous solution of C6H12O6? How many grams of CCl4 are in 300 mL of a 5M CCl4 solution? 15. How many grams of NH3 can be produced with 500 g of N2 and an unlimited amount of H2? Limiting Reactant Problem just for fun!

Molality concentration is expressed as the number of moles of solute dissolved in 1 kilogram of solvent volume can change with temperature but mass does not, so molarity can change if temperature changes but not molality use m, molal ex. 1.3 m solution is a 1.3 molal solution Conversion reminder: to convert g to kg must divide by 1000 (1000 g = 1 kg)

Molality Equation  

Molality Example Problems Example Problem #1 Calculate the molality of a solution that contains 15.7 g of NaCl in 100 g of water. Example Problem #2 Calculate the molality of a solution that contains 20.0 g CaCl2 in 700 g of H2O.