# Entry Task: Nov 21st Block 2

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Entry Task: Nov 21st Block 2
Question: What is the molality of a 200 g solution with 32 grams of NaCl? TURN IN ENTRY TASK SHEETS!! You have 5 minutes!

Agenda: Discuss Ch. 13 sec. 4 pHet Concentration and Molarity Lab
HW: Solutions ws

I can … Express a concentration of a solution in different ways- %, ppm, mole fraction, Molarity, & Molality

Chapter 13 Properties of Solutions

Ways of Expressing Concentrations of Solutions

Mass Percentage mass of A in solution Mass % of A =
total mass of solution Mass % of A =  100

Parts per Million and Parts per Billion
Parts per Million (ppm) mass of A in solution total mass of solution ppm =  106 Parts per Billion (ppb) mass of A in solution total mass of solution ppb =  109

13.3 problem (a) Calculate the mass percentage of NaCl in a solution containing 1.50 g of NaCl in 50.0 g of water. 1.50 51.5g solution X = 2.91%

13.3 problem (b) A commercial bleaching solution contains 3.62 mass % sodium hypochlorite, NaOCl. What is the mass of NaOCl in a bottle containing 2.50 kg of bleaching solution? X 2500g 36.2 100 100 X = 90500 X = 90.5g

total moles in solution
Mole Fraction (X) moles of A total moles in solution XA = In some applications, one needs the mole fraction of solvent, not solute—make sure you find the quantity you need!

Molarity (M) mol of solute M = L of solution
You will recall this concentration measure from Chapter 4. Because volume is temperature dependent, molarity can change with temperature.

Molality (m) mol of solute m = kg of solvent
Because both moles and mass do not change with temperature, molality (unlike molarity) is not temperature dependent.

Changing Molarity to Molality
If we know the density of the solution, we can calculate the molality from the molarity, and vice versa.

13.4 problem What is the molality of a solution made by dissolving 36.5 g of naphthalene (C10H8) in 425 g of toluene (C7H8)? 35g 1 mole = 0.28 mole = kg 128.1 g 0.425 kg

13.5 problem A commercial bleach solution contains 3.62 mass % NaOCl in water. Calculate (a) the mole fraction and (b) the molality of NaOCl in the solution. 3.62 % in water means 3.62 g in water 3.62 g – 100 = g of water 3.62g 1 mole = mole mole 5.398 mole 74 g 96.38g 1 mole 9.06 x 10-3 = 5.35 mole 18 g mole mole = mole

13.5 problem A commercial bleach solution contains 3.62 mass % NaOCl in water. Calculate (a) the mole fraction and (b) the molality of NaOCl in the solution. 3.62 % in water means 3.62 g in water 3.62 g – 100 = g of water 3.62g 1 mole = mole 74 g mole = m kg

13.21 13.21 a) Calculate the mass % of Na2SO4 in solution containing 14.7 g Na2SO4 in 345g H2O. b) Ore containing 7.35 g of silver per ton of ore. What is the concentration of silver in ppm? 14.7 g X 100 = 4.09% g 7.35 g 1.10 x 10-6 ton = 8.09 ppm 1 g

13.23 Calculate the mole fraction of methanol, CH3OH, in the following solutions: a) 7.5 g CH3OH in 245 gH2O; b)55.7 g CH3OH in 164g CCl4. 7.5 g 1 mole = 0.23 mole of methanol 32.01 g 245 g 1 mole = 13.6 mole of water 18.0 g 0.23 mole of methanol = mole fraction mole solution

13.23 Calculate the mole fraction of methanol, CH3OH, in the following solutions: a) 7.5 g CH3OH in 245 gH2O; b)55.7 g CH3OH in 164g CCl4. 55.7 g 1 mole = 1.74 mole of methanol 32.01 g 164 g 1 mole = 1.07 mole of CCl4 g 1.74 mole of methanol = mole fraction mole solution

13.25 Calculate the molarity of the following aqueous solutions: a) 10.5g KCl in ml of solution; b) 30.7g LiClO4•3H2O in 125ml o solution; c) 25.0 ml 1.50M HNO3 diluted to 0.500L 10.5 g 1 mole = 0.14 mole = M 74 g 0.250 L 30.7 g 1 mole = mole = 1.53 M g + 3(18g) 0.125 L (0.025L) (1.50) = (x)(0.500L) = M

13.27 13.27 Calculate the molality of each the following solutions; a) 13.0 g benzene, C6H6, dissolved in 17.0 g of CCl4; b) 4.75 g NaCl dissolved in L of water whose density is 1.00g/ml. 13.5 g 1 mole = mole = 9.79 m 78 g 0.017 kg 4.75 g 1 mole = mole = m 58.45 0.250 kg

13.29 13.29 A sulfuric acid solution containing 571.6g of H2SO4 per liter of solution has a density of g/cm3 , Calculate a) the mass percentage; b) the mole fraction; c) molality; d) molarity of H2SO4 571.6 g X = % 1329 g 571.6 g 1 mole = 5.83 moles of H2SO4 98 g 757.4 g 1 mole = 42.1 moles of H2O 18 g 5.83 moles of H2SO4 = 0.122 = moles

13.29 13.29 A sulfuric acid solution containing 571.6g of H2SO4 per liter of solution has a density of g/cm3 , Calculate a) the mass percentage; b) the mole fraction; c) molality; d) molarity of H2SO4 5.83 mol = m kg 5.83 moles of H2SO4 = 5.83M 1 L

13.30 13.30 A solution containing 80.5 g of ascorbic acid, C9H8O6, dissolved in 210 g of water has a density of 1.22 g/cm3 , Calculate a) the mass percentage; b) the mole fraction; c) molality; d) molarity of C9H8O6 80.5g X = % 210 g g 80.5 g 1 mole = moles of C9H8O6 176.1 g 210 g 1 mole = 11.7 moles of H2O 18 g 0.457 moles of C9H8O6 = = moles

13.30 13.30 A solution containing 80.5 g of ascorbic acid, C9H8O6, dissolved in 210 g of water has a density of 1.22 g/cm3 , Calculate a) the mass percentage; b) the mole fraction; c) molality; d) molarity of C9H8O6 0.457 mol = m 0.210 kg 290.5 g 1 mL 1 L = 0.238L 1.22 g 1000 mL 0.457 moles of C9H8O6 = 1.92 M 0.238 L

In-Class- pHet Molarity and concentration

HW: Ch. 13 sec. 5 reading notes