# NOTHING IN THE WORLD IS MORE DANGEROUS THAN SINCERE IGNORANCE AND CONSCIENTIOUS STUPIDITY.- Martin Luther King, Jr. -

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NOTHING IN THE WORLD IS MORE DANGEROUS THAN SINCERE IGNORANCE AND CONSCIENTIOUS STUPIDITY.- Martin Luther King, Jr. -

LET’S REVIEW SOLUTION CONCENTRATION: 1)% BY MASS – example – calculate the % of Na 2 CO 3 in a solution prepared by dissolving 24 g in 400 ml H 2 O.

LET’S REVIEW SOLUTION CONCENTRATION: 1)% BY MASS – example – calculate the % of Na 2 CO 3 in a solution prepared by dissolving 24 g in 400 ml H 2 O. % = (# g Na 2 CO 3 / total #g) x 100 % = 24/424 x 100 = 5.7%

2) % v/v or percent by volume – example – calculate the % v/v of a solution that has 50 ml ethanol in 120 ml solution.

% v/v = (50/120) x 100 = 41.7 %

3) Mole fraction, X- example – calcualte the mole fraction of KNO 3 in a solution prepared by dissolving 4.8 g KNO 3 in 200 ml H 2 O.

Formula mass of KNO 3 = 39 + 14 + 3(16) = 101 g/mol # moles KNO 3 = 4.8/101 = 0.048 # moles H 2 O = 200/18 = 11.111 Total # moles = 11.111 + 0.048 = 11.159 X KNO3 = 0.048/11.159 = 0.0043

4) Calculate the molarity of a solution containing 58 g Li 2 SO 4 per 1500 ml of solution.

Formula mass of Li 2 SO 4 = 2(7) + 32 + 4(16) = 110 g/mol # moles = 58/110 = 0.53 Molarity = M = 0.53/1.5 = 0.35 M

5) Molality, m – example – calculate the molality of a solution of 6.8 g BeCl 2 dissolved in 800 ml of H 2 O. Molality is the # of moles of solute per kilogram of solvent

5) Molality, m – example – calculate the molality of a solution of 6.8 g BeCl 2 dissolved in 800 ml of H 2 O. Formula mass BeCl 2 = 9 + 71 = 80 g/mol # moles BeCl 2 = 6.8/80 = 0.085 moles molality= 0.085/0.80 = 0.106 m

6) Dilution problems – concentrated HCl is 12 M. How many ml would you have to dilute to have 1000 ml of a 1.0 M solution?

Volume in liters x molarity = # moles When you do a dilution, you are not changing the number of moles of solute. You are just changing the volume of solvent. So, V 1 x M 1 = V 2 x M 2 V 1 x 12 = 1.0 x 1.0 = 1 V 2 = 1/12 = 0.083 L = 83 ml

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