12.1 Expressing Concentration

Transcription

1 12.1 Expressing Concentration The Amount of Solute in the solvent Dr. Fred Omega Garces Chemistry 201 Miramar College 1 Expressing Concentration

2 Components of Solution Mixtures: Variable components, retains properties of its component. Homogeneous systems: Solutions Solution - Homogeneous mixture of two or more substances Components of solution Solute - Substance being dissolve Solvent - Substance in which solute is dissolved in. If solvent is water, then solution is considered aqueous. 2 Expressing Concentration

3 9 Types of Solution (derived from 3 phases) Solute Solvent Solution gas O 2 in gas N 2 Air gas CO 2 in Liquid H 2 O Carbonated Water liquid H 2 O in Gas Air Fog liquid EtOH in Liquid H 2 O Wine Liquid Hg in Solid Ag Dental-filling Solid NaCl in Liquid H 2 O Brine Solid Ag in Solid Au 14 Karat gold 3 Expressing Concentration

4 Solution & Concentration Concentration - Proportion of substance in mixture or amount of solute in given amount of solvent. Most common type: Molarity (M) Molarity - moles solute / Liter solution Example: What mass (g) of copper(ii)sulfate pentahydrate (250. g/mol) is needed to make 1.00-L of 0.10M solution? MW CuSO4 5H 2 O = g mol Mass CuSO4 5H 2 O = 0.10 mol L g 1 mol 1 L Mass CuSO4 5H 2 O = or 25.0 g 4 Expressing Concentration

5 Expressing Concentration 5 ways of expressing concentration- Molarity (M) - moles solute / Liter solution Molality * (m) - moles solute / Kg solvent Conc. by parts (% m)- (solute [mass] / solution [mass]) * 100 w/v [mass solute (g) / volume solution (ml)] * 100 v/v [vol solute (ml) / vol solution (ml)] * 100 mole fraction ( χ A) - moles solute / Total moles solution Normality (N) - Number of equivalent / Liter solution Note that molality is the only concentration unit in which denominator contains only solvent information rather than solution. It is also a concentration unit together with mole fraction that are temperature independent. 6 Expressing Concentration

6 Concentration Relationship! Molecular Weight moles mass } Solute moles Molc Wt mass } Solvent χ Mass Solution m %m Density Solution M* Vol Solution Equivalence/mol N * Volume of solution must be used and not just volume of solvent 7 Expressing Concentration

7 Concentration Relationship! * Volume of solution must be used and not just volume of solvent 8 Expressing Concentration

8 Calculating molality (m): Example Example # g of CoCl 2 ( g/mol) is dissolved in water to produce 100-ml solution. Assume the density of the solution is 0.95g/mL, what is molal concentration of the solution? 9 Expressing Concentration

9 Calculating molality (m): Example Example # g of CoCl 2 ( g/mol) is dissolved in water to produce 100-ml solution. Assume the density of the solution is 0.95 g/ml, what is concentration the molality of the solution? mol CoCl2 = 3.5 g CoCl2 mol CoCl g = mol = mol mass H2O = (100ml 0.95 g) g 1 ml = 91.5 g m = 3.5 g CoCl2 mol CoCl g kg = m = 0.29 molal 10 Expressing Concentration

10 % Concentration Concentration by Parts Solute (mass or volume) Solution (mass or volume) x multiplier w/w = Wt Solute g 100 g % (pph) Wt Soln g w/v = Wt Solute g 100 g % (pph) Vol Soln ml v/v = Vol Solute ml 100 g % (pph) Vol Soln ml ppm & ppb (For dilute solution) m/m = mass Solute g 10 6 g ppm (ppm) mass Soln g v/v = Vol Solute ml 10 9 g ppb (ppb) Vol Soln ml 11 Expressing Concentration

11 Calculating % Concentration: Example Example # g of CoCl 2 is dissolved in a solvent to form a 100-ml solution. Assume the density of the solution is 0.95 g/ml, what is concentration of the solution in % mass? %m = 3.5 g CoCl2 x g Solution = 3.7% (m/m) 3.7% m/v CoCl 2 Example #3 What is the v/v concentration if one drop of alcohol (1/20 ml = ml) is added to 1.00L? % or ppm Ans: %(v/v) = (0.05mL/1000mL) 100 = % (pph) Answer ppm (v/v)= (0.05 ml/1000 ml) 10 6 = 50 ppm 12 Expressing Concentration

12 Shark Sense pp(?): Making Chem Relevant Example#4 A shark can smell blood in water from several miles away. What is the concentration of 1 drop blood in 1mi 3 volume? Ans: ppt= (0.05mL/ ml) 10 9 = ppb = ppt *Quintillion ( ) = 12 ppquintlllion 14 Expressing Concentration

13 Normality: Expressing Normality The number of equivalents of acid or base solute in one litter of solution. Equivalent: The number of specie (acid or base) that gives one mole of charge. Note: HCl : 1mol HCl = 1eq H + H 2 SO 4 : 1 mol H 2 SO 4 = 2 eq H + H 3 PO 4 : 1 mol H 3 PO 4 = 3 eq H + Mg +2 : 1 mol Mg +2 = 2 eq charge NaOH: 1 mol NaOH = 1 eq OH - Therefore: 5.0 M HCl = 5mol HCl 1eq = 5.0 N HCl 1 L 1mol and 5.0 M H 2 SO 4 = 5mol H 2 SO 4 2eq = 10.0 N H 2 SO 1 L 1mol 15 Expressing Concentration

14 Interconverting Concentration: A Calculation Example Example#5: A perchloric acid (HClO 4 MWt = g/mol) solution is 10.0 % m/m. The density of the solution is g/cc. What is the Molarity, molality, mole fraction and Normality of the solution? g mole 100 g solution cc Molarity = 1.05 M mole Kg H 2 O Answer molality = 1.11 m mole 5.00 mol H 2 O χa = Expressing Concentration

15 MW Na 2 S 2 O 3 = g/mol vol = ml H 2 O 1ml m = mol/kg solvent mol mol Na 2 S 2 O 3 = kg H 2 O kg H O = mol Na S O = 1 mol = g Na 2 S 2 O 3 = χ K2 = mass H CO 2 O = g H 2 O 3 MW K2 = g/mol CO 3 mol H 2 O = g H 2 O 1 mol 18.0 g = mol H O 2 χ K2 = = CO 3 x x mol H 2 O (x mol H 2 O) = x x = x =.9455 x x = mass K2 = mol g = g CO 3 1 mol χ K2 CO 3= % m= mol mol H 2 O mol = g g g H 2 O 100 = 30.68% Interconverting Concentration: More Examples Example#6: If sodium thiosulfate (Na 2 S 2 O 3, MW = g/mol) solution ( molal) contains 800. ml water, what is the mole fraction and the mass of the solute for this solution? Example#7: What is the % mass and the molality of a χk 2 CO 3 = solution which contains exactly g of water? MW K 2CO g/mol mol H 2 O = ml 1g 1 mol 18.0 g = mol H O 2 massna 2 S 2 O 3 = mol Na 2 S 2 O g mol fraction χ Na2 S 2 O mol Na 2 S 2 O mol Na 2 S 2 O mol H 2 O = Expressing Concentration

16 ...and ever more Examples Example#8: 50.00ml of ethylene glycol (ρ = g/ml; MW = g/mol) is added to L water (ρ = 1.00 g/ml) at 20 C. Answer the following questions and assume additive volumes. i) What is the density of the mixture ii) Calculate the % mass of the ethylene glycol in the solution. iii) Calculate the molarity and molality of ethylene glycol in the solution. Mass H 2 O = 1000 g vol = 50.0 ml ethylene Glycol ml g ml D = vol = 1000 ml H 2 O = g mass H2O + mass ethylene glycol vol H2O +vol ethylene glycol D = g ml = = g 19 Expressing Concentration ml % m = g g mol glycol, g mol mol H 2 O, 1000 g mol molality = Molarity = 100 = % mol 1.00kg mol L = m = M

17 Misc Problems Answers Harris 7 th ed p18 1. The density of 70.5 wt% aqueous perchloric acid, HClO 4, is 1.67 g/ml (a) How many grams of solution are in L 1670 g (b) How many grams of HClO 4 are in 1.000L? 1180 g (c) How many moles of HClO 4 in 1.000L? 11.7 mol 2. An aqueous solution containing 20.0% wt% KI has a density of g/ml. Find the molality, mole fraction, and molarity of the KI solution m 3. The concentration of sugar (glucose, C 6 H 12 O 6 ) in human blood ranges from about 80mg/100mL before meal to 120mg/100mL after eating. Find the molarity before and after eating e-3M, 6.7e-3M 4. It is recommended that drinking water contain 1.6 ppm fluoride (F-) for preventing of tooth decay. Consider a reservoir with a diameter of m and and average depth of 10.0 m. (V = π r 2 h) How many grams of fluoride should be added to give 1.6 ppm? How many grams of sodium fluoride, NaF contains this much fluoride? 1.25, 2.5e6 g F-, 5.6e6 g NaF 5. How many ml of 3.00 M H 2 SO 4 are required to react with 4.35 g of solid containing 23.2 m:m% Ba(NO 3 ) 2 if the reaction produces BaSO 4 precipitate. 133, 1.29 ml 20 Expressing Concentration

18 Solution at a Glance Solutions can be describe by the following: Solvent The component of a solution present in the greatest quantity Solute The component of solution present in the lesser quantity Solution A homogeneous mixture of two or more substances in which each substance retains its chemical identity Concentration of a Solution The amount of solute in a specific amount of solution. Molarity (M) moles of solute Liters of solution 22 Expressing Concentration