1 CHAPTER 4 Solutions A By Dr. Hisham Ezzat First year

2 The Dissolution Process Solutions are homogeneous mixtures of two or more substances. solvent  Dissolving medium is called the solvent. solute  Dissolved species are called the solute. There are three states of matter (solid, liquid, and gas) which when mixed two at a time gives nine different kinds of mixtures.  Seven of the possibilities can be homogeneous.  Two of the possibilities must be heterogeneous.

3 The Dissolution Process Seven Homogeneous Possibilities SoluteSolventExample Solid Liquidsalt water LiquidLiquidmixed drinks GasLiquidcarbonated beverages LiquidSoliddental amalgams SolidSolidalloys GasSolidmetal pipes GasGasair Two Heterogeneous Possibilities SolidGasdust in air LiquidGasclouds, fog

Ways of Expressing Concentration Qualitative Terms : Dilute Solution – A dilute solution has a relatively small concentration of solute. A concentrated solution has a relatively high concentration of solute. 4

5 Quantitative Terms Quantitative expressions of concentration require specific information regarding such quantities as masses, moles, or liters of the solute, solvent, or solution The solution process: Polar materials dissolve only in polar solvents (NaCI/H 2 O), and non - polar substances are soluble in non - polar solvents. This is the first rule of solubility "like dissolves like" e.g: benzene in CCI 4

6 [A] Weight to Weight expression.

7 1. Weight percent (wt %) Number of grams of solute which present in 100 gram of solution.

e.g. 10% by weight glucose means: 10 gm glucose + 90 gm H 2 O = 100 gm solution. % Solute = (10/100) x 100 = 10 %. % Solvent = (90/100) x 100 = 90 % 8

2. Mole fraction (X): 9

10 Molality is a concentration unit based on the number of moles of solute per kilogram of solvent. 3. Molality

11 N.B W solution = W solute + W solvent W solvent = W solution - W solute W solvent =dV solution - W solute Where d = density of the solution V = Volume of the solution

12 Example 1: What is the molality of 12.5 % solution of glucose C 6 H , in water? M.wt. of glucose is Solution: 1) in 12.5 % solution 12.5 gm C 6 H 12 O 6 is dissolved in l00 gm solution. W solvent = = 87.5 g H2O 2) no. of moles glucose = 12.5/180

13 Example 2: What are the mole fractions of solute and solvent in a 1.0m aqueous solution? Solution: The molecular weight of H 2 O is 18.0 we find the number of moles of water in 100 gm of H 2 O. no of moles of H 2 O A 1.0 aqueous solution contains n solute =1.0 mol The mole fractions are X solute X water =

14 [B] Weight to Volume expression:

15 Molarity

16 Example 3: a)How many grams of concentrated nitric acid solution should be used to prepare 250 ml of 2.0M HNO 3 ? The concentrated acid is 70.0 % Solution: a) 70 gm HNO 3  l00 gm solution Mass of pure HNO 3 mass of HNO 3 solution =

17 b) If the density of the concentrated nitric acid solution is 1.42 g/ml. What volume should be used? M.wt. (HNO 3 ) =63 ml cone. NHO 3 = (45/1.42) = 31.7 ml cone. HNO 3

18 An aqueous solution of acetic acid was prepared by dissolving gm of acetic acid in 800 ml of the solution. If the density of the solution was gm/ml. M. wt of acetic acid = 60 Calculate: a) The molar concentration of the solution b) The molality c) The mole fraction of both the solute and the solvent d) The mole % e) The weight %. Example 4:

19 Solution: a) b) d = 1.026g/mlV = 800 ml W solution = V x d = 800 x = gm W slvent = = gm

20 c) no. of acetic acid moles = / 60 = mole no. of H 2 O moles = / 18 = mole Mole fraction of acetic acid = Mole fraction of H 2 O = d) mole % acetic acid = x 100 = 6.99 % mole % of H 2 O = x 100 = % e) percentage weight of acetic acid = percentage weight of H 2 O=

21 Try ? 1.Five grams of NaCl is dissolved in 25.0 g of H 2 O. What is the mole fraction of NaCl in the solution? (Answer =0.0580) 2. What is the mole percent NaCl in the previous problem 1 (Answer = 5.80 mol %) 3. Ten grams of ascorbic acid (vitamin C), C 6 H 8 O 6, is dissolved in enough water to make 125 ml of solution. What is the molarity of the ascorbic acid? (Answer = 5.80 mol %) 4. What is the molality of NaCl in the solution in the previous problem 1? (Answer = 3.42 m) 5. What is the mass percent of NaCl in the solution in the previous problem 1? (Answer = 16.7 %)

Try ? Example 1 Five grams of NaCl is dissolved in 25.0 g of H 2 O. What is the mole fraction of NaCl in the solution? solution: The formula weight of NaCl is 58.44, so 5.00 g of NaCl is 22

The molecular weight of water is 18.02; so 25.0 g of H 2 O is In this solution, then, the mole fraction of NaCl is (The mole fraction of water is , or ) 23

Example 2 What is the mole percent NaCl in the of Example 1 mol % NaCI = X NaCl X 100 = 5.80 x x 100 = 5.80% The solution is 5.80 mol % NaCI and mol % H 2 O 24