Solutions

13.1 What is Solution? A solution is a stable homogeneous mixture of two or more substances uniformly dispersed throughout a single phase Mixtures can either be heterogeneous or homogeneous. The particles of a heterogeneous mixture are large enough In a homogeneous mixture, however, the particles are molecule-sized, so the mixture appears uniform, evenly mixed

Suspensions are temporary! A suspension is a mixture in which particles of a material are more or less evenly dispersed throughout a liquid or gas.

Solutions are stable homogenous mixtures

Solution is a broad term Solvent – Dissolving Medium (larger amount) Solutes – dissolved particles (smaller amount) Water is the most common solvent. Water is a unique solvent because so many substances can dissolve in it. Solutions in which water is the solvent are called aqueous solutions.

Solid + Solid = Solution Another type of solution involves one solid mixed with another solid. Examples include solid alloys, such as brass, bronze, and steel.

Colloids are stable heterogeneous mixture Heterogeneous mixtures not the same throughout Suspensions Mixture that eventually settles out (ex. Italian dressing) Colloid Mixture that does not settle out; particles are dispersed throughout the mixture (ex. milk)

13.2 Concentration and molarity a measure of the amount of solute dissolved in a given quantity of solvent A concentrated solution has a large amount of solute A dilute solution has a small amount of solute

Parts Per Million (ppm) Number of grams of solute in 1 million gram of solvent One unit of concentration used in pollution measurements that involve very low concentration

A chemical analysis shows that there are 2 A chemical analysis shows that there are 2.2 mg of lead in exactly 500 g of water. Convert this measurement to parts per million. parts solute mass of solute: 2.2 mg mass of solvent: 500 g parts per million = ? = ppm 1 million solvent 2.2 mg 1 g = 2.2 x 10-3 g 1000 mg 2.2 x 10-3 g 1,000,000 parts = 4.4 ppm 500 g 1 million

Helium gas, 3. 0 x 10-4 g is dissolved in 200. 0g of water Helium gas, 3.0 x 10-4 g is dissolved in 200.0g of water. Express this concentration in ppm. parts solute mass of solute: 3.0 x 10-4 g mass of solvent: 200.0 g parts per million = ? = ppm 1 million solvent 1,000,000 parts 3.0 x 10-4 g = 1.5ppm 200 g 1 million

% Composition by mass g of solute x 100 % % Composition = g of solution What is the percentage by mass of a solution made by dissolving 0.49 g of potassium sulfate in 12.70 g of water? = 0.49 K2SO4 12.70g water

What is the percentage concentration of 75 What is the percentage concentration of 75.0 g of ethanol dissolved in 500.0 g of water? g of solute x 100 % % Composition = g of solution 75.O g of ethanol x 100 % 500g water + 75.0 g of ethanol =13.0 % 75.0 g ethanol 500g water

Molarity (M) Molarity (M) is a concentration unit of a solution expressed as moles of solute dissolved per liter of solution.

What is the molarity of a potassium chloride solution that has a volume of 400.0 mL and contains 85.0 g KCl? 1 mol KCl solute = 85 g KCl = 1.14 mol KCl 74.55 g KCl solution = 400 mL 1 L = 0.4 L 1000 mL = 2.85 M

An aqueous solution of sodium carbonate, Na2CO3, contains 53 g of solute in 215 mL of solution. What is it concentration (M)? 1 mol Na2CO3 solute = 53 g Na2CO3 = 0.5 mol Na2CO3 105.99 g Na2CO3 solution = 215 mL 1 L = 0.215 L 1000 mL = 2.3 M

How many moles of sugar are dissolved in 202 mL of a 0. 150 M solution How many moles of sugar are dissolved in 202 mL of a 0.150 M solution? How many moles of C12H22O11 is that? solution = 202 mL 1 L x = 0.202 L 1000 mL Molarity = 0.150 M mol = M · L mol = M · L = (0.150 mol/L)(0.202 L) = 0.0303 mol C12H22O11

A mass of 98 g of sulfuric acid, H2SO4, is dissolved in water to prepare a 0.50 M solution. What is the volume of the solution in liters ? 1 mol H2SO4 solute = 98 g H2SO4 = 1.0 mol H2SO4 98.08 g H2SO4 solute = 1.0 H2SO4 Molarity = 0.50 M = 2.0 L H2SO4

Determine the moles of copper that will react with 0. 025 L of a 6 Determine the moles of copper that will react with 0.025 L of a 6.5 M HNO3 solution. 3 Cu (s) + 8 HNO3(aq) → 3 Cu(NO3)2(aq) + 2 NO(g) + 4 H2O(l) solution = 0.025 L Molarity = 6.5 M HNO3 mol = M · L = (6.5 mol/L)(0.025 L) = 0.1625 mol HNO3 0.1625 mol HNO3 3 mol Cu x = 0.061mol Cu 8 mol HNO3

What volume (in milliliters) of a 0 What volume (in milliliters) of a 0.500 M solution of copper(II) sulfate, CuSO4, is needed to react with an excess of aluminum to provide 11.0 g of copper? 3CuSO4(aq) + 2Al(s) → 3Cu(s) + Al2(SO4)3(aq) Solute = 11.0 g Cu Molarity = 0.500 M CuSO4 1 mol Cu solute = 11 g Cu = 0.17 mol Cu 63.5 g Cu 0.17 mol Cu 3 mol CuSO4 x = 0.17 mol CuSO4 3 mol Cu L = mol / M = (0.17 mol)/(0.500 mol/L) = 0.34 L CuSO4 = 340mL

Molality (m or molal) solute in moles and the mass of solvent in kilograms; 1 L = 1 Kg 1000 g = 1 Kg 1 mL = 1 g

What is the molality of a solution with 9 What is the molality of a solution with 9.3 mole of NaCl in 450 g of water? Mols of solute = 9.3 mol Kg of solvent = 450 g = 0.45 Kg 9.3 mol = 21 m 0.45 Kg

Determine the molality of a solution of 560 Determine the molality of a solution of 560. g of acetone, CH3COCH3, in 620 g of water. Mols of solute = 560g x (1 mol/58.09 g ) = 9.6 mol Kg of solvent = 620 g = 0.62 Kg 9.6 mol = 15.5 m 0.62 Kg

13.3 Solubility and Dissolving Process Solubility is the ability of one substance to dissolve into another at a given temperature and pressure “Like dissolves Like” Polar compounds dissolve in other polar compounds, nonpolar compounds dissolve in other nonpolar compounds. Ex: Oil (nonpolar) + Water (polar) = no solubility Ex: Salt (ionic/Polar) + Water (Polar) = solubility Ex: hydrocarbon(nonpolar)+ paint thinner(nonpolar) = soluable

Miscible vs. Immiscible liquids that are completely soluble with each other are described as being miscible in each other. The two liquids that do not mix are immiscible. The immiscible liquids form two layers. The polar water molecules attract each other, so they cannot be pushed apart by the nonpolar oil molecules to form a solution.

Water is a polar solvent, while hexane is a nonpolar solvent. Which of the examples above illustrates a nonpolar solute in a polar solvent? NH4Cl in water C10H8 in water C2H5OH in hexane CO(NH2) 2 in hexane Solute Water Hexane NH4Cl, ammonium chloride Soluble Insoluble C10H8, naphthalene C2H5OH, ethanol CO(NH2)2, urea

Solubilities of Solid Compounds To speed up the solubility Increase the surface area, by breaking into smaller pieces Molecules are dissolved faster when they are apart (ex: sugar cube vs. sugar granule) Agitation Stirring or shaking moves fresh solvent next to the solute thus increasing the rate Increase temperature solvent molecules with greater kinetic energy can dissolve more solute particles

Enthalpy and entropy affect solubility of salts The dissolving of an ionic compound involves a unique factor: the separation of ions from the lattice into individual dissolved ions. Dissociation is the separating of a molecule into simpler molecules, atoms, radicals, or ions. Dissociation can be represented as an equation. NaCl(s) → Na+(aq) + Cl−(aq) If water is the solvent, above dissociation is called hydration.

Saturation of Solutions A solution that contains the maximum amount of solute that may be dissolved under existing conditions is saturated. A solution that contains less solute than a saturated solution under existing conditions is unsaturated. A solution that contains more dissolved solute than a saturated solution under the same conditions is supersaturated.

no more solute dissolves SUPERSATURATED SOLUTION UNSATURATED SOLUTION more solute dissolves SATURATED SOLUTION no more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form concentration

Cloud seeding Ever heard of seeding the clouds to make them produce rain? Clouds- mass of air supersaturated with water vapor Silver Iodide (AgI) crystals are dusted into the cloud The AgI attracts the water, forming droplets to attract others

What happens if 46.4 g NaCH3COO added to 100. g of 20ºC water? It all dissolves What happens if add 46.5 g? Mostly dissolves Would stirring help dissolve more? No! It only makes what will dissolve do so faster

Solubility Equilibrium In a saturated solution, the solute is recrystallizing at the same rate that it is dissolving. When the amount of solute added to a solvent has reached its solubility limit, it is at equilibrium Solubility equilibrium is the physical state in which the opposing processes of dissolution and crystallization of a solute occur at equal rates.

Gases can dissolve in liquids Gas solubility depends on pressure and temperature Henry’s law states that the solubility of a gas increases as the partial pressure of the gas on the surface of the liquid increases Gases are less soluble in a liquid of higher temperature because the increased molecular motion in the solution allows gas molecules to escape their loose association with the solvent molecules Gas is soluble at LOW temperature, HIGH pressure SOLUBILITY, COKE

The gas is at equilibrium with the dissolved gas in this solution. The equilibrium is dynamic. Rf. Fig. 11.5 Z5e 523

If you increase the pressure the gas molecules dissolve faster than they escape. The equilibrium is disturbed.

The system reaches a new equilibrium with more gas dissolved. Henry’s Law. P= kC Pressure = constant x Concentration of gas Henry’s Law: Gas solubility in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid. Hrw 407

Solubility overview For gases in a liquid, as the pressure goes up-the solubility goes up For gases in a liquid, as the temperature goes up-the solubility goes down For solids in liquids, as the temperature goes up-the solubility usually goes up

13.4 Physical Properties of Solutions The conductivity of a substance is described as its ability to conduct an electric current. Electrolytes- compounds that conduct electricity when molten or dissolved All ionic compounds (ex. NaCl) Nonelectrolytes- Not composed of ionic cmpds (ex. Sucrose) Weak electrolytes- ex. Acetic acid Strong electrolytes- ex. NaCl STRONG vs. WEAK

Electrolytes

Surfactants Surfactant Soap is an emulsifying agent. surface active agent interferes with H-bond, reducing surface tension (Ex: Soaps and detergents) Long chain of polar and nonpolar Connects insoluble with water Soap is an emulsifying agent. An emulsion is made of colloid-sized droplets suspended in a liquid in which they would ordinarily be insoluble, unless stabilized by an emulsifying agent, such as a soap