Solutions Unit 13

13.2-13.5 Day One

Solutions Homogeneous mixtures. Composition may vary from one sample to another Appears to be one substance, though really contains multiple materials. Most homogeneous materials we encounter are actually solutions. E.g., air and lake water. Tro's Introductory Chemistry, Chapter 13

SOLUTIONS Consists of two parts Solute The substance that is being dissolved Solvent The substance that is “DOING” the dissolving Universal Solvent  water Solutions in which the solvent is water are called aqueous solutions.

SOLUTIONS Must fit three criteria Combination of two or more pure substances Must be able to vary in concentration Parts must be indistinguishable

Common Types of Solution Solution phase Solute phase Solvent phase Example Gaseous solutions Gas Air (mostly N2 and O2) Liquid solutions Liquid Solid Soda (CO2 in H2O) Vodka (C2H5OH in H2O) Seawater (NaCl in H2O) Solid solutions Brass (Zn in Cu) Tro's Introductory Chemistry, Chapter 13

How do we make solutions? Remember there are two parts to a solution Solute: stuff that is dissolving Solvent: stuff “doing” the dissolving When you talk about solutions you must talk about dissolving and solubility

What is solubility? Solubility : Amount of a substance to dissolve into another at a given temperature and pressure Not all substances are SOLUBLE!!! Meaning they WILL NOT dissolve How do I know what will be soluble? RULE: “Like dissolves Like”

Does temperature affect solubility? Solubility usually increases as temperature increases Lets look at an example! Think about Hot tea!!

Saturation of Solutions We can talk about saturation of solution in three ways!! Saturated: a solution that cannot dissolve any more solute Unsaturated: a solution that contains less solute than a saturated solution its able to dissolve more solute Supersaturated: a solution holding more dissolved solute than what its supposed to hold

Supersaturated Solution A supersaturated solution has more dissolved solute than the solvent can hold. When disturbed, all the solute above the saturation level comes out of solution. Tro's Introductory Chemistry, Chapter 13

Adding Solute to various Solutions Unsaturated Saturated Supersaturated Tro's Introductory Chemistry, Chapter 13

Solubility and Temperature The solubility of the solute in the solvent depends on the temperature. Higher temperature = Higher solubility of solid in liquid. Lower temperature = Higher solubility of gas in liquid.

Expressing Amounts with Solutions (A.K.A. CONCENTRATION) Molarity (M) Molality (m) Mole Fraction (X) Percent Composition or pph (% or pph)

Mole Fraction (X) X = moles solute/ total moles solution What is the mole fraction in a solution that contains 2.2 moles of sugar and 250 mL of water?

Percent Composition (%) or parts per hundred (pph) % = grams solute / total grams of solution What is the percent composition of salt in a solution that contains 15 grams of salt and 25 grams of water?

Practice—Calculate the Mass Percent of a Solution that Has 10 Practice—Calculate the Mass Percent of a Solution that Has 10.0 g of I2 Dissolved in 150.0 g of Ethanol. Tro's Introductory Chemistry, Chapter 13

Practice—Milk Is 4. 5% by Mass Lactose Practice—Milk Is 4.5% by Mass Lactose. Determine the Mass of Lactose in 175 g of Milk. Tro's Introductory Chemistry, Chapter 13