SOLUTIONS A solution is a homogeneous mixture of a solute dissolved in a solvent. The solvent is generally in excess. Example The solution NaCl(aq) is sodium chloride NaCl(s) dissolved in water H2O(l) The solute is NaCl(s) and the solvent is H2O(l)

Solute + solvent

Solutions: homogeneous mixtures Two components (at the least)- –Solute – the substance being dissolved –Solvent – the dissolving medium usually water – aqueous solution can have multi-solute solutions - seawater

4

Solubility experiment

Different solutions It’s possible to prepare solutions in all phases of matter.

Different solutions

However, The solutions in which the solvent is water are called “AQUEOUS SOLUTIONS.” Aqueous solutions are indicated as (aq) in reaction equations.

Ni(s) + HCl(aq) NiCl2(aq) + H2(g) NiCl2(s) dry Aqueous solutions

Types of Solutions Are solutions made from only one solvent and one solute? –By definition, there can only be one solvent –However, many solutes can be dissolved in a solvent to create a solution Air is an example of a solution with one “ solvent ” (nitrogen) and many “ solutes ” (oxygen, helium, argon, carbon dioxide, etc.)

Unsaturated solution- a solution that is able to dissolve more solute. Saturated solution- a solution that cannot dissolve any more solute at the given conditions.

Supersaturated solution- a solution holding more dissolved solute than is specified by its solubility at a given temperature

Electrolyte and Non-electrolyte Electrolyte: a substance that conducts electricity when dissolved in water. –Acids, bases and soluble ionic solutions are electrolytes. Non-electrolyte: a substance that does not conduct electricity when dissolved in water. –Molecular compounds and insoluble ionic compounds are non-electrolytes.

Electrolytes Some solutes can dissociate into ions. Electric charge can be carried.

Types of solutes Na+ Cl- Strong Electrolyte - 100% dissociation, all ions in solution high conductivity

Types of solutes CH3COOH CH3COO- H+ Weak Electrolyte - partial dissociation, molecules and ions in solution slight conductivity

Types of solutes sugar Non-electrolyte - No dissociation, all molecules in solution no conductivity

Strong Electrolytes Strong acids: HNO 3, H 2 SO 4, HCl, HClO 4 Strong bases: MOH (M = Na, K, Cs, Rb etc) Salts: All salts dissolving in water are completely ionized.

22

Concentration the amount of solute dissolved in a solvent at a given temperature described as dilute if it has a low concentration of solute described as concentrated if it has a high concentration of solute described as supersaturated ifsupersaturated contains more dissolved solute than normally possible

Units of Concentrations amount of solute per amount of solvent or solution Molarity (M) = moles of solute(n) volume in liters of solution (V) moles = M x V(L)

Examples: Example 1: What is the concentration when 5.2 moles of hydrosulfuric acid are dissolved in 500 mL of water? Step one: Convert volume to liters, mass to moles. 500 mL = 0.5 L Step two: Calculate concentration. C = 5.2 mol/0.5 L = 10mol/L

Example 2: What is the volume when 9.0 moles are present in 5.6 mol/L hydrochloric acid? Example 3: How many moles are present in 450 mL of 1.5 mol/L calcium hydroxide? Example 4: What is the concentration of 5.6 g of magnesium hydroxide dissolved in 550 mL? Example 5: What is the volume of a mol/L solution that contains 5.0 g of sodium chloride?

Answers 2) 9.0/5.6= = 1.6 L 3) 1.5x0.45= 0.675=0.68 mol 4) Mg(OH) 2 = g/mol 5.6/58.316= mol /0.55 = M 0.17 M 5) NaCl=58.5 g/mol 5.0/58.5= mol mol/0.100= L 0.85 L

HOW MUCH SOLUTE IS NEEDED FOR A SOLUTION OF A PARTICULAR MOLARITY AND VOLUME? EXAMPLE How much solute is required to make 300 mL of 0.8 M CaCl 2 ?

ANSWER (111.0 g) (0.8 mole) (0.3 L) = g mole L

CaCl 2 CaCl 2 solution CaCl 2

EXAMPLE: Prepare 1 L, 1M Na 2 SO 4 solution.

PREPARING DILUTE SOLUTIONS FROM CONCENTRATED ONES Concentrated solution = stock solution Use this equation to decide how much stock solution you will need: M 1 V 1 =M 2 V 2 M 1 = concentration of stock solution M 2 = concentration you want your dilute solution to be V 1 = how much stock solution you will need V 2 = how much of the dilute solution you want to make

EXAMPLE How would you prepare 1000 mL of a 1 M solution of KCl from a 3 M stock of the solution of KCl ? –The concentrated solution is 3 M, and is M 1. –The volume of stock needed is unknown, ?, and is V 1. –The final concentration required is 1 M, and is M 2. –The final volume required is 1000 mL and is V 2.

SUBSTITUTING INTO THE EQUATION: M 1.V 1 = M 2.V 2 3 M (?) 1 M (1000 mL) ? = mL So, take mL of the concentrated stock solution and BTV (Bring to Volume)1 L.

EXAMPLE How would you prepare 500 mL of a 1.2 M solution of NaNO 3 from a 2 M stock of the solution of NaNO 3 ? –The concentrated solution is 2 M, and is M 1. –The volume of stock needed is unknown, ?, and is V 1. –The final concentration required is 1.2 M, and is M 2. –The final volume required is 500 mL and is V 2.

SUBSTITUTING INTO THE EQUATION: M 1.V 1 = M 2.V 2 2 M (?) = 1.2 M (500 mL) ? = 300 mL So, take 300 mL of the concentrated stock solution and BTV (Bring to Volume)500 mL.