SolutionsHomogeneous Mixtures - Solute & Solvent

Objectives

Identify various types of solutions

Define solubility and the factors that affect it

Correctly use the terms unsaturated, saturated and supersaturated

Understand how to read a solubility graph

Express concentration in terms of molarity

Calculate the molarity of diluted solutions

Types of Solutions

Type Example Solvent Solute

Gas

Gas in Gas Air N2 O2

Liquid

Gas in

Liquid

Carbonated

H2OH2O CO2

Liquid in

LiquidVinegar H2O Acetic Acid

Solid in

LiquidOcean Water H2O NaCl

Solid

Liquid in

Solid

Dental

AmalgamAg Hg

Solid in

SolidSteel Fe C

Solvent and Solute

Solvent is the substance in the mixture in the greatest amount

Solute is the substance in the mixture in the lesser amount

Solvation

Process of surrounding solute particles with solvent particles

Solvation of ionic compound produces electrolyte (ions in solution - can conduct electricity)

Solvation of molecular compounds does not produce electrolyte

Which of the following would be a non-electrolyte?

HCl (hydrochloric acid)

NaOH (sodium hydroxide)

CaCl2 (calcium chloride)

C12H22O11 (sucrose)

Solubility

Situation: you add more and more sugar to your iced tea - sugar crystals start to collect at bottom of glass

Only a limited amount of solute can dissolve in a certain amount of solvent at a given set of conditions

Solubility

Solubility = maximum amount of solvent that will dissolve in a given amount of solvent at a specific temperature and pressure

Factors that affect Solubility

Temperature

Pressure

Agitation

Breakage into small particles

Solubility Graph - Solids

Most solids are more soluble as temperature of solution increases

Greater kinetic energy of solvent helps surround solute particles

Solubility Graph - Gases

Most gases are less soluble as temperature of solution increases

Greater kinetic energy helps gases escape intermolecular forces attracting them to solvent particles

Question

Given the following solubility curve for a particular solute in water, do you think the solute is a gas or a solid?

Saturated Solution

Saturated solution contains the maximum amount of dissolved solute for given solvent amount at particular temperature and pressure

Same rate of precipitation (solid coming out of solution) as dissolution (solid going into solution)

Unsaturated Solution

Less than the maximum amount of solvent in a solution at particular temperature and pressure

More solute can dissolve and stay in solution

Supersaturated Solution

More than the maximum amount of solvent in a solution at particular temperature and pressure

Can be made by dissolving solute in hot solvent and slowly cooling

Slight disturbance will cause crystallization

Watch video

Question

You have a glass of water with salt dissolved in it.

You add more salt, and it easily dissolves in the water.

Is the solution unsaturated, saturated or supersaturated?

Concentration

How much solute is dissolved in a solution

Qualitative expression: dilute, concentrated

Need quantitative way to express concentration

Expressing Concentration

Various quantitative concentration ratios: percent by mass, percent by volume, mole fraction, molality, molarity

We will focus on molarity - this is the most commonly used to express concentration of solute in liquid solution

Molarity

Ratio of moles of solute to liters of solution

Indicated by M

.85 mol solute in 1 liter of solution = 0.85 M

0.85 M read as “0.85 molar”

M = moles/liter

Question

What is molarity of aqueous solution containing 40.0 g of glucose (C6H12O6) in 1.5 liter of solution?

First - convert grams of glucose into moles

molar mass of glucose = 180 g/mol

Molarity Problem Continued

1mol/180 g (40 g) = 0.2 moles

0.2 mole/ 1.5 L = 0.133 M

Problems

What is molarity of bleach solution containing 9.5 g of NaOCl per liter of bleach?

Calculate the molarity of 1.60 L of a solution containing 1.55 g of dissolved KBr.

Preparing Molar Solutions

You want to make a 1 L of a 1.5 molar solution of sucrose (C12H22O11 - molar mass = 342 g/mol). How much sugar do you need?

First - figure out how many grams of sucrose you need -

1.5 moles (342 g/mol) = 513 g

Add 513 g of sucrose to volumetric flask. Add water until 1 liter mark reached.

Amount of water will be less than 1 L. Why?

Diluting Solutions

In labs, we use concentrated solutions of standard molarities called stock solutions

For example, concentrated HCl is 12 M

You want to have 1 liter of a 1.5 M solution of HCl - What do you do?

Preparing Dilutions

M1V1 = M2V2

You want 1 L of 1.5 M HCl

Figure out how much water you need to add:

Solve for V1 - this is how much concentrated solution you need

V1 = M2V2/M1

V1 = ((1.5 mol/L)(1 L))/(12 mol/L)

V1 = 0.125 L concentrated HCl - mix with DI water to dilute to 1 L

Questions - Write these down and work on them

What volume, in mL of 2.00 M CaCl2 stock solution would you use to make 0.50 L of 0.300M CaCl2 solution?

What volume of a 3.00 M KI stock solution would you use to make 0.300 L of a 1.25 M KI solution?

How many mL of a 5.0 stock solution would you need to prepare 100 mL of 0.25 M H2SO4?

If you dilute 20.0 mL of a 3.5M solution to make 100 mL of solution, what is the molarity of the dilute solution?