Solutions

Solutions

Definition: Homogeneous mixture of two or more substances in a single phase.

Like Dissolves Like (i.e. nonpolar molecules dissolve in nonpolar molecules) Solid mixtures: alloys (brass, sterling silver) Liquid mixtures: alcohol & water Gas mixtures: air

Other Terms

Soluble: capable of dissolving Insoluble: incapable of dissolving Miscible: 2 liquids dissolve into each other Immiscible: 2 liquids do not dissolve into

each other Solubility: how much of a given solute a

certain solvent can dissolve at a certain temperature & pressure

Components of Solutions

Solute: is dissolved by the solvent. Found in lesser quantities May be electrolytes (conduct electricity) or non-

electrolytes (does not conduct electricity) Solvent: does the dissolving

Water is the universal solvent http://www.dlt.ncssm.edu/TIGER/chem2.htm#sto

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Rates of Dissolving

Rate of dissolving may speed up due to the following:

1. Increased Surface Area: breaking the solute up into smaller pieces

2. Increased Stirring: increases particle collisions

3. Heating: particles move faster = more collisions.

Solubility

Varies with temperature Solids & Liquids: Temp ↑, solubility ↑ Gases: Temp ↑, solubility ↓

Henry’s Law: Solubility of a gas in liquid is directly proportional to pressure

Solubility

Saturated: The maximum amount of a solute that can be dissolved into a solvent.

Unsaturated: less than the maximum amount of solute that can be dissolved.

Supersaturated: More dissolved solute than a saturated solution at the same temperature Must be heated, then cooled slowly Very unstable

Solubility Curve

The lines represent the different saturation points for different compounds

Notice, the solubilities are measured in g/100 g H2O

Under the line is unsaturated, over the line is supersaturated

Solution Concentration

The concentration of a solution is measured in Molarity (M)

M = moles / liter M = mol/L

(moles of solute per liters of solution)

Diluting solutions: M1V1 = M2V2

Practice Problems

You have 3.50 L of solution that contains 90.0 g of NaCl. What is the molarity of this solution? Answer: 0.44 M

You have 0.8 L of a 0.5 M HCl solution. How many moles of HCl are present?

Answer: 0.4 mol HCl What volume of 3.00 M NaCl is needed for a

reaction that requires 146.3 g of NaCl? Answer: 0.834 L

Dilutions Practice Problems

You want to make 2.3 L of a 3.5 M H2SO4 solution. If you only have 12 M sulfuric acid in stock, how much must be added to water to make the solution you need?

Answer: In lab you produce 2.5 L of 6 M HNO3. If you

added 0.5 L of a concentrated solution to get this solution, what was the original concentration of the acid?

Molality:

Another way to measure concentration. Moles of solute per kilogram of solvent

m = mol / kg Notice: solvent must be in kg! Example: A solution was prepared by

dissolving 17.1 g of sucrose (C12H22O11) in 125 g of water. Find the molal concentration.

Answer: 0.400 m

Molality Examples

A solution of I2 in CCl4 is used when iodine is needed for certain chemical tests. How much iodine must be aded to prepare a 0.480 m solution of iodine in CCl4 if 100.0 g of CCl4 is used?

Answer: 12.2 g of I2

What is the molality of a solution composed of 255 g (CH3)2CO dissolved in 200. g of water?

Answer: 22 m