Solutions and Units of Concentration

FUNDAMENTALS

May 11, 2015

What is a Mixture?

Types of Mixtures

Definitions

A solution is a homogeneous mixture A solute is dissolved in a solvent.

– solute is the substance being dissolved– solvent is the liquid in which the solute

is dissolved

Definitions Continued Dilute: a solution with a small amount of solute Concentrated: a solution with a large amount

of solute A saturated solution is one where the

concentration is at a maximum - no more solute is able to dissolve

A super-saturated solution is one where the concentration has more solute than it can normally dissolve

Solubility: a measure of how easily a solute dissolves in a solvent

Some Examples

Solute Solvent Example

solid solid Alloys (brass, steel)

solid liquid Salt water

gas solid Air bubbles in ice cubes

liquid liquid Ethanol in water

gas liquid Soft drinks

gas gas Air

Solubility

We can measure how easily a solute will dissolve in a certain solvent.

This measure is called solubility

Dissolution of Solid Solute

What are the driving forces which cause solutes to dissolve to form solutions?

1. Covalent solutes dissolve by H-bonding to water

2. Ionic solutes dissolve by dissociation into their ions.

moles of soluteL of solution

M =

Concentration of moles of solute per given amount of volume

Concentration measurement Because volume is temperature

dependent, molarity can change with temperature

Concentrations: MOLARITY (M)

n (moles)

M V (liters)

Concentration: Molarity Example #1Calculate the molarity of the

following solution:

1) 2.3 moles of sodium chloride in 0.45 liters of solution

M = moles of solute = 2.3 liters of solution 0.45

M = [ 5.11 M ]

n (moles)

M V (liters)

Concentration: Molarity Example #2Calculate the molarity of the following

solution:

2) 10.3 moles of LiOH in 250 mL in solution.

**Need to convert mL to L (÷ by 1000) M = moles of solute = 10.3 moles = 41.2M

liters of solution 0.250 liters

Concentration: Molarity Example #3

Calculate the moles of the following solution:

3) How many moles are needed to make 2 L of a [5.5 M] solution of NaOH?

M = n (moles)

V (liters)

[5.5M] = n (moles)

2 Liters

n = 5.5 x 2 = 11 moles

n (moles)

M V (liters)

Concentration: Molarity Example #3

Calculate the moles of the following solution:

3) How many grams is this?

Need MOLAR MASS of NaOH: 40 grams

n = 11 moles

11 moles x 40 g = 440 g

n (moles)

M V (liters)

Na: 23 gO: 16 gH: 1 gTOTAL: 40g