1 / 22

# Chapter 11 – Measuring Solubility - PowerPoint PPT Presentation

Week 1, Lesson 1. Chapter 11 – Measuring Solubility. Solubility. Solubility of a substance refers to the maximum amount of that substance that can be dissolved in a given quantity of solvent at a certain temperature.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

Chapter 11 – Measuring Solubility

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Week 1, Lesson 1

## Chapter 11 – Measuring Solubility

### Solubility

• Solubility of a substance refers to the maximum amount of that substance that can be dissolved in a given quantity of solvent at a certain temperature.

• A solution in which no more solute can be dissolved at that temperature is described as a saturated solution.

• One way of measuring solubility is to determine the maximum mass of solute that can be dissolved in 100 grams of solvent at a particular temperature.

• Solubility values allow us to compare the extent to which different solutes dissolve.

### Solubility Curves

• The relationship between solubility and temperature can be represented by a solubility curve.

• Each point on the solubility curve represents a saturated solution – no more solute can be dissolved at the particular temperature.

• Any point below the curve represents an unsaturated solution for that solute.

• Any unsaturated solution contains less solute than is needed to make a solution saturated at that temperature.

### Crystallisation

• If a hot saturated solution of potassium nitrate is cooled, crystals of the solute will appear.

• This happens because potassium nitrate also becomes less soluble as the temperature falls.

• The potassium nitrate crystallises from solution.

• This process is known as crystallisation.

### Supersaturation

• With some substances, it is possible to produce an unstable solution that contains more dissolved solute than in a saturated solution.

• Such a solution is said to be supersaturated.

• In a solubility graph, any point above a solubility curve represents a supersaturated solution for that solute.

• A supersaturated solution of potassium nitrate can be prepared by cooling a saturated solution very carefully so that crystallisation does not occur.

• Adding a small seed crystal or knocking a supersaturated solution can cause the solute to crystallise or settle out until a saturated solution remains.

• Crystallisation is often accompanied by the evolution of much heat energy.

### Solubility of Gases

• Gases such as oxygen and carbon dioxide are much less soluble in water than solids such as sodium chloride and sucrose.

• The presence of oxygen and carbon dioxide is essential for the survival of aquatic life.

• Aquatic plants and animals require a source of oxygen for respiration and although oxygen is a part of all water molecules, they cannot extract it from these molecules.

• They must rely on the small amount of dissolved oxygen in the water.

• Similarly, aquatic plants rely on dissolved carbon dioxide for photosynthesis.

• The solubility of a particular gas in a liquid depends on the temperature of the liquid and the pressure of the gas.

### Temperature and Gas Solubility

• Unlike most solids, gases become less soluble as the temperature increases.

• Thermal pollution: a power station located next to a river or lake can release hot water as a waste material.

• As the temperature of the water increases, less oxygen remains dissolved.

• In addition, at increased temperatures, aquatic life becomes more active and so the demand for oxygen increases.

• Competition for oxygen can become intense and can lead to large decreases in certain animal populations.

### Pressure and Gas Solubility

• The solubility of gases increases with increasing pressure.

• Carbon dioxide is forced into soft drink under high pressure to increase the amount that can be dissolved.

• When the bottle top is removed, the carbon dioxide in the space at the top of the bottle escapes.

• The gas pressure above the drink falls and so the solubility of carbon dioxide in the drink is lowered.

• Dissolved carbon dioxide escapes from the liquid until only enough remains to saturate the solution at this pressure.

### Solubility Question Examples…

Use the data in Table 11.2 to calculate the percentage of oxygen that would be lost from a pond, saturated with oxygen, if the temperature of water in the pond rose from 0°C to 20°C

Mass of oxygen, in 1kg saturated solution of oxygen;

= 0.069g at 0°C

= 0.043g at 20°C

So, mass of oxygen lost:

0.069 – 0.043 = 0.026g

% of oxygen lost =

= 38%

Week 1, Lesson 2

### Concentration of Solutions

• The concentration of a solution describes the relative amounts of solute and solvent present.

• A solution in which the ratio of the solute to solvent is high is said to be concentrated.

• A solution in which the ratio of solute to solvent is low is said to be dilute.

### Concentrations of Solutions cont…

• Chemists use different measures of concentration depending on the particular situation.

• Earlier, units of grams of solute per 100 grams of solvent were used to describe the concentration of saturated solutions.

• Other ways of expressing concentration describe the amount of solute in a given solution.

• They vary only in the units used to measure the amount of solute and the amount of solution.

### Units of Measurement

• The most commonly used units of concentration are:

• Mass of solute per litre of solution

• Amount, in mol, of solute per litre of solution

### Mass of Solute per Litre of Solution

• This unit expresses concentration in terms of the mass of solute present in 1 litre of solution.

• Example: A 250mL glass of orange-flavoured mineral water contains 4.0mg of sulfate ions. What is the concentration (in mgL-1) of sulfate ions in the mineral water?

Concentration = mass of sulfate ions(mg)

volume of mineral water (L)

= 4.0

0.250

= 16mg/L or 16mg L-1

### Amount, in mol, of solute per solution

• Expressing concentration in moles per litre of solution allows chemists to compare relative numbers of atoms, molecules or ions present in a given volume of solution.

• This measure of concentration is known as molarity or molar concentration.

• Molarity is defined as the number of moles of solute particles per litre of solution.

• A one molar (1 M) solution contains one mole of solute dissolved in each litre of solution.

• A concentration of such a solution is said to be one mole per litre, 1 mol L-1 or 1 M.

• The term molarity can be used to mean concentration measured in moles per litre.

### Amount of Solute Equation

• The amount of solute is linked to the concentration (molarity) and volume of the solution by the relationship:

n = c x V

Where n = amount, mol

c = concentration, mol L-1

v = volume, L

### Example

• Calculate the molar concentration of a solution that contains 0.105 mol of potassium nitrate dissolved in 200mL of solution.

STEP 1: Convert volume into L

200mL = 200 x 10-3L

STEP 2: Calculate the molar concentration

c = n / v

c = 0.105 / 200 x 10-3

c = 0.525M

### Unit Conversion

grams M moles

litre x M litre

Molar Concentration and Solubility

### Dilution

• The process adding more solvent to a solution is known as dilution.

• When a solution is diluted, the solute particles are more widely spaced.

• A dilution formula exists, which can be used to find the concentration or volume changes of a solution.

### Dilution Formula

C1V1 = C2V2

C1 = Initial concentration

V1 = Initial volume

C2 = Final concentration

V2 = Final volume

In this equation, the concentration unit is g L-1

### Example

• The concentration of a seaweed extract in a bottle of seaweed fertiliser solution is 9.0gL-1. When used to fertilise plants, the seaweed fertiliser must be diluted. If 10mL of seaweed fertiliser is diluted with water to fill a 2.0L container, what is the new concentration?

C1V1 = C2V2C1V1 = C2V2

C1 = 9.09.0 x 0.010 = C2 x 2.0

V1 = 0.010L0.09 = C2 x 2.0

C2 = ?C2 = 0.09 / 2.0

V2 = 2.0C2 = 0.045g L-1