Unit1Topic10 - Solubility

Question 1

Properties of water

Answer 1

Clear, colourless liquid
Freezes at 0°C, boils at 100°C (physical test for water)
Density = 1g/cm3
Neutral (pH 7)
Chemical formula H2O (covalent molecule)
Most ionic compounds are soluble in water)

Question 2

Chemical tests for water

Answer 2

Anhydrous copper sulfate (white -> blue)

Cobalt chloride paper (blue -> pink)

Question 3

Steps involved in water purification

Answer 3

Water from reservoir

Sedimentation tank (some impurities sink to bottom)

Sand beds (sand and gravel filters trap more clay and silt)

Chlorination plant (small amount of chlorine added, kills bacteria that could cause typhoid and cholera)

Pumping station (storage)

Question 4

What are the 2 most important stages of water treatment?

Answer 4

Filtration and chlorination

Question 5

Pollutants of water supplies

Answer 5

Fertilisers (nitrates and phosphates)
Detergents (phosphates)
Thermal pollution
Pesticides
Industrial waste
Oil
Sewage

Question 6

Fertilisers

Answer 6

Contain nitrates and phosphates

Can get washed down through soil and rain and end up in streams and rivers - can cause eutrophication

Question 7

Detergents

Answer 7

Contain phosphates
From homes and factories
Most are biodegradable
Involved in eutrophication

Question 8

Thermal pollution

Answer 8

The warm water, released from industrial plants and disposed into rivers, increases the temperature of the river or lake causing the oxygen levels to decrease, as oxygen is less soluble in hot water.

Question 9

Pesticides

Answer 9

Designed to kill pests that eat crops

Often poisonous to humans

Question 10

Industrial waste

Answer 10

Common ones included acids and alkalis and compounds of poisonous metals

Question 11

Oil

Answer 11

May get spilt into sea from refineries or leaking oil tankers

Question 12

Sewage

Answer 12

Produced where humans live and work

Question 13

Eutrophication

Answer 13

Fertiliser runs into water following heavy rain

Leads to increased rate of growth in water plants eg algae

Algae forms blanket layer, preventing light from reaching plants beneath

The plants beneath die

The decomposition of the dead plants uses up oxygen

Therefore fish and other animals can’t survive in the water without oxygen (oxygen starvation)

Question 14

Solvent

Answer 14

A substance that does the dissolving

Question 15

Solute

Answer 15

A substance that dissolves

Question 16

Solution

Answer 16

A substance dissolved in a solvent, a mixture of a solute and a solvent

Question 17

A solution that has a lot of solute in a certain volume is said to be

Answer 17

Concentrated

Question 18

A solution with only a little solute in a certain volume of water is said to be

Answer 18

Dilute

Question 19

Saturated solution

Answer 19

A solution which contains as much of a dissolved solute that will dissolve in 100g of solvent at a given temperature

Question 20

Factors affecting solubility

Answer 20

Heat
Stirring
Volume of solvent
Amount of solute

Question 21

Gases and solubility

Answer 21

Gases are less soluble at higher temperatures

Question 22

Solubility

Answer 22

The solubility of a substance is the maximum mass of a solute that will dissolve in 100g of a solvent at a given temperature

Question 23

Solubility equation

Answer 23

Solubility(g/100g of water) = mass of solute/mass of solvent x100

Units = g/100g of water at … °C

Question 24

Solubility curves

Answer 24

X axis - temp (°C)

Y axis - solubility (g/100g water)