Equilibrium: Solubilities of Salts and Gases

Question 1

How do salts (ionic compounds) interact?

Answer 1

Dissociate to give + and – ions

Question 2

Why is water bad and good for dissolving substances?

Answer 2

• Good for dissolving ionic substances
• Bad for non-charged organic molecules

Question 3

What does ppm stand for?

Answer 3

Parts per million

Question 4

What does solubility stand for?

Answer 4

A measure of how much solute can be dissolved in a solvent - affected by temp and pressure

Question 5

What does unsaturated mean?

Answer 5

Solution can still dissolve more

Question 6

What does saturated mean?

Answer 6

Solution that contains the maximum of dissolved solute

Question 7

What does supersaturated mean?

Answer 7

Unstable solution, contains > solute
solubility

Question 8

What does precipitate mean?

Answer 8

Excess solute that comes out of solution

Question 9

How does solubility of gases change with increasing temp?

Answer 9

Decreases

Question 10

How does solubility of most solids change with increasing temp?

Answer 10

Increases

Question 11

What is concentration?

Answer 11

Amount of solute in a solution

Question 12

What is molarity?

Answer 12

Moles of solute/ Litres of solution

Question 13

What is normality?

Answer 13

Normality (N) = equivalent of solute/1 litre of solution

Question 14

What does equivalent mean in normality?

Answer 14

Where equivalent = equivalent weight = molecular weight/ion charge

Question 15

What is the equivalent weight of calcium 2+?

Answer 15

= molecular weight/Z = 40/2
= 20 g per equivalent

Question 16

What must all aqueous solutions maintain?

Answer 16

All aqueous solutions must maintain charge neutrality. The sum of the cations must equal the sum of all the anions

Question 17

What is the equilibrium constant?

Answer 17

The ratio between the amount of reactant and the amount of product which is used to determine chemical behaviour

Question 18

How do you find the equilibrium constant?

Answer 18

Always put products over reactants and raise each to the power of their stoichiometric coefficients

Question 19

What can the Keq constant predict?

Answer 19

Equilibrium constant predicts the predominant direction of the reaction

Question 20

What is the solubility product constant?

Answer 20

The equilibrium constant for a solid substance dissolving in an aqueous solution

Question 21

What does Henry’s Law determine?

Answer 21

Amount of a gas in a liquid

Question 22

What is solubility of a gas in a liquid proportional to?

Answer 22

The partial pressure of that gas in contact with the liquid

Question 23

What is Henry’s law constant for oxygen?

Answer 23

1.28 x 10^-3

Question 24

What does solubility in water depend on?

Answer 24

• Water temperature
• Partial pressure
• Salt content

Question 25

Why is oxygen content in water very important?

Answer 25

Determines if there are aerobic conditions or anaerobic conditions

Question 26

What are the dissolved oxygen requirements of different types of fish?

Answer 26

- Trout 4-5 mg/L - Bass 3-4 mg/L - Carp 2-3 mg/L

Question 27

What is BOD?

Answer 27

Is a measure of water pollution

Question 28

What does BOD measure?

Answer 28

It measures how much dissolved oxygen is consumed as microbes/bacteria break down organic matter

Question 29

What does high BOD indicate?

Answer 29

High BOD indicates that levels of dissolved oxygen will fall, with potentially dangerous implications for biodiversity

Question 30

What can high BOD be caused by?

Answer 30

- High BOD can be caused by high levels of organic pollution - Microbiological activity uses up O2

Question 31

What is BOD_5?

Answer 31

The amount of dissolved oxygen used in a water sample by micro-organisms in a closed system as they break down organic material at 20ºC over a 5 day period.

Question 32

What is BOD_5 of clean water?

Answer 32

< 1 mg/L

Question 33

What is BOD_5 of polluted water?

Answer 33

> 5 mg/L

Question 34

Wha are the test conditions for BOD test?

Answer 34

- Test is run for 5 days - Temperature is kept at 20ºC - Bottles are kept in the dark - Analysed by measuring the DO at the beginning and end of a time period

Question 35

What does it mean if waste is really strong?

Answer 35

If waste is very strong, it is diluted with a known amount of water