pH, dissolution & equilibrium

Question 1

Why does water have no overall charge?

Answer 1

Because the hydrogen and oxygen charges balances each other out

Question 2

How is ionic potential calculated?

Answer 2

charge/radius

Question 3

Describe the charges of cations and anions

Answer 3

Cation- negative charge

Anion - positive charge

Question 4

What is the ionic potential of insoluble hydroxides?

Answer 4

ionic potential; 3-12

Question 5

What is the ionic potential of a soluble cation?

Answer 5

Ionic potential is smaller than 3

Question 6

What is the ionic potential of soluble oxy-anions?

Answer 6

ionic potential greater than 12

Question 7

Why are soluble oxy-anions important in geochemistry?

Answer 7

They have soluble oxygen and these oxyanions are a way of getting oxygen into a sediment where you haven’t got any contact with the atmosphere

Question 8

Define stoichiometry

Answer 8

The study of the quantitative relationships or ratios between two or more substances undergoing a physical change/chemical reaction

Question 9

What does the la Chatelier’s principle quote?

Answer 9

When a system in equilibrium is subjected to an external constraint, the system responds in a way that tends to lessen the effect of that constraint”

Question 10

What is pH? (3)

Answer 10

• a measure of acidity
• negative logarithm to the base 10 with the concentration of hydrogen ions
• an equilibrium between H+ and OH- ions

Question 11

What does k represent?

Answer 11

equilibrium constant

Question 12

Whats the difference between an acid and a base?

Answer 12

• acid will donate one or more protons

- base will accept one or more protons

Question 13

What type of acid is rainwater?

Answer 13

a weak acid

Question 14

Why does soil water have high CO2 concentration?

Answer 14

from respiration reactions

Question 15

Why are oceans alkali?

Answer 15

because HCO3 is a weathering product of limestone and other rocks which get washed out oceans and therefore this high alkalinity buffers acidity

Question 16

What is alkalinity?

Answer 16

The capacity of water to neutralise an acid

Question 17

What is ionic dissociation?

Answer 17

ions in ionic compounds in an aqueous solution are freed from their mutual attractions and spread themselves throughout the solvent.

Question 18

Define dissolution?

Answer 18

the process of dissolving solutes in a solvent

Question 19

what ions are produced when magnesium nitrate dissolves in water?

Answer 19

Mg2+ (aq) + 2NO3- (aq)

Question 20

What defines an acid?

Answer 20

A substance that produces H+(aq) ions when dissolved in water

Question 21

What are the three most common acids?

Answer 21

• sulfuric acid (H2SO4)
• Hydrochloric acid (HCl)
• Nitric acid (HNO3)

Question 22

What defines a base

Answer 22

• a substance that reacts with an acid in solution producing a salt and water only

Question 23

What is the neutralization reaction?

Answer 23

acid + base => salt + water

Question 24

What defines an alkali?

Answer 24

a base that dissolves in water

Question 25

What defines an equilibrium constant (Kc)?

Answer 25

a ratio (defined by the reaction equation) involving the concentrations of reactants and products at equilibrium

Question 26

When does Kc vary?

Answer 26

only with the temperature of the equilibrium mixture, NOT with the concentrations of the reactants at teh start of the reaction

Question 27

What does Kc equal in an equilibrium expression?

Answer 27

Kc = products/reactants

Question 28

Whats the difference between a big K and a little k?

Answer 28

K = equilibrium constant
k = rate of constant

Question 29

How do we know if the reaction is forwards or backwards?

Answer 29

k > 1 = forwards

k < 1 = backwards

Question 30

Describe the rates of forwards and backwards reactions at equilibrium?

Answer 30

they are equal