20) Acids, bases and pH

Question 1

Define BrØnsted-Lowry acid

Answer 1

a species that is a proton donor

Question 2

Define BrØnsted-Lowry base

Answer 2

a species that is a proton acceptor

Question 3

Define conjugate acid-base pair

Answer 3

two species that can be interconverted by the transfer of a proton

Question 4

Define conjugate acid

Answer 4

a species that releases a proton to form a conjugate base

Question 5

Define conjugate base

Answer 5

a species that accepts a proton to form a conjugate acid

Question 6

How can acid-base pair by clearly linked together?

Answer 6

labelling acid 1 base 1, acid 2 base 2

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Question 7

Dissociation does not take place unless…?

Answer 7

water is present

Question 8

Define hydronium ion

Answer 8

H3O+ (aq); active ingredient in any aqueous acid and conjugate acid for water

Question 9

What is the simplified form of a hydronium ion?

Answer 9

H+

Question 10

What do the terms monobasic, dibasic and tribasic refer to?

Answer 10

the total number of hydrogen ions in the acid that can be replaced per molecule in an acid-base reaction

Question 11

Define spectator ions

Answer 11

ions that do not change during a reaction and therefore, can be cancelled out from ionic equations

Question 12

What do ionic equations help to do?

Answer 12

emphasise the role of H+

Question 13

How should you write a solid in an ionic equation?

Answer 13

with the full formula

Question 14

What is the ionic equation for neutralisation of acids with alkalis?

Answer 14

H+(aq) + OH-(aq) -> H2O(l)

Question 15

For any solution at 25 degrees C, pH < 7 indicates?

Answer 15

decreasing acidity

Question 16

For any solution at 25 degrees C, pH = 7 indicates?

Answer 16

neutral

Question 17

For any solution at 25 degrees C, pH > 7 indicates?

Answer 17

increasing alkalinity

Question 18

How can pH be measured?

Answer 18

indication paper

pH meter

Question 19

pH = ?

Answer 19

-log [H+(aq)]

Question 20

[H+(aq)] = ?

Answer 20

10^-pH

Question 21

A low value of [H+] matches a _ value of pH and vice versa.

Answer 21

high

Question 22

pH is a _ scale, this means that a pH of 1 has _ times the [H+] as a solution with a pH of 2?

Answer 22

logarithmic

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Question 23

Give the equation for the pH of strong acids

Answer 23

[H+(aq)] = [HA(aq)]

because a strong acid completely dissociates its H+

Question 24

Define acid dissociation constant Ka

Answer 24

equilibrium constant that shows the extent of dissociation of a weak acid

Question 25

Ka = ?

Answer 25

( [H+(aq)] [A-aq)] ) / [HA(aq)]

Question 26

Does temperature change Ka?

Answer 26

yes

Question 27

The larger the numerical value of Ka, the further the equilibrium is to _ and the _ dissociation and acid strength?

Answer 27

right | greater

Question 28

pKa = ?

Answer 28

-log Ka

Question 29

Ka from pKa?

Answer 29

Ka = 10^-pKa

Question 30

The stronger the acid, the _ the Ka val. and the _ the pKa value?

Answer 30

larger | smaller

Question 31

Give the 2 key equations for the pH of weak acids

Answer 31

1. ka = [H+(aq)]^2 / [HA(aq)] | 2. [H+(aq)] = √(Ka x [Ha])

Question 32

What 2 approximations is the key equation for the pH of weak acids based upon?

Answer 32

1. [H+(aq)]eqm = [A-(aq)]eqm the small amount of H+ from the dissociation of water is neglected 2. [HA(aq)]start = [HA(aq)]eqm dissociation of weak acids is small so any decrease in [HA] from dissociation is neglected

Question 33

Give the simplified equation for the pH of weak acids

Answer 33

Ka = ( [H+(aq)]eqm x [H+(aq)]eqm ) / ( [HA(aq)]start - [HA(aq)]eqm )

Question 34

How can Ka be determined experimentally?

Answer 34

preparing a standard solution of the weak acid of known conc. and measuring the pH of the standard solution using a pH meter

Question 35

When does the approximation that [H+(aq)]eqm = [A-(aq)]eqm for weak acids break down?

Answer 35

for very weak acids or very dilute solutions as if pH > 6 the dissociation of water becomes significant

Question 36

When does the approximation that [HA(aq)]start = [HA(aq)]eqm for weak acids break down?

Answer 36

for stronger weak acids w/ Ka > 10^-2 moldm^-3 or very dilute solutions as [H+] becomes significant and there is a real difference between [HA(aq)]eqm and [HA(aq)]start - [HA(aq)]eqm

Question 37

Define ionic product for water Kw

Answer 37

the product of the ions formed by partial dissociation of water, given by Kw = [H+(aq)] [OH-(aq)]

Question 38

At 25 degrees C, Kw = _ therefore, neutral water has a pH of _ as [H+] = _?

Answer 38

1.00 x 10^-14 mol2dm-6 7 [OH-(aq)]

Question 39

If [H+] > [OH-] in a solution it is _?

Answer 39

acidic

Question 40

If [H+] < [OH-] in a solution it is _?

Answer 40

alkaline

Question 41

Define strong base

Answer 41

an alkali that completely dissociates in solution e.g. NaOH

Question 42

Can bases be monobasic, dibasic and tribasic?

Answer 42

yes

Question 43

Give the key equation for the pH of solutions of strong bases

Answer 43

[H+(aq)] = Kw / [OH-(aq)] | uses concentration of the base and the ionic product of water

Question 44

HSO3- can act as either a BrØnsted-Lowry acid or a BrØnsted-Lowry base. Explain this statement, including equations for the reactions of HSO3-(aq) with H+(aq) and OH-(aq)

Answer 44

can accept protons acting as a base HSO3-(aq) + H+(aq) -> H2SO3 can donate protons acting as an acid HSO3-(aq) + OH-(aq) -> SO3 + H2O (neutralisation)