5.1.3 Acids and Bases (completed)

Question 1

What is a weak acid?

Answer 1

It partially dissociates in an aqueous solution

Question 2

What is a base?

Answer 2

A base is a hydrogen ion or proton acceptor

Question 3

What is an alkali?

Answer 3

A base that dissolves in water

Question 4

What is the equation for the neutralisation of acids with metal oxides/hydroxides?

Answer 4

Metal oxide/hydroxide + Acid –> Salt + Water

Question 5

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

Answer 5

Acid + Alkali –> Salt + Water

Question 6

What is the equation for the neutralisation of acids with carbonates?

Answer 6

Metal Carbonate + Acid –> Salt + Water + Carbon Dioxide

Question 7

What is a titration?

Answer 7

A technique used to accurately measure the volume of one solution that reacts exactly with another solution in order to find it’s concentration

Question 8

What are concordant results?

Answer 8

Results within 0.10 of each other

Question 9

How do you make a standard solution?

Answer 9

1. Weigh the solid using a balance
2. Transfer solid from weighing boat to beaker wash any left behind with distilled water
3. Dissolve solid fully with distilled water
4. Transfer solution to volumetric flask then rinse beaker and funnel into flask to ensure all solid is transferred
5. Fill with distilled water to graduation mark
6. Add a stopper and invert to mix

Question 10

Which base treats acid indigestion?

Answer 10

Magnesium hydroxide

Question 11

What is a buffer solution?

Answer 11

A solution that minimises pH changes when small amounts of an acid or a base are added.

Question 12

What two components does a buffer solution contain?

Answer 12

A weak acid HA and its conjugate base A-

Question 13

In a buffer solution, what occurs to increase pH when acid is added?

Answer 13

[H+] increases
H+ ions added react with conjugate base A- of buffer removing most H+ ions
Equilibrium shifts to the left

Question 14

In a buffer solution, what occurs to decrease pH when alkali is added?

Answer 14

[OH-] increases
H+ ions react with OH-
Equilibirum shifts to the right so more HA dissociates to restore H+ ions

Question 15

How can the pH of a buffer solution be calculated?

Answer 15

Ka=[H+][A-] / [HA]

pH = -log[H+]

Question 16

What is the dissociation constant?

Answer 16

Ka- It represents the strength of an acid and can sometimes be shown as a pKa value

Question 17

What is the pH of blood between?

Answer 17

7.35 and 7.45

Question 18

What is the equilibrium for the buffer system in blood?

Answer 18

H2CO3(aq) ⇌ H+(aq) + HCO3-(aq)

Question 19

When acid is added to blood, what happens?

Answer 19

[H+] increases
H+ ions react with HCO3- produing carbonic acid
Equilibrium position shifts to the left removing most of the H+ ions
Excess H2CO3 is converted to CO2 which is removed in the blood

Question 20

When alkali is added to blood, what happens?

Answer 20

[OH-] increases
H+ ions react with OH- ions to produce water
Equilibrium position shifts to the right
H2CO3 dissociates to restore H+ ions

Question 21

What are the significant points on a pH titration curve?

Answer 21

At first, excess of acid, pH increases slowly
Vertical section, pH increases rapidly
Equivalance point, centre of the vertical section, each are neutralised
At the end, excess of base, pH increases slowly

Question 22

What is the equivalence point?

Answer 22

The volume of one solution that exactly neutralises the other solution

Question 23

What is an an acid base indicator?

Answer 23

A weak acid that has a distinctive colour change from it’s conjugate base

Question 24

When is an indicator suitable for a titration?

Answer 24

The pH indicator range is in the vertical section of the pH titration curve

Question 25

What is a Bronsted-Lowry acid?

Answer 25

A proton donor

Question 26

What are conjugate systems?

Answer 26

When the acid and base are related
Acid ⇌ Proton + Conjugate Base
Base + Proton ⇌ Conjugate Acid

Question 27

What is a monobasic acid?

Answer 27

It has one H+ which it can replace and donate e.g. HCl

Dibasic has two e.g. H2SO4

Question 28

How do you work out pH of strong acids?

Answer 28

pH = -log [H+]

As they are strong the dissociate into a 1:1 ratio so it’s just the concentration of the acid is the concentration of H+

Question 29

How do you work out pH of weak acids?

Answer 29

[H+] = √[HA]Ka
pH = -log[H+]
You can work this out as yje ions of [H+] and [A-] are formed in equal amounts so they can be written as [H+]²

Question 30

What is the ionic product of water?

Answer 30

Kw = 1.0 x 10^-14 mol²dm^-6

Question 31

How do you work out the pH of a strong base?

Answer 31

Kw = [H+][OH-]
pH = -log[H+]

Question 32

What is the endpoint?

Answer 32

The point when the titration changes colour

Question 33

How do you use a pH meter?

Answer 33

1. Before use rinse probe with distilled water
2. Place probe in buffer of pH 4
3. Calibrate probe and then place in buffer of pH7 and then pH 10 to complete calibration

Question 34

What is enthalpy of neutralisation?

Answer 34

The energy change when a sufficient amount of acid or alkali is neutralised to produce one mole of water
-57kJ mol-1
Use q=mcΔT

Question 35

How do you convert from g/dm³ to mol/dm³

Answer 35

Divide by Mr

Question 36

What could be added to a weak acid to turn it into a buffer?

e.g. HCOOH

Answer 36

HCOONa / NaOH in order to produce HCOO- which is the conjugate base

Question 37

What factors determine pH of buffer solution?

Answer 37

• Ka of acid
• Temperature of solution
• Ratio/concentrations of weak acid and conjugate base

Question 38

How do you calculate the percentage dissociation of an acid?

Answer 38

[H+]
—— x 100
[HA]

Question 39

If the volume of a buffer solution is greater than expected how does the pH change?

Answer 39

Stays the same

The ratio of [HA] : [A] is the same