Acids And Bases

Question 1

Answer 1

Acid: Increase in concentration of H+ ions, equilibrium moves to the left.
Alkali: OH reacts with H+ ions, equilibrium moves to the right (to replace the H+ ions)
Concentration of H+ remains (almost) constant

Question 2

Suggest sources of error in using the burette to carry out a titration.

Answer 2

• not removing funnel - droplet from funnel could enter beretta
• air bubble in jet

Question 3

During the titration, the inside of the conical flask is rinsed with distilled water.
Suggest why rinsing improves the accuracy of the titre.

Answer 3

Ensures all reagents are able to react / mix / come into contact

Question 4

Explain why adding this extra water does not change the volume of EDTA solution that is required in the titration.

Answer 4

The added water does not affect the mols / amount of reagents / reactants

Question 5

Suggest a suitable piece of apparatus that could be used to measure out the sodium hydroxide solution in a titration.
Explain why this apparatus is more suitable than a pipette for this purpose.

Answer 5

Burette
Because it can deliver variable volumes

Question 6

Use information from the curve in the figure above to explain why the end point of this reaction would be difficult to judge accurately using an indicator.

Answer 6

The change in pH is gradual / not rapid at the end point
An indicator would change colour over a range of volumes of sodium hydroxide

Question 7

Answer 7

Question 8

Two solutions, one with a pH of 4.00 and the other with a pH of 9.00, were left open to the air.
The pH of the pH 9.00 solution changed more than that of the other solution.
Suggest what substance might be present in the air to cause the pH to change.
Explain how and why the pH of the pH 9.00 solution changes

Answer 8

Co2
Ph decreases
Acidic gas/reacts with OH-

Question 9

Suggest why chloroethanoic acid is a stronger acid than ethanoic acid.

Answer 9

Cl is more electronegative so withdraws electrons
Weakens O-H bonds

Question 10

Answer 10

pH = 0.49

Question 11

State why calibrating a pH meter just before it is used improves the accuracy of the pH measurement.

Answer 11

Over time / after storage meter does not give accurate readings

Question 12

Describe how you would obtain the pH curve for the titration.

Answer 12

Question 13

The dissociation of methanoic acid in aqueous solution is endothermic.
Deduce whether the pH of a solution of methanoic acid will increase, decrease or stay the same if the solution is heated. Explain your answer.

Answer 13

Decrease
Equilib shifts to RHS
To reduce temperature/oppose increase in temp

Question 14

Answer 14

Question 15

Which is an acid/base

Answer 15

BB

Question 16

Identify which is base/acid

Answer 16

1. AA
2. BA

Question 17

Answer 17

Question 18

Answer 18

Question 19

Answer 19

pH
[HA]=[A-]
pH = pKa

Question 20

Why is ethylamine a weak alkaline

Answer 20

Slightly dissociate
Reaction/equilib lies to left or low [OH-]

Question 21

State which is the stronger base, ammonia or ethylamine. Explain your answer.

Answer 21

Ethylamine
Alkyl gorup is electron releasing
Increases electron density of N(H2) - increased availability of lp

Question 22

Give the formula of an organic compound that forms an alkaline buffer solution when added to a solution of ethylamine.

Answer 22

Question 23

Answer 23

pH = 1.77

Question 24

Answer 24

indicator/ conc HCL
Colour for an alkali/white fumes

Question 25

Suggest a value for the ph of a 0.100 mol dm 3 solution of iron(Il) sulfate.

Answer 25

4 - 6.9

Question 26

Describe briefly how you would ensure that a reading from a pH meter is accurate.

Answer 26

Calibrate meter with solution of known pH/buffer
Adjust meter/plot calibration curve

Question 27

Answer 27

Question 28

Answer 28

B

Question 29

Answer 29

B

Question 30

Answer 30

D

Question 31

Answer 31

C

Question 32

Answer 32

A

Question 33

Answer 33

C

Question 34

Answer 34

Question 35

A solution of potassium hydroxide has a pH of 11.90 at 25°C. Calculate the concentration of potassium hydroxide in the solution

Answer 35

pH = 2.90

Question 36

Answer 36

Question 37

Calculate the volume of water which must be added to 30.0 cm3 of 0.250 mol dm-3 hydrochloric acid in order to reduce its concentration to 0.150 mol dm-3.

Answer 37

Question 38

Answer 38

BUFFER SOLUTION: a solution with resists a change in pH when small amounts of acid or base added

Question 39

A mixture of the acid HA and the sodium salt of this acid, Na, can be used to prepare a buffer solution.
State and explain the effect on the pH of this buffer solution when a small amount of hydrochloric acid is added.

Answer 39

pH stays same
H+ removed by A- forming HA/acid reacts with salt

Question 40

(a) By reference to the forces between molecules, explain why ammonia is very soluble in water.

Answer 40

Hydrogen bonding
Between H2O and NH3

Question 41

Explain why the pH of a solution containing 1.0 mol dm 3 of ammonia is less than 14 at 298 K.

Answer 41

Ammonia is a weak base
Equilib to left or incomplete reaction

Question 42

Identify a reagent which could be added to a solution of ammonia in order to form a buffer solution.

Answer 42

NH4Cl

Question 43

Define Kw

Answer 43

Kw = [OH-][H+]

Question 44

Answer 44

a) pH = 2.78

Question 45

A sample of the 0.220 mol dm-3solution of ethanoic acid was titrated against sodium hydroxide solution.

Answer 45