Acids, Bases & Buffers

Question 1

What is the Arrhenius concept?

Answer 1

• Acids are substances that when dissolved in water, increase the H+ concentration
• Bases are substances that when dissolved in water, increase the hydroxide ion concentration

Question 2

What is the Brønsted Lowry theory?

Answer 2

• An acid is a substance that can donate protons to another substances
• A base is a substance that can accept H+ from another substance

Question 3

What is the Lewis theory?

Answer 3

• An acid is a substance that can accept electrons from another substance
• A base is a substance that can donate electrons to another substance

Question 4

What is a monoprotic acid?

Answer 4

An acid that can transfer 1 H+ per molecule during an acid-base reaction

Question 5

What is a diprotic acid?

Answer 5

An acid that can transfer 2 H+ per molecules during an acid-base reaction

Question 6

What is a tripotic acid?

Answer 6

An acid that can transfer 3 H+ per molecule during an acid-base reaction

Question 7

What is the auto-ionisation of water?

Answer 7

The ability of water to act as either a proton acceptor (base) or a proton donor (acid)

Question 8

In the presence of a base, how does water act?

Answer 8

As an acid

Question 9

In the presence of acid, how does water act?

Answer 9

As a base

Question 10

What does Kw mean?

Answer 10

The ionisation constant of water

Question 11

What is the ionisation constant equation?

Answer 11

Kw = [H3O+] [OH-] = 1.0 x 10 -14

Question 12

How do you calculate H+ from OH-?

Answer 12

1 x 10 -14
/
Concentration of OH-

PH = -log [ans] =

Question 13

What is the concentration of H+ in a solution that contains 0.01M OH-?

Answer 13

[H+] = 1 X 10 -14 / .01M = 1 x 10 -12 M

-log10 [1 x 10 -12] = 12

Question 14

What are conjugate base pairs?

Answer 14

Consists of 2 substances that differ by the presence of a proton

Question 15

If the acid is strong, is the conjugate base strong or weak?

Answer 15

Weak

Question 16

If the base is strong, is the conjugate acid strong or weak?

Answer 16

Weak

Question 17

How do you calculate the pH of a strong acid?

Answer 17

PH. -log10 [H+]

Question 18

How do you calculate the pH of a strong base?

Answer 18

pOH = -log10 [OH-]

14 - pOH

Question 19

Which type of acid dissociates fully?

Answer 19

Strong acids

Question 20

What does Ka mean?

Answer 20

Acid-dissociation constant

The larger the Ka value, the stronger the acid

Question 21

What is the equation to work out Ka?

Answer 21

[Hydrogen ion] [Conjugate base]
/
[Weak acid]

Question 22

What does Kb mean?

Answer 22

Base-dissociation constant

Question 23

How do you calculate the pH of a strong acid?

Answer 23

-log10 (concentration)

Question 24

How do you calculate the pH of a weak acid?

Answer 24

1. Ka = [H+]² 
            /
         [HA]
2. REARRANGE 
Ha (Ka) = H+
3. Square root
4. -Log10 (ans)

Question 25

What is a buffer?

Answer 25

Weak acid-base conjugate pairs

Question 26

What 2 factors determine pH?

Answer 26

• Value of Ka

- Ratio of conjugate acid base pair concentrations

Question 27

Why do buffers resist changes in pH?

Answer 27

Because it contains:

• an acidic species to neutralise OH-
• a basic species to neutralise H+

Question 28

What is the Henderson-Hasselbalch equation?

Answer 28

pH = pKa + log [Base]
/
[Acid]

Question 29

How is the acid-dissociation constant (Ka) calculated?

Answer 29

[Hydrogen ion] [Conjugate base]
/
[Weak acid]

Question 30

How is the base-dissociation constant (Ka) calculated?

Answer 30

[Hydroxide ion] [Conjugate acid]
/
[Weak base]

Question 31

How do you determine pKa?

Answer 31

-log Ka