5.1.3 - Acids, Bases And Buffers

Question 1

What are acids?

Answer 1

Proton donors

Question 2

What are bases?

Answer 2

Proton acceptors

Question 3

What do H+ ions form in water?

Answer 3

Hydronium ions H3O+

Question 4

What is the conjugate base?

Answer 4

The species that has lost a proton.

Question 5

What is a conjugate acid?

Answer 5

Species that has gained a proton.

Question 6

What are monoprotic acids?

Answer 6

Have only 1 proton they can release into solution.

Question 7

Acid + alkali

Answer 7

Metal salt + Water

Question 8

Acid + base

Answer 8

Metal salt + Water

Question 9

Acid + carbonate

Answer 9

Metal salt + Water + Carbon dioxide

Question 10

Acid + Metal

Answer 10

Metal salt + hydrogen

Question 11

What is Ka used to calculate?

Answer 11

The concentration of a weak acid.

Question 12

The higher the Ka?

Answer 12

The stronger the acid.

Question 13

The lower the Ka?

Answer 13

The weaker the acid.

Question 14

Ka =

Answer 14

[H+]^2 / [HA]

Question 15

pKa =

Answer 15

-log Ka

Question 16

ph =

Answer 16

-log[H+]

Question 17

[H+] =

Answer 17

10^-pH

Question 18

Kw =

Answer 18

[H+] x [OH-]

Question 19

When a metal has a valency of 1 what does [OH-] =

Answer 19

[MOH]

Question 20

If you are using a metal with a valency of 2, e.g. calcium what do you need to do to the value of [MOH] to find [OH-]?

Answer 20

Times by 2

Question 21

What is a buffer?

Answer 21

A solution that as a system minimises pH changes on addition of small amounts of acid or base.

Question 22

What 2 ways are buffers made?

Answer 22

• weak acid with the salt of its conjugate base.

- mix of an excess weak acid with a strong alkali.

Question 23

In the buffer CH3COOH H+ + CH3COO- what happens when you increase H+ ?

Answer 23

The extra H+ ions combine with the CH3COO ions, causing the equilibrium to shift to the left reducing the concentration of H+.

Question 24

In the buffer CH3COOH H+ + CH3COO- what happens when you increase OH- ?

Answer 24

OH- ions react with the H+ ions forming water, removing H+ ions. This causes CH3COOH to dissociate to form H+ ions # shifting the equilibrium to the right.

Question 25

What does the pH in the blood need to be?

Answer 25

7.35 and 7.45

Question 26

What is the pH in the blood controlled by?

Answer 26

Carbonic acid-hydrogen carbonate buffer system.
H2CO3 H+ + HCO3-
H2CO3 H2O + CO

Question 27

How are levels of H2CO3 controlled in the body?

Answer 27

By respiration - by breathing out CO2 the level of H2CO3 is reduced as it moves this equilibrium to the right.

Question 28

How are the levels HCO3- controlled?

Answer 28

The kidneys - they excrete extra in the urine.

Question 29

How do you select an indicator for a titration?

Answer 29

The indicator just change colour over the narrow range that lies entirely on the vertical part of the pH curve.

Question 30

What is the colour change from acid to alkali for methyl orange?

Answer 30

Red to yellow

Question 31

What is the colour change from acid to alkali for phenolphthalein?

Answer 31

Colourless to pink.

Question 32

What can indicators be though of as?

Answer 32

Weak acids as they have conjugate pairs.