Proton transfer reactions - the pH scale

Question 1

What is the pH scale?

Answer 1

A measure of the concentration of H+ ions in solution relative to the concentration of OH- ions in a solution

Question 2

What does the pH scale show?

Answer 2

How acidic or alkaline a solution is

Question 3

What do the values on the pH scale mean?

Answer 3

Range from 0-14
Acidic < 7
Basic > 7
Neutral = 7
The lower the pH the more acidic the solution is.
The higher the pH the more alkaline the solution is.

Question 4

Formula to find pH

Answer 4

pH = – log10[H+]
Where [H+] = the concentration of H+ in moldm^-3
(in data booklet)

Question 5

What is the relationship between pH and H+?

Answer 5

Inverse relationship - as PH decreases, concentration of H+ increases.

Question 6

What type of scale is the pH scale?

Answer 6

A logarithmic scale with base 10 - each value is 10x the value below it (e.g. pH 5 is 10x more acidic than pH 6)

Question 7

How many decimal places are pH values usually given to?

Answer 7

2 decimal places

Question 8

H+ to OH- ion ratio in acids and bases

Answer 8

Acidic solutions always have more H+ than OH- ions.
Basic solutions always have more OH- than H+ ions.

Question 9

Amount of OH- and H+ ions in water at 298K?

Answer 9

Equal amounts, with concentrations of 10^-7 moldm^-3.

Question 10

Which formulas should be used to calculate the pH of water?

Answer 10

pH = – log10[H+ (aq)]

[H+ (aq)] = concentration of H+/H3O+ ions

pH = -log (10^-7) = 7

Question 11

What is the most accurate way to measure pH?

Answer 11

Using a pH meter - this is connected to the pH electrode which shows the pH value of the solution

Question 12

How can pH be measured, other than using a pH meter?

Answer 12

Using universal indicator paper - dipped into a solution upon which the paper changes colour. Colours correspond to different pH values.