3.1.5 - pH

Question 1

define electrolyte

Answer 1

chemical compound that conducts electricity by changing into ions when melted or dissolved into a solution

Question 2

is water a weak or strong electrolyte?

Answer 2

weak

Question 3

how can the self-ionisation of water be represented?

Answer 3

• Can ionise on its own – 2H2O can produce 1 H3O+ and a OH-
• ## represented by Kw = [H+] [OH-]

Question 4

what can Kw be used to calculate?

Answer 4

• the concentration of hydrogen ions from the concentration of hydroxide ions in a solution
• the concentration of hyroxide ions from the concentration of hydrogen ions in a solution

Question 5

Practise Question:
- Calculate the concentration of OH- for a 1.0 x 10^-4 M solution of HCl.

Answer 5

In order to solve for [OH-] we need to:
1. Solve for [H+]
2. Sub the [H+] into Kw = [H+][OH-]
3. Add the units

Question 6

Practise question:
Calculate the concentration of OH- for a 3.7 x 10-6 M solution of H2SO4

Answer 6

In order to solve for [OH-] we need to:
1. solve for the [H+]
2. Sub the [H+] into Kw = [H+][OH-]
3. Add the units

Question 7

Practise question:
- calculate the concentration of H+ for a 2.8 x 10-2 M solution of NaOH.

Answer 7

In order to solve for [H+] we need to:
1. solve for the [OH-]
2. sub in the [H+] into Kw=[H+][OH-]
3. add the units

Question 8

Practise question:
- calculate the concentration of [H+] for a 5.2 x 10-5 M solution of Ba(OH)2.

Answer 8

In order to solve for [H+] we need to:
1. solve for the [OH-]
2. Sub the [H+] into Kw = [H+][OH-]
3. add the units

Question 9

How does the pH scale work?

Answer 9

• a pH decrease of 1, means a ten-fold increase in the concentration of H+ ions

Question 10

Practise question pH scale:
- ‘Bottle A’ of hydrochloric acid contains 20 g dm-3 of H+ ions and is pH 1
- ‘Bottle B’ conatins 200g dm-3 H+ ions

Q1. What is the pH of Bottle B?
Q2. Bottle C is pH 3, what is its H+ concentration?

Answer 10

A1. pH 0 (ten x more H+)
A2. 0.2g dm-3 (100 x lower H+)

Question 11

How do you calculate pH using calculator?

Answer 11

practise question: (see photo for answer)
- 1 x 10^-3 M

Question 12

how do you calculate H+/H3O+ from the pH?

Answer 12

see photo for formula
NOTE: must convert to scientific notation

Question 13

practise question:
find the [H+], given the pH of the following?
1. pH = 2

Answer 13

see photo for answer

Question 14

what does a measure of alkalinity mean?

Answer 14

alkaline - base that can dissolve in water

Question 15

pH calculation - pH to [H+]

Answer 15

[H+] = 10^-pH

Question 16

pH calculation - [H+] to [pH]

Answer 16

pH = -log10[H+]

Question 17

pH calculation between [H+] and [OH-]

Answer 17

[H+] [OH-] = 1 x 10^-14

Question 18

pH calculation - pOH to [OH-]

Answer 18

[OH-] = 10^-pOH

Question 19

pH calculation - [OH-] to pOH

Answer 19

pOH = -log10[OH-]

Question 20

pH calculation between pH and pOH

Answer 20

pH + pOH = 14

Question 21

answer question

Answer 21

refer to photo