Chemical Changes PAPER 1

Question 1

What does pH measure?

Answer 1

How acidic (H⁺ concentration) or alkaline (OH⁻ concentration) a solution is

Question 2

pH ranges from _ to _

Answer 2

0 to 14

Question 3

Give 2 ways pH can be measured

Answer 3

1. Using a chemical indicator
2. Using a pH probe

Question 4

Suggest why scientists use a pH probe rather than a chemical indicator

(2 marks)

Answer 4

• A pH probe is not subjective (not bias)
• This makes the readings more reliable/precise/accurate
  OR
• A chemical indicator requires human judgment (of colour)
• So the readings aren’t very reliable/precise/accurate

Question 5

State an acid

(H⁺ donor)

Answer 5

These are most common:
* Hydrochloric acid (HCl)
* Sulfuric acid (H₂SO₄)
* Nitric acid (HNO₃)

Question 6

State a base

(OH⁻ donor)

Answer 6

These are most common:
* Sodium hydroxide (NaOH)
* Calcium carbonate (CaCO₃)
* Ammonia (NH₃)

Question 7

What factors determine the pH of an acid?

Answer 7

• The strength (how well an acid ionises)
• The concentration (how much of an acid per unit volume)

these both change the H⁺ concentration

Question 8

Acid + Metal → ____ + ____

Answer 8

salt, hydrogen

Question 9

Acid + Metal Oxide →____ + ____

Answer 9

salt, water

Question 10

Acid + Metal Hydroxide →____ + ____

Answer 10

salt, water

Question 11

Acid + Metal Carbonate →____ + ____ + ____

Answer 11

salt, water, carbon dioxide

Question 12

Define the term salt

Answer 12

An ionic compound usually formed through a neutralisation reaction

Question 13

Define the term electrolyte

Answer 13

An ionic compound (salt) molten or dissolved that can conduct electricity

Question 14

Phenolphthalein is an indicator that turns ____ in acidic solutions and ____ in alkaline solutions

Answer 14

colourless, pink

Question 15

Method: making salts?

Answer 15

1) measure 20cm³ of SO⁴ using measuring cylinder into beaker
2) add excess CuO into beaker and stir thoroughly (heat mixture?)
3) once fully reacted filter solution using filter paper and funnel. Transfer the filtrate to an evaporating basin
4) heat evaporating basin till solution evaporated using busen burner blue flame leaving crystals
5) leave crystals to form for a few days

Question 16

Phe _ _ _ _ _ _ _ _ lein indicator?

Answer 16

Phenolphthalein

Question 17

What is ORRL?

Answer 17

Oxidation
Right (electrons lost in half equation)
Reduction
Left (electrons gained in half equation

Question 18

As pH goes down by 1, what does H+ concentration go by?

Answer 18

X10

Question 19

As pH goes down by 2, what does H+ concentration go by?

Answer 19

×100 (10²)

Question 20

As pH goes up by 1, what does H+ concentration go by?

Answer 20

÷10

Question 21

As pH goes up by 2, what does H+ concentration go by?

Answer 21

÷100 (10²)