Acids and Bases

Question 1

When is an acid not an acid?

Answer 1

• If there are no H⁺ ions present - this will happen if the compound containing hydrogen cannot dissociate.

Question 2

What does polar mean and what are examples of things which are polar?

Answer 2

• Oppositely charged areas in a molecule, water is polar.

Question 3

What are the colours of methyl orange and when is it those colours?

Answer 3

Methyl orange is red in acidic solutions and goes through orange to yellow in alkaline solutions.

Question 4

What are the colours of litmus paper and when is it those colours?

Answer 4

Litmus paper is red in acidic solutions, purple in neutral solutions and blue in alkaline solutions.

Question 5

What are the colours of phenolphthalein and when is it those colours?

Answer 5

Phenolphthalein is colourless in acidic solutions and bright pink in alkaline solutions.

Question 6

Acid + Alkali/Base goes to…

Answer 6

Salt + Water

Question 7

What do metal hydroxides and oxides react with and produce?

Answer 7

React with acids to produce a salt and water.

Question 8

Acid + Metal goes to…

Answer 8

Salt + Hydrogen

Question 9

What do metals above hydrogen in the Reactivity Series react with to produce?

Answer 9

React with dilute acids to produce salts and hydrogen gas.

Question 10

Acid and Carbonate goes to…

Answer 10

Salt + Carbon dioxide + Water

Question 11

What salt does hydrochloric acids produce?

Answer 11

Chloride

Question 12

What salt does sulphuric acid produce?

Answer 12

Sulphate

Question 13

What salt does nitric acid produce?

Answer 13

Nitrate

Question 14

What salt does phosphoric acid produce?

Answer 14

Phosphate

Question 15

How does one name a salt?

Answer 15

• First part - metal present.

* Second part - parent acid.

Question 16

What is the definition of an acid?

Answer 16

• Acids are a source of hydrogen ions.

* Acids donate hydrogen ions.

Question 17

What nitrates are soluble?

Answer 17

All nitrates are soluble

Question 18

What chlorides are soluble?

Answer 18

All chlorides are soluble except silver chloride.

Question 19

What sulphates are soluble?

Answer 19

All sulphates are soluble except barium sulphate and calcium sulphate.

Question 20

What carbonates are soluble?

Answer 20

Most carbonates are insoluble, except for sodium, potassium and ammonium carbonates.

Question 21

What hydroxides and oxides are soluble?

Answer 21

All hydroxides and oxides are insoluble expect potassium, sodium and ammonium.

Question 22

Which bases are insoluble?

Answer 22

Most metal oxides, metal carbonates and metal hydroxides are insoluble.

Question 23

What is the method to make soluble salts from acids?

Answer 23

• Add excess of an insoluble base to an acid and mix them together.
• Filter off the unused solid.
• Heat the solution to evaporate the water.
• Leave the solution to form of the salt crystals.
• Pour off any uncrystallised solution.
• Blot crystals dry with paper tissue.

Question 24

Why do crystals form when magnesium sulphate is cool?

Answer 24

Solubility decreases with temperature, causing crystals when it’s cool and the solubility changes.

Question 25

Why do we not heat magnesium sulphate until it’s dry?

Answer 25

We want to make hydrates magnesium sulphate, but if it’s heated until all the water is gone it would be anhydrous magnesium sulphate.

Question 26

What is the equation for the making of magnesium sulphate?

Answer 26

• sulphuric acid + magnesium -> magnesium sulphate + hydrogen
• H₂SO₄(aq) + Mg(s) -> MgSO₄(aq) + H₂(g)

Question 27

What is the method to make an insoluble salt (precipitation reaction)?

Answer 27

• Mix two soluble salt solutions together.
• Filter the mixture through filter paper.
• Wash the solid precipitate with water.
• Leave it in a warm place to dry.

Question 28

How do ionic equations work?

Ba₍aq₎²⁺ + SO₄₍aq₎²⁻ –>

Answer 28

BaSO₄₍s₎

Question 29

Explain, with reference to protons, why a reaction would be a neutralisation reaction.

Answer 29

An acid would provide protons and the products would be neutral therefore.

Question 30

Why would blue litmus turn red when added to a solution?

Answer 30

The solution would be acidic and there would be hydrogen ions present.

Question 31

Why would blue litmus stay blue when added to a solution?

Answer 31

The solution would not have any hydrogen ions present and would not be acidic.

Question 32

How do you make a sodium, potassium or ammonium salt? (6)

Answer 32

• Add a measured volume of alkaline solution to a flask using a pipette/measuring cylinder.
• Add a named indicator (e.g. methyl orange).
• Add acid from a burette until a correctly stated colour change (e.g. turns orange).
• Note the volume of acid added.
• Mix the same volume of acid and alkaline solution without the indicator.

Question 33

How do you convert from mol/dm³ into g/dm³?

concentration is 0.6 dm³

Answer 33

mass = moles x RFM = 0.6 x 58.5 = 35.1
concentration = mass ÷ volume = 35.1 ÷ 1 = 35.1g/dm³

Question 34

What is an alkali?

Answer 34

A source of hydroxide ions.