8 - Acids & Alkalis

Question 1

What is an Alkali?

Answer 1

• A substance producing more hydroxide ions than hydrogen ions when dissolved in water.
• pH more than 7

Question 2

What is an Acid?

Answer 2

• A substance producing more hydrogen ions than hydroxide ions when dissolved in water.
• pH less than 7

Question 3

What is the pH of a neutral solution?

Answer 3

7

Question 4

What colour is litmus paper in alkaline solutions?

Answer 4

Blue

Question 5

What colour is litmus paper in acidic solutions?

Answer 5

Red

Question 6

What colour is methyl orange in alkaline solutions?

Answer 6

Yellow

Question 7

What colour is methyl orange in acidic solutions?

Answer 7

Red

Question 8

What colour is phenolphthalein in alkaline solutions?

Answer 8

Pink

Question 9

What colour is phenolphthalein in acidic solutions?

Answer 9

Colourless

Question 10

What is an Aqueous solution?

Answer 10

A mixture that is formed when a substance is dissolved in water

Question 11

What is the pH scale?

Answer 11

• Ranges from 0 - 14
• Measures the acidity or alkalinity of a solution

Question 12

What is an Indicator?

Answer 12

A substance that can change colour depending on the pH of a solution

Question 13

What do Alkalis produce an excess of in water?

Answer 13

Hydroxide ions (OH-)

Question 14

What do Acids produce an excess of in water?

Answer 14

Hydrogen ions (H+)

Question 15

What can be used to measure the pH of a solution? (give some examples)

Answer 15

• Indicators (e.g. Universal indicator etc)
• pH probe

Question 16

Suggest a problem with using universal indicator to test the pH of a solution

Answer 16

The colour of solution is matched to a chart. This is subjective as people may disagree with the colour matches

Therefore, it doesn’t provide an exact pH value.

Question 17

What happens to the pH if the
concentration of hydrogen ions in an alkaline solution is high?

What happens to the pH?

Answer 17

The pH will be lower

Question 18

What happens to the pH if the
concentration of hydroxide ions in an alkaline solution is high?

What happens to the pH?

Answer 18

The pH will be higher

Question 19

What happens if the hydrogen ion concentration in a solution increases by a factor of 10?

What happens to the pH?

Answer 19

The pH of the solution
DECREASES by 1

Question 20

What happens if the hydrogen ion concentration in a solution decreases by a factor of 10?

Answer 20

The pH of the solution
INCREASES by 1

Question 21

What is an Ion?

Answer 21

An atom (or a group of atoms) with an electrical charge due to the gain or loss of electrons

Question 22

What type of ions are produced when they lose electrons?

Answer 22

Positive ions

E.g. Cl+

Question 23

What type of ions are produced when they gain electrons?

Answer 23

Negative ions

E.g. Cl-

Question 24

What are Polyatomic ions?

Answer 24

A group of atoms that have a positive or negative charge due to the loss or gain of electrons

Question 25

When are *polyatomic ions* formed?

Answer 25

When small groups of atoms lose or gain electrons

Question 26

What are *polyatomic ions* held together by?

Answer 26

Covalent bonds

Question 27

Describe the balance of hydroxide & hydrogen ions in a *neutral* solution:

Answer 27

Low & equal concentrations of hydroxide & hydrogen ions

Question 28

What is the formula for *Hydrochloric* acid?

Answer 28

Question 29

What is the formula for *sulfuric* acid?

Answer 29

Question 30

What is the formula for *nitric* acid?

Answer 30

Question 31

What is the formula for *sodium* hydroxide?

Answer 31

Question 32

What is the formula for *potassium* hydroxide?

Answer 32

Question 33

What is the formula for *calcium* hydroxide?

Answer 33

Question 34

What is a **base**?

Answer 34

Any substance that reacts with an acid to form a salt and water only

Question 35

What does a *concentrated solution* mean?

Answer 35

Containing a large amount of solute dissolved in a small volume of solvent

Question 36

What does a *dilute solution* mean?

Answer 36

Contains a small amount of solute per unit per volume

Question 37

What is the formula for *concentration*?

Answer 37

Question 38

What are the units for *concentration*?

Answer 38

Question 39

How much more acidic is hydrochloric acid (pH of 0) than vinegar (pH of 4)?

Answer 39

10 x 10 x 10 x 10 = 10, 000

Question 40

What are **Strong acids**?

Answer 40

* An acidic solute that dissociates completely into ions when it dissolves in water * Produce high concentrations of hydrogen ions

Question 41

What are **Weak acids**?

Answer 41

An acidic solute that DOES NOT dissociate completely into ions when it dissolves in water

Question 42

Give the general equation for neutralisation of a metal oxide:

Answer 42

Metal oxide + acid ---> salt + water

Question 43

What is a **neutralisation** reaction?

Answer 43

A reaction between an acid and a base

Question 44

Explain an acid-alkali neutralisation:

Answer 44

A reaction in which hydrogen ions (H+) from the acid react with hydroxide ions (OH–) from the alkali to form water And so the pH increases (as the hydrogen ions are removed)