Acids and alkalis

Question 1

which type of solutions do acids and alkalis form in water? (2)

Answer 1

acids =  acidic solutions
alkalis = alkaline solutions

Question 2

ph values of acids, alkalis and neutral solutions:

Answer 2

acids= under 7
neutral= 7
alkalis= over 7

Question 3

what are acids and alkalis sources of? (2)

Answer 3

acids= hydrogen ions, H+
alkalis= hydroxide ions, OH-

Question 4

what can acid-alkaline indicators show?

Answer 4

whether a solution is acidic, neutral (pH 7) or alkaline

Question 5

Litmus paper: acidic, neutral solutions and alkaline solutions

Answer 5

acidic: red
neutral: purple
alkaline: blue

Question 6

Methyl orange: acidic, neutral solutions and alkaline solutions

Answer 6

acidic: red
neutral: yellow
alkaline: yellow

Question 7

Phenolphthalein: acidic, neutral solutions and alkaline solutions

Answer 7

acidic: colourless
neutral: colourless
alkaline: pink

Question 8

Describe the limitations of methyl orange when determining if a solution is alkaline. (2)

Answer 8

• methyl orange is yellow in neutral solutions as well as in alkaline solutions,
• so you can only be sure that a solution is acidic if methyl orange turns it red.

Question 9

Describe the limitations of phenolphthalein when determining if a solution is acidic. (2)

Answer 9

• phenolphthalein is colourless in neutral solutions and in acidic solutions
• so you can only be sure that a solution is alkaline if phenolphthalein turns it pink.

Question 10

what does a pH scale measure?

Answer 10

the acidity or alkalinity of a solution.

Question 11

how can the pH of a solution be measured? (2)

Answer 11

• using a pH probe

- estimated using universal indicator and a colour chart.

Question 12

products of: acid + metal

Answer 12

acid + metal → salt + hydrogen

Question 13

products of: acid + metal oxide/ hydroxide

Answer 13

acid + metal oxide/ hydroxide → salt + water

Question 14

products of: acid + carbonate

Answer 14

acid + carbonate → salt + water + carbon dioxide

Question 15

Describe the laboratory test for carbon dioxide. (2)

Answer 15

Bubble the gas through limewater.

Carbon dioxide turns limewater milky or cloudy white.

Question 16

what is a base?

-which two oxide substances are bases?

Answer 16

any substance that reacts with an acid to form a salt and water only.
-metal oxides and hydroxides

Question 17

what are bases that is soluble in water called?

-what do they dissolve in water to form?

Answer 17

alkalis

-alkaline solutions

Question 18

Explain why all alkalis are bases, but not all bases are alkalis. (2)

Answer 18

• alkalis are soluble bases, but only some bases are soluble in water
• the insoluble ones cannot be classified as alkalis

Question 19

what is a neutralisation reaction?

Answer 19

a reaction between an acid and a base forming water.

Question 20

describe the reactants in a neutralisation reaction:

Answer 20

hydrogen ions from the acid react with hydroxide ions from the alkali

Question 21

what is pure water (in terms of acidity-alkalinity) ?

-how can a neutral solution be produced?

Answer 21

• pure water is neutral (its pH is 7).

- if the correct amounts of acid and alkali react together.

Question 22

how does a solution form?

Answer 22

when a solute dissolves in a solvent

Question 23

what is the concentration of a solution?

-what is the correlation between concentration and particles in a given volume?

Answer 23

• a measure of how ‘crowded’ the solute particles are.

- the more concentrated the solution, the more particles it contains in a given volume.

Question 24

what does a dilute and concentrated solution contain? (2)

Answer 24

• a dilute solution contains a relatively small amount of dissolved solute
• a concentrated solution contains a relatively large amount of dissolved solute

Question 25

how are hydrogen ions produced?

Answer 25

when the acid dissociates or breaks down to form ions.

Question 26

define ‘dissociation’

Answer 26

-the breaking up of a molecule into ions when dissolved in water.

Question 27

what is the difference between strong and weak acids? (2)

Answer 27

• Strong acids completely dissociate into ions in solution

- Weak acids only partially dissociate into ions in solution

Question 28

what is the pH of a solution?

Answer 28

a measure of its concentration of hydrogen ions

Question 29

what is the correlation between hydrogen and hydroxide ions and pH?

Answer 29

the higher the concentration of hydrogen ions in an acidic solution, the lower the pH
the higher the concentration of hydroxide ions in an alkaline solution, the higher the pH

Question 30

how do you calculate a change in the concentration of hydrogen ions?

Answer 30

-if the hydrogen ion concentration in a solution increases by a factor of 10, the pH of the solution decreases by 1.