5 - Acids

Question 1

Define acid

Answer 1

pH lower than 7

Question 2

Define alkali/base

Answer 2

• pH higher than 7

- alkalis are bases that can dissolve

Question 3

Define indicator

Answer 3

A substance that tells you whether something is an acid or alkali. Some indicators can give an idea of pH

Question 4

Define neutralisation

Answer 4

Acid + alkali = salt + water, mixing an acid and an alkali to form a neutral solution

Question 5

Define salt

Answer 5

• neutral ionic compound

- eg. potassium chloride, sodium chloride, lithium fluoride

Question 6

Define soluble

Answer 6

• can dissolve

Question 7

Define insoluble:

Answer 7

• cannot dissolve

Question 8

Colour of acid in Universal Indicator:

Answer 8

• red

Question 9

Colour of acid in Litmus paper:

Answer 9

• red

Question 10

Colour of acid in Methyl orange:

Answer 10

• red

Question 11

Colour of acid in phenolphtalein:

Answer 11

• colourless

Question 12

Colour of alkali in Universal Indicator

Answer 12

• purple/blue

Question 13

Colour of alkali in Litmus paper:

Answer 13

• blue

Question 14

Colour of alkali in Methyl orange:

Answer 14

• yellow

Question 15

Colour of alkali in Phenolphthalein:

Answer 15

• pink

Question 16

Colour of neutral solution in Universal Indicator:

Answer 16

• green

Question 17

Colour of neutral solution in Litmus paper:

Answer 17

• no change

Question 18

Colour of neutral solution in Methyl orange:

Answer 18

• orange

Question 19

Colour of neutral solution in Phenolphthalein:

Answer 19

• colourless

Question 20

What is an acid in an aqueous solution a source of?

Answer 20

• a source of hydrogen ions

- hydrogen ions are positively charged

Question 21

What is an alkali in an aqueous solution a source of?

Answer 21

• hydroxide ions

- hydroxide ions are negatively charged

Question 22

How to calculate moles?

Answer 22

mass/relative molecular mass

Question 23

“Calculate the mass of KOH when HNO3+ KOH = KNO3+ H2O when HNO3is 3g”

Answer 23

HNO3: mass = 3g, Mr = 63, moles = 0.048KOH : Mr = 56, moles = 0.048, mass = mol by Mr = 0.048 by 56 = 2.67g

Question 24

What is neutralisation?

Answer 24

acid + base = salt + water

Question 25

How to calculate the concentration of an acid or alkali?

Answer 25

Titration

Question 26

What is the apparatus needed for titration?

Answer 26

- burette - conical flask - pipette - pipette filler - clamp and stand

Question 27

What is the titre (cm3) in titration?

Answer 27

The difference between the reading at the start and the final reading gives the volume of the acid (or alkali) added. 

Question 28

When do we know when neutralisation has taken place in a titration experiment?

Answer 28

- when the alkali in the conical flask which phenolphthalein has been added turns colourless

Question 29

metal + acid = ?

Answer 29

metal + acid = salt + hydrogen

Question 30

acid + base = ?

Answer 30

acid + base = salt + water

Question 31

acid + carbonate = ?

Answer 31

acid + carbonate = salt + water + carbon dioxide

Question 32

Are common sodium, potassium and ammonium compouds soluble or insoluble?

Answer 32

soluble

Question 33

Are all nitrates soluble or insoluble?

Answer 33

soluble

Question 34

Are common chlorides soluble or insoluble? Which 2 are an exception?

Answer 34

- soluble | - silver and lead(II) are insoluble

Question 35

Are common sulfates soluble or insoluble? Which 3 are an exception?

Answer 35

- soluble | - barium, calcium and lead(II) are insoluble

Question 36

Are common carbonates soluble or insoluble? Which 3 are an exception?

Answer 36

- insoluble | - sodium, potassium and ammonium are soluble

Question 37

Are common hydroxides soluble or insoluble? Which 3 are exceptions?

Answer 37

- insoluble | - sodium, potassium and calcium are soluble

Question 38

Method of knowing if a salt is soluble:

Answer 38

- measure out acid If base is soluble: - add base (excess) If base is insoluble: - add base - when fizzing stops and the solid has disappeared, add more base (keep repeating). There should now be excess, unreacted powder in the flask - filter the mixture For both methods, then: - pour the solution into an evaporating dish and heat to concentrate the solution by evaporating some of the water - leave the solution to cool and crystallize - filter off the crystals and pat dry between clean dry filter papers

Question 39

Method of knowing if a salt is insoluble:

Answer 39

- measure out acid - add base (excess) until no more precipitate is produced - filter the mixture - pat dry between clean dry filter papers