Acid and Base Titrations

Question 1

What is concentration?

Answer 1

It is defined as the amount of solute in a specified amount of solution

Question 2

How is the concentration of a solution expressed?

Answer 2

Mol/l, g/l, p.p.m, % w/v, % v/v, % w/w

Question 3

What is a primary standard solution?

Answer 3

It is a water soluble substance that is stable and available in pure form and can be used to make a solution of known concentration

Question 4

What is a standard solution?

Answer 4

Is a solution whose concentration is accurately known

Question 5

What does 1M solution contain

Answer 5

1 mole of a solute dissolve in 1 litre of a solution

Question 6

How is a standard solution prepared

Answer 6

Using a primary standard or by titrating with another solution

Question 7

What unit of concentration is particularly useful for very dilute solutions?

Answer 7

P.p.m , if concentration of fluoride in a water sample is 2 p.p.m that means that there are 2mg of fluoride ion in every litre of water

Question 8

What is required to make standard solutions?

Answer 8

Primary standard solution

Question 9

What care just be taken when making up a standard solution?

Answer 9

Volumetric flask - when filled to calibration mark at temp states, it contains specific known volume
Analytical balance - extremely accurate to measure solute
Wash bottle - no solution is lost

Question 10

How is a solution of known concentration made up?

Answer 10

• solute is weighed accurately and transferred to clean beaker + small volume of pure water added [wash bottle]
• the mixture is stirred with stirring rod in order to dissolve properly [washbottle]
• poured into volumetric flask using funnel [washbottle with beaker and funnel]
• flask filled to within about 1cm3 of calibration mark and water then added in drops until bottom of meniscus rests on the calibration mark
• flask sealed with stopper and inverted to make sure it is homogenous

Question 11

What water is added when making standard solution?

Answer 11

Deionised water or pure water

Question 12

Give an example of a standard solution?

Answer 12

Sodium carbonate

Question 13

How is the concentration of a solution found?

Answer 13

By titrating with standard solution

Question 14

Precautions to ensure accurate titration results

Answer 14

• burette is washed out with pure water and then solution it is to contain
• solution added using beaker and funnel
• tap of burette is opened briefly to fill the part of the burette below the tap [displaces air]
• burette filled up until the label of the liquid is above the 0cm3 mark
• tap is opened of burette to ensure its at definite mark
• burette readings taken at eye level : bottom of meniscus read
• pipettes washed with pure water and then solution to be contained [conical with only water]
• indicator either weak acids or weak bases adding too much with affect accuracy
• white tile
• conical flask swirled and any solution on sides can be washed down using water bottle
• rough titrations
• mean of titres is result

Question 15

Why is a burette more accurate than a graduated cylinder

Answer 15

Markings easier to read

Question 16

Why is the funnel removed after filling burette?

Answer 16

To control flow - may be drops

Question 17

Why can’t standard solutions be prepared directly?

Answer 17

They are not readily available in pure form

Question 18

What’s the objective of standardisation?

Answer 18

To find its concentration accurately

Question 19

What three things are needed to find unknown concentration?

Answer 19

• balanced equation - mole ratio
• concentration of one of the reagents
• volume of both reagents

Question 20

Standardisation of hydrochloric acid using a standard solution of sodium carbonate what indicator is used?

Answer 20

Methyl orange = yellow to peach/pink

Question 21

Hydrochloric acid/sodium hydroxide titration and then in making salt sodium chloride, indicator?

Answer 21

Methyl orange = yellow - peach/pink

Question 22

How do you obtain a sample of salt from hydrochloric acid and sodium carbonate titration?

Answer 22

• place 25cm3 of the sodium hydroxide solution in a beaker with no indicator
• using results from earlier, add enough hydrochloric acid to neutralise it
• gently hear solution until all water has been evaporated. Sample of sodium chloride will remain

Question 23

Applications of acid-base titrations

Answer 23

Find concentration of everyday materials, the concentration of the weak acid in vinegar ethanoic acid found by titrating against sodium hydroxide

Question 24

Determination of concentration of ethanoic acid in vinegar, indicator?

Answer 24

Phenolphthalein - pink=colourless

Question 25

Why is diluted vinegar used?

Answer 25

Acid in vinegar is too concentrated. If undiluted vinegar was used, small acid titration volume would result and increase percentage error

Question 26

Determination of the amount of water of crystallisation in hydrated sodium carbonate, indicator?

Answer 26

Methyl orange - yellow = pink/peach

Question 27

Give two essential properties of a primary standard for volumetric analysis?

Answer 27

Pure

Water soluble