U4-1 - Volumetric Analysis

Question 1

Which 4 terms must be included in the procedure for preparing a standard solution?

Answer 1

Deionised/distilled water

Transfer with rinsings

Volumetric flask

Fill up to the mark

Question 2

Standard solution

Answer 2

A solution of accurately known concentration.

Question 3

Name this piece of equipment

Answer 3

Volumetric flask

Question 4

Name this piece of equipment

Answer 4

Pipette

Question 5

Name this piece of equipment

Answer 5

Burette

Question 6

Accurately approximately

Answer 6

Exact value should be known (e.g. accurate balance reading), and needs to be close to target value.

Question 7

Primary standard

Answer 7

A substance that can be used to standardise the concentration of a solution.

Question 8

Characteristics of primary standards (state 2)

Answer 8

Any 2 of:

high state of purity

stable in air and in solution

soluble

reasonably high GFM.

Question 9

Why is NaOH not a primary standard?

Answer 9

Low GFM, hygroscopic (absorbs water)

Question 10

What must be done to a non-primary standard solution before it can be used in titration?

Answer 10

Must be standardised by titrating against a known accurate mass/concentration of a primary standard solution.

Question 11

Give an example of a primary standard.

Answer 11

Any one of:

sodium carbonate

oxalic acid

potassium hydrogen phthalate

silver nitrate

potassium iodate

potassium dichromate.

Question 12

What is an advantage of using potassium permanganate in titrations?

Answer 12

Reactions are self-indicating (endpoint is purple)

Question 13

What indicator can be used if iodine is produced during a reaction?

Answer 13

Starch (endpoint is blue/black)

Question 14

What type of ions can be determined using complexometric titration?

Answer 14

Metal ions

Question 15

Common reagent in complexometric titrations

Answer 15

EDTA

Question 16

Molar ratio of metal ions : EDTA

Answer 16

1 : 1

(EDTA is hexadentate, can only bind to 1 metal ion)

Question 17

A titration is carried out using a 50 cm³ burette, but the titre value is only 6.0 cm³.

What can be done to decrease the uncertainty in the titre value?

Answer 17

• Titrate a larger sample (titre value will increase)
• Use a less concentrated standard solution (prepare a lower conc. or dilute)
• Use a micro-burette (10 cm³ or less).

Question 18

A titration is carried out to determine the content of vitamin C in fruit juice.

What can be used as a control experiment?

Answer 18

Carry out a titration with a known mass/concentration of pure vitamin C.

(control experiment = use pure substance)

Question 19

Give a reason for using back titration instead of regular titration.

Answer 19

One of:

analyte is insoluble or partially soluble in water/very volatile