3. volumetric analysis

Question 1

how does volumetric analysis work?

Answer 1

it uses a standard solution to determine the concentration of another solution

Question 2

what are complexometric titrations based upon?

Answer 2

the formation of a complex between a metal ion and complexing agent

Question 3

what is the most common complexing agent used in complexometric titrations?

Answer 3

EDTA

Question 4

what is titrating with EDTA useful for?

Answer 4

determining the concentration of metal ions in a solution

Question 5

EDTA reactions with metal ions in a _ ratio

Answer 5

1:1

Question 6

name the indicator commonly used in redox titrations and the colour it turns at the end of the reaction

Answer 6

murexide, purple

Question 7

what is a standard solution?

Answer 7

a solution with an accurately known concentration

Question 8

how can standard solutions be prepared (2 ways)?

Answer 8

accurate dilution of existing solution or from a primary standard

Question 9

describe the process of preparation from a primary standard

Answer 9

1) accurately weigh out required mass of primary standard
2) dissolve in small volume of solvent in beaker
3) transfer solution and rinsings to volumetric flask
4) make up to mark with solvent
5) stopper and invert to mix

Question 10

describe the process of preparation by dilution

Answer 10

1) pipette required volume of standard solution into volumetric flask
2) make up to graduation mark, stopper and invert

Question 11

describe the necessary characteristics of a primary standard

Answer 11

• high purity
• stable as a solid in air and when in solution
• soluble in water
• reasonably high formula mass

Question 12

common primary standards include:

Answer 12

sodium carbonate, EDTA, silver nitrate and oxalic acid

Question 13

why isn’t sodium hydroxide a primary standard?

Answer 13

is absorbs moisture from the air and is unstable as both a solid and in solution

Question 14

what can be done if sodium hydroxide (for example) must be used in titration?

Answer 14

a solution of approximate concentration can be prepared and standardised

Question 15

what does standardising involve?

Answer 15

carrying out another titration first to determine the accurate concentration of the NaOH solution

Question 16

what is stoichiometry?

Answer 16

the study of mole relationships in chemical reactions

Question 17

how is percentage yield reduced?

Answer 17

• mechanical losses
• purification of product
• side reactions
• equilibrium position

Question 18

what are the three main sources of error in an experiment?

Answer 18

• human error. e.g. reading a scale incorrectly
• methodology e.g. side reactions
• uncertainties in equipment e.g. pipettes/burettes

Question 19

which class of equipment has a greater accuracy/smaller uncertainty?

Answer 19

class A

Question 20

what is the general rule for sig figs?

Answer 20

final result should have the same no. of sig figs as the measurement with the lowest no. of sig figs