Volumetric + titrations

Question 1

Volumetric analysis

Answer 1

Uses standard solution in a **quantative **reaction to determine concentratrion of other reactant

This is called a titration

Question 2

Standard solution

Answer 2

Solution of accurately known concentration

Question 3

Primary standard

And its 4 characteristics

Answer 3

Substance from which a standard solution can be prepared directly.
1. available in high state of purity(99.9%)
2. stable when solid and solution so can be stored indefinitely without change to composition
3. soluble in water
4. have reasonably high formula mass (to reduce percentage errors when weighing it out.)

To ensure iyts uncontaminated

Question 4

Why are some substancers like

NaOH unable to be used as a primary standard?

Answer 4

It absorbns both water and carbon dioxide from the air, affecting its concentarion.
Has low gfm.

Question 5

Preparation of a standard solution

Answer 5

1. Primary standard accurately weighed
2. Dissolved in small volume of solvent in a beaker
3. Transfer solution and rinsings to volumetric flask
4. Making up to graduation mark with solvent
5. Stoppering and inverting volumetric flask several times.

Question 6

Titrations

Answer 6

A permanent colour change is used to determine the end point of a reaction, using a white tile. Repeated until concordant results obtained.

Question 7

Three main types of titrations

Answer 7

1. Acid/Base
2. Complexometric
3. Redox

Question 8

A control

Answer 8

Validates a technique and may include carrying out a determination on a known solution.

Question 9

WHy are

back titrations carried out

Answer 9

Substances that are insoluble in water cant be determined by a direct titration.

Question 10

Back titration

Answer 10

• Reacting a known amount of insoluble substance with an excess of a reactant standard solution.
• Because an excess is used, the reactant remaining can be determined by titrating with a standard solution.
• Difference between initial and excess moles of reactant solution allows amount of insoluble substance to be calculated.

Question 11

Complexometric Titrations

Answer 11

Titrations based on the formation of complex between a metal ion and a chelating agent such as EDTA

Question 12

Chelating meaning

Answer 12

A chelating agent is a substance which can form several bonds to a single metal ion.

Question 13

EDTA

Answer 13

• Important complexometric reagent
• Determines concentration of metal ions in solution.
• Forms stable complexes by donating electrons to central metal ion.
• End point of titrations with it involes involves colour change by an indictator.
• Reacts 1:1 with metal.

Question 14

What indicators are used in in titartions involving EDTA

Answer 14

Murexide and Erichome black. They have diff colours when metal ion is attatched to EDTA and unattatched, because they bind less strongly than EDTA to metal.