CH106 Analytical Chemistry

Question 1

What is qualitative analysis?

Answer 1

This identifies which compounds are present in a sample.

Question 2

What is quantitative analysis?

Answer 2

This measures the proportions of each compnent in a sample.

Question 3

Define component

Answer 3

A chemical compound, ion or element. All components combined form the element being analysed.

Question 4

Define sample

Answer 4

A smaller representative part of the material being analysed.

Question 5

Define analyte

Answer 5

The particular component to be identified or measured.

Question 6

Define interference

Answer 6

Any process or compnent that causes the answer from chemical analysis to be wrong.

Question 7

Outline the typical process of chemical analysis.

Answer 7

1. Take a sample.
2. Prepare the sample (disolve/ dilute usually)
3. Remove or compensate for interferences.
4. Identify and/or measure the analyte.
5. Calculate results.

Question 8

What are the different types of chemical analysis?

Answer 8

Gravimetric
Titrimetric
Spectroscopic
Electrochemical
Radiochemical

Question 9

What is gravimetric analysis?

Answer 9

Measures the mass of the analyte.

Question 10

What is titrimetric (volumetric) analysis?

Answer 10

Measures the quantity of reagent that reacts with the analyte.

Question 11

What is spectroscopic analysis?

Answer 11

Measures the intensity of electromagnetic radiation absorbed or emitted by the analyte.

Question 12

What is electrochemical analysis?

Answer 12

Measures current, voltage or conductivity due to the analyte.

Question 13

What is radiochemical analysis?

Answer 13

Measures the nuclear radiation emitted by the analyte.

Question 14

What is accuracy?

Answer 14

The closeness of a measurement to the true result.

Question 15

What is precision?

Answer 15

The closeness of multiple measurements to each other.

Question 16

What is a titrant in a titration?

Answer 16

The reagent.

Question 17

What is the the titrand in a titration?

Answer 17

The analyte.

Question 18

What is the equivalence point of a titration?

Answer 18

The exact point in the reaction where the correct volume of titrant has been added to react with the titrand.

Question 19

What are the main types of titration reactions?

Answer 19

Ion combination reactions: Acid-base, precipitation and complexometric reactions.

Electron transfer reactions: Redox.

Question 20

What are the main charactoristics of a titration reaction?

Answer 20

It is fast
It is complete
It has no alternative reactions

Question 21

What is primary reagent indication?

Answer 21

One of the reactants or products indicates the equivilence point. Only works if one of the reactants or products are coloured.

Question 22

What is ancillary reagent indication?

Answer 22

This is where a dye is added as an indicator.

Question 23

What is instrumental indication?

Answer 23

Electrochmical methods are used to estimate the equivalence point.

Question 24

What is standardisation?

Answer 24

The exact concentration of a titrant in measured with respect to a primary standard.

Question 25

What properties should a primary standard have?

Answer 25

A primary standard should: A readily available solid Of a known composition A substance that can weighed out in a pure, dry form Stable in solution Reaction with the tritrand via a suitible reaction Have a high molecular weight

Question 26

What is the process of standardisation?

Answer 26

1. Make up the titrant solution 2. Make up the solution of the primary standard. 3. Titrate the primary standard against the titrant solution. 4. Use the results to calculate the accurate concentration of the titrant.

Question 27

What is the pH end point and colour change of bromothymol blue?

Answer 27

pH 6.9 Yellow (acid)/blue (alkali)

Question 28

What is the pH end point and colour change of methyl orange?

Answer 28

pH 3.5 red (acid)/yellow (alkali)

Question 29

What is the pH end point and colour change of phenolphthalein?

Answer 29

pH 9.5 Colourless (acid)/red (alkali)

Question 30

At what point on a titration curve is the equivalence point estimated to be?

Answer 30

The point at which the slope is steepest.

Question 31

What can the precipitaion reaction between silver nitrate and sodium chloride be used to estimate? What indicator is used?

Answer 31

The quantity of salt in the sea. Potassium chromate. Turns from yellow to red when it reacts with excess silver ions

Question 32

What is a complexometric titration?

Answer 32

A complex is formed when a metal cation and ligand react together.

Question 33

What is the most important titrant in complexometric analysis?

Answer 33

EDTA Bond to metal cations in a 1:1 ratio

Question 34

What is a complex?

Answer 34

A compound containing a metal atom surrounded by ligands. Complexes can be charged and neutral

Question 35

What is a ligand?

Answer 35

A molecule bound to a metal centre in a complex

Question 36

What charges are EDTA complexes best formed with?

Answer 36

4+ > 3+ > 2+ 1+ will form a salt, not a complex

Question 37

What pH are Metal-EDTA complexes most stable? How can this be benificial?

Answer 37

Most stable at higher pH Controlling the pH can allow some metals to be selectively titrated.

Question 38

What properties should an indicator in a complexometric titration have?

Answer 38

Should react with excess metal ions and give a colour change when it does so Should complex more strongly with the metal than the titrant.

Question 39

What indicator should be used in a alkaline complexometric titration? And what is the colour change?

Answer 39

Eriochrome black (pH10) Blue (uncomplexed)/ red ( complexed)

Question 40

What indicator is most suitible for Mg2+, Sr2+, Ca2+

Answer 40

Eriochrome black

Question 41

What indicator should be used in an acidic complexometric titration? And what is the colour change?

Answer 41

Xylenol orange (pH5) Yellow (uncomplexed)/ red (complexed)

Question 42

What is concentration and its relationship?

Answer 42

The mass of a substance per dm. has units of g/dm^3

Question 43

What is molarirty and its relationship?

Answer 43

The number of moles per dm. has units of mol/dm^3 n = M x V

Question 44

What is stoichiometry?

Answer 44

It is the ratio of moles of reactants and products involved in a reaction

Question 45

What is a redox reaction?

Answer 45

A reaction where are transfered from a reductant to an oxidant. it is the combination of half equations