CH106 Analytical Chemistry Flashcards
What is qualitative analysis?
This identifies which compounds are present in a sample.
What is quantitative analysis?
This measures the proportions of each compnent in a sample.
Define component
A chemical compound, ion or element. All components combined form the element being analysed.
Define sample
A smaller representative part of the material being analysed.
Define analyte
The particular component to be identified or measured.
Define interference
Any process or compnent that causes the answer from chemical analysis to be wrong.
Outline the typical process of chemical analysis.
- Take a sample.
- Prepare the sample (disolve/ dilute usually)
- Remove or compensate for interferences.
- Identify and/or measure the analyte.
- Calculate results.
What are the different types of chemical analysis?
Gravimetric
Titrimetric
Spectroscopic
Electrochemical
Radiochemical
What is gravimetric analysis?
Measures the mass of the analyte.
What is titrimetric (volumetric) analysis?
Measures the quantity of reagent that reacts with the analyte.
What is spectroscopic analysis?
Measures the intensity of electromagnetic radiation absorbed or emitted by the analyte.
What is electrochemical analysis?
Measures current, voltage or conductivity due to the analyte.
What is radiochemical analysis?
Measures the nuclear radiation emitted by the analyte.
What is accuracy?
The closeness of a measurement to the true result.
What is precision?
The closeness of multiple measurements to each other.
What is a titrant in a titration?
The reagent.
What is the the titrand in a titration?
The analyte.
What is the equivalence point of a titration?
The exact point in the reaction where the correct volume of titrant has been added to react with the titrand.
What are the main types of titration reactions?
Ion combination reactions: Acid-base, precipitation and complexometric reactions.
Electron transfer reactions: Redox.
What are the main charactoristics of a titration reaction?
It is fast
It is complete
It has no alternative reactions
What is primary reagent indication?
One of the reactants or products indicates the equivilence point. Only works if one of the reactants or products are coloured.
What is ancillary reagent indication?
This is where a dye is added as an indicator.
What is instrumental indication?
Electrochmical methods are used to estimate the equivalence point.
What is standardisation?
The exact concentration of a titrant in measured with respect to a primary standard.
What properties should a primary standard have?
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
What is the process of standardisation?
- Make up the titrant solution
- Make up the solution of the primary standard.
- Titrate the primary standard against the titrant solution.
- Use the results to calculate the accurate concentration of the titrant.
What is the pH end point and colour change of bromothymol blue?
pH 6.9
Yellow (acid)/blue (alkali)
What is the pH end point and colour change of methyl orange?
pH 3.5
red (acid)/yellow (alkali)
What is the pH end point and colour change of phenolphthalein?
pH 9.5
Colourless (acid)/red (alkali)
At what point on a titration curve is the equivalence point estimated to be?
The point at which the slope is steepest.
What can the precipitaion reaction between silver nitrate and sodium chloride be used to estimate?
What indicator is used?
The quantity of salt in the sea.
Potassium chromate. Turns from yellow to red when it reacts with excess silver ions
What is a complexometric titration?
A complex is formed when a metal cation and ligand react together.
What is the most important titrant in complexometric analysis?
EDTA
Bond to metal cations in a 1:1 ratio
What is a complex?
A compound containing a metal atom surrounded by ligands.
Complexes can be charged and neutral
What is a ligand?
A molecule bound to a metal centre in a complex
What charges are EDTA complexes best formed with?
4+ > 3+ > 2+
1+ will form a salt, not a complex
What pH are Metal-EDTA complexes most stable?
How can this be benificial?
Most stable at higher pH
Controlling the pH can allow some metals to be selectively titrated.
What properties should an indicator in a complexometric titration have?
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.
What indicator should be used in a alkaline complexometric titration?
And what is the colour change?
Eriochrome black (pH10)
Blue (uncomplexed)/ red ( complexed)
What indicator is most suitible for Mg2+, Sr2+, Ca2+
Eriochrome black
What indicator should be used in an acidic complexometric titration?
And what is the colour change?
Xylenol orange (pH5)
Yellow (uncomplexed)/ red (complexed)
What is concentration and its relationship?
The mass of a substance per dm. has units of g/dm^3
What is molarirty and its relationship?
The number of moles per dm. has units of mol/dm^3
n = M x V
What is stoichiometry?
It is the ratio of moles of reactants and products involved in a reaction
What is a redox reaction?
A reaction where are transfered from a reductant to an oxidant.
it is the combination of half equations
