Analytical Chemistry Flashcards by Amy Neill

What does ‘Analytical Chemistry’ mean ?

concerned with finding out the identities and quantities of the different chemical components which a substance contains.

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What are the applications of analytical chemistry ?

Chemistry, Medicine, Forensic Science, Metallurgy, Environmentally and Pharmacology.

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What are the two types of chemical analysis ?

Qualitative analysis and Quantitative analysis

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What is ‘Qualitative analysis’ ?

Identifies which compounds are present

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What is ‘Quantitative analysis’ ?

Measures the proportion of compound in the sample

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Definition of ‘Component’

Chemical compound, ion or element .ie. all components together are material being analysed.

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Definition of ‘Sample’

A smaller representative part of the material to be analysed.

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Definition of ‘Analyte’

The particular component to be identified or measured

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Definition of ‘Interference’

Any process or component that causes the wrong answer from chemical analysis to be obtained

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What is the Analyte, sample and interference in the determination of Calcium in seawater ?

Analyte- Calcium
Sample- Seawater
Interference- Water, Na2+ …

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What is the typical process for chemical analysis ?

Take a sample
Prepare for analysis (dissolve or dilute)
Remove/compensate for interference if present
Identify or measure analyte
Calculate and report result

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What are the five types of chemical analysis ?

Gravimetric analysis
Titrimetric analysis
Spectroscopic analysis
Electrochemical analysis
Radiochemical analysis

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What are the steps in Gravimetric analysis?

Dissolve solid (soluble salt) and other chemical species
Add solution
Filter and weigh the solid

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What is Gravimetric analysis ?

Measure the mass of compound (analyte)

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What is titrimetric analysis ?

Measure the quantity of a reagent that reacts with the analyte

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What another term for titrimetric analysis ?

Volumetric analysis

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What is spectroscopic analysis ?

Measure the intensity of electromagnetic radiation absorbed or emitted by the analyte

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What is electrochemical analysis ?

Measure the current, voltage or conductivity due to the presence of the analyte.

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What is Radio chemical analysis ?

Measure the nuclear radiation (no. of radioactive particles) emitted by the analyte.

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Definition of ‘Accuracy’

The closeness of a measurement to the ‘true’ result

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Definition of ‘Precision’

The closeness of a series of measurement to each other

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What is the ‘titrant’ ?

the reagent (in the burette)

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What is the titrand ?

the analyte (in the conical flask)

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What are the three Ion Combination reactions ?

Acid-base reaction
Precipitation reaction
Complexation reactions

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What is the aim of an 'Acid-base reaction' ?

To change the pH

What is the aim of 'Precipitation reaction' ?

To form a solid

What is the aim of 'Complexation reaction' ?

To form a complex

What is the name of an electron transfer reaction ?

Redox Reaction

What are the characteristics for a titration ?

- Fast reaction (catalyst or heating) - Complete reaction (At equivalence point there should only be a small amount of unreacted titrant and titrand. - Have no reaction alternative reactions

What is a redox reaction ?

Electrons are transferred between titrand and titrant

What quality makes for poor titrations ?

Reactions that are reversible or have parallel alternative reactions

Give an example of why titrations shouldn't occur with Parallel reactions ?

Potassium permanganate at pH 1 forms Manganese ions which are very soluble where at pH 7 it forms Manganate which is a brown, thick solid

How is the course of reaction followed during titrimetric analysis ?-

- Consumption of a reactant - Formation of a product

Definition of 'Equivalence point'?

The point in the titration where exactly the right volume of titrant has been added to react with the titrand present in the sample.

What are the three methods of indication in a titration, and what do they mean ?

- Primary reagent indication: No need to add indicator as reagent or product indicated equivalence point via colour change( eg- permanganate) - Ancillary reagent indication: Indicator required if titrant/titrand cant be used and only a small volume of this is added (eg methyl red) - Instrumental Indication: Conductometer and Potentiometric methods are used

What is the difference between end point and equivalence point ?

End point is one drop above the equivalence point

Why is standardisation used ?

Titrant can't be weighed out accurately and form solutions that may change conc. in time

Characteristics are of primary standard are:

- A readily known solid - Substance which can be weighed out in a pure, dry form - Gives stable solution - A high molecular weight - Reacts with titrant via. a suitable reaction - Known composition

What are the standards for the following titrants: 1. HCl 2. NaOH 3. AgNO3 4. NaCl 5. EDTA 6. KMnO4

1. Sodium Carbonate 2. Potassium Acid Phthalate 3. Sodium Chloride 4. Silver Nitrate 5. Lead Nitrate 6. Sodium Oxalate

What are the steps in standardisation ?

1. Make up a solution of titrant 2. Make up solution of primary standard 3. Titrate primary standard with titrant 4. Calculate accurate conc. of titrant 5. Titrate sample with titrant 6. Calculate conc. of analyte in sample

What if the formula for calculating pH ?

pH = -log₁₀ [H+]

What is the units for [H+] ?

mol dm-3

What is the pH of the equivalence point when: 1. Strong acid/ Strong base 2. Strong acid/ weak base 3. Weak acid/ strong base 4. Weak acid/ weak base

1. ~ 7 2. <7 3. > 7 4. reversible so no equ. point

What is the suitable indicator when: 1. Strong acid/ Strong base 2. Strong acid/ weak base 3. Weak acid/ strong base 4. Weak acid/ weak base

1. Bromothymol Blue 2. Methyl orange 3. Phenolphthalein 4. Unsuitable

What is the colour change when: 1. Strong acid/ Strong base 2. Strong acid/ weak base 3. Weak acid/ strong base 4. Weak acid/ weak base

1. Yellow (acid)/ blue (alkali) 2. Red (acid)/ yellow (alkali) 3. Colourless (acid)/ red (alkali) 4. Unsuitable

When is the highest rate of change during a titrimetric analysis ?

At the equivalence point

Definition of a 'Complex'

Chemical compound containing metal atom surrounded by ligands arranged in a defined geometric function

Ligand

A molecule bound to a metal centre in a complex

What does ETDA stand for ?

Ethylene Diamine Tetraacetic acid

How many bonds can ETDA form and where do they come from ?

total of 6 bonds: - 4 bonds from Tetraacetic acid - 2 bonds from lone pairs on Nitrogen

What is the ration between ETDA and metal ions ?

1:1

True of false ? the lowest oxidation state metals from the strongest complexes ?

What oxidation state do metal ions that react with EDTA have ?

+2 or greater

Definition of concentration and Units

Mass of a substance per unit volume (C) - g dm-3

What is the formula for calculating mass when we have a known conc and known volume - give units

mass = C X V g = g sm-3 X dm3

Definition of Molarity (molar conc) and units

The number of moles per unit volume

What is the formula for calculating number of moles when we have a known molarity and volume - give units

n = M X V mol = mol dm-3 X dm3

What is the formula(s) for converting between M and C ?

n = Mass/ MW , M = C/ MW

What does MW mean ?

Molecular Weight

Definition of 'Stoichiometric'

The ration of numbers of moles of reactants (and products) involved in a reaction

What is the formula for determining the Unknown conc. ?

MAVA/a = MBVB/ b

Which of these does not have a 1:1 ratio with metal: A. Acid-base B. Precipitation C. Redox D. EDTA

C. Redox

What is a redox titration ?

A titration where electrons are transferred from one species (reductant) to another (oxidant).

What is a half reaction ?

A half reaction involves 'free electrons' and is the reaction which occurs at the electrode in electrolysis

Definition of an Oxidising agent

A chemical which is used to remove electrons from a reductant and is itself reduced

What are the steps in balancing redox reactions ?

1. Write components of redox 2. If one side has Oxygen, balance the opposite side with H20 3. Balance Hydrogens on each side 4. Add electrons to balance the charge 5. Combine reactions 6. Cancel common species

What has an impact on permanganate titration and give an example ?

The pH impacts this reaction eg- An acid form forms Manganese ions (5 electrons) A neutral substance forms Manganese dioxide (3 electrons) An alkali solution forms Manganate (green) (1 electron)