Analysis I

Question 1

Purpose of a volumetric flask

Answer 1

Makes up an accurately known volume of solution

Question 2

Purpose of a volumetric pipette

Answer 2

Dispenses an accurately known volume (aliquot) of a solution

Question 3

What is an aliquot?

Answer 3

An accurately known volume of a solution

Question 4

Purpose of a burette

Answer 4

Delivers an accurately known but variable amount of solution

Question 5

How many decimal places on a volume measurement made with a burette?

Answer 5

Two decimal places, but the second decimal place is always 0 or 5 (ie nearest 0.05mL)

Question 6

What is a primary standard substance?

Answer 6

A substance that can be prepared pure and dissolved in water to make a solution whose concentration is accurately known

Question 7

What are the features of a primary standard?

Answer 7

Can be made pure. Does not degrade or react with air. Known molar mass. Preferably dissolves well in water and is inexpensive.

Question 8

What is a primary standard solution?

Answer 8

A solution containing one solute, that has been prepared by dissolving a known mass of that solute in a known volume of pure water. As a result the concentration is accurately known.

Question 9

What is the name given to the solution in the burette during volumetric analysis?

Answer 9

Titrant

Question 10

What is the name given to the solution in the conical flask during volumetric analysis?

Answer 10

Analyte

Question 11

What name is given to the volume of titrant dispensed into the conical flask during a titration?

Answer 11

Titre

Question 12

What is the total range of concordant titres?

Answer 12

0.10 mL

Question 13

What is a mean titre; how is it calculated?

Answer 13

The average of all concordant titres in a titration experiment. Calculated to two decimal places.

Question 14

What is a dilution factor and how is it calculated?

Answer 14

The final volume divided by the initial volume, where water has been added to dilute a solution.

Question 15

Why is an indicator added to the analyte before a titration?

Answer 15

The indicator changes colour at or near the equivalence point. This colour change indicates the end point.

Question 16

What is the equivalence point?

Answer 16

The point at which the exact mole ratio of reactants has been added, according to the balanced equation. At this point neither reactant is in excess.

Question 17

What is the end point?

Answer 17

The point at which observable experimental evidence shows that the equivalence point has been reached

Question 18

What is a titration curve?

Answer 18

A graph plotting pH against volume of titrant added

Question 19

When discussing errors, what is a ‘mistake’ and how should it be treated?

Answer 19

An avoidable error that may cause the experimental result to be inaccurate. Experimental results involving mistakes should be rejected.

Question 20

When discussing errors, what is a systematic error?

Answer 20

An error introduced by the method or apparatus, that cannot be eliminated by repeating the experiment. This error causes inaccuracy in the same direction for each experiment.

Question 21

When discussing errors, what is a random error?

Answer 21

An error that may cause the experimental result to be higher or lower than the true value.

Question 22

How can the effect of random errors be minimised?

Answer 22

Repeat the experiment multiple times and take an average value.

Question 23

What is the empirical formula of a compound?

Answer 23

A chemical formula showing the simplest whole number ratio between the elements in a compound

Question 24

What is the molecular formula of a compound?

Answer 24

A chemical formula showing the exact number of atoms of each element in a molecule of that substance.

Question 25

What is a precipitate?

Answer 25

A solid formed in a reaction between two solutions.

Question 26

How is heating to constant mass achieved?

Answer 26

A substance is alternately heated and weighed until its mass is the same in multiple measurements (often 3).

Question 27

Why is heating to constant mass performed?

Answer 27

This ensures that no water is present in the sample

Question 28

What does an emission spectrum look like?

Answer 28

Coloured lines on a black background

Question 29

What does an absorption spectrum look like?

Answer 29

Black lines on a coloured background

Question 30

What is absorbance?

Answer 30

A measure of the intensity of light remaining after some has been absorbed, compared with the intensity of light when none has been absorbed.

Question 31

What is transmittance?

Answer 31

The opposite of absorbance; A measure of the proportion of light that has been transmitted through a substance (or solution), where 100% transmittance means that no energy has been absorbed.

Question 32

What name is given to the distance between the same point on two successive waves?

Answer 32

Wavelength

Question 33

What name is given to the number of waves that pass a given point in one second, and what units are given to this value?

Answer 33

Frequency, measured in Hertz (Hz)

Question 34

In spectroscopy, what is a cuvette?

Answer 34

A cell or small test tube used to hold the analyte

Question 35

What is a calibration curve?

Answer 35

A plot of the results of an experiment at a range of known concentrations, so that an unknown concentration within that range can be assessed.

Question 36

How do you identify the parent or molecular ion (M) peak in Mass Spectrometry? What information does it give us?

Answer 36

The furthest peak to the right (excluding very small peaks). This shows the molar mass of the parent molecule.

Question 37

How do you identify the base peak in Mass Spectrometry?

Answer 37

The highest peak (most abundant fragment)

Question 38

Chlorine has two main isotopes, Cl-35 and Cl-37. Identify the molecular ion peaks that would be seen in mass spectrometry of chlorine gas (Cl2).

Answer 38

There would be a peak at m/z = 70 (2 x Cl-35 isotopes), a peak at m/z = 72 (1 x Cl-35 and 1 x Cl-37) and one at m/z = 74 (2 x Cl-37 isotopes)