What pure means to a chemist compared with everyday use, what a formulation is, and the chromatography required practical including Rf calculations.
You can study this deck without signing up — your progress is kept in this browser. An account saves it properly, syncs it across devices, and lets you edit the cards.
1.What does pure mean in chemistry?
A single element or compound, not mixed with any other substance.
2.How does that differ from the everyday meaning?
In everyday use pure often means natural or unadulterated, such as pure orange juice, which a chemist would call a mixture.
3.How can melting point identify a pure substance?
A pure substance melts at one specific temperature. An impure substance melts over a range of temperatures.
4.What does an impurity do to a melting point?
It lowers it and spreads it over a range rather than a single value.
5.What is a formulation?
A mixture that has been designed as a useful product, with each component present in a carefully measured quantity.
6.Why is each component measured carefully in a formulation?
So the product has exactly the properties it is designed for, and every batch behaves the same.
7.Give five examples of formulations.
Paints, fuels, cleaning agents, fertilisers, medicines, alloys and foods.
8.Is an alloy a formulation?
Yes. The proportions of each metal are chosen deliberately to give particular properties.
9.What does chromatography separate?
Substances in a mixture, based on how they distribute between two phases.
10.Name the two phases in paper chromatography.
The stationary phase, which is the paper, and the mobile phase, which is the solvent.
11.Why do different substances travel different distances?
Each has a different balance of attraction to the paper and solubility in the solvent.
12.Which substance travels furthest?
The one most attracted to the mobile phase and least attracted to the paper.
13.Why is the baseline drawn in pencil?
Pencil is insoluble, so it will not travel up the paper and interfere with the results.
14.Why must the solvent start below the baseline?
Otherwise the spots would dissolve directly into the solvent instead of travelling up the paper.
15.Why is a lid put on the container?
To stop the solvent evaporating, which would change the results.
16.How many spots does a pure substance produce?
One, in any solvent.
17.What does more than one spot tell you?
The substance is a mixture.
18.State the equation for Rf value.
Rf = distance travelled by the substance divided by distance travelled by the solvent.
19.A spot travels 4.5 cm and the solvent travels 9 cm. Calculate the Rf.
4.5 divided by 9 = 0.5.
20.Why is Rf always between 0 and 1?
The substance is carried by the solvent, so it can never travel further than the solvent front.
21.Where is the distance to a spot measured to?
The centre of the spot.
22.Why is Rf useful for identification?
For a given solvent and paper, a substance always has the same Rf value, so it can be compared with known references.
23.Why must the same solvent be used for comparison?
Rf values change with the solvent, so values from different solvents cannot be compared.
24.How could you identify an unknown substance using chromatography?
Run it alongside known reference substances and see which one it matches in distance travelled and Rf value.
25.Why might two different substances appear to have the same Rf?
In one particular solvent they may happen to travel the same distance, which is why more than one solvent is often used.
26.What is the mobile phase in gas chromatography?
A gas, rather than a liquid solvent.
You remember far more by trying to recall an answer than by reading it. Run these as flashcards and the ones you keep getting wrong will come back more often.
Start studyingOr see the other Chemical Analysis decks.