Topic 2 - Experimental Techniques (PMT/CIE Chemistry IGCSE)

A set of practice flashcards on experimental techniques for PMT/CIE Chemistry IGCSE, covering measurement apparatus, paper chromatography concepts, Rf values, and separation methods (filtration, crystallisation, distillation).

What is paper chromatography used for?

Separating and identifying a mixture of substances.

What apparatus is suitable for measuring time, temperature and mass?

Time: stopwatch; Temperature: thermometer or temperature probe; Mass: digital mass balance.

What apparatus are suitable for measuring volume?

Measuring cylinder; burette; pipette with pipette filler.

Describe the steps to separate a mixture of food colourings using paper chromatography.

Draw a pencil line 2 cm from the bottom; place dots of known food colourings and one unknown along the line; place paper in beaker with 1 cm of water; allow solvent to travel up; mark the solvent front; dry the paper; observe and record results.

What should the stationary phase be in paper chromatography?

The chromatography paper.

What should the mobile phase be in paper chromatography?

The solvent.

Why should pencil be used to draw the baseline on chromatography paper?

Because pencil is insoluble in the solvent and will not affect the results.

Why should the solvent depth be no deeper than 1 cm in paper chromatography?

If deeper, the solvent can wash away substances from the paper.

In paper chromatography, what is the stationary phase?

The chromatography paper.

In paper chromatography, what is the mobile phase?

The solvent.

What two factors affect how long molecules spend in each phase in paper chromatography?

Solubility in the mobile phase and attraction to the chromatography paper.

What is an Rf value?

The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent.

How do you calculate Rf values?

Rf = distance travelled by substance / distance travelled by solvent.

What affects the Rf value of a substance in paper chromatography?

The solvent; changing solvent changes the Rf value.

Where should you measure the distance moved by a substance on the chromatography paper?

From the pencil baseline to the middle of the spot.

How many spots will be observed on a chromatogram of a pure substance?

One.

How can you identify that two mixtures contain a substance that is the same using a chromatogram?

If a spot in both chromatograms matches in position.

How does solubility affect the distance a substance travels in paper chromatography?

More soluble in the mobile phase means it travels further up the paper.

How can paper chromatography be used if a mixture contains colourless substances?

Use a locating agent after developing the chromatogram to make spots visible.

What is a mixture?

A combination of two or more elements or compounds that are not chemically joined.

What is a pure substance?

A single element or compound not mixed with any other substance.

How can a pure substance be identified using melting or boiling points?

Pure substances have a sharp melting/boiling point; impure substances melt/boil over a range of temperatures.

What method can be used to separate an insoluble salt from a solution?

Filtration: filter through paper, collect in a beaker, wash and dry the solid.

What method can be used to separate a soluble salt from a solution?

Crystallisation: evaporate to concentrate, allow to crystallise, filter and dry.

When is simple distillation used as a separating technique?

To separate and purify a liquid from a mixture of liquids with different boiling points.

Describe how to separate a mixture of water and ethanol using simple distillation.

Heat the mixture in a round-bottom flask with a condenser; ethanol boils first due to lower boiling point, condenses in the condenser and is collected.

What mixture is fractional distillation commonly used to separate?

Crude oil.

Describe how fractional distillation separates crude oil.

Crude oil is heated to form vapours that rise up a fractionating column with a temperature gradient; different components condense at different heights according to boiling points.