Chemistry ✿ chemical analysis

pure substance

substances with a single element or compound and isnt mixed with any other substance

impurities

substances that are present in small quantities in another substance

pure substances melt and boil at ________ temperatures

specific temperatures

formulation

a mixture that has been designed as a useful product

give 3 examples of formulations

• fuels

• alloys

• paints

active ingredient

the main chemical in a formulation

what is chromatography used for?

to separate coloured substances from a mixture

equation for Rf value

distance moved by ink / distance move by water

why are Rf values calculated?

to identify chemicals in a substance by comparing it with the database

why is chromatography repeated when finding the Rf value of a substance?

because several chemicals could have the same Rf value so it must be repeated using a different solvent to narrow it down further

stationary phase

the phase in chromatography where the molecules cant move (filter paper)

mobile phase

the phase in chromatography where the molecules can move (solvent)

suggest an alternative solvent (other than water) to use in chromatography

ethanol

test for hydrogen

• insert a burning splint

• a squeaky pop will be produced

test for oxygen

• insert a glowing splint

• splint will relight is oxygen is present

test for carbon dioxide

• prepare tube of limewater

• draw some gas using a pipette

• bubble the gas through limewater several times until it turns cloudy/milky

limewater

an aqueous solution of calcium hydroxide

test for chlorine

• insert damp brown litmus paper into mouth of tube

• if chlorine is present it will bleach the paper white

how can we can tell if a substance is soluble in chromatography?

it will spend more time in the mobile phase and move further up the paper

Rf value

retention factor

The Rf value of a dye depends on:

• the solubility of the dye in the solvent

• the attraction of the dye to the paper

what changes will produce a smaller Rf value if the solvent and paper are changed?

dye is less soluble in new solvent and more attracted to new paper

equation for Rf value

distance moved by ink / distance moved by solvent