1b - elements, compounds, and mixtures

define an element.

a substance consisting of only one type of atom

define a compound.

a substance of two or more different types of atom that are chemically bonded together.

define a mixture.

two or more substances that are not mixed together.

describe a substance's boiling point.

a substance has a fixed melting and boiling point.

describe a mixture's boiling point.

a mixture melts or boils over a range of temperatures.

what is simple distillation used for?

separating substances with different boiling points.

what is fractional distillation used for?

separating substances with similar boiling points.

what does the term 'miscible' mean?

fairly similar boiling points

what is filtration used for?

separating insoluble solids from a liquid or solution

what is crystallisation used for?

separating a dissolved solute from a solvent.

what is paper chromatography used for?

separating soluble substances.

describe the technique for simple distillation.

• heat solution with bunsen burner

• the substance with the lower boiling point will evaporate and rise

• then the vapour will pass into the condenser where it will cool and condense

• it will collect in a beaker underneath

what equipment is needed for simple distillation?

• bunsen burner

• distilling flask

• thermometer

• condenser

• collection beaker

describe the technique for fractional distillation.

• heat solution to the temperature of the substance with the lowest boiling point

• the solution with the lower boiling point will reach the top of the column first, and then condense in the condenser and collect in a beaker

• the solution with the higher boiling point will also evaporate, but then it will condense and fall back into the original beaker

what equipment is needed for fractional distillation?

• electric heater

• distilling flask

• fractionating column

• thermometer

• condenser

• collection beaker

describe the technique for filtration.

• place filter paper in funnel above beaker

• pour mixture through

• insoluble solids will remain in filter paper as the residue

• soluble solids and liquids will pass through as the filtrate

what equipment is needed for filtration?

• funnel

• filter paper

• conical flask

• beaker

describe the technique for crystallisation.

• gently heat solution to evaporate some of the water and create a saturated solution

• leave to cool and crystallise

• decant off the excess solution

• pat the crystals dry with paper towel

what equipment is needed for crystallisation?

• crucible

• bunsen burner

• tripod and gauze

• tissue paper

describe the technique for paper chromatography.

• draw pencil line on chromatography paper and place spots of sample on it

• lower paper into solvent container

• (pencil line must be above solvent level)

• substances will travel upwards via capillary action

how do we interpret a chromatogram?

• pure substances will produce only one spot on the chromatogram

• impure substances will produce more than one spot on the chromatogram

• if two or more substances are the same, they will produce identical chromatograms

• if the substance is a mixture, it will separate on the paper to show all the different components as separate spots

what equipment is needed for paper chromatography?

• chromatography paper

• beaker

• pencil

how do we calculate Rf value?

Rf value = substance distance / water distance