C10- chemical analysis 🧪

• a pure substance, is a single element or compound not mixed with any other substance

• a substance’s melting and boiling point can be measured. • this is because, a pure substance will melt at a specific fixed temperature • and a pure substance, will have a specific boiling point

• like pure substances, a substance’s melting and boiling point can be measured. • this is because, impure substances melt and boil over a range of temperatures

• For substances used in preparing food and drugs, it is important that only permitted pure substances are being used. • this is because, if a substance is impure, and laced with some other substances, these unapproved impurities might not be safe for human consumption- which could lead to undesirable effects on human health.

• a formulation, is a complex mixture that has been designed as a useful product • [and in a formulation, the quantity of each component is carefully measured, so that the product has the required properties]

• fuels • paints • cleaning products • medicines • alloys • fertilisers • and, food

• paper chromatography, is a physical separation technique that separates substances based on their different solubilities

• draw a pencil line across chromatography paper (about 1 cm above the bottom) • use a pipette, or capillary tube, to add small spots of each ink (A,B, C and D) to the line on the paper, as well as unknown ink (U) (equally spread across the paper) • place the paper into a container with a suitable solvent (e.g. water) in the bottom - making sure the pencil line is above the water line • and allow the solvent to move through the paper, but remove the chromatogram before it reaches the top • then allow the chromatogram to dry, and measure the distance travelled by each spot and by the solvent

• no, with chromatography this can be done with several colours; there has to be enough space on the paper.

• In paper chromatography, the stationary stage is called the paper- because it doesn’t move.

• In paper chromatography, the mobile phase is the solvent- since it does move.

• the stationary stage is called the paper- because it doesn’t move • ; the mobile phase is the solvent- since it does move.

• there will be only one spot

• paper chromatography works, because each chemical in the mixture will be attracted to the stationary phase (the paper), to a different extent. • and chemicals that are strongly attracted to the stationary phase (the paper) will not move very far. • chemicals that are weakly attracted, will move further up the paper.

• a pure chemical produces singles spot in all solvents • ; a chemical in a mixture may separate into different spots, based on the solvent.

• We draw our starting line in pencil, since if it was in pen: the pen ink would move up the paper with the solvent.

• Rf value= distance moved by substance ➗ distance moved by solvent

• use a burning splint held at the open end, of a test tube of a gas. • and if hydrogen gas is present, hydrogen gas burns rapidly with a squeaky pop sound

• use a glowing splint inserted into a test tube of oxygen gas, and oxygen has will relight a glowing splint

• use an aqueous solution of limewater [calcium hydroxide], and draw some of the gas into a plastic pipette • and when carbon dioxide is shaken with or bubbled through limewater, the limewater turns cloudy

• insert damp litmus paper, into the mouth of a test tube containing chlorine gas • and if chlorine gas is present, the damp litmus paper is bleached and turns white