Chapter 12 Flashcards
Measuring volume of liquids: measuring cylinder
Most useful in large amounts of solution -> not very accurate
Measuring volume of liquids: volumetric pipette
Used to measure out single fixed volume of liquid -> accurate
Measuring volume of liquids: Burette
Used to measure out volumes more accurately than a measuring cylinder
Titrations (6 steps)
1) using pipette measure out a set volume of the alkali into a flask, and add a few drops of an indicator -> thymolpthalein or methyl orange
2) fill a burette with known concentration of acid
3) use burette to add acid to alkali a bit at a time, swirling the flask regularly
4) indicator changes colour when all alkali has been neutralised
5) record the volume of acid used to neutralise alkali
6) repeat process without indicator (no stain)
Purity
. Pure: made up of a single elements or compound -> if more than one compound is a mixture
- Testing for purity
. If substances impure (mixture) then it will melt gradually over a range of temperatures
. Impurities: increase boiling points and decrease melting point
Solution
Mixture of a solute and a solvent that doesn’t separate
Solute
Substance that dissolves
Solvent
Liquid solute dissolves into
Saturated solution
Maximum amount of solute has been dissolved -> no more solute dissolves at that temperature
Residue
Substance remaining at end of process of separation or purification
Filtrate
Solution or a liquid that has been filtered
Chromatography
Separates a mixture of soluble substances and identifies them -> works as different substances will move up paper at different rates
Chromatography steps (4 steps)
1) add a spot of mixture to baseline (drawn in pencil) on chromatography paper
2) end of paper is placed in solvent with solvent, just below the baseline -> mixture should be soluble in solvent, and solvent shouldn’t react with mixture
3) solvent travels up the paper and carries substances in a mixture with it and these separate out -> further point reached by solvent is called solvent front
4) resulting pattern is called chromatogram -> you can compare it to a pure sample of a substance you might think is in the mixture to identify it
-> if mixture separates into colourless substances, spray locating agent onto paper to show where spots are
Simple distillation
Separates out a liquid from a solution where different parts have very different boiling points
Simple distillation (two steps)
1) solution heated in flask using a Bunsen burner and a part of solution that has lowest boiling point evaporates
2) vapour is cooled by a condenser, causing it to condense and it’s collected in a beaker -> rest of solution is left in flask
Fractional distillation
Separates a mixture of liquids with similar boiling points
Fractional distillation (six steps)
1) put mixture in a flask and put a fractionating column on top
2) heat mixture using Bunsen burner
3) different liquids will all have different boiling points SO they’ll evaporate at different temperatures
4) liquid with lowest boiling point evaporates and reaches top of column first
5) liquid with higher boiling point might also start to evaporate -> column is cooler towards top SO they’ll only get parts of way up before condensing and running back down into flask
6) when first liquid has been collected, raise temperature until next liquid reaches top
Filtration
Separates an insoluble solid from a liquid
Filtration (two steps)
1) put filter paper into a funnel and pour your mixture into it
2) liquid part of mixture runs through paper and leaves a solid residue -> wash, solid with distilled water and leave to dry
Crystallisation
Separates a soluble solid from a solution
Crystallisation (four steps)
1) pour solution into evaporating dish, and gently heat solution
2) some of water will evaporate and solution will get more concentrated
3) when you see crystals start to form (point of crystallisation) remove dish from heat and leave solution to cool
4) filter crystals out of solution and leave them in warm place to dry or use a drying oven
Test for ions: test for ammonium ions (2 steps)
1) add sodium hydroxide solution to a solution being tested, and gently heat it
2) if ammonia gas is given off, it means that they’re ammonium ions in the solution -> test for ammonia gas by holding a piece of damp red litmus paper over it and see if it turns blue
Test for ions: testing for metal ions using flame tests
1) clean nichrome wire loop by dipping it into hydrochloric acid and rinse it in distilled water
2) dip wire loop into a sample of metal compound and put loop in clear blue part of a Bunsen flame
3) record what colour flame goes
