Core Practicals Flashcards
(24 cards)
How do you calculate Rf value?
Distance travelled by substance divided by distance travelled by solvent
What’s the method for chromatography?
- Draw pencil line across paper
- Use pipette to add small spots of ink to the line on the paper
- Place paper into container with suitable solvent at the bottom
- Allow solvent to move through the paper, but remove before it reaches the top
- Allow it to dry, then measure the distance travelled by each spot & solvent.
Why do we draw the line with pencil?
Because pencil is insoluble in the solvent
What is the purpose of chromatography?
Used to separate mixtures of soluble substances and find identities of substances present in the mixture.
eg: inks and dyes
What is the rule with Rf value?
Always less than 1
How do you improve accuracy of the practical?
Use a longer piece of chromatography paper
What is the conclusion with chromatography?
The higher the spot travels the move soluble in the solvent it is.
What do you get when you react a acid with a base?
Salt+ water
What colour is copper oxide?
Black- base for copper sulfate reaction
It insoluble in water- so isn’t a alkali
Process of preparing copper sulphate crystals?:
1.Add copper oxide to sulfuric acid and add in excess in order to make sure everything is fully reacted.
2. Solution is now copper sulfate- using filter paper; filter the solution to get rid of excess copper oxide.
3. Add solution above a Bunsen burner and heat over a measuring cylinder of water ( safer than just putting it on top of Bunsen burner to avoid spitting of the copper sulfate) to evaporate.
4. Once crystals start to from leave to cool and leave by a windowsill for 2 days.
5. Once crystals are fully formed, dry between filter paper, as there may still be excess copper sulfate.
What do we use to measure the mass of a substance?
A balance
What is a base?
A base is anything that reacts with a acid to form a salt + water (metal oxides and metal hydroxides are bases)
> bases that are soluble in water are called alkalis and they dissolve in water to form a alkaline.
What is a neutralisation reaction?
A reaction between a acid and a base
Acids in a reaction form H+ ions
Alkalis in water form H- ions
> a reaction between hydroxide and hydrogen ions to forming water.
What is the method for neutralisation reaction?
- Add dilute hydrochloric acid to beaker and record the ph of solution at the start.
- Use glass rod and dip into liquid then tap onto universal indicator paper and wait 30 seconds then match the colour of the paper to the pH scale then rinse glass rod with water.
- Measure out 0.3 grams of calcium hydroxide powder onto a piece of paper using a balance and add to the beaker stir, then estimate & record pH of mixture.
- Repeat step 3 7 times so that you add a total of 2.4 grams of calcium hydroxide to the acid.
What is filtration used for?
Only used to separate mixtures
Why is copper oxide not a alkali?
It’s insoluble in water but IS STILL a base
(bases that dissolve in water are alkalis)
What is a neutralisation reaction?
Reacting a base with an acid to achieve a pH of 7
What do you use for filtration?
A conical flask
Filter paper to separate the solid and liquid
What is crystallisation used for?
Used to separate a soluble solid from a liquid by heating, then evaporating them leaving the crystals to form
Why do you heat the solution for crystallisation?
Speeds up the separation process
What is simple distillation?
Separating a dissolved solid from a liquid but keeping the liquid
What are the two stages of simple distillation?
- Evaporate the liquid by heating into vapour
- Condense vapour back into liquid via a condenser
What is fractional distillation used for?
Separate multiple different liquids with different boiling points
What happens in fractional distillation?
The lower boiling point liquid will make its way up the fractioning column and separate from the other mixtures as the temperature reaches its boiling point for that liquid
