T&P Synthesis Flashcards
Describe what heating under reflux is used for.
- Used for reactions involving volatile/flammable liquids
- Unreacted vapour condensed + returned to mixture
- Ensures reactants/products do not escape during reaction
Draw the apparatus used for heating under reflux.
Describe how to heat a mixture under reflux.
- Add reactants + some anti-bumping granules to pear-shaped flask
- Attach condenser to flask vertically so that water flows in at bottom + out at top
- Gently boil mixture in flask with heating mantle / Bunsen flame
- If vapours travel more than halfway up condenser before condensing, reduce heat
A mixture is heated under reflux. Explain:
- the purpose of anti-bumping granules
- why the flask is not stoppered
- Burst bubbles in boiling mixture to reduce chance of boiling over
- Would cause pressure to build, causing glassware to crack or stopper to fly out
Many ionic substances dissolve readily in water. List the ones which are insoluble.
- Silver/lead/barium/calcium sulphates
- Silver/lead halides
- Metal carbonates
- Metal hydroxides, except group 1 metals
Name 3 types of ionic substance which are always soluble in water.
- Group 1 compounds
- Ammonium compounds
- Nitrates
Name the method(s) used to synthesise a:
- water-insoluble, inorganic salt
- water-soluble, inorganic salt
Water-insoluble:
Reacting two soluble salts in solution
Water-soluble:
- Reacting an acid with a soluble base
- Reacting an acid with an insoluble base
Describe a method which could be used to produce a pure, dry sample of barium sulphate.
Preparing an anhydrous. water-_insoluble_, inorganic salt by reacting 2 soluble salts in solution
- Add equal volumes of solutions of barium nitrate + sodium sulfate to a beaker to form ppt of barium sulfate
- Filter
- Wash (with deionized water)
- Transfer to watch glass
- Heat to constant mass (in drying oven, regularly removing, cooling in dessicator + weighing)
- Cool (in dessicator)
Describe a method which could be used to produce pure copper sulphate crystals from copper carbonate and sulphuric acid.
Preparing crystals of a water-_soluble_, inorganic salt by reacting an acid + insoluble base
- Warm excess CuCO3 in dilute H2SO4 until all acid has reacted: test pH (with universal indicator paper) until neutral
- Cool
- Filter off excess CuCO3
- Heat filtrate in evaporating basin with Bunsen flame until crystals form on the sides
- Cool basin + contents
- Filter
- Wash solid (with distilled water)
- Transfer to watch glass
- Evaporate to half volume (don’t want anhydrous solid)
- Allow to crystallise
Describe a method which could be used to produce anhydrous sodium ethanoate from ethanoic acid of known concentration and sodium hydroxide of unknown concentration.
Preparing an anhydrous, water-_soluble_, inorganic salt by reacting an acid + soluble base
- Add CH3COOH to burette + use graduated pipette to add 25 cm3 NaOH to conical flask
- Add 3 drops indicator to flask
- Titrate to find volume of acid needed to neutralise alkali
- Add 25 cm3 alkali to clean flask (but no indicator)
- Use burette to add titre volume of acid to flask
- Transfer solution to evaporating basin
- Heat gently over Bunsen flame to evaporate water
- Cool
- Filter
- Wash (with distilled water)
- Transfer to watch glass
- Heat to constant mass (in drying oven, regularly removing, cooling in dessicator + weighing)
- Cool (in dessicator)
Describe a method which could be used to produce pure crystals of sodium ethanoate from sodium hydroxide of known concentration and ethanoic acid of unknown concentration.
Preparing crystals of a water-_soluble_, inorganic salt by reacting an acid + soluble base
- Add CH3COOH to burette + use graduated pipette to add 25 cm3 NaOH to conical flask
- Add 3 drops indicator to flask
- Titrate to find volume of acid needed to neutralise alkali
- Add 25 cm3 alkali to clean flask (but no indicator)
- Use burette to add titre volume of acid to flask
- Transfer to evaporating basin + heat gently over Bunsen flame until crystals form on the sides
- Cool
- Filter
- Wash (with distilled water)
- Transfer to watch glass
- Evaporate to half volume (don’t want anhydrous solid)
- Allow to crystallise
Which is the correct method of making a pure, dry sample of barium sulfate?
- Mix impure barium sulfate with sulfuric acid. Filter. Evaporate filtrate.
- Mix barium chloride solution with sodium sulfate solution. Filter + dry precipitate.
- Mix barium nitrate solution with sulfuric acid. Filter, wash + dry precipitate.
- Add barium to sulfuric acid. Evaporate solution.
Preparing a water-insoluble, inorganic salt
- Can’t evaporate since BaSO4 is insoluble. Soluble impurities remaining in filtrate need to be washed out
- Soluble impurities remaining in filtrate need to be washed out
- Correct
- Can’t evaporate since BaSO4 is insoluble. Soluble impurities remaining in filtrate need to be washed out
Some students attempt to make pure copper sulphate crystals from copper carbonate and sulphuric acid. They plan to use the following methods:
A: react excess copper carbonate with sulphuric acid. Evaporate. Allow to crystallise.
B: React copper carbonate with excess sulphuric acid. Filter, wash + dry.
C: react excess copper carbonate with sulphuric acid. Filter. Evaporate filtrate until dry.
None of these students would end up with pure crystals of copper sulphate. Outline the method which should be used.
Preparing a water-insoluble, inorganic salt
- React excess CuCO3 with H2SO4
- Filter (to remove excess CuCO3)
- Evaporate filtrate to half volume (don’t want anhydrous solid)
- Allow to crystallise
Draw a diagram of an apparatus which could be used to prepare a test-tube full of hydrogen chloride gas in the laboratory. Label the reactants.
- Test tube / flask containing NaCl + conc. H2SO4
- Delivery tube with downward delivery into a test tube / boiling tube
Not collection over water, or into a sealed vessel
