what is standard solution?
a solution of known concentration
how do you prepare a standard solution?
- weigh a mass of solid using a 3 decimal place balance and transfer to a beaker
- dissolve the solid in distilled water
- transfer the solution to a 250cm3 volumetric flask
- rinse the beaker and transfer the washings to the flask
- add distilled water until the level is just below the mark
- use a dropping pipette to make up to the mark so that bottom of the meniscus is on the mark
- stopper and invert several times to mix the solution
what are redox reactions?
ones which involve the transfer of electrons from one species to another
how do the redox reactions work?
one species must lose one or more electrons, the other must gain the same number of electrons. Both processes must take place simultaneously
what can acidified potassium manganate be used for?
to oxidise many other substances.
what do redox titrations do?
determine the concentration of an acid or base solution.
how do you check the equation is correctly balanced?
you should have the same number of each type of atom present on both sides and the overall charge on both sides should be the same
how is the titration carried out?
at room temperature
what can potassium dichromate solution be used for?
oxidising many other substances
- used to determine the concentration of iron (II) ions in a solution
what does sodium oxalate form?
oxidises the oxalate ion to form carbon dioxide
how you determine the concentration of a solution?
- write the balanced equation
- record the values under each substance
- calculate the number of moles
- use the mole ratio to find moles
- calculate the unknown (concentration) using the moles and volume
how do you determine the amount of element present in an ore, an alloy or even tablets
- write the equation for the redox reaction and include the amounts you know
- calculate moles of element 1
- mole ratio
- calculate mass of element present
- percentage composition
ppt.
precipitate.
how do you test for ammonium ions:
- procedure
- result
- add NaOH and HEAT: ammonia gas produced NH3
- test for ammonia gas using damp red litmus paper
- blue result
what is the result for aluminium ions?
Produces a white precipitate with sodium hydroxide and ammonia which dissolves in
excess sodium hydroxide only.
what is the result for copper (II) ions?
gives a blue/turquoise ppt.of copper(II) hydroxide with ammonia or sodium
hydroxide, which dissolves in excess ammonia to give a deep blue solution of an amine complex, but copper(II) hydroxide is NOT soluble in excess NaOH.
what is the result for chromium (III) ions?
gives a grey green precipitate of chromium (III) hydroxide,
which is soluble in excess NaOH to give a dark green solution of the hexahydroxo-complex ion [Cr(OH)6]3-
but not excess ammonia NH3(aq)
what is the result for Iron (II) ions?
gives a grey green precipitate of chromium (III) hydroxide,
which is soluble in excess NaOH to give a dark green solution of the hexahydroxo-complex ion [Cr(OH)6]3-
but not excess ammonia NH3(aq)
what is the result for Iron (III) ions?
forms a brown precipitate of iron(III) hydroxide with ammonia or sodium hydroxide, which is not soluble in excess of NH3 or NaOH.
Another test for iron(III) ions is to add a few drops of potassium/ammonium
thiocyanate solution and a blood-red coloured compound forms.
what is the result for Manganese (II) ions?
forms an off-white precipitate of manganese (II) hydroxide which is not soluble in excess NaOH or NH3(aq)
it rapidly turns brown / black in air due to oxidation to manganese(III) oxide Mn2O3 and then manganese (IV) oxide MnO2
what is the result for zinc ions?
Produces a white precipitate with ammonia and sodium hydroxide which dissolves in excess ammonia and sodium hydroxide
what is the observation/test for carbonate ions?
add dilute acid, bubbles of CO2 gas produced
what is the observation/test for sulfate ions?
Add a soluble barium compound (chloride or nitrate)
A white precipitate of barium sulfate will be produced
what is the observation/test for halide ions?
Add silver nitrate solution
A precipitate of the silver halide will be produced.
