Chemistry y10 Flashcards
Flame test colour of Li+?
Red
Flame test colour of Na+?
Yellow
Flame test colour of K+
Lilac
Flame test colour of Ca2+
orange-red
Flame test colour of Cu2+?
blue-green
Describe an experiment to prepare a pure, dry sample of a soluble salt, starting from an insoluble reactant
Preparing pure dry crystals of copper sulfate (CuSO4) from copper oxide (CuO) and sulfuric acid (H2SO4)
copper oxide + sulphuric acid -> copper sulfate + water
How to prepare a sample of pure, dry hydrated copper(II) sulfate crystals starting from copper(II) oxide
- Add 50 cm3 dilute acid into a beaker and warm gently using a bunsen burner
- Add the copper(II) oxide slowly to the hot dilute acid and stir until the base is in excess (i.e. until the base stops dissolving and a suspension of the base forms in the acid)
- Filter the mixture into an evaporating basin to remove the excess base
- Gently heat the solution in a water bath or with an electric heater to evaporate the water and to make the solution saturated
- Check the solution is saturated by dipping a cold glass rod into the solution and seeing if crystals form on the end
- Leave the filtrate in a warm place to dry and crystallise
- Decant excess solution and allow the crystals to dry
Look at savemyexams if you still dont know
What 3 things that can act as bases and what is soluble in water
metal oxides, metal hydroxides and ammonia can act as bases, and that alkalis are bases that are soluble in water
What are the general rules for predicting the solubility of ionic compounds in water:
- common sodium, potassium and ammonium compounds are soluble
- all nitrates are soluble
- common chlorides are soluble, except those of silver and lead(II)
- common sulfates are soluble, except for those of barium, calcium and lead(II)
- common carbonates are insoluble, except for those of sodium, potassium and ammonium
- common hydroxides are insoluble except for those of sodium, potassium and calcium (calcium hydroxide is slightly soluble).
know the charges of these ions:
* metals in Groups 1, 2 and 3
* non-metals in Groups 5, 6 and 7
* Ag, Cu, Fe(II), Fe(III), Pb, Zn
* hydrogen , hydroxide , ammonium , carbonate ,
nitrate , sulfate.
- metals in Groups 1, 2 and 3
- non-metals in Groups 5, 6 and 7
- Ag+, Cu2+, Fe2+, Fe3+, Pb2+, Zn2+
- hydrogen (H+), hydroxide (OH-), ammonium (NH4+), carbonate (CO32-),
nitrate (NO3-), sulfate (SO42-).
know how to determine the formula of a metal oxide by combustion (e.g. magnesium oxide)
- Weigh a crucible and lid
- Place the magnesium ribbon in the crucible, replace the lid, and reweigh
- Calculate the mass of magnesium
(mass of crucible + lid + Magnesium – mass of crucible + lid) - Heat the crucible with lid on until the magnesium burns
(lid prevents magnesium oxide escaping therefore ensuring accurate results) - Lift the lid from time to time (this allows air to enter)
- Stop heating when there is no sign of further reaction
(this ensures all Mg has reacted) - Allow to cool and reweigh
- Repeat the heating , cooling and reweigh until two consecutive masses are the same
(this ensures all Mg has reacted and therefore the results will be accurate) - Calculate the mass of magnesium oxide formed (mass of crucible + lid + Magnesium oxide – mass of crucible + lid)
Then you can do the empirical formula with your info
how can the formulae of simple compounds can be obtained experimentally including water and salts containing water of crystallisation
Finding the formula of a salt containing water of crystallisation
When some substances crystallise from solution, water becomes chemically bound up with the salt. This is called water of crystallisation and the salt is said to be hydrated. For example, hydrated copper sulfate has the formula CuSO4.5H2O which formula indicates that for every CuSO4 in a crystal there are five water (H2O) molecules.
When you heat a salt that contains water of crystallisation, the water is driven off leaving the anhydrous (without water) salt behind. If the hydrated copper sulfate (CuSO4.5H2O) are strongly heated in a crucible then they will break down and the water lost, leaving behind anhydrous copper sulfate (CuSO4). The method followed is similar to that for metal oxides, as shown above. The difference of mass before and after heating is the mass of the water lost. These mass numbers can be used to obtain the formula of the salt.
Explain: Melting, Freezing, Boiling, Condensing, and sublimation
Melting: When a solid is heated, the energy makes the particles vibrate fast enough so that the forces of attraction between the particles break. For example H2O(s) –> H2O(l)
Freezing: When a liquid is cooled, the particles move slow enough so that the forces of attraction between them will hold them into a solid. For example H2O(l) –> H2O(s)
Boiling: When a liquid is heated strongly, the energy makes the particles move fast enough so that all forces of attraction are broken. For example H2O(l) –> H2O(g)
Condensing: When a gas is cooled, the particles move slow enough so that the forces of attraction between them will hold them as a liquid. For example H2O(g) –> H2O(l)
Sublimation: A small number of substances have the ability to change directly from a solid to a gas when heated. For example CO2(s) –> CO2(g)
