What is the molecular and empirical formula for ethene
- Empirical: CH2
- Molecular: C2H4
What formula of an ion makes a hydrogen chloride solution acidic
- H+
Why may a water with impurities be potable
- Because the impurities are harmless (made up of minerals and ions)
It was concluded that the best way to purify 1000cm3 of the waste water is to add 100mg of salt B, Use the information about salt A and salt B to evaluate this conclusion.
- 100 mg of A removes 40% impurities
- 100 mg of B removes 44% impurities
- so salt B is better than salt A as more impurities are removed for same mass of salt
Aluminium ions react with phosphate ions to form aluminium phosphate.
Complete the ionic equation for the formation of aluminium phosphate in this reaction
- Al(3+) + PO^4(3-) → AlPO^4
A sample of molten potassium bromide is electrolysed.
What are the two products formed?
- potassium and bromine
Zinc chloride mixed with water can be electrolysed.
Zinc carbonate mixed with water cannot be electrolysed.
Explain this difference.
- zinc chloride is soluble and zinc carbonate is insoluble
- so ions free to move only in zinc chloride solution
Explain how hydrogen is formed at the cathode
- hydrogen ions attracted to cathode
- two hydrogen ions gain two electrons and are reduced
- 2H + 2e- —> H^2
During the electrolysis, the anode gets smaller, the cathode gets larger and
the solution remains the same shade of blue in copper sulfate solutions
Why?
- Anode: smaller because copper atoms form ions and go into solution (oxidation of Cu atoms)
- Cathode: larger because copper atoms are formed from ions in the solution and reduction of Cu(2+)
- Solution: the same number of ions enter and leave solution
During the reaction, the pH of the mixture changed from 2 to 6.
By what factor has the concentration of the hydrogen ions in the mixture changed?
- 1/10,000
CuSO4.5H2O → CuSO4 + 5H2O
Calculate the mass of hydrated copper sulfate that was heated.
- Mass / MR = Mole
- moles of H2O = 4.5 / 18.0 = 0.25
- moles CuSO4.5H2O = 0.25/5 = 0.05
- mass CuSO4.5H2O = 0.05 x 249.5 = 12.475 g
The order of reactivity of copper, magnesium and zinc can be determined by the displacement reactions between these metals and solutions of their salts.
Describe the experiments that can be done to determine the order of reactivity of these metals by displacement reactions
- place separate pieces of each metal into solutions of each of salt
- observe changes in colour of solution
- the more reactive metal shows the greater number of reactions
Explain why aluminium cannot be extracted from its ore by heating with carbon but can be extracted by electrolysis.
- aluminium is more reactive than carbon
so electrolysis required - carbon cannot remove the oxygen as aluminium is more reactive
- electrolysis can be used to reduce aluminium ions
Suggest how pure titanium chloride could be separated from the impurities
- simple distillation
there is a mixture of the solids magnesium, titanium and magnesium chloride. Titanium does not react with dilute hydrochloric acid.
Suggest a simple method to separate titanium from the mixture.
- filter off the titanium
- Then wash the titanium
Deduce, using the information in Figure 4, the structure and bonding of substances A, B and C, explaining their properties in terms of their structure and bonding.
- Substance A: giant ionic structure, strong electrostatic attractions between ions from high melting point needs a lot of energy to overcome it, poor conductor when solid as ions can’t move freely
- Substance B: metallic structure, strong attraction between metal ions and delocalised electrons from high melting point and needs a lot of energy to overcome it, free to move throughout metallic lattice so good conductor when solid
- Substance C: covalent simple molecular, weak attractions between molecules from low melting point so doesn’t need that much energy to overcome it, in solid and when molten, no delocalised electrons so it’s a poor conductor
Element X has an atomic number of 18.
State the electronic configuration of an atom of element X.
- 2.8.8
In an experiment, 3.5 g of element A reacted with 4.0 g of element G to form
a compound.
Calculate the empirical formula of this compound.
- Find moles from each (mass/mr)
- Empirical formula = 2:1
When molten zinc chloride is electrolysed, zinc ions, Zn2+, form zinc atoms.
Write the half equation for this reaction.
- Zn (2+) + 2e- → Zn
Nickel is extracted from nickel compounds.
State an advantage of extracting nickel by phytoextraction rather than from
its ore.
- decontaminates ground
- less carbon dioxide
An advantage of producing a metal by electrolysis is that
- the metal produced by electrolysis is very pure
Describe what you would see when an excess of zinc is added to copper sulfate solution and the mixture left until the reaction is complete.
- orange solid formed
- some grey solid will remain
- blue solution becomes colourless
Zn(s) + CuSO4(aq) o ZnSO4(aq) + Cu(s)
This reaction is described as a redox reaction.
Explain, in terms of electrons, which particles have been oxidised and which
particles have been reduced in this reaction.
- zinc oxidised
- because zinc lose electrons
- copper ions reduced
- because copper ions gained electrons
State how you could change the method so that the amounts of dilute
hydrochloric acid and of the base can be measured more accurately.
- Dilute HCL: use measuring cylinder
- Base: Weigh out amount using a balance
