topic 8 Flashcards
Explain the origin of the colours in flame tests (2)
Excited electrons. (1)
move down energy levels. (1)
State what would be seen when concentrated sulfuric acid is added to separate solid samples of each of these compounds. (4)
(i) Lithium chloride
(ii) Sodium bromide
(iii) Potassium bromide
(i) steamy fumes
(ii) brown vapour
(iii) purple vapour.
Explain the term oxidation in terms of electron transfer. (1)
loss of electrons
Explain the term oxidising agent in terms of electron transfer
a substance which gains electrons
Which process explains the flame colour produced by the compounds of Group 1 elements?
A- absorption of visible light energy as electrons are promoted to higher energy levels.
B- absorption of visible light energy as electrons are removed from gaseous atoms.
C- emission of visible light energy as electrons return to lower energy levels.
D- emissions of visible light energy as electrons are added to gaseous ions.
C- emission of visible light energy as electrons return to lower energy levels.
When sodium chlorate(I), NaClO, is heated, sodium chlorate (V) and sodium chloride are formed.
(i) Write the ionic equation for this reaction
(ii) What type of reaction is this?
(i) 3OCl- —-> ClO3- + 2Cl-
(ii) Disproportionation.
Name a reagent that could be used to confirm that a solution contains iodine, and state what would be seen. (2)
starch
blue-black.
How could you confirm that a solution said to be HCl(aq) contained chloride ions?
- add silver nitrate
- white ppt
- soluble in dilute ammonia.
Hydrogen chloride is soluble in water. Explain why the solution is acidic.
changes into ions as it dissolves.
Give a chemical test for chlorine, stating what you would do and what you would see. (2)
damp litmus paper
bleached.
Iodine, I2, can be reduced to iodine ions, I- by tin(II) ions, Sn2+, which are themselves oxidised to tin(IV) ions, Sn4+
(i) Construct the oxidation and reduction half-equations for the above system.
Sn2+ - 2e- —> Sn4+
I2+2e- —->2I-
(ii) Use the above half equations to construct the overall ionic equation for the reaction. (1)
Sn2+I2 —>Sn4+ + 2I-
Define reduction in terms of change in oxidation number. (1)
decrease in oxidation number of an element.
Write an ionic half-equation for the reduction of chlorine molecules to chloride ions. State symbols are not required. (1)
Cl2 + 2e(−) → 2Cl-
Write an ionic half-equation for the oxidation of chlorine molecules to chlorate(I) ions in the presence of cold, aqueous hydroxide ions. State symbols are not required. (1)
Cl2 + 4OH- → 2ClO- + 2H2O + 2e(−)
Combine the two equations in (a)(i) and (ii) to give the ionic equation for the reaction of chlorine molecules with cold, aqueous hydroxide ions. (1)
Cl2 + 2OH- → Cl- + ClO- + H2O
Use your answer to (a)(iii) to explain why the reaction is described as a disproportionation reaction.
- disproportionation is simultaneous oxidation and reduction of an element in the same species (1)
- chlorine changes from 0 to -1 and +1 (1)
Which element in group 7 has the highest first ionisation energy. (1)
A - iodine
B- bromine
C- chlorine
D- fluorine.
The first five ionization energies of an element, X, are: 578, 1817, 2745, 11578 and 14831 kJ mol-1, respectively. In which group of the Periodic Table is X found?
A- 1
B- 2
C- 3
D- 4
21 (a) (i) An alkaline solution is produced when barium reacts with cold water. Write the equation for this reaction, including all state symbols. (2)
Ba(s) +2H2O(l)-> Ba(OH)2(aq) + H2(g)
(ii) The reaction in (a)(i) is a redox reaction. State the initial and final oxidation number of any element that changes its oxidation number. (2)
- Ba(increases in ON) from 0 to +2 (1)
- H (decreases in ON) from +1 to 0(1)
b) Dilute hydrochloric acid is added to the solution produced in (a)(i). Write the equation for the reaction which occurs. State symbols are not required. (1
Ba(OH)2 + 2HCl->BaCl2 +2H2O
An oxidising agent
A- gains electrons and is oxidised
B- loses electrons and is oxidised
C- gains electrons and is reduced
D- loses electrons and is reduced
C- gains electrons and is reduced
