redox wrong epqs Flashcards
Describe what you would see when magnesium reacts with an excess of sulfuric
acid.
[2]
Mg/solid dissolves OR Mg/solid disappears
OR (Mg/solid) forms a solution
bubbles OR fizzes OR effervesces OR gas produced
The student had added the exact amount of calcium required to react with the
hydrochloric acid used. After carrying out the experiment, the student accidentally
added some more calcium. The student was surprised that the extra calcium still
reacted.
Explain this observation. Include an equation in your answer. (2)
Calcium reacts with water producing hydrogen/H2/calcium/hydroxide/Ca(OH)2
(1) (i.e. one product)
Ca(s) + H2O(l) → Ca(OH)2
(aq) + H2
(g) (1) (i.e. full equation)
Equation would subsume both two marks
(i) 12 × 50/1000 = 0.600 mol (1)
(ii) 4 mol HCl → 1 mol Cl2
/ moles Cl2
= 0.15 mol (1)
vol of Cl2= 0.15 × 24 = 3.60 dm3
(1)
2nd mark is consequential on molar ratio given
Draw a ‘dot-and-cross’ diagram to show the arrangement of electrons in
magnesium oxide. Show outer electron shells only and include any charges.
[2]
Amount of substance that has the same number of
particles as there are atoms in 12 g of 12C/
6 × 1023/ Avogadro’s Number
(ii) How many moles of NaOH were in the 120 cm3
volume of NaOH(aq)? (1)
(iii) Calculate the volume of Cl2(g) that was needed to react with the NaOH(aq) used. (2)
What is a common use for the solution that the student prepared?
In the second experiment, the student repeated the procedure in (a) but with hot
concentrated sodium hydroxide. A different reaction took place in which sodium
chlorate (V) was formed instead of NaClO.
Suggest the formula of sodium chlorate (V). (1)
NaClO3
Pierre and Marie Curie extracted radium from radium chloride by reduction.
Explain what is meant by reduction, using this reaction as an example. (2)
Oxidised
AND
(Mg) transfers/loses/donates 2 electrons ✓
Oxidised AND because aluminium has lost
(three) electrons ✔
(Mg) loses / transfers / donates two
electrons ✓
Magnesium (atoms) has been oxidised
AND
Because it has lost two electrons ✓
Copper (ions) has been reduced
AND
Because it has gained two electrons ✓
How could the student obtain a sample of magnesium phosphate after reacting
magnesium with phosphoric acid?
Separation of solid
Filter to obtain solid/precipitate ✓
Requires realisation that solid is
filtered off.
Solid may be stated within in
‘removal of water’
Removal of water
Dry (solid)
OR Evaporate (water/solution/liquid)✓
Element
oxidised: aluminium/Al 0 to +3 ✓
Element
reduced: hydrogen/H/H+ +1 to 0 ✓
Chlorine is used to purify water on a large scale.
State one disadvantage of using chlorine for the purification of drinking water.
Chlorine is toxic/poisonous
OR
forms halogenated hydrocarbons
OR
forms carcinogens/toxic compounds ✓
