Hello! I'm currently practicing some multiple choice questions, and I'm a tad confused on a couple of them, was hoping for some help and explanations behind what the answer is?
also-apologies if something's really easy and I should know it, if that's the case then it's probably because they haven't finished teaching us the course yet, so i haven't come across it all.
These questions are on the latest specimen paper for OCR H032/01
Q4) Which row is correct?
Highest pH when added to water / Most reactive halogen
MgO / F2
BaO / F2
BaO / I2
I know Fluorine is more reactive than iodine but how are we supposed to know the alkalinity of the metal hydroxide formed? o.o
Q5) Which equation represents a redox reaction?
A) Mg + 2HCl -> MgCl2 + H2
B) MgO + 2HCl -> H2O + MgCl2
C) MgCO3 + 2HCl -> CO2 + H2O + MgCl2
D) Mg(OH)2 + 2HCl -> MgCl2 + 2H2O
i wrote out the oxidation states before and after but I don't understand the difference between each because atoms are losing/gaining electrons in every reaction?
Q8) A student mixes 100cm3 of 0.200 mol dm-3 NaCl (aq) with 100cm3 of 0.200 mol dm-3 Na2CO3(aq).
What is the total concentration of Na+ ions in the mixture formed?
A) 0.100mol dm-3
B) 0.200 mol dm-3
C)0.300 mol dm-3
D)0.400 mol dm-3
I honestly had no clue for this one. The only thing I could do was work out the moles of NaCl/Na2CO3 which were 0.02mol
Any help would be so much appreciated!
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- Thread Starter
- 17-03-2016 19:07
- 17-03-2016 21:40
Hello, I'm doing Edexcel AS Chemistry and I think I can try to answer Q4
Q4) You're correct as F2 is more reactive than I2. The other factor is which of the two [Mg(OH)2 or Ba(OH)2] has a greater pH or is more alkaline.
FACT -> As you go down the group 2 the solubility increases for group 2 metal hydroxides.
Hence Mg(OH)2 will be relatively insoluble compared to Ba(OH)2 which will be soluble, meaning that less Mg(OH)2 will dissolve in the water to form an alkaline solution(another way to think of this is less OH- ions are available for the water to become alkaline) hence the pH of Mg(OH)2 will be lower than the pH of Ba(OH)2 as Ba(OH)2 is more soluble hence will dissolve in the water more creating a more concentrated alkaline with a greater pH. So finally, the answer will be BaO/F2.Last edited by wenogk; 17-03-2016 at 21:42.