IGCSE Chemistry Multiple Choice?

Question

My test is coming up soon (in a few days) and so I decided to look at a few pastpapers.
There were two questions I was unsure of even after I was told the answers from the mark scheme.
The paper is June 2005 Paper 1:

Question 22- In an experiment shown, the dilute sulphuric acid is run into the flask of aqueous barium hydroxide until the reaction is complete. Which processes occur in this reaction? A- Neutralisation and Precipitation B- Just Neutralisation C- Just Precipitation D- None. I chose B but the answer is A?

Question 28- Which metal reacts quickly with cold water only when it is finely powdered? A- Calcium B- Copper C- Sodium D- Magnesium. I chose C as sodium is the most reactive out of all of them (according to the reactivity series) but the answer is D?

I would appreciate any help. Thank you!

Thank you for the answers but I am not sure what you meant for Q28, I didn't take E (I am not sure what you mean) Is it to do with bond energy?
Thanks again

Answer 1

Since Ba(OH)2 is a base, you would expect a neutralisation reaction with H2SO4. But BaSO4 is insoluble, so you get a precipitate as well.

Ca reacts quickly in lump form. Na reacts very quickly. Cu doesn't react at all. A strip of Mg collects a few bubbles on the surface, but the reaction is quicker if it is in powdered form.

The above answerer obviously doesn't realise that talking about electrode potentials (E values) to an IGCSE candidate is a non-starter!

Answer 2

question 22-
the reaction that occur is :

H2SO4 + Ba(OH)2 >> BaSO4 (s) + 2H2O

(precipitation)

if moles of H2SO4 = moles Ba(OH)2 we get also a neutralizazion

question 28 - looking at the reactivity series Ca would be the most reactive ( for the half-reaction Ca >> Ca2+ + 2e- we have E° = + 2.87 ; for Mg >> Mg2+ + 2e- E° = +2.37 ; for Na>> Na+ + 1e- E° = + 2.71)