chem questions

[kawfee]

2002 VCAA MC

- 1 g of each of the following substances is dissolved in 1 L of water. Which one would have pH of the resultant solution be closest to 7?

Do I need to perform any sort of calculation or look at theory?

My thoughts:
H2SO4 -Cannot be sulfuric acid because it's very acidic = low pH
NH3 < weak base ... so close to pH of 7 ?
NaHSO4 < is this a salt? Also is this weakly acidic or ?
NaCl - dissolves in water, resultant pH close to 7 .... < Answer

Please correct any of my 'thoughts/comments' and I'd appreciate an explanation or way of approaching this question.

Also Q4)

When concentrated sulfuric acid is poured into solid sodium bromide, the liq turns brown as bromine is produced
Sulfuric acid is acting as...?
- oxidant reductant dehydrating agent strong acid
Answer is = oxidant ... how so? Is this still examinable for this year's study design?
I wrote an equation > H2SO4 + 2NaBr > Na2SO4 + 2HBr ...and check oxidation no.s, however nothing has changed?
Is what I'm doing wrong..? Please explain


thank you

[jgoudie]

As most people have said, this study design really isn't until 2008 onwards, so a lot of questions you may come across, although increasing your knowledge of chemistry in general, may not help with this years exam. 

HOWEVER, these two are fine, you should be able to do them.

1) Your logic is good for the first question.  NaHSO₄, the HSO₄^- ion will act as a weak acid.

2) For you second question you need to think about the half equation for the bromine. NaBr (Br^-), Bromine is Br₂.

So: 2Br^- --> Br₂ +2e^-  You can see that this oxidation, thus the sulphuric acid must be the oxidant, causing the oxidation.

2002 VCAA MC

- 1 g of each of the following substances is dissolved in 1 L of water. Which one would have pH of the resultant solution be closest to 7?

Do I need to perform any sort of calculation or look at theory?

My thoughts:
H2SO4 -Cannot be sulfuric acid because it's very acidic = low pH
NH3 < weak base ... so close to pH of 7 ?
NaHSO4 < is this a salt? Also is this weakly acidic or ?
NaCl - dissolves in water, resultant pH close to 7 .... < Answer

Please correct any of my 'thoughts/comments' and I'd appreciate an explanation or way of approaching this question.

Also Q4)

When concentrated sulfuric acid is poured into solid sodium bromide, the liq turns brown as bromine is produced
Sulfuric acid is acting as...?
- oxidant reductant dehydrating agent strong acid
Answer is = oxidant ... how so? Is this still examinable for this year's study design?
I wrote an equation > H2SO4 + 2NaBr > Na2SO4 + 2HBr ...and check oxidation no.s, however nothing has changed?
Is what I'm doing wrong..? Please explain


thank you

[Robert123]

For question 2, your equation is wrong. Look at what your question say is the prodcuct, bromine. In your equation, your product is a bromide, there is a subtle but important difference between the two.
If something end with ide, then the atom has a negative charge. If it ends in ine, then that atom has a neutral charge