Chemistry Questions

[taiga]

Hey guys, can you check out these questions.

I'm pretty sure I am correct for them, but the answers seem to be giving me a different indication, if you could just try them and tell me what you think for each one that would be cool (so i can compare them to the answers and confirm they are wrong).

[m@tty]

As a disclaimer, please bear in mind that I haven't even thought about Chem in the past three weeks. But seeing as no one has posted yet..

19. C

17. A

15. ? D

18. A

14. D

5. A

6. I have no idea. C? As neither can release positive ions..

[toshibaj]

I got D for question 17, and C for 18. Not sure about 6. Everything else I got the same as m@tty.

EDIT: Googled buffer solution - which is a solution that resists pH change as it consists of an acid or base (can be weak or strong), thus answer is C.

[scocliffe09]

19C - draw yourself a mini-electrochemical series
17D - in electrolysis / electroplating, metal always deposited at negative terminal (which is the cathode in electrolysis) --> hence anode loses mass
15D - delta H for CO2 is not in the data book, and without a delta H value you can only tell that heat will be produced as it is an exothermic combustion reaction - you cannot tell how much heat though, I don't think.
18C - not happy with this question... delta H is negative, so it's definitely exothermic, hence B,D are wrong. As you know from the reaction that for every 2 mol of Al (s), you get 1674 kJ of energy, for 0.5 mol, you should get 1674/4=418.5 mol of heat, which is C, but with a dodgy decimal place. I'm hoping/guessing that that's a typo? I could understand if it were, say, 418.3 mol if they were trying to be smart and take into account (somehow) heat loss / incomplete reaction, but I dunno why it would give off more heat than delta H predicts...
14D - draw a funky little energy profile
5A - more molecules on LHS; exothermic.
6C - you need an acid + a base - C has two bases.

[taiga]

Aah thanks guys, pretty much confirms that some of the answers they have provided are incorrect.

If anyone would like the exam just pm me. (Don't want to upload it as teachers may have a whine)

[m@tty]

I got D for question 17, and C for 18. Not sure about 6. Everything else I got the same as m@tty.

EDIT: Googled buffer solution - which is a solution that resists pH change as it consists of an acid or base (can be weak or strong), thus answer is C.

Okay, yeah, you're right.

Forgot that cathode is negative in electrolosis and didn't realise that there was only one quarter of the Al required for the equation...