ATAR Notes: Forum

VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: Dark Horse on May 06, 2009, 06:31:18 pm

Title: Esters
Post by: Dark Horse on May 06, 2009, 06:31:18 pm
Hey guys, I was wondering, what is the purpose of sulfuric acid in condensation reactions apart from being a catalyst? I just want to know because I heard that sulfuric acid acts as a dehydrating agent, but lol, why do you need a dehydrating agent?

Thanks :)
Title: Re: Esters
Post by: Mao on May 06, 2009, 07:07:49 pm
to understand this you kinda need a little bit of knowledge about equilibrium.

The esterification reaction is reversible. In fact, the reaction never occurs one way, it is a constant dynamic of forward reaction and backwards reaction. The point where concentration stabilizes and reaches an equilibrium is when the rate of forward and backwards reaction are the same (and this rate depends on an equilibrium constant, which is related to collision between molecules and activation energy and all that jazz).



As a dehydrating agent, water is removed from the right hand side. That is, the amount of water available for the backwards reaction is reduced, hence the number of collisions between ester and water is reduced, hence the rate of reaction is less. Therefore, there is a net increase in forward reaction rate. :)
Title: Re: Esters
Post by: jaja on May 06, 2009, 07:10:00 pm
Glycine is one of the amino acids that forms proteins. Protein that is not required in the body is broken down in the liver. Unwanted nitrogen is converted to urea and eliminated in the urine.

The maximum mass of urea (relative molecular mass = 60) that could be eliminated as a result of the breakdown of 1.00 g of glycine (relative molecular mass = 75) is, in gram,
A. 0.40
B. 0.80
C. 1.00
D. 1.60
Title: Re: Esters
Post by: TrueTears on May 06, 2009, 07:22:05 pm
http://vcenotes.com/forum/index.php/topic,9769.msg147236.html#msg147236
Title: Re: Esters
Post by: jaja on May 06, 2009, 08:08:27 pm
One litre of an aqueous solution of potassium hydroxide (KOH) has a pH of 12.0 at 25°C.
Question 15
The amount of solid KOH, in mol, that must be added to the solution to raise the pH to 13.0 would be
A. 10–13
B. 10–12
C. 0.09
D. 0.10

Do we have to know this? Is isnt in the 2007 section of checkpoints.
Title: Re: Esters
Post by: shinny on May 06, 2009, 08:15:11 pm
You should be able to do pH calculations in unit 3 from what I remember, so yep you do.

On a side note, you shouldn't be posting these questions in this thread anyway...should go make your own so you don't hijack this one.
Title: Re: Esters
Post by: jaja on May 07, 2009, 03:34:22 pm
The person's question has been answered...so there is not need for this thread anymore.
Title: Re: Esters
Post by: Toothpaste on May 07, 2009, 03:39:29 pm
I think you should just make a thread called "jaja's chemistry questions" and post all your questions there. That way you can go back and look over everything you had troubles with as well as keeping the forum more organised.