/0's Chem Questions

[/0]

Potassium hydroxide reacts with carbon dioxide as follows:


Which expression correctly represents the volume of 0.1M KOH solution that will react with 56 mL of at STP?

A. L

B. L

C. L

D. L








Consider the following reaction:



Which statement about this reaction is not true?

A. Dichromate ions have been oxidised (doesn't the dichromate split up? so how can you tell)
B. Chloride ions have been oxidised.
C. Hydrogen ions have been reduced. (why?)
D. Sulfate ions have not been oxidised or reduced. (?)

[TrueTears]

Hence B

[/0]

Thanks TT !

Also,

Can the bonds in glucose, fructose or galactose rotate, or are they fixed in place?

[TrueTears]

Thanks TT !

Also,

Can the bonds in glucose, fructose or galactose rotate, or are they fixed in place?

What exactly do you mean by "rotate"?

You can 'flip' the molecule upside down. For example, this is what happens between the glucose monomers when cellulose is formed.

[/0]

I mean, if you rotate one of the bonds in glucose, it becomes galactose. So I'm wondering if the other bonds also can't rotate. Thanks again

[TrueTears]

I mean, if you rotate one of the bonds in glucose, it becomes galactose. So I'm wondering if the other bonds also can't rotate. Thanks again

No they can not rotate, it is because they can't rotate that makes them unique. ie, the difference b/w glucose and galactose is the H-OH on glucose but it is OH-H on galactose (Vertically)

[/0]

thx m8 that is well interesting

However in one the questions it asks you to draw the products of a hydrolysis reaction involving Lactose
In the picture below, the top structure is Lactose as given in the question, and the bottom structures are the products (glucose and galactose) as given in the answer.

However, notice in the product that one of the bonds in galactose is pointing in the opposite direction. Do you endorse this or is it wrong?

[TrueTears]

For some reason I knew you were going to ask this.

I do not endorse this.

The question is wrong.

Look at the 2nd row, first picture. I assume it is a Galactose molecule, it must have the H and OH swapped around on the right side.

As a result the lactose diagram is also wrong. The picture of the glucose (the top right one on the first row) is right, however the galactose must have the OH and H swapped around.

[/0]

I did some research and apparently there are two forms of Galactose and Glucose.

There are and forms of glucose and galactose.

In the form, the -OH of the rightmost carbon (carbon 1) points downwards, but in the form, the -OH of carbon 1 points upwards, so I guess both forms are acceptable.

The carbons are numbered clockwise starting from the rightmost carbon which is carbon 1. Thus the difference between glucose and galactose lies on carbon 4.

Sources: http://www.biotopics.co.uk/JmolApplet/galactosejdisplay.html, http://www.biotopics.co.uk/JmolApplet/glucosejdisplay.html

[/0]

Why is it that in organic chemistry, states for organic compounds are often given as (l) instead of (aq)? Are we to assume that these compounds are completely pure, even if the question does not state so?

[TrueTears]

If the question states they are pure then you would put (l). I'm not sure what you would do if they don't tell you though.

[/0]

Oh ok, thanks TT

I have so many questions lol

Is it necessary to draw the lone pairs on elements like nitrogen in or oxygen in ? Could marks be deducted for it... the book never does it.

[dekoyl]

Oh ok, thanks TT

I have so many questions lol

Is it necessary to draw the lone pairs on elements like nitrogen in or oxygen in ? Could marks be deducted for it... the book never does it.

When I went to the UoM lecture, I think she said we should but I never do (and yeah, the book doesn't either).
I do hope we don't.

[TrueTears]

I asked Dr Slade (author of checkpoints). He said you should.

[ice_blockie]

I was told you should too. (An aside, hasn't Slade retired???)