VCE Chemistry Question Thread

[grannysmith]

During reaction pathways would you just give the organic compounds the states that they would be found in at room temperature?

Also, how do you know when something should be considered a reactant, or placed on top of the arrow or not? (e.g. The chlorine in the chlorination process of an alkane is placed on top of the arrow, and not with the reactants. Why?)

I believe so, unless they specifically mention otherwise.

Cl_2(g) could technically be placed on the left-hand side, as it is a reactant, however you'd have to make sure the equation is balanced whereas if you place it on top/below the arrow, it doesn't have to be balanced. I'm not exactly sure when it's possible to do this or not, but I have a feeling it's a convention more than anything else. Not 100% though.

[lzxnl]

During reaction pathways would you just give the organic compounds the states that they would be found in at room temperature?

Also, how do you know when something should be considered a reactant, or placed on top of the arrow or not? (e.g. The chlorine in the chlorination process of an alkane is placed on top of the arrow, and not with the reactants. Why?)

During organic reactions, people only care what happens to the organic molecule. Drawing reactants over arrows just means 'use this reactant'. It also means 'this reaction isn't going to be balanced but I don't care'. In research, the number of molar equivalents of reagents is often given too.

[Sundal]

Is the colour of a light said to be the colour absorbed rather than the colour it is observed as?

For example, for the wavelength of 450nm of light my textbook says: "Colour absorbed is blue and colour observed is orange", however light of 450nm is said to be blue and not orange.

[Redoxify]

Is the colour of a light said to be the colour absorbed rather than the colour it is observed as?

For example, for the wavelength of 450nm of light my textbook says: "Colour absorbed is blue and colour observed is orange", however light of 450nm is said to be blue and not orange.

maybe my diagram will help below haha

[blue light] -----> [orange solution] --------> detector

we use complementary colours because we know from chemistry that colours reflect the light they reflect, hence leaves absorb other colours and reflects the green colour

[Redoxify]

can someone help me with the systematic name of serine, the amino acid

[biy]

"Fractional distillation involves a series of evaporation-condensation cycles. The concentration of the more volatile component in the vapour increases after each cycle"

Can someone explain what this means, and why is it so?

[lzxnl]

can someone help me with the systematic name of serine, the amino acid

The one that our bodies use? It would be called L-2-amino, 3-hydroxypropanoic acid. The L refers to a property of the molecule that you probably don't need to worry about for this year.

"Fractional distillation involves a series of evaporation-condensation cycles. The concentration of the more volatile component in the vapour increases after each cycle"

Can someone explain what this means, and why is it so?

As you keep evaporating and condensing the vapour, the less volatile components will condense more and evaporate less, leaving the more volatile components. However I'm sure it's not part of the course...

[warya]

I'm confused about how an NH2 group can exist without a negative charge? Doesn't it have an unbonded electron? In light of this, why does NH3 not have a positive charge? :/

[lzxnl]

I'm confused about how an NH2 group can exist without a negative charge? Doesn't it have an unbonded electron? In light of this, why does NH3 not have a positive charge? :/

NH3 consists of nitrogen bonded to three hydrogens. Nitrogen starts off with 5 2s and 2p electrons and bonds 3 of these with 3 hydrogens to complete its octet. As it hasn't gained or lost electrons, it is neutral.
NH2 groups consist of nitrogen bonded to two hydrogens and one other atom. Again, the nitrogen hasn't lost any electrons.

There IS a lone pair, but that's fine. That does not make the nitrogen negative. The nitrogen still has 7 protons in its core and 2 1s and 5 2s/2p electrons around it, so it's still neutral.

[qwerty101]

i dont quite understand this question. i know what saturated fats etc are, but i dont like how this question is worded. I thought saturated fats are the end product after glycerol and 3 fatty acids react, rather then being "the fatty acid"

According to this logic, mono-unsat fats are a result of glycerol + fatty acids with single bonds, rather then determining mono unsat as the final product? if that makes sense.

Alsom why do poly-unsat contain multiple double bonds? it says "unsat" i would've thought polysat contains multiple C=C

[grannysmith]

i dont quite understand this question. i know what saturated fats etc are, but i dont like how this question is worded. I thought saturated fats are the end product after glycerol and 3 fatty acids react, rather then being "the fatty acid"

According to this logic, mono-unsat fats are a result of glycerol + fatty acids with single bonds, rather then determining mono unsat as the final product? if that makes sense.

Alsom why do poly-unsat contain multiple double bonds? it says "unsat" i would've thought polysat contains multiple C=C

The fatty acids themselves determine whether its poly/mono/saturated. If they contain no double bonds, then the triglyceride or whatever fat will be saturated. If it has one C=C, then the fat will be monounsaturated, and so forth.

'Unsaturated' means at least one C=C i.e. Monounsaturated. Polyunsaturated means more than one double bond. We don't mention 'polysaturated' because this is the same thing as saying 'saturated'.

[qwerty101]

oh yeap that was stupid, thanks for that.

[qwerty101]

difference between esterification and condensation reaction?

[Kel9901]

difference between esterification and condensation reaction?

esterification is specifically for reactions when esters are formed. condensation reactions are for any type of reaction that produce water molecules as a result of two relatively small molecules joining together. All esterification reactions are condensation.

[warya]

Can someone please explain the processes of hydrogenation and dehydrogenation, are they only used in addition reactions of alkenes to produce alkanes?

Also, how does an alkane become an alkene, like how do you add an extra bond