VCE Chemistry Question Thread

[darklight]

Although benzene does not undergo the bromine test, will other cyclic molecules undergo addition reactions with bromine, causing the red solution to turn colourless?

[Reus]

Thanks scooby!

[Yacoubb]

What are the functional groups of aspirin? Carboxyl group and...?

[Reus]

What are the functional groups of aspirin? Carboxyl group and...?

Is it not Ester?

[Yacoubb]

Is it not Ester?

Yeah just making sure! Thanks

[eagles]

Page 137 of Heinemann textbook, Table 9.4 Common functional groups in organic compounds.

Why do some of the formula for functional groups, eg. Chloro, hydroxyl and amino don't have the 'R' group whereas ester, amiss and ether do?

Thank you.

[lzxnl]

Although benzene does not undergo the bromine test, will other cyclic molecules undergo addition reactions with bromine, causing the red solution to turn colourless?

Benzene...under certain conditions will react with bromine, although it's not an addition reaction; rather, if you have FeBr3 as a catalyst, you'll promote a substitution reaction where one of the bromine in Br2 substitutes for a H in benzene.

[Reus]

A few questions once again!

• Balanced equation for the conversion of CH₃CHO to CH₃COOH in the presence of NAD⁺
• The type of reaction of this would be?
  
• How does the omission of coenzymes and cofactors effect on the enzyme's activity?

Thanks!

[lzxnl]

A few questions once again!

• Balanced equation for the conversion of CH₃CHO to CH₃COOH in the presence of NAD⁺
• The type of reaction of this would be?
  
• How does the omission of coenzymes and cofactors effect on the enzyme's activity?

Thanks!

Ok first one.
CH3CHO to CH3COOH? NAD+ just goes to NADH, so the half reaction is NAD+ + H+ + 2e- => NADH for the reduction
As for the oxidation, CH3CHO => CH3COOH          Balance oxygens by adding water
CH3CHO + H2O => CH3COOH     Balance hydrogens
CH3CHO + H2O => CH3COOH + 2H+ + 2e-   See how I added electrons to balance the charge?
Put the two equations together to give NAD+ + CH3CHO => CH3COOH + H+ + H2O
This is a redox reaction

Omitting coenzymes and cofactors means the enzyme can't work. They're a crucial part of the enzyme's function. For example, the zinc cation in carbonic anhydrase is what facilitates the entire catalysis of H2CO3 formation.

Thanks so much! SO much clearer now. :
However how does the accumulation affect the production of CO₂?
I'm taking a wild guess that it increases it?

What happens is that by consuming ethanol and requiring the use of the oxidant NAD+,  your body has less NAD+. Remember how the Krebs/citric acid cycle requires 3 lots of NAD+ and 1 lot of FAD per molecule of acetyl CoA? If you run low on NAD+, the Krebs cycle can't run as fast and less CO2 is produced.

[Reus]

Ok first one.

Thank you!

[danman.9]

Note that ethanol consumption leads to an accumulation of NADH. How will this accumulation affect
glycolysis and the pathways that produce CO2???

[Reus]

Note that ethanol consumption leads to an accumulation of NADH. How will this accumulation affect
glycolysis and the pathways that produce CO2???

Well well well...

It's oxidation. Ethanol is metabolised in the liver, which involves it first being converted to acetaldehyde, which is converted to ethanoic acid, which is converted to acetyl Co-A. As ethanol is metabolised, NAD+ is consumed and converted to NADH. Since NAD+ is required for glycolysis, the rate at which glycolysis occurs would reduce if NAD+ is depleted (NAD+ is essentially a limiting reactant).

What happens is that by consuming ethanol and requiring the use of the oxidant NAD+,  your body has less NAD+. Remember how the Krebs/citric acid cycle requires 3 lots of NAD+ and 1 lot of FAD per molecule of acetyl CoA? If you run low on NAD+, the Krebs cycle can't run as fast and less CO2 is produced.

[danman.9]

thank you Reus 

[Einstein]

why exactly do shells further from the nucleus have higher energy?

also if metals have high melting and boiling points, and alkali (group 1 ) are metals, why do they have low melting and boiling points?

[lzxnl]

why exactly do shells further from the nucleus have higher energy?

also if metals have high melting and boiling points, and alkali (group 1 ) are metals, why do they have low melting and boiling points?

These 'shells' can be thought of as electrons spending most of their time in a region of space. Now, electrostatic attraction, mathematically, behaves like gravitational attraction. They're both inverse square laws. Given this, do you expect a rock half a metre off the surface of the Earth or a rock 20 m above the surface of the Earth to have more potential energy? Similar idea for electrons.

why exactly do shells further from the nucleus have higher energy?

also if metals have high melting and boiling points, and alkali (group 1 ) are metals, why do they have low melting and boiling points?

Alkali metals only have 1 valence electron to contribute to the delocalised electron sea. The attractions between the cations and the electron sea are therefore much weaker. In addition, group 1 metals are the largest elements when it comes to ionic radii for their period, so the electrons are further away from the cations, weakening attractions.