VCE Chemistry Question Thread

[sparkyblossom]

When writing an esterification equation, are we expected to use a double arrow (equilibrium) or a single arrow?

[Alter]

Similar to the above, in terms of reaction pathways, is sulphuric acid the only catalyst/condition we're supposed to mention when doing a typical alkanol + carboxylic acid esterification reaction?

[warya]

Similar to the above, in terms of reaction pathways, is sulphuric acid the only catalyst/condition we're supposed to mention when doing a typical alkanol + carboxylic acid esterification reaction?

Yep, you just need it there to act as a dehydrating agent. Just make sure u don't put h2SO4(aq), it must be in the liquid state

[HighTide]

When writing an esterification equation, are we expected to use a double arrow (equilibrium) or a single arrow?

Yes double headed.

Similar to the above, in terms of reaction pathways, is sulphuric acid the only catalyst/condition we're supposed to mention when doing a typical alkanol + carboxylic acid esterification reaction?

Yh concentrated sulfuric acid in a liquid state as warya said. In addition, my school chem teacher told me to write heat denoted by a triangle below the arrow. However, I don't think that's necessary.

[Alter]

Yep, you just need it there to act as a dehydrating agent. Just make sure u don't put h2SO4(aq), it must be in the liquid state

Whew, thanks! I would've made this mistake if you didn't tell me. What state are/is the catalyst(s) for alkanol to aldehyde->carboxylic acid?

[Impulse]

Does anyone know if it is acceptable to write answers in scientific notation (1.5*10^3 instead of 1500)? The examiners report doesn't use it but I find it easier to use this with significant figures.

[Impulse]

Yes double headed.

Why is it double-headed?

[HighTide]

Does anyone know if it is acceptable to write answers in scientific notation (1.5*10^3 instead of 1500)? The examiners report doesn't use it but I find it easier to use this with significant figures.

It's allowed as long as it's to the same significant figures I think.

Why is it double-headed?

Double headed arrow because esterification reaction is reversible.

[warya]

Whew, thanks! I would've made this mistake if you didn't tell me. What state are/is the catalyst(s) for alkanol to aldehyde->carboxylic acid?

ACIDIFIED dichromate i.e. H+/CrO72- AQUEOUS, must have the ionic charges and the H+ there otherwise you'll get marked wrong.
I'm assuming you mean like ethanol--->ethanoic acid right? No idea what an aldehyde is haha

[paper-back]

Just confirming; When Cl2 is added to a solution of propane and irradiated with UV light, dichloropropane and H2 gas can be formed as products right?

When aspartic acid is placed in a solution with pH of 10, does it lose a proton from it's z-group?

[Alter]

ACIDIFIED dichromate i.e. H+/CrO72- AQUEOUS, must have the ionic charges and the H+ there otherwise you'll get marked wrong.
I'm assuming you mean like ethanol--->ethanoic acid right? No idea what an aldehyde is haha

Aldehyde as in a C is double bonded to an O and a single bonded to a H at the same time. Alkanol needs dichromate to oxidise into an aldehyde, and then the aldehyde undergoes another oxidation reaction to turn into a carboxylic acid. I don't know if the middle step is necessary for marks in VCE as a complete oxidation will turn an alkanol into a carboxylic acid.

[jyce]

Aldehyde as in a C is double bonded to an O and a single bonded to a H at the same time. Alkanol needs dichromate to oxidise into an aldehyde, and then the aldehyde undergoes another oxidation reaction to turn into a carboxylic acid. I don't know if the middle step is necessary for marks in VCE as a complete oxidation will turn an alkanol into a carboxylic acid.

The middle step is not necessary.

[jyce]

Just confirming; When Cl2 is added to a solution of propane and irradiated with UV light, dichloropropane and H2 gas can be formed as products right?

When aspartic acid is placed in a solution with pH of 10, does it lose a proton from it's z-group?

Yes to your first question, although there are quite a few other possible products.
As for your second question, in an aqueous solution of aspartic acid at pH 10:
- some molecules would have both carboxyl groups ionised
- others would have only the carboxyl group in the z-group ionised
- and still others would have only the carboxyl group not in the z-group ionised.
If you were asked this in an exam, I would have both carboxyl groups ionised.

[jyce]

But if there's a voltmeter and no battery pack, how can I assume electrolysis and not galvanic?

I think this is a galvanic cell, not an electrolytic cell. A voltmeter does not provide energy; rather, it measures energy. A battery is what would provide an external source of energy, and the question does not allude to a battery. So, energy is being generated but not from a battery; therefore, I would conclude that electrical energy is being generated by the cell, so the cell is galvanic. In this case then, the zinc discs are oxidised and therefore are the anodes, i.e. the negative electrodes of the galvanic cell. The negative terminal of the voltmeter needs to be connected to a negative electrode, meaning the answer is Zn.

EDIT: Also, the fact that soaked filter paper was used to connect the discs suggests that the cell is galvanic.

[paper-back]

A colorimeter containing 1000ml of water was calibrated using 2g of Methanol, it was recorded that the temperature rose by 10K. The volume of water was then increased to 2000ml and 2g of Ethanol was entirely combusted which raised the temperature of the colorimeter by 6.81K. Calculate the molar enthalpy of Ethanol
Is the answer to this question -1364KJ/mol?