General thoughts: HSC chemistry 2015 (1 Viewer)

[band6man]

Not necessarily. You needed the catalyst in order to make the temperatures a "compromise"

Yeah but I don't see why its necessary to add this information for the question tbh.

What was the answer for radioisotopes mc question

A

 

[Mr_Kap]

Yeah but I don't see why its necessary to add this information for the question tbh.


A

because you wouldn't be able to have temperatures of 400 - 450°C if you didn't have the catalyst. You would need higher temperatures without the catalyst which means the yield of ammonia will be less.

 

[TQuadded]

because you wouldn't be able to have temperatures of 400 - 450°C if you didn't have the catalyst. You would need higher temperatures without the catalyst which means the yield of ammonia will be less.

I think in Science subjects in general, the more information you provide, the better, as long as it's relevant to the topic. Having said that I didn't mention the catalyst.

 

[malcolm21]

You can have marks deduced for incorrect/conflicting info.

in the hsc? i thought they only look for marks to give?

 

[diladial]

in the hsc? i thought they only look for marks to give?

If you write statements which contradict each other they take your marks off you. Other than that they try be as kind as they can.

 

[myinnermonkey]

Yeah but I don't see why its necessary to add this information for the question tbh.


A

The question didn't specifically ask for temperature and pressure; they asked for conditions with reference to the graph. This means that you talk about all the conditions, and talk about the graph in relate to temp and pressure. To talk about temp conditions, you have to say that haber process uses moderate temperatures of 400-450 degrees, however the graph shows that maximum yield is obtained from 500atm and 200 degrees. This low temperature would however mean that the reaction rate is very slow so production isn't efficient, thus that's why 400 degrees is usually used. To further compensate for the slow reaction rate, magnetite catalyst is used. For a six mark question, I don't think talking only about temperature and pressure is enough tbh

 

[Librah]

in the hsc? i thought they only look for marks to give?

Oh i meant they won't give you marks if you write a correct statement, but somewhere else you contradicted it.

 

[BlueGas]

The question didn't specifically ask for temperature and pressure; they asked for conditions with reference to the graph. This means that you talk about all the conditions, and talk about the graph in relate to temp and pressure. To talk about temp conditions, you have to say that haber process uses moderate temperatures of 400-450 degrees, however the graph shows that maximum yield is obtained from 500atm and 200 degrees. This low temperature would however mean that the reaction rate is very slow so production isn't efficient, thus that's why 400 degrees is usually used. To further compensate for the slow reaction rate, magnetite catalyst is used. For a six mark question, I don't think talking only about temperature and pressure is enough tbh

lol, do you know what you are saying? When they say with reference to the graph, that means you only speak about temperatures and pressures. You wouldn't speak about ratio of reactants or concentrations of contaminants as it wasn't mentioned in the graph. 3 marks for temperature and 3 marks for pressure is enough, no need to speak about anything else unless if it relates to temperature (for example excessively high temperatures melt catalyst) and pressure (excessively high pressures are hard to maintain, dangerous, etc.)

 

[Dellrune]

I hope everyone drew a diagram for the polyethylene and polystyrene question because you MUST have a diagram to get full marks. This question is straight from a previous HSC exam where the marking criteria stated you had to have a diagram to receive 3+ marks

 

[BlueGas]

I hope everyone drew a diagram for the polyethylene and polystyrene question because you MUST have a diagram to get full marks. This question is straight from a previous HSC exam where the marking criteria stated you had to have a diagram to receive 3+ marks

Question didn't say include diagram.

 

[band6man]

because you wouldn't be able to have temperatures of 400 - 450°C if you didn't have the catalyst. You would need higher temperatures without the catalyst which means the yield of ammonia will be less.

Bolded doesn't reference the graph

 

[Librah]

Again if anyone has it, the K question from Industrial that everyone's complaining about please.

 

[Dellrune]

Question didn't say include diagram.

the past HSC question didnt say include a diagram either! i remember VIVIDLY being angry at the criteria since it didnt specify, but I learnt my lesson and drew a diagram of each one today.

I swear on my life brah

 

[Torque]

Hey guys. Would I lose marks for explaining the thermal decomposition of sodium hydrogen carbonate before ammonia recovery for part (i) of the Solvay Process question with the given flow chart?

 

[Crisium]

the past HSC question didnt say include a diagram either! i remember VIVIDLY being angry at the criteria since it didnt specify, but I learnt my lesson and drew a diagram of each one today.

I swear on my life brah

Marking criteria changes over time

I think they'd be looking for you to be specific with the type of polystyrene and polyethylene so I talked about LDPE, HDPE, crystal polystyrene and expanded polystyrene just to be safe

 

[HecticLad]

lol, do you know what you are saying? When they say with reference to the graph, that means you only speak about temperatures and pressures. You wouldn't speak about ratio of reactants or concentrations of contaminants as it wasn't mentioned in the graph. 3 marks for temperature and 3 marks for pressure is enough, no need to speak about anything else unless if it relates to temperature (for example excessively high temperatures melt catalyst) and pressure (excessively high pressures are hard to maintain, dangerous, etc.)

the graph also did refer to yield on it, so you could talk about why the yield is balanced with the rate of reaction, which would be influenced by a catalyst, if there is a greater rate from the catalyst, then they could decrease the temperature a bit more to increase yield a bit while still maintaining the original rate of reaction

 

[Dellrune]

yeah tru I feel like the whole paper was awarding stacks of marks for questions that in the past would be worth only 2 or 3, like I felt that the baso4 and titration calculations were generous and well as the radioisotope

significant figures for the BaSo4 question mate. 3 marks for calculation and equation + 1 mark for correct sig figs

 

[el_manu]

Again if anyone has it, the K question from Industrial that everyone's complaining about please.

the K question wasnt even hard lol. Just use an ICE table and you are sweet. I'm glad they asked a K question as it is by far the most routine and easiest part of industrial chemistry.

 

[Crisium]

Hey guys. Would I lose marks for explaining the thermal decomposition of sodium hydrogen carbonate before ammonia recovery for part (i) of the Solvay Process question with the given flow chart?

I thought I was the only one who thought this haha

I always go with ammonia recovery coming after the thermal decomposition of sodium hydrogen carbonate but I followed the flowchart just to be safe

They said with reference to the flowchart so if you referred your other processes such as brine purification, etc you should be fine

 

[BlueGas]

the graph also did refer to yield on it, so you could talk about why the yield is balanced with the rate of reaction, which would be influenced by a catalyst, if there is a greater rate from the catalyst, then they could decrease the temperature a bit more to increase yield a bit while still maintaining the original rate of reaction

Yield is not a "condition" lol, obviously you would reference to yield though as a result of temperature and pressure but that's the only thing you could speak about since those were the only conditions mentioned in the graph.