Chemistry 52? Discussion after 24 hours

[farhan141]

How did it go? How much marks do u expect to get?

If anyone wants to compare answers please PM me.

I screwed up in Q.1 and last part of Q.2.

 

[muhammadali233]

Went Perfect,alhumdillah.It was easy.

 

[farhan141]

Went Perfect,alhumdillah.It was easy.

Independent and dependent? Hr increasing with Ecell or not? (Endo or Exo?)

 

[Laibaaa]

Pm me answers too guys

 

[muhammadali233]

24 ghantay sabar.

 

[farhan141]

24 ghantay sabar.

Pm it..

 

[Sadia Ahmad]

for Q2 last part about molecular formula, was it C6H12 (hexene) ? i tried it using the mass spectrum and the Mr calculated in the previous part and i got the same answer each time.

 

[Dark Destination]

for Q2 last part about molecular formula, was it C6H12 (hexene) ? i tried it using the mass spectrum and the Mr calculated in the previous part and i got the same answer each time.

Yes, I got the same answer. But did it without the mass spectrum tho.
What about the relation between E cell and delta H? I wrote that if E cell increases, Delta H decreases...

 

[asadalam]

Yes, I got the same answer. But did it without the mass spectrum tho.
What about the relation between E cell and delta H? I wrote that if E cell increases, Delta H decreases...

Imo it should be proportional,Large e cell shows reaction is very feasible and Large Del H shows that as well,as energy released and products are stable,so more exothermic.The more feasible a reaction the more its exothermic.

 

[Dark Destination]

Imo it should be proportional,Large e cell shows reaction is very feasible and Large Del H shows that as well,as energy released and products are stable,so more exothermic.The more feasible a reaction the more its exothermic.

I had the exact same reasoning, but you're saying the opposite of what it is.
You're saying that a Larger E Cell means MORE exothermic, and more exothermic means the value will be MORE NEGATIVE... and more negative means it will be LESSER. (Isn't -500 LESSER than -200?)
You have to consider the sign too, because we're considering the sign of E cell and Delta H. The magnitude alone is useless.
We're looking at the feasibility here, and the more the feasible, the lesser the delta H value.

For example, if the E cell is 100 ... delta H is -50
But if E cell INCREASES to 500 ... delta H is now -250

So as E cell increases, delta H decreased from -50 to -250.
We have to take the sign into account; magnitude alone means nothing because it can't differentiate between exothermic and endothermic.

 

[asadalam]

I had the exact same reasoning, but you're saying the opposite of what it is.
You're saying that a Larger E Cell means MORE exothermic, and more exothermic means the value will be MORE NEGATIVE... and more negative means it will be LESSER. (Isn't -500 LESSER than -200?)
You have to consider the sign too, because we're considering the sign of E cell and Delta H. The magnitude alone is useless.
We're looking at the feasibility here, and the more the feasible, the lesser the delta H value.

For example, if the E cell is 100 ... delta H is -50
But if E cell INCREASES to 500 ... delta H is now -250

So as E cell increases, delta H decreased from -50 to -250.
We have to take the sign into account; magnitude alone means nothing because it can't differentiate between exothermic and endothermic.

Jee jee bro take it easy , i wrote it gets more exothermic so thats what i meant,although i did forget to include the sign in the calculation,so maybe one or two marks lost for that :/

 

[Sean Tan]

I wrote as Ecell increases, delta H becomes more exothermic

 

[Sean Tan]

The more exothermic the reaction, the more feasible the reaction (as less heat is required for the reaction to proceed to the RHS).
This correlates with the Ecell values.
The reaction between Zn and Cu2+ is really feasible as Zn is a strong reducing agent, Zn will reduce Cu2+ to Cu metal.
That is why the Ecell value for Zn and Cu2+ is really high compared to the reaction with the other two metals.

 

[Dark Destination]

What about that anomaly part? Why was the anomaly caused, and how can it be reduced?

And for measuring E cell, we had to draw two different half cells right?

And how did we have to find the Molecular formula of compound?

 

[asadalam]

What about that anomaly part? Why was the anomaly caused, and how can it be reduced?

And for measuring E cell, we had to draw two different half cells right?

And how did we have to find the Molecular formula of compound?

I wrote some vapour lost bw measuring mass and injecting it into gas syringe,and for the ecell that normal 2 cells like in p4.Molecular was just to find empirical and deduce a value close to mr found in previous part.

 

[Sean Tan]

What about that anomaly part? Why was the anomaly caused, and how can it be reduced?

And for measuring E cell, we had to draw two different half cells right?

And how did we have to find the Molecular formula of compound?

1. For the anomaly, i said it is caused by a decrease in volume of liquid Y, (as we are only using a very little amount of liquid Y in g)
to minimise the anomaly, i suggested increasing the mass of liquid Y used, as that would reduce the percentage error.
Many suggested using ice to condense the liquid, but it would be hard to assemble that onto the apparatus, (unsure if that's acceptable)

2.Yes. two different half cells. you are correct.

3. Molecular formula of the compound? you mean the last question of the paper? analyse the mass spectra, the highest m/e was 84. they said 84.7% is composed of carbon. Do the maths and you will obtain 6 carbon. 84-72 = 12 Mr left.
since the question indicates that it is a hydrocarbon...
C6H12 is the answer

 

[Dark Destination]

I wrote some vapour lost bw measuring mass and injecting it into gas syringe,and for the ecell that normal 2 cells like in p4.Molecular was just to find empirical and deduce a value close to mr found in previous part.

Yes, i found empirical and then its mass, and divided Mr by this.. and then multipled the empirical formula to get molecular formula. But didn't we have to do this question using the mass spectrum given?

 

[Dark Destination]

1. For the anomaly, i said it is caused by a decrease in volume of liquid Y, (as we are only using a very little amount of liquid Y in g)
to minimise the anomaly, i suggested increasing the mass of liquid Y used, as that would reduce the percentage error.
Many suggested using ice to condense the liquid, but it would be hard to assemble that onto the apparatus, (unsure if that's acceptable)

2.Yes. two different half cells. you are correct.

3. Molecular formula of the compound? you mean the last question of the paper? analyse the mass spectra, the highest m/e was 84. they said 84.7% is composed of carbon. Do the maths and you will obtain 6 carbon. 84-72 = 12 Mr left.
since the question indicates that it is a hydrocarbon...
C6H12 is the answer

I wrote that the hypodermic syringe should be kept in a cool environment to reduce evaporation.

 

[Sean Tan]

I wrote that the hypodermic syringe should be kept in a cool environment to reduce evaporation.

May be correct.

 

[Dark Destination]

May be correct.

Hmm, I guess P5 went good.
P4 tho :/