HSC Chemistry Question Thread

[mxrylyn]

Hey. Happy new years everybody.
On Process information from secondary sources to summarise the processes involved in the industrial production of ethanol from sugar cane

My excel study guide has process which goes sugarcane > fermentation >distillation > bioethanol,
Whereas my AN Chemistry poster goes sugar cane >cellulose >glucose>ethanol (>Fractional distillation > ethylene)

Are these processes  The same? Are they different? If so, what is the difference between them? And which one is better to memorise for HSC.

Also, I haven't gotten up to this point in my notes yet, but I know I'm gonna have trouble with it so I would like to ask now. What is the balanced equation for the fermentation of glucose to ethanol?

[Natasha.97]

Hey. Happy new years everybody.
On Process information from secondary sources to summarise the processes involved in the industrial production of ethanol from sugar cane

My excel study guide has process which goes sugarcane > fermentation >distillation > bioethanol,
Whereas my AN Chemistry poster goes sugar cane >cellulose >glucose>ethanol (>Fractional distillation > ethylene)

Are these processes  The same? Are they different? If so, what is the difference between them? And which one is better to memorise for HSC.

Also, I haven't gotten up to this point in my notes yet, but I know I'm gonna have trouble with it so I would like to ask now. What is the balanced equation for the fermentation of glucose to ethanol?

Hi!

The excel version has simplified the process (They didn't include the smashing of sugarcane to extract cellulose, nor the acid digestion of cellulose to form glucose [specific details aren't needed]). In the second process, fermentation (yeast) is how glucose is turned into ethanol. Fractional distillation allows the ethanol to increase its purity (from ~15% to ~95%).

Balanced equation:

C₆H₁₂O_6(aq) --> 2C₂H₅OH_(aq) + 2CO_2(g)

Hope this helps

[mxrylyn]

What do the equations, C6H12O6 ---yeast--->2CH3CH2OH +2CO2  and Ca(OH)2 + CO2 ------> CaCO3 + H2O, represent in the syllabus dotpoint
solve problems, plan and perform a first hand investigation to carry out the fermentation of glucose and monitor mass changes

What do the equations, C6H12O6 ---yeast--->2CH3CH2OH +2CO2  and Ca(OH)2 + CO2 ------> CaCO3 + H2O, represent in the syllabus dotpoint
solve problems, plan and perform a first hand investigation to carry out the fermentation of glucose and monitor mass changes

I just realised that the first one is the fermentation of Glucose to ethanol. I still don't know what the second one is

Mod edit: Merged double post. Please edit your existing post instead of posting two in a row.

[Natasha.97]

What do the equations, C6H12O6 ---yeast--->2CH3CH2OH +2CO2  and Ca(OH)2 + CO2 ------> CaCO3 + H2O, represent in the syllabus dotpoint
solve problems, plan and perform a first hand investigation to carry out the fermentation of glucose and monitor mass changes

I just realised that the first one is the fermentation of Glucose to ethanol. I still don't know what the second one is

Mod edit: Merged double post. Please edit your existing post instead of posting two in a row.

Hi!

The second equation is a confirmation test for carbon dioxide: calcium hydroxide is soluble. Upon reaction with carbon dioxide, it forms calcium carbonate, which is insoluble (forms a white precipitate: it appears milky). It's relevant to the dot-point as the mass change is due to the carbon dioxide formed.

[itssona]

hii so for the formation of PVC I would say the equation is nCH2CHCl--> (CH2CHCl)n

what about for formation of polystyrene? not sure how to write the benzene ring in the equation
thank you!!

[Natasha.97]

hii so for the formation of PVC I would say the equation is nCH2CHCl--> (CH2CHCl)n

what about for formation of polystyrene? not sure how to write the benzene ring in the equation
thank you!!

Hi!

I have yet to see a HSC question asking about the formation of these two polymers. Styrene is commonly written as C₈H₈, so the equation would be _nC₈H₈ --> (C₈H₈)_n.

[itssona]

does ethanol have a high molar heat of combustion? is this a good thing for its use as a fuel?
thank youu

[kiwiberry]

does ethanol have a high molar heat of combustion? is this a good thing for its use as a fuel?
thank youu

Compared to petrol, ethanol has a lower molar heat of combustion, meaning that it will release less energy and be less efficient - this is a disadvantage of using ethanol as an alternative fuel

[itssona]

When zinc metal is placed in copper sulfate solution, the zinc will displace the copper ions, forming zinc sulfate and solid copper

I know zinc is oxidising and copper is reducing but how do I write the equations for copper reducing?
Cu2So4..

thank you

also, when copper is dipped in silver nitrate solution, what is formed? and if copper loses electrons, what does it become?

[RuiAce]

When zinc metal is placed in copper sulfate solution, the zinc will displace the copper ions, forming zinc sulfate and solid copper

I know zinc is oxidising and copper is reducing but how do I write the equations for copper reducing?
Cu2So4..

thank you

Recall that sulfate is just a spectator ion

[itssona]

if I have a galvanic cell in which copper electrode is in CuSO4 and zinc is in ZnSO4 then why does the cathode electrode (copper) become bigger due to a deposit? is it because it is reducing and thus the solution of CuSO4 becomes an atom instead of remaining as an ion?

thank you

[Natasha.97]

if I have a galvanic cell in which copper electrode is in CuSO4 and zinc is in ZnSO4 then why does the cathode electrode (copper) become bigger due to a deposit? is it because it is reducing and thus the solution of CuSO4 becomes an atom instead of remaining as an ion?

thank you

Hi!

In the galvanic cell, electrons flow from the Zinc anode to the Copper cathode as Zn is more reactive than Cu. The Zinc anode is oxidised (loses electrons, AN OX) and the Copper cathode is reduced (gains electrons, RED CAT). The Zinc anode loses mass as it forms ions, and the Copper cathode gains mass as the copper ions from the CuSO₄ solution are displaced.

Hope this helps

[swordkillz]

Can someone clarify whether Cobalt-60 is a medical or industrial radioisotope? I see many people say it is used industrially as a food stain removal/irradiation function while others say that it is used medically for killing cancer cells deposited across the human body. Can someone explain benefits and problems of both?

[Natasha.97]

Can someone clarify whether Cobalt-60 is a medical or industrial radioisotope? I see many people say it is used industrially as a food stain removal/irradiation function while others say that it is used medically for killing cancer cells deposited across the human body. Can someone explain benefits and problems of both?

Hi
Cobalt-60 can be used for both medical and industrial purposes! However, if you're using it as a medical isotope, know a different industrial isotope e.g. Mg-24, and if you're using it as an industrial isotope, know a different medical isotope e.g. Tc-99m.

Industrial
(1) Benefits:
        - Low energy emitting (reduced radiation exposure)
        - Gamma ray emitter (able to penetrate metals)
(2) Problems:
       - Health of workers is still at risk (low gamma radiation can still cause harm, expensive to implement safety measures)
       - Relatively short half-life (5 years), frequent equipment replacement required [/list]

Medical
Benefits:
       - Able to attack malignant tumours (can penetrate body tissue)

Hope this helps

[itssona]

heey to calculate the potential E, do we subtract the cathode metal from the anode always?