Hsc Marathon 2009 - Chemistry (2 Viewers)

[arjungamer123]

Fermentation is where carbohydrates such as glucose and starch are chemically converted into other industrially/commercially viable substances such as ethanol and by products including carbon dioxide. Fermentation requires yeast catalysts which produce enzymes needed to convert the starting material. Ethanol is produced via the fermentation of glucose expressed in the following reaction:
C₆H₁₂O₆(aq) --> (yeast cat.) 2C₂H₅OH(aq) + 2CO₂(g) + heat
The process is exothermic.
Two ideal conditions for this reaction are:
> a constant temperature (37^oC)
> anaerobic (air-free).

Is that enough detail? That's all I know.

That's pretty good. But it's better if you say "constant removal of ethanol" as a condition. In school, our fermentation took place in an aerobic environment.

 

[bored of sc]

That's pretty good. But it's better if you say "constant removal of ethanol" as a condition. In school, our fermentation took place in an aerobic environment.

Oh, okay. Wow. Didn't know that.

 

[arjungamer123]

Oh, okay. Wow. Didn't know that.

Well ethanol is anti-septic, so it can kill the yeast.

 

[bored of sc]

New question (reposted since it wasn't answered):

Indicators can be used to test the pH of the following:
(a) Soil
(b) Swimming pools
(c) Aquariums
(d) Water testing of streams, lakes and rivers

For each part:
(i) Why is it important to test the acidity?
(ii) What can be done to correct the situation if the test result indicates that the substance is too acidic or too basic?
(iii) How is the test performed (as in the use of indicators)?<!-- google_ad_section_end --></SPAN>

 

[Kaatie]

because the wrong ph can casue eye/skin irritations, not good for fish etc use an acid or base to bring it up or down to required ph. indicator is put into a test tube of substance tested and pH can be dertermined by colour.

in the cabbage indicator prac, how can it be improved

 

[shady145]

aww my school is not doing that prac, my chem teacher said it is to stinky, so we are doing one with flowers.

 

[Pwnage101]

Well ethanol is anti-septic, so it can kill the yeast.

only if the (aq) solution of ethanol is >15% in concentration

 

[Kaatie]

In the reaction
2Fe2O3Cr2O3 + 4Na2CO3 + 3O2 --> 2Fe2O3 + 4Na2CrO4 + 4CO2

what is Cr original oxidation state and what oxidation state has it changed to (number)

 

[aero135]

original 0?

 

[Kaatie]

nah options are
3 to 6
3 to 2
2 to 6
2 to 3

 

[bored of sc]

In the reaction
2Fe2O3 + Cr2O3 + 4Na2CO3 + 3O2 --> 2Fe2O3 + 4Na2CrO4 + 4CO2

what is Cr original oxidation state and what oxidation state has it changed to (number)

Is that the equation you wanted?

If so, it goes from +3 to +6 --- so Cr is being oxidised right?

New question:
Tell me three key facts about petroleum (any areas e.g. economic, chemical etc will do).

 

[Kaatie]

no you copied the equation wrong its
2Fe2O3Cr2O3 + 4Na2CO3 + 3O2 --> 2Fe2O3 + 4Na2CrO4 + 4CO2

 

[shady145]

petrleum is a mixture
petroleum has may fractions
these fractions are sperated and used for different things
petroleum is made from organic compounds continually being compressed over a long period of time.

there's three in there somewhere. if they are facts is another question

Q. identify some naturally occuring acids and bases

 

[shady145]

any1 want the answers, or you could simply google it if u dnt know the answer.

 

[Kaatie]

ethanoic acid
citric acid
ascorbic acid
HCl

dont know about bases ill leave that for someone else

 

[gifted:)]

i havent the faintest idea ... could you say CuO, or is that man made??? my chem teacher just done the cabbage exp. today!

 

[arjungamer123]

only if the (aq) solution of ethanol is >15% in concentration

...No wait.

You're right.

But I meant pure ethanol is anti-septic though.

Ethanol mixtures are only anti-septic to yeast cells when >15% enthanol in the solution.

 

[shady145]

CaCO3 is a good one, lafge component of limestone.

Kaatie you can ask another question

 

[Kaatie]

ummm... identify the monomer from which cellulose forms

 

[shady145]

glucose.

Q. what are some examples of indicators