HSC 2012-2015 Chemistry Marathon (archive) (10 Viewers)

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

The pressure is ON!

Ok so:
1-Obtain 2-3 red cabbage leaves and tear them into pieces.
2-Place the torn cabbage leaves into 100mL beaker filled with water.
3-Heat the beaker till the water becomes purple and the leaves become pale in colour.
4-Leave the beaker to cool (Safety first kids!)
5-Decant the beaker to obtain your new red cabbage indicator!
6-Obtain 0.1Molar samples of known household bases and acids.
7-Test by placing a few drops of your red cabbage indicator into your known household substances and record the change in colour

EDIT: They don't have to be at 0.1 Molar concentrations, but I usually say that because Chemistry procedures require numerical measurements.

That's a great answer! I'd suggest adding in a test for a known neutral solution too (eg NaCl) and perhaps name the household acids/bases you're using (caustic soda, vinegar, lemon juice, etc) but other than that it's perfect. Also, the inclusion of a molarity is something you should definitely get into the habit of doing, they do like to see that precision. So good work!

Next question: summarise the chemistry of the fermentation process (5 marks)

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Next question: summarise the chemistry of the fermentation process (5 marks)

Fermentation is the conversion of glucose into ethanol and carbon dioxide.

For fermentation a few environmental factors need to be taken into consideration they are:
-Low concentration of oxygen
-Around 37 degrees
- Low concentration of Ethanol
-Presence of yeast
Oxyegen is kept low so it doesnt take part in the reaction
37 degrees is about the temperature perfect for yeast
Ethanol kills the yeast therefore low concentration needed
Notsureif enough?

 

[zhertec]

re: HSC Chemistry Marathon Archive

Fermentation is the conversion of glucose into ethanol and carbon dioxide.

For fermentation a few environmental factors need to be taken into consideration they are:
-Low concentration of oxygen
-Around 37 degrees
- Low concentration of Ethanol
-Presence of yeast
Oxyegen is kept low so it doesnt take part in the reaction
37 degrees is about the temperature perfect for yeast
Ethanol kills the yeast therefore low concentration needed
Notsureif enough?

Dont forget diammonium phosophate for nutrients, pH of around 3.7-4.6 to prevent microbial growth, presence of sulfur dioxide in solution 30-50 ppm also to prevent microbial growth, oxygen is not kept low but absent (hence anaerobic fermentation) if oxygen is present fermentation stops and the yeast uses the oxygen to undergo budding etc, ethanol concentrations must not reach over 15% (yeast dies due to interruption with their membranes) and 3-5 day waiting period.

EDIT: Also require alcohol tolerant yeast species, forgot that one for a sec...

 

[SuchSmallHands]

Chemistry marathon 2015

Fermentation is the conversion of glucose into ethanol and carbon dioxide.

For fermentation a few environmental factors need to be taken into consideration they are:
-Low concentration of oxygen
-Around 37 degrees
- Low concentration of Ethanol
-Presence of yeast
Oxyegen is kept low so it doesnt take part in the reaction
37 degrees is about the temperature perfect for yeast
Ethanol kills the yeast therefore low concentration needed
Notsureif enough?

Excellent answer! However, for five marks you might want to include
- the role of the yeast enzyme zymase as a catalyst
- the ABSENCE of oxygen
- the production of a low concentrated ethanol (~15%). I wouldn't really consider low ethanol concentration a reaction condition since ethanol is the product, but that's probably me just being picky on semantics. You're correct in saying that high concentrations will kill off the yeast
- maybe a mention the exothermic nature of the reaction and how it affects conditions, though that probably wouldn't be necessary

And pH and microbial control, mentioned already

 

[anomalousdecay]

re: HSC Chemistry Marathon Archive

This thread is an archive. Please post in the thread linked below for anything regarding a question in this thread:

http://community.boredofstudies.org/17/chemistry/334262/chemistry-marathon-2015-a.html

Make sure to quote what you are inquiring about!

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Excellent answer! However, for five marks you might want to include
- the role of the yeast enzyme zymase as a catalyst
- the ABSENCE of oxygen
- the production of a low concentrated ethanol (~15%). I wouldn't really consider low ethanol concentration a reaction condition since ethanol is the product, but that's probably me just being picky on semantics. You're correct in saying that high concentrations will kill off the yeast
- maybe a mention the exothermic nature of the reaction and how it affects conditions, though that probably wouldn't be necessary

And pH and microbial control, mentioned already

My teacher told me that i know the general idea of every question but i miss parts or i dont articulate well enough.. hopefully this threqd can help thanks

 

[Gabriel Moussa]

re: HSC Chemistry Marathon Archive

Common safety precautions in school laboratories include the use of safety glasses, gloves and lab coats. Justify the use of another safety precaution specifically required to safely make ethyl butanoate.

(2 marks)

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Common safety precautions in school laboratories include the use of safety glasses, gloves and lab coats. Justify the use of another safety precaution specifically required to safely make ethyl butanoate.

(2 marks)

Since ethyl butanoate is made by the combination of ethanol and butanoic acid so the use of gloves, safety glasses and lab coats are needed. Gloves protect the hands from corrosive acid. The safety glasses protect the eyes from splashes of the acid. The lab coats protect the body from accidental spillage of the acid. Thus showing the safety precautions that must be made to protect oneself in the production of ethyl butanoate.

 

[Librah]

re: HSC Chemistry Marathon Archive

Since ethyl butanoate is made by the combination of ethanol and butanoic acid so the use of gloves, safety glasses and lab coats are needed. Gloves protect the hands from corrosive acid. The safety glasses protect the eyes from splashes of the acid. The lab coats protect the body from accidental spillage of the acid. Thus showing the safety precautions that must be made to protect oneself in the production of ethyl butanoate.

The question asked you to justify the use of ANOTHER safety precaution.

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

Common safety precautions in school laboratories include the use of safety glasses, gloves and lab coats. Justify the use of another safety precaution specifically required to safely make ethyl butanoate.

(2 marks)

Be careful when reading questions

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

From the top of my head i cant really think of another one

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

From the top of my head i cant really think of another one

Did you use a Bunsen flame or a heating mantle to heat the reactants? Why did you you use one and not the other?

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Did you use a Bunsen flame or a heating mantle to heat the reactants? Why did you you use one and not the other?

Our class is still up to acid rain so i havn't done the experiment yet

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

Our class is still up to acid rain so i havn't done the experiment yet

Oh okay, I thought you guys were moving really fast! (This time last year I was on PoM still). We'll save questions on the second half of acidic and monitoring and management for later on in that case

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Oh okay, I thought you guys were moving really fast! (This time last year I was on PoM still). We'll save questions on the second half of acidic and monitoring and management for later on in that case

Can you post questions on the first half not really confident in it

 

[someth1ng]

re: HSC Chemistry Marathon Archive

The pressure is ON!

Ok so:
1-Obtain 2-3 red cabbage leaves and tear them into pieces.
2-Place the torn cabbage leaves into 100mL beaker filled with water.
3-Heat the beaker till the water becomes purple and the leaves become pale in colour.
4-Leave the beaker to cool (Safety first kids!)
5-Decant the beaker to obtain your new red cabbage indicator!
6-Obtain 0.1Molar samples of known household bases and acids.
7-Test by placing a few drops of your red cabbage indicator into your known household substances and record the change in colour

EDIT: They don't have to be at 0.1 Molar concentrations, but I usually say that because Chemistry procedures require numerical measurements.

You should make sure you do the same for just water, you need it as a control.

 

[someth1ng]

re: HSC Chemistry Marathon Archive

Fermentation is the conversion of glucose into ethanol and carbon dioxide.

For fermentation a few environmental factors need to be taken into consideration they are:
-Low concentration of oxygen
-Around 37 degrees
- Low concentration of Ethanol
-Presence of yeast
Oxyegen is kept low so it doesnt take part in the reaction
37 degrees is about the temperature perfect for yeast
Ethanol kills the yeast therefore low concentration needed
Notsureif enough?

You need to be more specific, what do you mean low concentration of ethanol? Where?

 

[someth1ng]

re: HSC Chemistry Marathon Archive

Are they both soluble not sure

Yes.

What do you think would happen if you used something for the salt bridge that reacted with the half cells?

 

[Ekman]

re: HSC Chemistry Marathon Archive

Yes.

What do you think would happen if you used something for the salt bridge that reacted with the half cells?

Wouldn't the whole cell short-circuit?

 

[siggy]

re: HSC Chemistry Marathon Archive

Yes.

What do you think would happen if you used something for the salt bridge that reacted with the half cells?

The cell would no longer be neutralised and the cell would become incomplete as the salt bridge reacted. This would stop the ions from each cell from moving to the other cell and hence the cell would no longer give a voltage.