VCE Chemistry Question Thread

[VanillaRice]

Hey, this might be a dumb question however... What is respiration? do i need to know about it for the course?
like if i had glucose (any sugar) and yeast in warm water it would undergo fermentation and create ethanol and carbon dioxide right? would it also undergo respiration at the same time? or do i need a certain enzyme for it? i am currently clueless with respiration (I have tried looking it up on google but it was too confusing)
thanks

There are no dumb questions here
Fermentation is also known as anaerobic respiration (since there is lack of oxygen). The function is performed by the yeast itself, and I don't think you need to know the name of the enzyme (but it does involve the action of enzymes within the yeast).

Hope this helps

[Bri MT]

Hey, this might be a dumb question however... What is respiration? do i need to know about it for the course?
like if i had glucose (any sugar) and yeast in warm water it would undergo fermentation and create ethanol and carbon dioxide right? would it also undergo respiration at the same time? or do i need a certain enzyme for it? i am currently clueless with respiration (I have tried looking it up on google but it was too confusing)
thanks

Respiration, or cellular respiration, is a process conducted by organisms to get them energy.
Both humans and yeast can do anaerobic respiration, but make different products because of the different enzymes each organism has. Know the formula for anaerobic respiration in yeast.
Yeast doesn't have the right structures in its cells to do aerobic cellular respiration
Humans do have the right structures in their cells, but sometimes they can't do aerobic respiration because there's no oxygen available. This significantly reduces how much energy we can produce.
Know the formula for aerobic cellular respiration

[Somedudelmaoy]

What are the physics formula we need to know for chemistry. Like would we need to be able to get voltage when given the current and charge?

[Phenomenol]

What are the physics formula we need to know for chemistry. Like would we need to be able to get voltage when given the current and charge?

It would be a good idea to know how to interchange between all of charge, energy, time, voltage, current and power. The basic definitions are:

I = Q/t (the charge transfer per unit time)
P = E/t (the energy delivered per unit time)
V = E/Q (the energy delivered per unit charge)

(The last equation is seldom used but it's nice to see the symmetry in the whole trio of formulas. You can ignore this one if you want to)

In addition to these, a commonly used rearrangement of the power formula is:

E = IVt

I think that should be enough to be prepared for any electricity calculations. If you want more elaboration on the other formulas in the subject then ask away!

[tinagranger]

Hello! Please help as I have a SAC TOMORROW.

When alanine and glycine react, 2 different dipeptides can be formed.
a) Write the condensed structural formula of each dipeptide. I don't get how to do this? How do we know what alanine and glycine are/do we need to know their formulae?
b) How many tripeptides can be formed from 3 amino acids? Why isn't it just 1?

Also
Write equations for condensation reactions between:
2 glucose molecules - how are we meant to know this forms maltose??
a glycerol molecule and 3 palmitic acid molecules - how are we meant to know the structure of palmitic acid, and what type of substance it is???
2 alanine molecules - how are we meant to know the structure of alanine, and what type of substance it is?

And
A sample of 1 tonne of vegetable oil requires 4.9kg of hydrogen gas to hydrogenate the triglyceride.
Determine the average number of CC double bonds that have react4ed per triglyceride molecule in the sample.

What percentage of the CC double bonds in the sample of vegetable oil have been hydrogenated?

[Bri MT]

Hello! Please help as I have a SAC TOMORROW.

When alanine and glycine react, 2 different dipeptides can be formed.
a) Write the condensed structural formula of each dipeptide. I don't get how to do this? How do we know what alanine and glycine are/do we need to know their formulae?
b) How many tripeptides can be formed from 3 amino acids? Why isn't it just 1?

Also
Write equations for condensation reactions between:
2 glucose molecules - how are we meant to know this forms maltose??
a glycerol molecule and 3 palmitic acid molecules - how are we meant to know the structure of palmitic acid, and what type of substance it is???
2 alanine molecules - how are we meant to know the structure of alanine, and what type of substance it is?

And
A sample of 1 tonne of vegetable oil requires 4.9kg of hydrogen gas to hydrogenate the triglyceride.
Determine the average number of CC double bonds that have react4ed per triglyceride molecule in the sample.

What percentage of the CC double bonds in the sample of vegetable oil have been hydrogenated?

The structures of amino acids and triglycerides are in the days booklet.
You need to remember the monomers of maltose, sucrose, and galactose  & be able to draw these disaccharides based on the diagrams of the their monomers (which are in the data booklet)
Order matters A LOT with polypeptides; different order = different polypeptide.

For the last one,  use n=m/M, and the knowledge that 2 hydrogens react per double bond

[tinagranger]

Thanks! Please help me with these, kind of freaking out for my sac

1. Also what exactly do we have to know about the bonds involved in each structure of a protein? Just the types of bonds for all 4 structures, or the type AND location? Also there only seems to be info for bonds for some of the structures in the TB, so could you please summarise the actual bonds we have to know for each structure so I make sure I learn eveyrthing?

2. There are 2 dot points in the study design where I am not sure what we need to know - are you able to tell me the main things I need to know for each of these?

Glycaemic index (GI) of foods as a ranking of carbohydrates based on the hydrolysis of starches (varying proportions of amylose and amylopectin) to produce glucose in the body

The comparison of energy values of carbohydrates, proteins and fats and oils

3. Do we need to know specific enzymes involved in specific reactions? Eg: amylase and maltase in the hydrolysis of starch to maltose and glucose, and lactase for the hydrolysis of lactose to glucose and galactose

4. Are disaccharides considered as polymers?

5. What is a lipid?
 

[tinagranger]

Somebody please help with my questions!! Really need to do well on this sac.

[Cassidyhogi]

I have attached my notes according to the study design and a glossary for biochem terms
Hope this helps

[tinagranger]

Thank you so much! If someone is able to answer my specific questions (I have found some out now, so these are the rest), that would be great:

1. There are 2 dot points in the study design where I am not sure what we need to know - are you able to tell me the main things I need to know for each of these?

Glycaemic index (GI) of foods as a ranking of carbohydrates based on the hydrolysis of starches (varying proportions of amylose and amylopectin) to produce glucose in the body

The comparison of energy values of carbohydrates, proteins and fats and oils

2. Do we need to know specific enzymes involved in specific reactions? Eg: amylase and maltase in the hydrolysis of starch to maltose and glucose, and lactase for the hydrolysis of lactose to glucose and galactose

3. Are disaccharides considered as polymers?

4. What is a lipid?

[sweetiepi]

Thank you so much! If someone is able to answer my specific questions (I have found some out now, so these are the rest), that would be great:

1. There are 2 dot points in the study design where I am not sure what we need to know - are you able to tell me the main things I need to know for each of these?

Glycaemic index (GI) of foods as a ranking of carbohydrates based on the hydrolysis of starches (varying proportions of amylose and amylopectin) to produce glucose in the body

The comparison of energy values of carbohydrates, proteins and fats and oils

2. Do we need to know specific enzymes involved in specific reactions? Eg: amylase and maltase in the hydrolysis of starch to maltose and glucose, and lactase for the hydrolysis of lactose to glucose and galactose

3. Are disaccharides considered as polymers?

4. What is a lipid?

Hey there!

I've noticed you've bumped this a few times in the past 24 hours or so. As ANers volunteer their time to answer questions, sometimes it takes a while to answer them/for a person knowledgeable in a topic to see a question.
Unfortunately I'm not as knowledgeable as I should be for this branch of chemistry, I'd recommend exercising a bit of patience until someone more knowledgeable in this area sees this.
Have a great night!

[Phenomenol]

Glycaemic index (GI) of foods as a ranking of carbohydrates based on the hydrolysis of starches (varying proportions of amylose and amylopectin) to produce glucose in the body

You need to know what GI is, why glucose has a standardised GI value of 100, and to be able to use the proportion of amylose/amylopectin in a food to predict a high or low GI content.

e.g. Amylose is unbranched, so it is packed more tightly. Amylopectin has branches, so it is packed less tightly, and enzymes are more easily able to access the glycosidic links to break them. Thus, food with higher amylopectin content are broken down into glucose faster than those with amylose, and therefore have a higher GI value.

The comparison of energy values of carbohydrates, proteins and fats and oils

You need to be able to use the energy content for each class of biomolecule (in the data book) in calculations. e.g. the energy value of a food given the percentage of each biomolecule class.

2. Do we need to know specific enzymes involved in specific reactions? Eg: amylase and maltase in the hydrolysis of starch to maltose and glucose, and lactase for the hydrolysis of lactose to glucose and galactose

Yes (as far as I know).

3. Are disaccharides considered as polymers?

Tricky question. Polymers usually refer to a molecule comprised of many monomer units - disaccharides are not usually referred to as polymers as far as I know. There is probably a grey area in terms of what starts being considered a polymer.

4. What is a lipid?

As the wiki page states: "a lipid is a substance of biological origin that is soluble in nonpolar solvents". So this would include triglycerides, cholesterol and fat soluble vitamins.

[peanut]

Does oxidative rancidity only occur in unsaturated triglycerides and not saturated triglycerides? Or do they occur in both, with it being more common in unsaturated triglycerides?

[Phenomenol]

Does oxidative rancidity only occur in unsaturated triglycerides and not saturated triglycerides? Or do they occur in both, with it being more common in unsaturated triglycerides?

I've googled a few articles, and the general consensus seems that saturated triglycerides are still able to undergo rancidification, but at a much slower pace than their unsaturated equivalent.

[KATA]

Hi! I was just wondering whether there was a dedicated post/resource to learn about all the chemical tests used for identifying substances (e.g. how to identify an ester or carboxylic acid, etc.?

Also, do we need to know the specific subunits that make up certain disaccharides (e.g. maltose)?