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August 02, 2021, 01:09:43 pm

Author Topic: Challenging chemistry questions  (Read 2517 times)  Share 

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insanipi

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Challenging chemistry questions
« on: January 18, 2020, 10:01:44 pm »
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As per the subject, this thread is a place to discuss and solve challenging chemistry questions.

These challenging questions are past VCAA exam questions on which 50% of the state didn’t get full marks (for multiple choice questions) or for which the average mark is less than half of the full available marks (for short answer questions). Please note that while these questions are from VCE study designs, since there is significant overlap between science across the different states, most of these questions should be able to be answered by those from other states.

This thread will be updated weekly with a new batch of 5 Multiple Choice questions and 10 Marks worth of Short Answer questions.
Here is your first batch:
Chem
Multiple Choice
question 1
Aspartame
A.    contains a glycosidic link.
B.    is a naturally occurring sugar.
C.    has an energy content similar to that of sucrose.
D.    contains two amino groups in its chemical structure
question 2
Organic acids, including vitamin C (ascorbic acid), are present in lemon juice. Since organic acids and vitamin C are weak acids, they will undergo acid-base reactions. Only vitamin C, not the organic acids, will undergo a redox reaction with iodine, I2.
Which one of the following methods would be most appropriate to determine the concentrations of the organic acids and the vitamin C in a sample of lemon juice?
A.    an acid-base titration with sodium hydroxide and phenolphthalein indicator
B.    an acid-base titration with ammonia and phenol red indicator, and a redox titration with iodine and permanganate ion indicator
C.    an acid-base titration with sodium hydroxide and methyl orange indicator, and a redox titration with iodine and a starch indicator
D.    an acid-base titration with potassium hydroxide and phenolphthalein indicator, and a redox titration with iodine and a starch indicator
question 3
A hydrolytic reaction occurs when
A.   a dipeptide is formed.
B.   a triglyceride is formed.
C.   water is a reaction product.
D.   glucose is formed from maltose.
 
question 4
Which one of the following is a correct statement about the denaturation of a protein?
A.   Denaturation is characterised by the release of peptides.
B.   Alcohol denatures proteins by disrupting the hydrogen bonding.
C.   Denaturation involves disruption of all bonds in the tertiary structure.
D.   The primary and secondary structures are disrupted when denaturation occurs
 
question 5
Ammonia, NH3, can be produced by the reaction of hydrogen, H2, and nitrogen, N2. When this reaction takes place in a sealed container of fixed volume, an equilibrium system is established. The equation for the reaction is shown below.

N2(g) + 3H2(g) ⇌ 2NH3(g) ΔH = –92 kJ mol–1

If the pressure and volume remain constant when the temperature is increased, the forward reaction rate will
A.   increase and the [NH3] will increase.
B.   increase and the [NH3] will decrease.
C.   decrease and the [NH3] will decrease.
D.   decrease and the [NH3] will remain the same.
 
Short Answer
question 1
Give the IUPAC name for this molecule (1 mark)

question 2
Hydrogen peroxide, H2O2, in aqueous solution at room temperature decomposes slowly and irreversibly to form water, H2O, and oxygen, O2, according to the following equation.    
2H2O2(aq) → 2H2O(l) + O2(g)    ∆H < 0
A solution of H2O2 is labelled ‘10 volume’ because 1.00 L of this solution produces 10.0 L of O2 measured at standard laboratory conditions (SLC) when the H2O2 in the solution is fully decomposed.
a) Calculate the concentration of H2O2 in the ‘10 volume’ solution, in grams per litre, when this solution is first prepared. (2 marks)
b) Propose a method to determine how quickly a solution of H2O2 decomposes when stored at a particular temperature (3 marks)
question 3
There are a number of structural isomers for the molecular formula C3H6O. Three of these are propanal, propanone and prop-2-en-1-ol. The skeletal structure for the aldehyde propanal is as follows.


The mass spectrum below was produced by one of the three named isomers of C3H6O.


Name the isomer of C3H6O that produced this spectrum and justify your answer. (3 marks)
question 4
Describe how enzymes and coenzymes interact to catalyse a reaction (2 marks)

When Answering your questions, please write your answer inside of a spoiler like this:
question 1
Spoiler
This is my answer
The reason behind this is just so that other users who are having a go at answering these questions don’t accidentally see what others have put down and can have a go at it themselves.
I would also like to encourage everyone to have a go at answering these questions without looking at other user’s responses – this will help develop your ability to really critically think about a question independently. Remember, there is no harm in getting something wrong and making a mistake is an opportunity to learn!

Good luck :)
« Last Edit: January 20, 2020, 11:05:36 am by Erutepa »
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ArtyDreams

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Re: Challenging chemistry questions
« Reply #1 on: January 20, 2020, 07:14:07 pm »
+5
I'll get these questions started :)

MC Question 3
D

SA Question 1
2,3di Bromo, 4Methyl Hexane

Need to do some more research for the other questions....I shall add to this later.
« Last Edit: January 23, 2020, 08:00:15 pm by ArtyDreams »

ssillyssnakes

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Re: Challenging chemistry questions
« Reply #2 on: January 20, 2020, 11:07:48 pm »
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I'm just going to answer a few of the MC (for now), as I'm not entirely sure about others

1) D (I just used some base knowledge for this, aspartame is low calorie and thus cant have an energy content similar to sucrose, it is not a carbohydrate so I dont think its have a glycosidic link, and it isnt a sugar. Therefore I assume D must be correct
3) D - not sure on this but I figure that hydrolysis results in the breakdown of a polymer into a monomer and D was the only option I could see that fits that.
4) I'm going to go with B, as I dont think ALL tertiary bonds would be disrupted (very likely wrong here) and I dont think the primary structure is altered by denaturation, and I dont think A is right
5) B - I ruled out C and D as I figure a higher temp = higher reaction rate. As the forware reaction is exothermic, the high temp I think would result in it being easier for the reverse reaction (endothermic) to happen making less NH3?

I'd love for any feedback on my answers/reasoning
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Erutepa

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Re: Challenging chemistry questions
« Reply #3 on: January 26, 2020, 08:55:39 pm »
+3
1) D (I just used some base knowledge for this, aspartame is low calorie and thus cant have an energy content similar to sucrose, it is not a carbohydrate so I dont think its have a glycosidic link, and it isnt a sugar. Therefore I assume D must be correct
Aspartame actually does have the same energy content as sucrose, however it is far sweeter (200 times sweeter) so small amounts are used in drinks, thus making the drink of a lower energy content, but not making aspartame of lower energy content.
Additionally, the chemical structure of Aspartame does not have 2 amino groups - Thus making the answer C

5) B - I ruled out C and D as I figure a higher temp = higher reaction rate. As the forware reaction is exothermic, the high temp I think would result in it being easier for the reverse reaction (endothermic) to happen making less NH3?
You're right about this, however I will just offer a bit more of an explanation. In chem for questions like these, we can use le chatelier’s principle to predict the effect of a change (i.e. an increase in temperature) on the equilibrium system (in this case we are concenred with the NH3 concentration). This principle states that a system will partially oppose any changes made to it, so if the temperature is increased, the system will oppose this by decreasing the temperature by favouring the endothermic reaction. In this case, the endothermic reaction is the reverse reaction (as you have noted) meaning the concentration of NH3 will decrease. While its not incorrect to reason the question as you haved, for VCE chemistry (not sure about for other states) you will need to explain your reasoning interms of this principle.

Other than this, your other responses have been correct! Good work!
« Last Edit: February 21, 2020, 08:35:53 pm by Erutepa »
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ssillyssnakes

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Re: Challenging chemistry questions
« Reply #4 on: January 28, 2020, 09:07:10 am »
+1
Aspartame actually does have the same energy content as sucrose, however it is far sweeter (200 times sweeter) so small amounts are used in drinks, thus making the drink of a lower energy content, but not making aspartame of lower energy content.
Additionally, the chemical structure of Aspartame does not have 2 amino groups - Thus making the answer D
You're right about this, however I will just offer a bit more of an explanation. In chem for questions like these, we can use le chatelier’s principle to predict the effect of a change (i.e. an increase in temperature) on the equilibrium system (in this case we are concenred with the NH3 concentration). This principle states that a system will partially oppose any changes made to it, so if the temperature is increased, the system will oppose this by decreasing the temperature by favouring the endothermic reaction. In this case, the endothermic reaction is the reverse reaction (as you have noted) meaning the concentration of NH3 will decrease. While its not incorrect to reason the question as you haved, for VCE chemistry (not sure about for other states) you will need to explain your reasoning interms of this principle.

Other than this, your other responses have been correct! Good work!

Thank you for this!
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Erutepa

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Re: Challenging chemistry questions
« Reply #5 on: January 28, 2020, 09:47:53 am »
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Christmas this year must be coming early becuase here are another fresh serving of challanging Chemistry questions!
Plenty of time left to earn points for the science games and revise/learn chem content by going through these questions!
If you haven't completed the previous questions posted here last week you can still earn points by completing them, but for those who have already given them a crack, here are some more
Multiple Choice
Question 1
Lithium-ion rechargeable batteries are used in mobile phones. Environmental conditions can affect the number of charge cycles for a lithium-ion battery until the end of its useful life. Which of the following environmental conditions would be expected to result in the largest number of charge cycles for a lithium-ion battery?

Question 2
The nutrition information panel on a packet of muesli includes the following information.

Using the information above, the percentage energy content due to protein in an average serving size of this muesli is
A) 31.2%
B) 29.3%
C) 14.0%
D) 13.2%
Question 3
Four identical vehicle models, 1, 2, 3 and 4, were tested for fuel efficiency using LPG, petrol (unleaded, 91 octane),
E10 (petrol with 10% ethanol added) and petrodiesel. Carbon dioxide, CO2, emissions per litre of fuel burnt were
also determined. The following table summarises the results.

The use of which vehicle has the smallest impact on the environment, in terms of the grams of CO2 produced per 100 km?
A) Vehicle model 1
B) Vehicle model 2
C) Vehicle model 3
D) Vehicle model 4
Question 4
The mass of caffeine in a particular coffee drink was determined by high-performance liquid chromatography (HPLC).
The calibration curve produced from running standard solutions of caffeine through an HPLC column is shown below.

A 5.0 mL aliquot of the coffee drink was diluted to 50.0 mL with de-ionised water. A sample of the diluted coffee drink was run through the HPLC column under identical conditions to those used to obtain the calibration curve. The peak area obtained for this diluted sample was 2400 arbitrary units.
The mass of caffeine, in grams, in 350 mL of the undiluted coffee drink is closest to
A) 0.014
B) 0.070
C) 0.14
D) 0.40
Question 5
The heat of combustion of a sample of crude oil is to be determined using a bomb calorimeter. All of the students in a class are given the same method to follow. The apparatus used by the students is shown below.

For this experiment, the students could maximise
A) precision by using a digital thermometer ± 0.2 °C.
B) validity by calculating the heat of combustion per mole.
C) accuracy by taking samples from three different sources.
D) uncertainty by having all students closely follow the same experimental procedure.
Short Answer
Question 1
A vehicle that is powered by a diesel engine is able to use either petrodiesel or biodiesel as a fuel. Petrodiesel and biodiesel are not pure substances, but are a mixture of molecules. In general, petrodiesel consists of molecules that are shorter in length, on average, than those found in biodiesel. Biodiesel contains molecules that include functional groups.
The table below lists some of the properties of the two fuels.

Describe and explain the difference in viscosity, under the same conditions, of the two fuels and how this would affect the flow of each fuel. (3 marks)
Question 2
Glucagon is a peptide hormone that works with insulin to help regulate blood glucose levels. Glucagon acts to increase blood glucose levels through targeted action on the polysaccharide stored in the liver. Glucagon consists of a chain of 29 amino acids, the sequence of which is given below, and folds to form a short alpha-helix.
Describe the bonding that is found in the primary and secondary structures of the glucagon molecule (3 marks)
Question 3
State the function of the electrolyte in a fuel cell (1 mark)
Question 4
Submarines operate both on the surface and underwater. When operating underwater, the submarine acts as a closed system, where there is no interaction with the atmosphere.
Give two safety considerations for the safe storage of hydrogen, H2, gas on a submarine (2 marks)
Question 5
Fluorine, F2, gas is the most reactive of all non-metals. Anhydrous liquid hydrogen fluoride, HF, can be electrolysed to produce F2 and hydrogen, H2, gases. Potassium fluoride, KF, is added to the liquid HF to increase electrical conductivity.
The equation for the reaction is

2HF(l) → F2(g) + H2(g)

F2 is used to make a range of chemicals, including sulfur hexafluoride, SF6, an excellent electrical insulator, and xenon difluoride, XeF2, a strong fluorinating agent.
The diagram below shows an electrolytic cell used to prepare F2 gas

Liquid HF, like water, is an excellent solvent for ionic compounds. In the same way that water molecules in an aqueous solution form the ions K+(aq) and F–(aq), when KF is dissolved in HF, the K+ and F– ions form ions that are written as K+ (HF) and F– (HF).

Write the equation for the half-reaction occurring at the anode. (1 mark)
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ArtyDreams

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Re: Challenging chemistry questions
« Reply #6 on: January 28, 2020, 12:19:20 pm »
+3
No clue how to do the rest, but heres MC Q4:

Spoiler
C1V1 = C2V2

V1 = 0.005 L
C1 = ?
V2 = 0.05 L
C2 = 0.040 g/L (looking at the curve)

0.005x = 0.05 x 0.040
0.005x = 0.002
x = 0.4 g/L

Therefore:
0.4 g/L in 0.005L
0.4 g/L in 0.35L

0.4 * 0.35 = 0.14

The answer is C

Also I think I overcomplicated this a lot ha ha.

Erutepa

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Re: Challenging chemistry questions
« Reply #7 on: February 03, 2020, 09:20:30 pm »
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As we are entering the second half of the epically epic science games, its as good a time as ever to jump into this thread and answering some tough questions.
Since last weeks questions didn't see to much activity, there won't be a fresh batch of questions this week as I don't want to bombard users with too many questions. So for now, the last couple weeks of questions will sit here patiently waiting to be answered.
If you haven't had a go yet at any questions or have only answered some of the questions, now would be a great time to have a crack at them and earn some points. And remember, don't worry about being wrong - if you make an error or get the wrong answer, we can give you some feedback and hopefully guide you to the correct answer!
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rory.andersen

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Re: Challenging chemistry questions
« Reply #8 on: February 15, 2020, 11:54:55 am »
+9
Decided I would join the science Games. Could someone check my answers to see how I went and explain any errors.
{b] Multiple Choice
question 1
Aspartame
D.    contains two amino groups in its chemical structure
question 2
Organic acids, including vitamin C (ascorbic acid), are present in lemon juice. Since organic acids and vitamin C are weak acids, they will undergo acid-base reactions. Only vitamin C, not the organic acids, will undergo a redox reaction with iodine, I2.
Which one of the following methods would be most appropriate to determine the concentrations of the organic acids and the vitamin C in a sample of lemon juice?
B.    an acid-base titration with ammonia and phenol red indicator, and a redox titration with iodine and permanganate ion indicator
question 3
A hydrolytic reaction occurs when .
D.   glucose is formed from maltose.
 
question 4
Which one of the following is a correct statement about the denaturation of a protein? 
B.   Alcohol denatures proteins by disrupting the hydrogen bonding.
 
question 5
Ammonia, NH3, can be produced by the reaction of hydrogen, H2, and nitrogen, N2. When this reaction takes place in a sealed container of fixed volume, an equilibrium system is established. The equation for the reaction is shown below.

N2(g) + 3H2(g) ⇌ 2NH3(g) ΔH = –92 kJ mol–1

If the pressure and volume remain constant when the temperature is increased, the forward reaction rate will
B.   increase and the [NH3] will decrease.
 


Erutepa

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Re: Challenging chemistry questions
« Reply #9 on: February 21, 2020, 09:28:07 pm »
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No clue how to do the rest, but heres MC Q4:

Spoiler
C1V1 = C2V2

V1 = 0.005 L
C1 = ?
V2 = 0.05 L
C2 = 0.040 g/L (looking at the curve)

0.005x = 0.05 x 0.040
0.005x = 0.002
x = 0.4 g/L

Therefore:
0.4 g/L in 0.005L
0.4 g/L in 0.35L

0.4 * 0.35 = 0.14

The answer is C

Also I think I overcomplicated this a lot ha ha.
I don't think you overcomplicated the question - I just think your working out was throrough. you will get faster the more you practice these kind of questions. That being said, one thing that could have sped your working out for this question in particular, was noticing that the original coffee sample was diluted by a factor of 10. As such, to work out the concentration of the original 5ml sample from the concentration of the diluted 50ml sample, all you had to do was multiply it by 10 intead of setting up an equation as you did - however this is not that big of a deal.

Decided I would join the science Games. Could someone check my answers to see how I went and explain any errors.
{b] Multiple Choice
question 1
Aspartame
D.    contains two amino groups in its chemical structure
question 2
Organic acids, including vitamin C (ascorbic acid), are present in lemon juice. Since organic acids and vitamin C are weak acids, they will undergo acid-base reactions. Only vitamin C, not the organic acids, will undergo a redox reaction with iodine, I2.
Which one of the following methods would be most appropriate to determine the concentrations of the organic acids and the vitamin C in a sample of lemon juice?
B.    an acid-base titration with ammonia and phenol red indicator, and a redox titration with iodine and permanganate ion indicator
question 3
A hydrolytic reaction occurs when .
D.   glucose is formed from maltose.
 
question 4
Which one of the following is a correct statement about the denaturation of a protein? 
B.   Alcohol denatures proteins by disrupting the hydrogen bonding.
 
question 5
Ammonia, NH3, can be produced by the reaction of hydrogen, H2, and nitrogen, N2. When this reaction takes place in a sealed container of fixed volume, an equilibrium system is established. The equation for the reaction is shown below.

N2(g) + 3H2(g) ⇌ 2NH3(g) ΔH = –92 kJ mol–1

If the pressure and volume remain constant when the temperature is increased, the forward reaction rate will
B.   increase and the [NH3] will decrease.
 


Welcome to the Forums Rory!
Its awesome that you have decided to have a go at the science games!
Here is some feedback on your answers
Question 1
Unfortunately aspartme doesnt actually have 2 amino groups. The chemical structure of aspartme (which you can see here) contains 1 amino group and 1 amide group. An amino group is a nitrogen bonded to hydrogens and/or alkyl or aryl groups (which are basically just carbons bonded to hydrogens). Amide groups however, are nitrogens bonded to a C=O - They are nitrogens bonded to a carbon which is double bonded to an oxygen.
Instead, the correct answer is C - aspartme and sucrose have the same energy content  :)

Quesiton 2
You are correct in identifying that we will need to perform both an acid base titration and a redox titration, however you didn't quite selecd the right one. The key to answering this question was to identify (as mentioned above) that we would need both a acid base and a redox titration, thus emiminating option A. Then to get to the right answer you need to select the procedure which uses the correct indicator for the acid base titration. Since for all option B, C, and D, the weak (as mentioned in the stem) organic acids are titrtated with strong bases, the equivilance point (the point at which the molar amounts of the acid and base are equal) will occur at a high pH. The acid-base indicator from option B operates over a mostly nuetral pH range and thus would not be suitable. Option C uses a acid-base indicator which has a range over a low pH, while option D is correct and has an indicator which changes colour over the high pH's that we are looking for.

Question 3,4 and 5
These are correct! good work :)
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