2017 Paper 1 Suggested Solution

2017 A Level Chemistry, H2 Chemistry Paper 1 Suggested Solution - Chemistry Guru

Check out the suggested solutions for A Level 2017 H2 Chemistry Paper 1 by Maverick Puah the Chemistry Guru.

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A Level Chemistry 2017 Paper 1 Question 30 Solution - Exclusive

In this exclusive video we want to discuss the suggested solution for A Levels Chemistry (H2 Chemistry) 2017 Paper 1 Question 30.

Let's take a look at this question:

2017 A Level H2 Chemistry P1 Q30 question

The topic tested in this question is on Electrochemistry, in particular the concept on Hydrogen-Oxygen Fuel Cell.

Let's do a very brief recap:

2017 A Level H2 Chemistry P1 Q30 hydrogen oxygen fuel cell overall reaction

H2 is oxidised and O2 is reduced to water in the overall reaction.

1. Determine Direction of Electron Flow

2017 A Level H2 Chemistry P1 Q30 deduce direction of electron flow

Since H2 is oxidised, electrode X will be the anode and is negatively charged for an electrochemical cell.

O2 is reduced and electrode Y will be the cathode and hence it will be positively charged.

This means direction of electron flow will be from anode X to cathode Y.

We can then look through the options and eliminate options C and D.

2017 A Level H2 Chemistry P1 Q30 eliminate C n D

2. Determine E value of Oxygen Electrode

Since O2 is reduced, we need to choose the relevant half equations from the Data Booklet where O2 is on the left-hand side of the half equation.

Also, the electrolyte is alkaline NaOH, so we also need to choose the half equation which contains OH-.

2017 A Level H2 Chemistry P1 Q30 choosing reduction of O2 in alkaline medium

From the Data Booklet we should be able to find these 2 half equations where O2 is on the left-hand side, hence undergoes reduction.

2017 A Level H2 Chemistry P1 Q30 half equations for O2

The first half equation where E0 = +1.23V should be used for acidic medium due to presence of H+.

The second half equation where E0 = +0.40V should be used for alkaline medium due to presence of OH-.

For this question we should be using the half equation in alkaline medium, where E0 = +0.40V.

Finally we can look at the options and choose option A as the correct answer to this question.

2017 A Level H2 Chemistry P1 Q30 compare option A n B

Check out this video for the full solution and detailed explanation!

Topic: Electrochemistry, Physical Chemistry, A Level Chemistry, Singapore

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A Level Chemistry 2017 Paper 1 Question 29 Solution - Exclusive

In this exclusive video we want to discuss the suggested solution for A Levels Chemistry (H2 Chemistry) 2017 Paper 1 Question 29.

Let's take a look at this question:

2017 A Level H2 Chemistry P1 Q29 question

The topic tested in this question is on Electrochemistry, in particular the quantitative determination of species discharged for an electrolytic cell.

We first start with the 2 Faraday's Equations and work out the number of moles of electrons.

We can then determine the moles of copper deposited from the moles of electrons involved in the electrolysis.

2017 A Level H2 Chemistry P1 Q29 determine mole of Cu from Faradays Equation

From this expression we can see that the moles of copper deposited is only affected by current and time, and not by the concentration of Cu2+ in the solution.

Finally we can compare the options and determine the answer to this question is option C.

2017 A Level H2 Chemistry P1 Q29 compare options

Check out this video for the full solution and detailed explanation!

Topic: Electrochemistry, Physical Chemistry, A Level Chemistry, Singapore

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A Level Chemistry 2017 Paper 1 Question 28 Solution - Exclusive

In this exclusive video we want to discuss the suggested solution for A Levels Chemistry (H2 Chemistry) 2017 Paper 1 Question 28.

Let's take a look at this question:

2017 A Level H2 Chemistry P1 Q28 question

The topic tested in this question is on Ionic Equilibria.

Strong acids are proton or H+ donors that are fully dissociated, while weak acids donate H+ but are partially dissociated.

2017 A Level H2 Chemistry P1 Q28 dissociation of strong acid and weak acid

Therefore we will expect for the same concentration of strong acid and weak acid, the amount of ions dissociated by the weak acid will be smaller as compared to that of the strong acid.

Option A - 1 mol dm-3 aqueous ethanoic acid

2017 A Level H2 Chemistry P1 Q28 option A

Since ethanoic acid is a weak acid, 1 mol dm-3 of CH3COOH will dissociate partially to give less ions in solution.

This means there are less mobile charge carriers and the solution will be less conducting.

Option B - 1 mol dm-3 aqueous hydrogen chloride

2017 A Level H2 Chemistry P1 Q28 option B

HCl is a strong acid so 1 mol dm-3 of HCl will dissociate fully to give 1 mol dm-3 of H3O+ and 1 mol dm-3 of Cl- ions.

There are more mobile charge carriers in the solution hence it will be more conducting.

Options C & D - pure ethanoic acid and pure liquid hydrogen chloride

2017 A Level H2 Chemistry P1 Q28 option C n D

Interestingly pure acids are non-conducting as there is no H2O to act as a Bronsted base to accept H+ from the acids, hence no ions are formed and pure acids cannot conduct electricity.

Therefore the liquid which is the best conductor of electricity and the answer to this question would be B.

Check out this video for the full solution and detailed explanation!

Topic: Ionic Equilibria, Physical Chemistry, A Level Chemistry, Singapore

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A Level Chemistry 2017 Paper 1 Question 27 Solution - Exclusive

In this exclusive video we want to discuss the suggested solution for A Levels Chemistry (H2 Chemistry) 2017 Paper 1 Question 27.

Let's take a look at this question:

2017 A Level H2 Chemistry P1 Q27 question

The topic tested in this question is on SN1 Mechanism of Halogenoalkane.

Since the solvent has to be polar, we can immediately eliminate option B since C6H14 is non-polar.

From the second step of the mechanism, OH- from NaOH acts as a nucleophile and attack the carbocation to form an alcohol product.

2017 A Level H2 Chemistry P1 Q27 SN1 second step

A by-product can be formed in the second step when the polar solvent acts as a competing nucleophile to attack the carbocation.

Hence we need to consider the nucleophilic attack for each polar solvent and determine if a by-product is formed.

A. H2O solvent

2017 A Level H2 Chemistry P1 Q27 h2o solvent

On nucleophilic attack of H2O and subsequent deprotonation, the product formed is an alcohol which is the same product formed from NaOH.

Therefore there are no by-products and option A is the most likely answer.

C. CH3CH2NH2 solvent

2017 A Level H2 Chemistry P1 Q27 amine solvent

On nucleophilic attack of amine CH3CH2NH2 and subsequent deprotonation, produced formed is a secondary amine.

A different by-product is formed.

D. CH3CH2OH solvent

2017 A Level H2 Chemistry P1 Q27 alcohol solvent

On nucleophilic attack of alcohol CH3CH2OH and subsequent deprotonation, produced formed is an ether.

A different by-product is also formed.

Finally we can compare the options and confirm the answer to this question is option A.

2017 A Level H2 Chemistry P1 Q27 compare options

Check out this video for the full solution and detailed explanation!

Topic: Halogenoalkanes, Organic Chemistry, A Level Chemistry, Singapore

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A Level Chemistry 2017 Paper 1 Question 26 Solution - Exclusive

In this exclusive video we want to discuss the suggested solution for A Levels Chemistry (H2 Chemistry) 2017 Paper 1 Question 26.

Let's take a look at this question:

2017 A Level H2 Chemistry P1 Q26 question

The topic tested in this question is on Primary Structure of Proteins under Nitrogen Compounds. If you are keen to know more about alpha amino acids and drawing primary structure of proteins, check out this video lesson here.

The primary structure of protein is the unique sequence of amino acids joined together via peptide linkages to form a polypeptide chain or backbone.

Since all amino acids in proteins are alpha amino acids, the primary structure of protein follows a very predictable repeat unit:

2017 A Level H2 Chemistry P1 Q26 repeat unit of protein primary structure

The first thing to do is to find the continuous polypeptide chain (repeat unit of positions 1,2 and 3) and to identify all the R groups that are attached to position 2.

2017 A Level H2 Chemistry P1 Q26 find position 123 and R group

We can now look through the options and see if the R groups for the amino acids in options A to D could be found in the primary structure.

2017 A Level H2 Chemistry P1 Q26 compare option to eliminate R group

Hence we can eliminate option D, since the R group -CH2CH2-Ph-OH is not found in the protein given.

Next we need to determine the structure of amino acid at low pH.

2017 A Level H2 Chemistry P1 Q26 structure of amino acid at low pH

We would expect the acid group to remain as -COOH group, while the amine will accept a proton to form conjugate acid -NH3+ group.

Finally we can look through the remaining options again and determine the answer to this question is option A.

2017 A Level H2 Chemistry P1 Q26 compare option to identify answer

Check out this video for the full solution and detailed explanation!

Topic: Nitrogen Compounds, Organic Chemistry, A Level Chemistry, Singapore

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