Category Archives: VCE Chemistry

Chapter 27/28: Six Universal Principles of Redox Reactions

Redox can be a confusing topic for VCE Chemistry students. It’s also taught right at the end of the year, when students are tired and some teachers are rushing their lessons so they can finish the course before the end of Term 3. Student motivation levels are at their lowest time of the year, which means that students often finish the course with an incomplete understanding of Redox.

Fortunately, there are six universal principles that are always true in Redox no matter what type of cell is being studied.

First, here’s a reminder of the types of cells you need to have studied in this course.

Galvanic Cells

  • Primary (can’t be recharged)
  • Secondary (can be recharged)
  • Fuel Cells (reactants are supplied continuously)

Electrolytic Cells

  • Electroplating Cells (no overall reaction)
  • Electrolytic Cells (non-spontaneous reaction)
  • Commercial Cells (usually molten electrolytes)
  • Recharge reaction of a secondary cell (non-spontaneous)

Now, here are the six universal Redox principles.

1. The strongest oxidant at the cathode reacts with the strongest reductant at the anode (SOC SRA)

To predict which species will react with each other, circle all the species present at the cathode on the electrochemical series. The highest species on the left will always react. Now, circle all the species present at the anode… the lowest species on the right will react.

2. The half-reaction with the highest E° value is always positive

In all cells, the half-equation with the highest electrode potential (also called ‘reduction potential’ or E° value) always occurs at the positive electrode. Similarly, the half-equation with the lowest electrode potential (E°) will always occurs at the negative electrode.

3. OIL RIG

Oxidation is loss of electrons. Reduction is gain of electrons.

4. ←AN OIL RIG CAT→

Anode reaction (oxidation reaction) is whichever reaction is happening to the left in the electrochemical series.

Cathode reaction (reduction reaction) is whichever reaction is happening to the right in the electrochemical series.

5. Electrons always flow in this order (RACO)

Reductant → anode → cathode → oxidant

6. In the internal circuit, cations always flow to the cathode, and anions always flow to the anode.

The internal circuit might be an electrolyte or a salt bridge that contains soluble weak oxidants and reductants such as KNO3(aq) (potassium nitrate). Either way:

  • cations always flow to the cathode; and
  • anions always flow to the anode.

Keep practicing redox questions by completing past papers, Checkpoints and Lisachem questions. If you need more help, contact me via the Get a Tutor button in the site’s menu bar. Students learn much faster with a tutor than on their own.

For more Study Tools for Year 12 students, click here.

Image courtesy of Annenberg Learner

What do I need to know for the Chemistry Exam?

VCE Chemistry Marks Allocated by Chapter 2013 2014 combined data chart
Click to download PDF version

We all remember the endless ‘cells’ questions at the end of the 2014 Chemistry exam. Less memorable was that the 2013 examination awarded a similar number of marks for ‘cells’ knowledge. Exams that test knowledge of these last two chapters in the course (Galvanic Cells and Electrolytic Cells) separate good students from great students because these topics are taught at the end of the course when students are getting tired and teachers are rushing to finish the course before trial examinations and the Term 3 holidays. Only the most diligent students go out of their way to get a complete understanding of these topics at this stage in the year – and they’re the ones who benefit from this type of exam.

Interestingly, in 2013 and 2014, 33% of the marks in the VCE Chemistry examination were awarded for knowledge of just four of the textbook’s 28 chapters. Therefore, if you’re short of time, focus your efforts on these four chapters (28, 27, 16 and 12) before working on the rest.

“Based on past examinations, students should focus their revision on Electrolysis (28), Galvanic Cells (27), Equilibrium (16) and Biomolecules (12) before working on the rest…”

While the structure of past examinations provide no guarantees about future examinations, it’s still reasonable to expect that the top 5 subjects will remain mostly the same in 2015 as in previous years.

Correlation of the total number of marks awarded per chapter is moderate with R² = 0.48 for 2013 and 2014.

Consider getting a home tutor who can answer your questions and explain difficult concepts to you. Students learn much faster with a tutor than on their own.

For more Study Tools for Year 12 students, click here.

Free VCE Chemistry Progress Tracker Wall Chart

Chemistry LADDER progress chart for VCE students
Click to download PDF version (A3 size)

Track your progress in VCE Chemistry with this A3 size progress tracker. Cross out or colour in each box as you complete it, and write your scores in . Start at the bottom (highlighted) and work your way upwards.

A ‘minimum expected level of examination preparation’ of 26 examination papers is labelled on the chart. Write your percentage scores in each of the boxes as you mark each paper. When you’re achieving past/practice examination scores concordantly above 90%, you’re ready to sit the VCE Chemistry examination.

For more Study Tools for Year 12 students, click here.

How to Make Time for 100 Days of Revision

Revision Timetable for GCSE studies
A well-planned revision timetable

Students who aim for a Study Score of 42 or above complete at least 20 practice papers for each subject they’re studying and correct them critically before examinations begin. High-achieving students print these 20 practice papers and make a detailed revision schedule before full-time revision sets in.

Learn how to make a quality revision timetable here.

Twenty practice papers, with proper correction and revision of theory, require 20 days to complete. A student studying 5 VCE subjects therefore needs 100 Days of Revision before their examinations begin.

VCE exams begin on October 28th, 2015, and 100 Days of Revision therefore begins on July 20th, 2015 for students who want to excel. Most schools plan to finish teaching Unit 4 at the end of August, which is just 40 days before the final examination. Forty days allows you only 8 days of revision for each of your 5 VCE subjects, and this simply isn’t enough practice for students who want to excel.

The best way to make time for 100 Days of Revision is to study Unit 4’s Area of Study 2 during this upcoming Easter Holiday.

In this upcoming Easter Holiday, by yourself, or with the help of a home tutor, you can study the topics that your school has planned to teach after July 20th, 2015. Typically, this is Unit 4’s Area of Study 2 (Chapters 23 to 28 in the Heinemann Chemistry 2 textbook). By studying this topic early, you’ll save time later in the year, which will allow you to complete 20 practice exams per subject instead of using that time to learn new theory.

Easter Holiday Tutoring 2015

If you want to learn Unit 4’s Area of Study 2 this holiday, and free up your homework schedule later in the year, get in touch for a short-term set of tutoring sessions in April 2015. I am offering new students a short-term Easter Holiday tutoring package for $300.

The $300 tutoring package includes:

  • Chemistry Unit 3 & 4 diagnostic test;
  • Quizzes based on knowledge areas that need to be improved upon (as identified in the diagnostic test);
  • Three home tutoring sessions of 2 hours each, which includes:
    • Critical review of the student’s homework answers;
    • 1-to-1 teaching of Unit 4 Area of Study 2 (Chapters 23-28) with homework exercises and quizzes;
    • Answering any Chemistry questions the student has accumulated while doing homework exercises.
  • Personalised Chemistry study timetable for the whole year; and
  • 24/7 email and phone support for the duration of the Easter Holiday.

The program includes 6 hours of home tutoring and requires 15 to 18 hours of self-study to be completed by the student during the holiday.

Get ahead in Chemistry this Easter. I am available for VCE Chemistry tutoring on the following dates and times.

Monday 30th March 2015 to Friday 3rd March 2015: 9am – 5pm daily
Monday 6th April 2015 to Friday 10th March 2015: 9am – 5pm daily

*UPDATE: I am now fully booked for the 2015 Easter Holiday. Fill in the contact form below to enquire about term-time tutoring at evenings and weekends.

Request VCE Chemistry tutoring using this online form.

More information about my tutoring services can be found here.

Chapter 10: Organic reactions: pathways to new products

10.1 Reactions of Alkanes

Alkanes contain strong carbon-carbon single bonds and strong carbon-hydrogen bonds. There are no partial charges on alkane molecules that might initiate reactions. The effect is that alkanes only undergo very few reactions.

(1) Combustion of alkanes

Alkanes can undergo combustion, producing CO2(g) and H2O(g)

When asked to create a combustion equation for a particular fuel, do the following steps:

  1. Write the fuel’s molecular formula
  2. Add excess O2(g)
  3. Produce CO2(g) and H2O(g)
  4. Balance C, H and O in that order.
  5. REMEMBER TO INCLUDE ALL THE STATES!

General formula: alkane + O2(g) → CO2(g) + H2O(g)

Example: C6H14(l) + O2(g) → 6CO2(g) + 7H2O(g) (halves are okay!)

(2) Substitution of alkanes

Alkanes can also undergo substitution, in which one of the hydrogen atoms is replaced with a halogen (e.g. F, Cl, Br, or I).

General formula: alkane + X2 → chloroalkane

Example: CH3CH3(g) + Cl2(g) + UV light → CH3CH2Cl(g) + HCl(g) (note that HCl is a gas!)

10.2 Reactions of alkenes

(1) Addition of alkenes

Alkenes can under addition reactions with halogens, hydrogen gas or water.

addition reactions of alkenes
Source: VCEasy.org

The first reaction happens at room temperature. If you have a gaseous alkene like ethene, you can bubble it through either pure liquid bromine or a solution of bromine in an organic solvent like tetrachloromethane. The reddish-brown bromine is decolourised as it reacts with the alkene.

(2) Addition polymerisation of alkenes
Source: Chemhume.co.uk

Chemguide links

Chemguide is an excellent revision resource that goes a little further than VCE. Read the relevant Chemguide pages below.

http://www.chemguide.co.uk/organicprops/alkanemenu.html
http://www.chemguide.co.uk/organicprops/alkenemenu.html
http://www.chemguide.co.uk/organicprops/estermenu.html

10.3 Oxidising ethanol to ethanoic acid

You will need to memorise the following ways to oxidise an alkanol into a carboxylic acid.

3 ways to oxidise alcohols
Source: VCEasy.org

For more information, visit this Chemguide page.

10.4: Making Esters

Table of Esters and their Smells
Click to enlarge

10.5: Organic Reaction Pathways

making esters from alkenes
Source: VCEasy.org

10.6: Fractional distillation

Fractional distillation can be used to separate compounds with different boiling points. It is commonly used in the separation of the compounds contained within crude oil.

More information about fractional distillation can be found here.

When hydrochloric acid is added to propene, two products can be produced: 1-chloropropane and 2-chloropropaneOnly the 1-chloropropane can be made into a carboxylic acid. We must therefore separate the 1-chloropropane from the 2-chloropropane by fractional distillation.

When reacting alkenes with 3 or more carbons (such as propene) with hydrochloric acid, we must write “HCl and fractional distillation” on the arrow.

For example:

propane fractional distillation
Source: Heinemann Chemistry 2

Click here for a 4-minute explanatory video about fractional distillation (beyond the VCE Chemistry course).

Read: Heinemann Chemistry 2 Chapter 10

Annotated VCAA Chemistry Data Booklet

Annotated VCAA Chemistry Data Booklet image
Click to download my Annotated VCAA Chemistry Data Booklet

The VCAA Chemistry Data Booklet contains answers to many questions you’ll be asked in the end-of-year examination. Unfortunately for students, however, the information it contains is neither explicit nor complete. Students need to know how to use the data booklet if they are to make the most of it.

Many formulae and definitions still need to be learned. For example, the data booklet doesn’t give you calorimetry formulae, and hydrogen bonds aren’t shown on DNA nucleotides. Trends are missing from the periodic table, and the electrochemical series comes with no annotations whatsoever! All this extra information needs to be memorised for VCE Chemistry.

I’ve annotated a real VCAA Chemistry Data Booklet to help you understand it. You can download it here.

Features include:

  • Trends are now shown on the periodic table (page 3);
  • Electrochemical series is fully labelled and explained (page 4);
  • 17 equations and 4 gas laws are given on page 5;
  • NMR data is now labelled to help you identify functional groups (pages 6 & 7);
  • Infrared absorption data is now pictured with 3 peaks described (page 7);
  • Amino acids are now labelled “polar/non-polar” and “acidic/basic” (pages 8 & 9);
  • Number of C=C bonds is now included for fatty acids (page 10);
  • DNA structure is explained in much more detail (page 10);
  • Colours of two indicators are corrected (page 11);
  • Ka is explained (page 11);
  • Solubility rules are added on the back.
Annotated VCAA Chemistry Data Booklet
Every page is colour-coded and annotated with explanations

Chemistry data booklets make great revision tools. Check out the following data booklets from around the world:

Chapter 4: Relative Atomic Mass & the Mole

These ‘chapter’ posts are not complete summaries or sets of notes. They are simply collections of supplementary resources that I recommend using in the classroom in addition to the textbook and any other assignments on the course. Most of the resources here are videos, but I will also occasionally put worksheets, quizzes, books, apps and games here as well.

4.1: Masses of particles

Watch the following introductory videos on relative atomic mass.

You no longer need to know the workings of a mass spectrometer because it’s been deleted from the VCE Chemistry study design. However, many schools still use older worksheets, which ask you to label the function of each part of the machine. Ask your teacher whether the mass spectrometer machine will be examined in your school’s Year 11 examination.

Mass spectrometer
Source: Piercenet.com

Even though knowledge of the mass spectrometer is not required, understanding how it works can help students to interpret the kinds of graphs that it produces. This video explains how the mass spectrometer works (beyond VCE level).

Here are some sample questions for you to try.

4.2: The mole

We have several ‘number-words’ in English. Examples include ‘pair’, which means ‘2’; ‘dozen’, which means ’12’, and ‘ream’, which means ‘500’. A mole is a very large number-word with a value of 6.02×1023.

The mole is also called ‘Avogadro’s number’.

Most important formula here is n = N ÷ NA

  • n is the number of moles in your sample;
  • N is the number of particles (either molecules or atoms);
  • NA is Avogadro’s number (6.02×1023).

Click here for the lesson that accompanies the above video.

4.3: Molar mass

Relative molar mass is the mass of a molecule, formula, isotope or atom compared to the molar mass of carbon-12, which has a molar mass of exactly 12.

The following are all forms of relative molar mass and have no units:

  • relative molecular mass (used for molecules)
  • relative formula mass (used for repeating structures such as crystals)
  • relative isotopic mass (used for single isotopes)
  • relative atomic mass (used for single elements that contain mixtures of isotopes)

Most important formula here is n = m ÷ M

  • n is the number of moles of particles in your sample;
  • m is the mass of the sample in grams;
  • M is the relative molar mass of your sample.

4.4: Percentage composition

Use the m-n-ratio method to find the percentage composition of any particular compound. A demonstration is shown below.

Read: Heinemann Chemistry 1 Chapter 4