Monthly Archives: November 2014

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

Common Names of Carboxylic Acids

Ever wondered why ‘formic acid’ is so-called? Or montanic acid? Or melissic acid? This handy A3 poster shows you the Latin/Greek/Persian origins of each of the carboxylic acids’ common names from ‘formic acid’ (no. 1) to ‘hexatriacontylic acid’ (no. 36). Each acid comes with a cute graphical description of where its name comes from.

Common Names of Carboxylic Acids
Click to enlarge

There are some interesting origin stories behind each of these names. Formic acid, for example, is found in insect stings (hence the name). Palmitic acid is found in palm trees (hence the name), and myristic acid is found in nutmeg.

Three of the carboxylic acids are named after goats: caproic acid, caprylic acid and capric acid. Together, these three molecules comprise 15% of the fatty acids found in goats’ milk, and many reports also suggest that they smell ‘goat-like’!

Many of the odd-numbered higher carboxylic acids are rarer in nature and thus didn’t earn a common name until recently. Undecylic acid, for example, which has eleven carbon atoms in its backbone, is named simply after the Greek word for ‘eleven’.

Click here for more Chemistry posters.

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:

The most beautiful Chemistry videos I’ve ever seen

Beautiful Chemistry banner
Image via BeautifulChemistry.net

I’ve discovered the most beautiful Chemistry website ever created via someone’s Twitter feed. It was created by several researchers at the Institute of Advanced Technology at University of Science and Technology in China. The goal of this project is to bring the beauty of chemistry to the general public through digital media and technology.

The first project of the collaboration used a 4K UltraHD camera to capture beautiful chemical reactions in specially-designed glass containers that eliminate the problems of refraction and reflection caused by rounded beakers and test tubes. I also love how the researchers play with time, slowing down and speeding up the videos at just the right moments. The video footage is then annotated and matched perfectly with background music to give a truly mesmerising result. Here are three of my favourites:

Precipitation reactions (my favourite)

Metal displacement reactions

Bubbles!

As a visual learner and a huge fan of new ways to pique people’s interest in science, I got in touch with Yan Liang, an Associate professor at the Department of Science and Technology Communication at the University of Science and Technology of China (USTC).

Yan Liang, like the visionary data-visualisation gurus David McCandless and Hans Rosling, is passionate about bringing hidden data to the public domain in a form that’s really easy to digest. When I asked him what inspired him to make these videos, he said:

“To me, science is beautiful and full of wonders. However, the beauty of science is often hidden inside research laboratories and buried in scientific literature. By creating engaging visuals and make them available to the general public, I believe more people would appreciate the beauty and wonders of science, and hopeful get interested in science.”

Just like the All-Natural Banana poster series I posted one year ago, the goal of the BeautifulChemistry.net project is mostly about education and scientific outreach.

“The goal is to bring the beauty of chemistry to the general public. To many people, Chemistry might usually be associated with pollution, poison, explosions, etc. We want to show them the other side of chemistry, which is much less well-known. We also want to get more kids and students interested in chemistry and inspire them to learn more chemical knowledge.”

Since Yan Liang, Edison Zheng, Jiyuan Liu, Xiangang Tao and Wei Huang launched Beautiful Chemistry on September 30th, 2014, they have received over 110,000 unique visitors and over 2 million page views. The project has been a huge success, and has already inspired young people worldwide to pursue Chemistry.

“People love our videos of chemical reactions. Some people commented if they saw these videos when they were in high schools, they might work harder and learn more chemistry. A 15-year old student from Germany and others told us our videos inspired them to shoot their own videos of chemical reactions. Artists like these videos and many request our footage to make music videos.”

They’ve got some exciting plans for the future, too. Yan Liang tells me they’re planning to use microscopes to film future videos and that they’re developing a fashionable clothing line-up as well!

Beautiful Chemistry Metal Displacement Clothing for Women
Reaction between Zn(s) + Pb(NO3)2(aq) to produce beautiful crystals of lead

There are currently 33 gorgeous 4K videos on their website, and there’s even a Chinese version as well. Check out their website and subscribe to their blog here. You can see more of Yan Liang’s projects, including amazing scientific illustrations, at l2molecule.com.

Significant Figures: 6.0 Rules

Ruler

Significant figures tell you how accurately a number is known. This invariably depends on the precision of your instruments.

To illustrate this, use a pencil and a ruler to draw a square with sides of 8.109435 cm in length. Now, calculate the area of the square that you’ve drawn.

A ruler can only measure length to within ±0.1 cm. Our square therefore has sides 8.1 cm in length (not 8.109435 cm) because our measurements are limited by the accuracy of the ruler. The area of our square is therefore 8.1×8.1=66 cm², not 65.762936019225 cm², because there was no way to measure all of those decimal places precisely using a ruler.

Accurately-known digits are known as significant digits. All other digits are described as not significant. We must always round our final answer (not the intermediate steps) to the correct number of significant digits by following the six rules below.

1. Numbers without a decimal point

  1. First non-zero digit is significant
  2. Last non-zero digit is significant
  3. All digits in-between are significant
  • 45 is to 2 significant figures (s.f.)
  • 1,240 (3 s.f.)
  • 68,686,000 (5 s.f.)

2. Numbers with a decimal point

  1. First non-zero digit is significant
  2. All digits afterwards are significant
  • 1.2 (2 s.f.)
  • 6.810 (4 s.f.)
  • 900,001 (6 s.f.)

3. Scientific notation

Scientific notation is a way of writing numbers in the form:

a × 10 where 1 ≤ a < 10.

Count the number of significant figures in a to find the number of significant figures in the number (a × 10b).

  • 5.56 × 103 is to 3 significant figures
  • 2.012 × 10-4 is to 4 significant figures

4. Conversions

Some unit conversions are exact and are said to have an unlimited number of significant figures.

  • 1 minute = 60.0000000000… seconds (infinite s.f.)
  • 1 metre = 100.0000000000… metres (infinite s.f.)

Temperatures usually have 3 (sometimes 4) significant figures when converted into Kelvin!

  • 10°C = 283 K (3 significant figures)
  • 100°C = 373 K (3 significant figures)
  • 4000°C = 4273 K (4 significant figures)

5. Addition and subtraction

Rule: Always round your final answer (not any intermediate answers!) to the smallest number of decimal places.

  • 441 + 65.42 = 506 (use zero decimal places)
  • 200.1 – 144.2456 = 55.9 (use 1 decimal place)

6. Multiplication and division

Rule: Always round your answer so it has the same number of significant figures as the input value with the smallest number of significant figures.

  • 481.56 × 14.5 = 6980 (use only 3 s.f.)
  • 7800 ÷ 41.1 = 190 (use only 2 s.f.)

Remember to round your ANSWER (not the intermediate steps) to the correct number of significant figures.

Questions? Comments? Still confused? Leave a message in the comments below. I’ve tried to make sig figs as simple as I can in this post.

More great resources:

Crash Course Chemistry Explains All!

Help! My exam is in 3 days’ time and I haven’t studied for it. What should I do?

jameskennedymonash Beat Exam Stress

First, relax.

The priority at this late stage is that you enter the examination hall well-rested, well-fed and with an appropriate level of stress.

1. Sleep early every night

  • Go to bed before 10pm (or 9pm with an exam the next day)
  • Wake up naturally. If you’re waking up too late, go to sleep at 7pm.
  • Avoid backlit screens for one hour prior to sleeping. Backlit screens emit light in the 484-nanometre range, which excites melanopsin in the retinal ganglion cell photoreceptor. This disrupts your circadian rhythm and keeps you awake!

2. Eat healthily

  • Eat regular meals at regular times.
  • Eat plenty of fruit. (Five per day.)
  • Drink plenty of water.

3. Get some lighter exercise

  • Avoid exhausting sports around exam time (e.g. rugby).
  • Do more walking, jogging, and lighter sports at exam time (e.g. badminton).
  • Drink plenty of water(!) Aim to drink 3 litres per day.

Research has shown that you perform difficult tasks (such as a Chemistry exam) much better under moderately relaxed conditions. The famous Yerkes-Dodson curve illustrates this beautifully.

The Yerkes–Dodson law is an empirical relationship between arousal and performance level. Source: Uni of Minnesota
You want to be on top of that blue curve.

More information about the Yerkes-Dodson curve.

Light exercise will help you to position yourself at the tip of that blue curve, which will optimise your state of mind for learning as much as possible in the few days you’ve got left.

Second, do targeted revision.

4. Mise en place (get everything ready)

5. Spend 3½ hours doing a practice examination

  • Spend 3½ hours doing the exam in semi-exam conditions.
  • Mark it immediately afterwards.
  • Keep it for next time: you’ll use the incorrect questions to guide your theory revision (step 6).

6. Spend 3½ hours reading & annotating your textbook

  • Read and annotate the textbook chapters relating to questions you got wrong.
  • DON’T READ YOUR NOTES. Read the textbook instead: it’s much clearer.
  • Re-do those questions now you’ve learned the theory behind them.
  • Follow steps 1-4 on How to use a Textbook: 6 Rules to Follow. This includes making vocabulary lists and beautiful, clear theory notes to go on your wall.
  • Repeat steps 5 and 6 (in this article) every day. (Study at least 7 hours per day.)

Finally, get help.

7. Get help!

  • Contact your teacher with any questions you have; exam content you don’t understand or worries you have about the exam.
  • Talk to a friend if you’re stressed about the exam.
  • Check out the resources below if your stress levels are still too high.

8. More resources

Veritasium image

10 Best Science Channels on YouTube

1. Veritasium blows your mind by breaking misconceptions

2. Periodic Videos: experiments you’d love to do but can’t

3. SciShow blasts fun facts

4. Numberphile makes you LOVE mathematics

5. AsapSCIENCE: fascinating hand-drawn mini-tutorials

6. MinutePhysics: fascinating mini-Physics tutorials

7. Vsauce investigates fascinating questions

8. SmarterEveryDay explains cat-flipping, and more

9. Science Channel gives you the latest Science news

10. NASA gives you real-life science inspiration

Are there any that I missed from this list? Add them in the comments section below.