Syntactic and Syndiotactic are NOT Synonymous

 

Question 20 from paper 1 of the QCAA chemistry exam 2022 is shown below. Can you answer it?

 

 You can if you make a couple of assumptions first:

1/ The 3D structure isn't given, so you have to assume (given the possible answers) that methyl groups above the chain are in fact coming out of the plane, while methyl groups below the chain are behind the plane.

2/ You have to assume that "syntactic" is a misprint of "syndiotactic" since there was no mention of this being a composite material.

Then you can choose (A) as the answer, and according to the answer sheet you would be correct.

 

However, here is an excerpt from the draft new Queensland Chemistry syllabus (for implementation in 2025 I believe),

      "Describe the structure features of

           -polyethene (LDPE and HDPE), polypropene (syntactic, isotactic and atactic) and                                             polytetrafluorethene."

(Cross my heart, this is what is says, the syllabus writers seem to have difficulties with adjectives as well as chemical nomenclature, where are the round brackets around tetrafluoroethene?)

 

So, it appears that students will study tacticity of polymers but only isotactic and atactic not syndiotactic, then they will look at composite materials in the form of syntactic foams.

Really?

 

Dear Queensland Chemistry syllabus and exam writers, the 3D structure of a polymer results in an isotactic, syndiotactic or atactic polymer.

A syntactic foam refers to a composite material in which hollow spheres are bound together by a polymer.

Converting Between Concentration Units

The concentration of carbon dioxide dissolved in water is about 0.000011 mol/L, while the concentration of carbon dioxide in blood is about 1100 ppm. It is not easy to tell which of these two solutions is the most concentrated because they are in different units. However, if we were to convert the concentration of carbon dioxide in water from mol/L to ppm, we could easily compare these two concentrations.

AUS-e-TUTE has just added a new tutorial, game, test, drill, prac, flashcards, quiz, worksheet wizard, and problem solving template to help!

 

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South Australia sets a poor example

 I've always admired South Australia for its innovative and interesting chemistry syllabi, and it's great that females are being featured in chemistry labs, but the current image on their website is a big fail in terms of chemistry education.

 

https://www.sace.sa.edu.au/web/chemistry

 

Can you see any problems with this photo?

(revise "Safety in the Lab" at https://www.ausetute.com.au/safety.html)

Shapes of Melting Ice

 What shape is submerged ice as it melts?

That depends on temperature apparently ..

 Which suggests that we can infer water temperature in nature by observing the shape of its melting ice.

Scott Weady, Joshua Tong, Alexandra Zidovska, and Leif Ristroph (2022); Anomalous Convective Flows Carve Pinnacles and Scallops in Melting Ice. Phys. Rev. Lett 128(4)  https://doi.org/10.1103/PhysRevLett.128.044502

Mass Concentration (m/v)

 There are lots of ways to measure concentration in chemistry.

One method is to divide the mass of solute by the volume of solution: m/v

This is called a mass concentration and common units for mass concentration are g/L or g L^-1

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How to study for Chemistry exams

As your chemistry exam gets closer, I'm sure you've been "studying" hard, probably reading through your notes, making summaries, summarizing the summaries, putting important concepts on flash cards... and a whole lot more. But will any of that help you achieve a good result on a chemistry exam?

Probably not. So, put your notes away and read on.

Chemistry examiners are not interested in whether you have memorized the "facts" (definitions, formulae etc). It is most unlikely that the following question will appear on a chemistry exam paper,

Question 1: "State Le Chatelier's Principle"

Chemistry examiners are interested in how you apply chemical principles to solve problems. So the following question is much more likely to be found on a chemistry exam paper,

Question 2: "A student dissolves some solid FeSCN²⁺ in water in a test tube at room temperature and pressure, producing a mixture of reddish-brown FeSCN²⁺(aq), pale yellow Fe³⁺(aq), and colourless SCN^-(aq). The student observes that the test tube feels cooler as the solute dissolves.

(a) Write an equation to describe the process.

(b) Describe what colour change, if any, would occur if the test tube was placed in an ice-bath. Explain your answer"

Question 2 is asking you to apply Le Chatelier's Principle to a given chemical process.

The best way to study for your chemistry exam is to answer a variety of questions. AUS-e-TUTE Members have access to thousands of problems (with worked solutions and tutorials if you need some help). If you are not an AUS-e-TUTE member you can often find books of problems for a given course, and you probably have access to "past papers". 

Here's another question you might like to try,

Question 3: One step in the Ostwald process for manufacturing nitric acid from ammonia involves the production of nitrogen dioxide as shown in the chemical equation below:

2NO(g) + O₂(g) ⇋ 2NO₂(g)

A 10.00 L reaction vessel initially contained 2.50 mol NO(g) and 1.20 mol O₂(g).

0.50 mol NO(g) remained in the vessel after equilibrium was established.

(a) Calculate the equilibrium constant for this reaction.

(b) A second experiment was conducted using the same initial amounts of NO(g) and O₂(g) but in a reaction vessel of about half the volume. What affect would this have on the value of the equilibrium constant? Explain your answer. 

If you find these questions a bit tricky, then AUS-e-TUTE might help you become more familiar with exam-type questions and how to answer them. Join AUS-e-TUTE today

WA Chemistry Syllabus Study Guide

Do you live in Western Australia?
Are you a Year 11 or 12 student studying chemistry?
We have listed all the free tutorial links relevant to your syllabus in our syllabus study guide at https://www.ausetute.com.au/ssgwaatar2017.html

Saturation

What does it mean when a Chemist refers to a molecule as saturated or unsaturated?
How do you test a compound to see if it is saturated or unsaturated?
The answers to these questions, with examples, are given in AUS-e-TUTE's new tutorial Saturated and Unsaturated Organic Compounds

AUS-e-TUTE Members should log-in to access the game, test and exam (with worked solutions) on this topic.

VCE Chemistry Syllabus Study Guide

Do you live in Victoria?
Are you a Year 11 or 12 student studying chemistry?
We have listed all the free tutorial links relevant to your syllabus in our syllabus study guide at
https://www.ausetute.com.au/ssgvce16.html

HSC Chemistry Syllabus

Do you live in New South Wales?
Are you a Year 11 or Year 12 student studying chemistry?
We have listed all the free chemistry tutorials you need in our syllabus study guide at https://www.ausetute.com.au/ssgnsw2018.html

Queensland Chemistry Syllabus

Do you live in Queensland?
Are you a Year 11 or Year 12 student studying chemistry?
We have listed all the free chemistry tutorials you need in our syllabus study guide at https://www.ausetute.com.au/ssgqld2019.html

Nitrogen vs Air in Car Tyres

The tread on my car tyres had worn down, so I popped into my local tyre retailer to buy 4 new tyres.

"We can inflate your new tyres with air, or, for an extra $5 per tyre we can fill them with nitrogen gas", the sales person told me, " Nitrogen gas doesn't react with tyre and rim material so your tyres will last longer, it will help maintain the pressure in your tyres so you won't need to check your tyre pressure as often, and it reduces the running temperature of the tyres so your tyres are less likely to explode."

Is this just marketing hype or are there good reasons for choosing to inflate your car tyres with nitrogen instead of air?

Read the March 2020 edition of AUS-e-NEWS to find out more.

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How to Maximise Marks in Your Chemistry Exam

Are you ready for your chemistry exam?
The Sydney Morning Herald provided 8 dot points to help you answer Chemistry exam questions, which we have expanded out below:

• Write correctly balanced equations.(Include state, or phase, of matter)
• Structure your answers to ensure they are logical. Written calculations should be neatly organised and sequential.
  • If you dilute an acid with water at 25°C, the pH of the solution will not rise above 7
  • If you dilute a base with water at 25°C, the pH of the solution will not fall below 7
• Clearly label your graphs (plots, scale, axis, line of best fit).
• Use relevant scientific terminology.
  • Check your spelling! Ethane is NOT the same as ethene! Molarity is NOT the same as morality! Calorimetry is NOT the same as colorimetry!
  • If the question is about physical properties, think about intermolecular forces.
  • If the question is about chemical properties, think about intramolecular forces, and think about types of chemical reactions for inorganic chemicals and for organic chemicals (combustion, addition, substitution, elimination, condensation, polymerisation)
• Explain the underlying chemistry and provide relevant chemical equations.
  • Is it a gas question? Ideal Gas Law? Molar Volume? 
  • Precipitation question? Solubility Rules? Solubility Product? Gravimetric Analysis? Conductometric Analysis?  Argentimetric Analysis?
  • Equilibrium question? Equilibrium concepts? Le Chatelier's Principle? Equilibrium law?
  • Acid/base question? Definitions? Properties? Acid strength? Acid-dissociation constant? Neutralisation reaction? Titration techniques? Titration calculations?
  • Chemical kinetics question? Reaction rate? Maxwell-Boltzmann distribution?
  • Determination of organic structure? C-13 NMR, Mass Spectroscopy? IR Sopectroscopy?
• Use subscripts and superscripts where appropriate.
  • Formula of ions, superscript to right of symbol (number first followed by sign)
  • Formula of isotopes, mass number superscript to left of symbol, atomic number subscript to left of symbol 
  • Molecular formula or empirical formula, number of atoms of each element shown as a subscript to the right of the element's symbol
  • "States" or "phases" of matter are sometimes written as a subscript to the right of a molecular formula, eg, CO_2(g), but are usually written in line with with formula, eg, CO₂(g)
• Use stimulus materials to answer the question.
• Use clear labels when continuing responses in a different booklet.

ALWAYS check that you have answered the question that was asked, and not provided an answer to a question that you wish had been on the paper!

Gold Nuggets in 2019

Between 1850 and 1900, the city of Bendigo in Victoria, Australia, was the centre of a Gold Rush. Central Deborah Gold Mine, the last commercial gold mine to operate in Bendigo, re-opened as a tourist attraction in 1986.
Gold can still be found in the Bendigo area.
On Mothers' Day 2019, a family out walking Lucky their dog on the outskirts of Bendigo walked onto a gold nugget. They took it along to the local IGA supermarket to weigh it. The gold nugget weighed 624 grams (about 20 ounces).
Today, the price of gold in Australia is listed as $65.76 per gram. So, if pure, the gold in this nugget would be worth 624 × $65.76 ≈ $41,000.
How big would this gold nugget be?
We know the mass of the nugget is 624 grams.
We can look up the density of gold in tables, ρ = 19.3 g cm^-3
Since density = mass (g) ÷ volume (cm³)
19.3 = 624 ÷ volume (cm³)
volume (cm³) = 624 g ÷ 19.3 g cm^-3 = 32.3 cm³
Which could be represented by a cube approximately 3.2 cm × 3.2 cm × 3.2 cm
Not very big at all is it!

Ballarat, another Victorian Gold Rush town and site of the historic "Eureka Stockade", was also the place where another spectacular gold nugget was found in June 2019 (and reported nationally in July 2019). This gold nugget weighed about 2 kilograms, or 2,000 grams.
At today's prices, it would have a value of about 2,000 × $65.76 ≈ $130,000
And how big would this nugget be?
density = mass (g) ÷ volume (cm³) volume (cm³)
density = mass (g) ÷ density (g cm^-3) = 2,000 g ÷ 19.3 g cm^-3 = 103.6 cm³
The dimensions of a cube with this volume would be about 4.7 cm × 4.7 cm × 4.7 cm
Which would fit nicely into the palm of your hand as shown in the photograph below

Further Reading:
Density Calculations

Suggested Study Questions:

1.  The density of gold is 19.3 g cm^-3. Calculate the mass of
   • 1 cm³ of gold 
   • 10 cm³ of gold 
   • 1 m³ of gold
2.  The density of gold is 19.3 g cm^-3. Calculate the volume of
   • 1 g of gold
   • 10 g of gold
   • 1 kg of gold 
3.  The density of gold is 19.3 g cm^-3. Calculate the dimensions of a cube of gold which has a mass of
   • 5 g
   • 500 g
   • 5 kg
4. The density of gold is 19.3 g cm^-3. Calculate the diameter of a sphere of gold which has a mass of
   • 2 g
   • 200 g
   • 2 kg
5. A credit card has the approximate dimensions 65 mm × 55 mm × 1 mm. Calculate:
   • volume of the credit card in cm³
   • mass of a gold credit card
   • value of a gold credit card if the cost of gold is $65 per gram
   • Why aren't "gold" credit cards really made out of gold?
6. Gold is one of the few metals that is found in nature as the "native" element (that is, it is found as the element and not in compounds). Explain why gold can be found in nuggets.
7. Name some other metals that can also be found in their native state (that is, found as the element and not as compounds). Explain why these metals can be found in their native state. 
8. Name a metal that is not found on Earth in its native state, and explain why it is not found in nature as the uncombined element.

Word Equations for Chemical Reactions

A word equation is Chemistry short-hand for describing how new substances can be made using an initial substance (or substances).
The initial substances are called reactants.
The new substances formed are called products.
The most general form of a word equation is:

reactants  →   products

AUS-e-TUTE has just added a new tutorial, game and test to help our members understand and use word equations. Members should log-in to the Test Centre to use these resources.

A "free-to-view" tutorial on word equations is currently available for non-members to access at

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Rosalind Franklin and the Structure of DNA

Three men, James Dewey Watson,  Francis Harry Compton Crick and Maurice Hugh Frederick Wilkins, shared the The Nobel Prize in Physiology or Medicine 1962 "for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material.", that is, they  modeled DNA as a double helix, each strand of the helix has a backbone of  sugar molecules held together by phosphate groups. The two strands are twisted together and held together by hydrogen bonds. But how did they learn what DNA was made up of?

 This is where Rosalind Elsie Franklin enters the story of DNA. In 1951 she was a Research Associate at Kings College London where she worked on  X-ray diffraction studies with her colleague Maurice Wilkins. Her x-ray diffraction images of DNA led to the discovery of the DNA helix. The image on the left is known as "photograph 51" and was an x-ray diffraction image of DNA obtained by Franklin's Ph.D student Raymond Gosling.

X-ray diffraction is an instrumental technique used to elucidate the structure of crystals of chemical compounds. Incoming x-rays are diffracted by the crystal lattice and they exit the crystal at different angles. An x-ray crystallographer like Franklin can measure the angles and intensities of these diffracted x-rays to produce a 3-dimensional picture of the density of electrons in the crystal lattice. The electron density can then be used to determine the locations of atoms within the crystal lattice.

Without Franklin's knowledge, Maurice Wilkins showed this image to James Watson who used it, along with other evidence, to develop a model of DNA. Science historians still debate whether Franklin would have determined the structure of DNA on her own had her images not been shared with Watson.

Rosalind Franklin made important scientific contributions, not only to the discovery of the structure of DNA and RNA, but also in helping us to understand the structure of viruses, coal and graphite.
Unfortunately, Rosalind Franklin died of ovarian cancer in 1958. Nobel Prizes are not generally awarded posthumously so her contribution to the elucidation of the structure of DNA is not well-known.


Further Reading:
Chemistry of DNA
Intramolecular Forces
Intermolecular Forces

Suggested Study Questions:

1. Explain the terms crystalline and amorphous.
2. Give an example of a crystalline substance and an example of an amorphous substance.
3. Explain why DNA had to be crystallised before useful information could be obtained using x-ray diffraction.
4. What does the abbreviation DNA stand for?
5. What are the 4 principle bases that make up DNA?
6. These principle bases occur in pairs; what are these 2 pairs?
7. What kind of chemical bonds act between the atoms making up each base in a strand of DNA?
8. What kind of chemical forces join one of the bases on one strand of DNA to its corresponding pair on the other strand of DNA?
9. If you wanted to separate the 2 strands of a DNA double helix, what sort of chemical bonds would you need to break?
10. If you wanted to separated each base from the backbone of sugar molecules, what sort of chemical bonds would you need to break?

What is chemistry?

Lots of students study "chemistry" at school, often because High School Chemistry is a prerequisite for some tertiary course they'd like to undertake in the future. But how many of these students start their chemistry course with a good understanding of just what chemistry is?
It's time to come to terms with the unique adventure that is chemistry ....
https://www.ausetute.com.au/chemistry.html

International Year of the Periodic Table

It's 2019, and, the Periodic Table of the Elements is officially 150 years old.

The United Nations General Assembly and UNESCO (United Nations Educational, Scientific and Cultural Organization) has proclaimed 2019 as the International Year of the Periodic Table.
Look at activities, or register your own activity at https://www.iypt2019.org/

And you can download a free copy of the most recent periodic table (last updated 1^st December 2018) here

Effect of Dilution on pH of Strong Acid Solution

Need to know what the pH of your hydrochloric acid is after you dilute it?
Need to know how much water to add to your hydrochloric acid to make a solution with a particular pH?
AUS-e-TUTE has just added a new tutorial, game, test and exam to help you with this.
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Introduction to Entropy

What is entropy?
What is meant by a chemical system having low entropy or high entropy?
What is the relationship between disorder, energy and entropy?

If you are asking these questions, then you will find AUS-e-TUTE's new entropy introductory tutorial, game and test very helpful! AUS-e-TUTE Members should log in to use these new resources (under the topic heading Thermodynamics in the Test Centre).

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