How long is a piece of string?

How long is a piece of string?
What units of length you use to measure a piece of string will depend on how long the string is.
If you are putting up a string of Christmas lights you might measure the length of the string in metres or centimetres.
But if you are measuring the length of string, or ribbon, to tie back your hair you might measure the length of string in centimetres or millimetres.
1 centimetre is a hundredth of a metre: 1 cm = 10^-2 m
1 millimetre is a thousandth of a metre: 1mm = 10^-3 m
The metre is the SI base unit of length.
On the other hand, if your piece of string is holding 2 atoms together in a molecule you are going to need a very tiny piece of string, less than a billionth of a metre. Which is why chemists use units of length like the nanometre (1nm = 10^-9 m), the Ångstrom (1 Å = 10^-10 m), and the picometre (1 pm = 10^-12 m).
You will need to be familiar with these units and be able to convert one unit of length into another, so AUS-e-TUTE has just added new tutorials, games, tests to help our members do this.
If you are not a member, you can access a "free-to-view" tutorial at https://www.ausetute.com.au/lengthconv.html

X-Ray Diffraction and Electron Density Maps

Have you ever wandered how chemists determine the shape of molecules and ionic compounds?
How can they measure bond angles and bond lengths?
One of the most important ways to do this is to use X-ray diffraction.
AUS-e-TUTE has just added a new tutorial, game, test and exam to help you understand X-ray diffraction and electron density maps and to apply that understanding to solving problems in chemistry. AUS-e-TUTE Members should log-in to use these resources (under the Solid State Chemistry topic heading).
If you are not yet an AUS-e-TUTE Member then you can access the "free to view" tutorial at
https://www.ausetute.com.au/xdiffraction.html

Mendeleev's Biggest Failure

2019, the International Year of the Periodic Table, marks the 150^th anniversary of Dmitri Mendeleev's formal presentation of his Periodic Table to the Russian Chemical Society on 6^th March 1869.
His Periodic Table is arguably the most important breakthrough in the history of Chemistry because it not only organised the elements into groups based on their properties, it also continues to allow us to make predictions about the physical and chemical properties of elements.
Yet, despite its predictive capacity, Mendeleev failed to predict an entire group of elements!

Read all about it in the March 2019 issue of AUS-e-NEWS.

Subscribe to AUS-e-TUTE's free quarterly newsletter AUS-e-NEWS at 

https://www.ausetute.com.au/ausenews.html 

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?

Dangerous Chemical Spill at Lucas Heights

This is a headline from the Sydney Morning Herald, Friday 1^st March 2019, "Three hospitalised after chemical spill at Lucas Heights nuclear facility" and an excerpt from the newspaper story is below:

"Two men in their 30s, and a woman, 26, were injured when a cap came off a pipe at the Australian Nuclear Science and Technology Organisation facility at Lucas Heights, spilling about 250 millilitres of sodium hydroxide, also known as caustic soda, onto their arms and faces.

 Sodium hydroxide, also known as caustic soda, is corrosive to the skin and eyes and can cause severe burns."

This "sodium hydroxide" or "caustic soda" sounds like really dangerous stuff doesn't it?  I mean to say, it must be if just 250 mL (a quarter of a litre, a bit less than half a pint)  causes 3 people in an up-to-date, modern, nuclear-medicine manufacturing building, to be hospitalized!

 Well, sodium hydroxide is a caustic substance, that is, corrosive to skin, and it is dangerous if handled incorrectly, however, it is also readily available to non-scientists! You will probably find sodium hydroxide in your own home.

Sodium hydroxide is commonly found in household cleaning products that are used to unblock drains. One such product is Mr Muscle Drano  The directions for use including the following:

WEAR EYE PROTECTION AND PROTECTIVE GLOVES WHEN MIXING OR USING. AVOID CONTACT WITH EYES AND SKIN. DO NOT MIX WITH HOT WATER. 

Keep hands and face away from drains and wash hands after use. Ensure adequate ventilation.
• Do NOT mix with other cleaning products or acids as it may give off a dangerous gas
• Open carefully, do not squeeze the bottle, avoid splashing and clean up spills at once.
• Never use a plunger during or after use, as there may be some Mr Muscle® Drano® in the pipe if the blockage did not completely clear.
• Do NOT use in spas, dishwashers, washing machines, rubbish disposals, toilets or any pipes leading to these outlets. Will not remove roots, leaves or non-organic matter. Always refer to product label for full directions.

You will find sodium hydroxide pellets ("crystals") are also readily available, the website of one such product even suggests you use it to make your own soap ...

METHOD 

1. READ THE DANGEROUS GOODS INFORMATION BELOW BEFORE BEGINNING THIS RECIPE. 

2. Pour cold water into the plastic jar. 

3. Measure Glitz Caustic Soda (into a dry plastic cup).

 4. Slowly and carefully add the Glitz Caustic Soda to the cold water, stirring continuously with a plastic rod. (Wear plastic gloves and goggles; test gloves for holes first.) Do not breath the vapor or lean over the container or have children nearby. The mixture will get very hot.  

5. Allow the solution to cool down to a warm temperature (approx 40oC) in a safe place. 

 6. Melt the Coconut Oil (Copha) at a low heat in a stainless steel saucepan. Add the Canola Oil and Olive Oil to the melted Coconut Oil. Mix well 

7. Allow the oil mixture to cool down to a warm temperature (approx 40oC)

 8. Slowly and carefully, pour the Caustic Soda solution into the stainless steel saucepan containing the oil mixture. Mix thoroughly for at least 30 minutes or until it looks like thick pudding. 

9. If desired, select one fragrance from the optional fragrances. Add the fragrance to the soap mixture and mix for a further 30 minutes.  

10. Pour the finished soap into the tupperware container and allow 24hrs of setting. 

11. Cut the set soap into bars and leave it to cure for at least 6 weeks before use

But honestly, making your own soap at home might sound like fun, but unless you fully understand what you are doing then you should NOT use your soap to wash yourself or you might be the one that is rushed to hospital!

Suggested further reading:
Properties of Acids and Bases 
Definitions of Acids and Bases 
Strength of Bases
Heat of Solution
Neutralisation Reactions 
Heat of Neutralisation
Safety in the Lab 
Soaps and Saponification

Suggested Study Questions:

1. Sodium hydroxide is a caustic substance. What GHS (Globally Harmonised System) pictogram would you find on a container of sodium hydroxide.
2. Sodium hydroxide is a caustic substance. What personal protective equipment (PPE) should you use when handling sodium hydroxide?
3. Write a set of instructions, including all required safety precautions, for dissolving 1 g of sodium hydroxide in 1 L of water.
4. Consider the instructions for using Mr Muscle Drano. Why do you think it advises you to NOT use the product in dishwashers, washing machines and toilets?
5. Consider the instructions for using Mr Muscle Drano. Why do you think it advises you to use ONLY in well ventilated areas?
6. Consider the instructions for making soap. Should you use a plastic drinking cup from the kitchen to measure out the caustic soda? Explain your answer.
7. Why do the soap-making instructions tell you to add the caustic acid to the water AND NOT tell you to add the water to the caustic soda? Do you think it matters which you do this step? Explain your answer.
8. The soap-making instructions tell you to use a stainless steel saucepan. Do you think it would matter if you used an aluminium saucepan or a glass saucepan? Explain your answer.
9. Do you think it is advisable to use a saucepan from the kitchen to make soap? Explain your answer.
10. Imagine you were at the Lucas Heights facility when 3 of your co-workers were injured in this chemical spill. What would you do first to help them?