Empirical Formula of Magnesium Oxide

It's one of the "classic" experiments in school chemistry, combusting (burning) some magnesium in a crucible to make magnesium oxide.
While the lab questions usually focus on identifying that a chemical change has occurred, and calculating either percentage composition and/or empirical formula of magnesium oxide, I wonder how many students are really thinking about the experiment?
So, AUS-e-TUTE has written a tutorial that (hopefully) will help students think about why certain procedures are followed, and the kinds of errors one can expect.

AUS-e-TUTE members should log-in to use the new tutorial, game and test.

If you are not an AUS-e-TUTE Member, a "free-to-view" tutorial is currently available for evaluation purposes at http://www.ausetute.com.au/mgo.html

Information about AUS-e-TUTE Membership is available at www.ausetute.com.au/membership.html

and you can become an AUS-e-TUTE member at http://www.ausetute.com.au/register.html

Where to Study Chemistry?

Are you thinking about studying chemistry at a university?
How should you choose which university?

For those of you who like lists ("The 10 most jocular jokes", "The 10 cutest cat videos", etc, etc), here is a list of the "best" universities: you can visit http://www.topuniversities.com



Now that you've got that "list thing" out of your system, it's time to think seriously about where you will study chemistry.It's probably a good idea to visit the website of the universities you are interested in and get a feel for what you will be studying, who will be teaching you, and what the research interests of the lecturers are.
I hesitate to suggest this next move, but I know you will have thought of it before me, so here goes...  lots of those lectures will be available on youtube, so you "can test and try and before you buy" so to speak. The reason I hesitate to suggest you do this is that quite a number (possibly a very large number) of these videos should never have been made (well, not without some professional film-making advice, and in a number of instances they would have been improved enormously by the substitution of the lecturer by a professional, or even amateur, actor), or having been made, should not have been released into the public domain. They are often just recorded lectures, no green-screen, no whiz-bang CGI, no bombs going off, no exciting car chases, just lots of information delivered by someone competent to deliver it. If the thought of that excites you, please go and view the videos (and you should certainly study chemistry!), if not, don't bother with the videos, but do visit each university's website.
You should also visit your Careers Adviser, he/she will have lots of information!

Equilibrium Constants and Balanced Chemical Equations

Consider the reaction in which carbon monoxide gas reacts with oxygen gas to produce carbon dioxide gas:

CO_(g) + ½O_2(g) ⇔ CO_2(g)   with equilibrium constant = K₍₁₎ (at temperature = T)

and this reaction:
2CO_(g) + O_2(g) ⇔ 2CO_2(g)   with equilibrium constant = K₍₂₎ (also at temperature = T)

 Is the value of K₍₁₎ the same as the value of K₍₂₎ ?
 Not sure?
That's why AUS-e-TUTE has just added a new set of resources to help you understand this concept!

AUS-e-TUTE members should log-in to view the new Members Only resources.

 If you are not an AUS-e-TUTE member, there is a "free-to-view" tutorial available for evaluation purposes at http://www.ausetute.com.au/kstoichio.html

Find out more about AUS-e-TUTE membership at http://www.ausetute.com.au/membership.html

Become an AUS-e-TUTE Members at http://www.ausetute.com.au/register.html

Science Knowledge Quiz

The Pew Research Centre in Washington DC has just released the results of its survey of what adults in the USA know (or think they know) about science. It appears that very few of those surveyed had any real understanding of waves, and almost no understanding of boiling. But the saddest result of all, I think, is that about one third of those surveyed could not correctly interpret a graph.

You can do the 12 question multiple-choice quiz yourself online at:

http://www.pewresearch.org/quiz/science-knowledge/

When you finish (it won't take long) you will then be taken to a page that gives you the results of your quiz, and puts this in relation to the official survey results.

AlP Rat Poison

Dozens of mysterious sealed silver canisters containing aluminium phosphide have washed up on Australian beaches between 2012 and 2015. The Australian Maritime Safety Authority (AMSA) suspects all the canisters have come from the same ship which dumped or lost its cargo in the Pacific Ocean. Aluminium phosphide is used as a fumigant to poison rats on ships.

When solid aluminium phosphide, AlP, is exposed to water, it releases highly toxic phosphine gas, PH₃, which smells like rotting fish. The chemical reaction can be represented by the balanced chemical equation shown below:
AlP_(s) + 3H₂O_(l) → PH_3(g) + Al(OH)_3(aq)

This is a proton-transfer reaction in which water is acting as Brønsted-Lowry acid by donating a proton to phosphorus. Phosphorus is therefore acting as a Brønsted-Lowry base by accepting a proton from water. Aluminium phosphide will react with acids according to the following chemical
AlP_(s) + 3H⁺_(aq) → PH_3(g) + Al³⁺_(aq)

These reactions make aluminium phosphide a good choice for ridding a ship of rats.
Firstly, as a solid, AlP can easily be stored as pellets in air-tight, water-tight, containers until it is ready to be used. When required, the pellets can be scattered in the effected area . In the humid air aboard ship, the AlP will start reacting to produce toxic phosphine gas, that is, the area will be fumigated. But it is also possible to entice rats to eat AlP pellets mixed with food, in which case it will act as pesticide, because on entering the acidic stomach of the rat, it will produce the toxic phosphine.

Aluminium phosphide is  a very effective way to get ride of rats, so much so, that is widely used in agriculture to remove rats from grain silos.

References:
"Toxic canisters washing up on Australian beaches pose serious health risk"
 http://www.smh.com.au/environment/toxic-canisters-washing-up-on-australian-beaches-pose-serious-health-risk-20150917-gjp5se.html

"Controlling rabbits with aluminium phosphide tablets"
 http://agriculture.vic.gov.au/agriculture/farm-management/chemical-use/publications/chemical-industry-news/chemical-industry-news-no.-75-summer-autumn-2013

"Phosphine fumigation"
https://www.worksafe.qld.gov.au/injury-prevention-safety/hazardous-chemicals/specific-hazardous-chemicals/phosphine-fumigation

Further Reading
Definition of Acids and Bases
Proton-transfer Reactions
Mass-mole Calculations
Molar Volume of Gases

Suggested Study Questions:

1. The symbols of some elements are listed below. Name each element.
   • Al
   • P
   • H
   • O
   • K
   • He
   • At
2. Calculate the amount of aluminium phosphide in moles given the masses of AlP given below:
   • 10 g
   • 10 kg
   • 10 mg
   • 10 μg
3. Calculate the moles of phosphine gas produced when each mass of AlP below reacts with excess water in a ship's hull:
   • 10 g
   • 10 kg
   • 10 mg
   • 10 μg
4. Based on your answers to question 3 above, calculate the mass of phosphine produced for each mass of AlP used.
5. Your ship is sailing towards eastern Australia and has just crossed the Tropic of Capricorn. You have been asked to estimate the volume of phosphine gas that will be produced when you release AlP pellets into the ships hold. Which molar gas volume will you use; 22.71 L or 24.79 L ? Explain your answer.
6. Rats are currently infesting a small part of your ship, about 150 m³. How much solid AlP would be required to fumigate this area, but not leave any AlP residue left over?
7. The Cook has already tried to fumigate the pantry and is sure there is a silver canister around that still contains some AlP, it could be in the pile of empty canisters, or, it could be in the pile of full canisters. No-one wants to kill themselves by opening the canisters to find out, so can you suggest a method that could be used on board ship to determine how much AlP is present in each canister.
8. Explain why the reaction between aluminium phosphide and water is described as a proton-transfer reaction and not as a redox reaction.
9. Explain why, even though aluminium phosphide and phosphine are toxic, it is considered safe to use these to fumigate silos containing grain which will be eaten by humans.
10. The silver canisters that have washed up on Australian beaches have no labels, presumably these have come off while they were in the ocean. You have been asked to design new labels for the canisters. The labels must include suitable safety and handling information.

Elemental Fun

For this activity you will need a modern Periodic Table
(here's one I prepared earlier at http://www.ausetute.com.au/pertable.html )

This activity is designed to let students have some fun while they use a Periodic Table to extract information about elements (names, symbols, atomic number and atomic weight).

Ask the students a question.
Students use a Periodic Table find the answers.
After doing a few of these, the students will usually start making up their own questions and answers.
They can try out their questions/answers on their fellow students (and you!).

Names from Symbols

1. Question: What is candy made of?
    Answer: calcium, nitrogen and dysprosium (Ca N Dy )

2. Question: What ingredients do you need to make chocolate?
    Answer: carbon, holmium, cobalt, lanthanum, tellurium (C Ho Co La Te)

3. Question: What elements make up a body?
    Answer: boron, oxygen, dysprosium (B O Dy)

4. Question: What makes up the atmosphere?
     Answer: astatine, molybdenum, sulfur, phosphorus, helium, rhenium (At Mo S P He Re)

5. Question: Prove that these elements are compounds!

• xenon (It's made up of xenon, nobelium nitrogen, Xe No N)
• neon (It's made up of neon, oxygen, nitrogen, Ne O N)
• iron (It's made up of iridium, oxygen, nitrogen, Ir O N)
• copper (It's made up of cobalt, phosphorus (twice), erbium, Co P P Er)
• silver (It's made up of sulfur, iodine, livermorium, erbium, S I Lv Er)
• arsenic (It's made up of argon, selenium, nitrogen, iodine, carbon, Ar Se N I C)

6. Question: What is the most negative element?

    Answer: nobelium, it always spells No

Symbols from Names

1. Question: What fruit is made up of 1 part barium and two parts sodium?

    Answer: Ba Na Na

2. Question: Can you use potassium, nickel and iron to cut an apple?

    Answer: Yes because they make a K Ni Fe

3. Question: If you add some fluorine, uranium and nitrogen to a game, what will happen?

    Answer: It will be more F U N !

4. Question:  What natural fiber is made up of lithium, neon and nitrogen?

    Answer: Li Ne N 

5. Question: What sort of jokes do chemists make out of cobalt, radon, and yttrium?

   Answer: Co Rn Y jokes.

Symbols from Atomic Numbers (crack the code)

1. Code: 1,18,15 

    Clue: A heavenly musical instrument?

    Answer: harp, H (Z=1), Ar ( Z=18), P (Z=15)

2. Code:  66, 7, 95, 53, 52

    Clue: Explosive stuff!

    Answer: dynamite, Dy(Z=66), N(Z=7), Am(Z=95), I(Z=53), Te(Z=52)

3. Code: 20, 28, 10

    Clue: What a cat is afraid of?

    Answer: canine, Ca(Z=20), Ni(Z=28), Ne(Z=10)

4. Code: 1, 85

    Clue: Head covering?

    Answer: hat, H(Z=1), At(Z=85)

5. Code: 67, 8, 19

    Clue: Somewhere to hang your coat?

    Answer: hook, Ho(Z=67), O(Z=8), K(Z=19)

Molecular Weight from Symbols

1. Question: What is a Chemist's favourite number?

    Answer: 315.02 because it is Lu C K Y (175 + 12.01 + 39.1 + 88.91 = 315.02)

2. Question: What is the molecular weight of a gene?

    Answer: 92.82 because it's made up of Ge and Ne (72.64 + 20.18 = 92.82)

3. Question: What is the value of life?

    Answer: 62.791 Li Fe (6.941 + 55.85 = 62.791)

4. Question: What does a boy weigh?

    Answer: 115.72 B O Y (10.81 + 16.00 + 88.91 = 115.72)

5. Question: How heavy is a phone?

    Answer: 68.158 P H O Ne (30.97 + 1.008 + 16.00 + 20.18 = 68.158)

Words You Can Make Using the First Twenty Elements Only

• Al O Ne
• Ar C
• Ar K
• B Ar
• B Ar K
• B Ar N
• Be Ar
• B Li N K
• B Li S S
• B O Ar
• B O Ne
• B O O K
• B O S S
• Ca B
• C Al F
• Ca N
• Ca N Al
• Ca Ne
• Ca N O N
• Ca P
• C Ar
• C Ar B O N
• Ca S H
• C H O O K
• C H O P
• C Li C K
• C Li F F
• C Li N K
• Cl O C K
• Cl O Ne
• C O B
• C O Ne
• C O O K
• C O S H
• F Ar
• F Li C K
• F Li P
• F O Al
• H Al F
• H Al O
• H Ar K
• H Ar P
• He Al
• He Ar
• H O C K
• H O N K
• H O P
• K Na C K
• K N O B
• K N O C K
• Li Ar
• Li C K
• Li Ne
• Li N K
• Li P S
• Li S P
• Na B
• Na P
• Ne O N
• Ne P Al
• N O O K
• O Ne
• O P Al
• P Al
• P Ar
• P Ar K
• P H O Ne
• P O P
• S Ca N
• S C O Ne
• S He
• S He Ar
• Si C K
• Si N
• Si N K
• S Li C K
• S Li P
• S Na C K
• S Na P
• S O B
• S O C K
• S O N Ar
• S P O O K

Uranium Glass

Uranium compounds have been used to colour glass since ancient times. A mosaic found in a Roman villa dated to about 79 AD used yellow glass containing 1% uranium oxide. Between 1880 and the 1920s, uranium glass was quite popular, not only because of its interesting yellow-green colour, but because it fluoresces in ultra-violet light as shown in the image of a vase below.
The image on the left hand side shows the vase under normal daylight, while the image on the right shows the same vase in the dark exposed to UV light.

Why does uranium glass glow green in the dark like this?
Well, it has nothing to do with the radioactivity of uranium isotopes. The green glow does not occur because of changes within the nucleus of uranium atoms, it occurs because of changes in the energy of electrons surrounding the nucleus.
A ground state electron in a uranium atom absorbs the energy of a photon  of ultra-violet light causing the electron to jump to a higher energy level known as the excited state. This new excited state electron configuration is not stable, so, the electron falls back down to to the ground state energy level, which is a lower energy state, by losing energy which it does by emitting a photon of light. Some of the energy of the original photon used to excite an electron is dispersed as molecular vibration and heat, so the energy of the photon emitted when the excited electron falls back to the ground state is less than the energy originally absorbed.
That is: E = hν/λ
where E = energy, h = Planck's constant, ν = speed of light , λ = wavelength of light
If the speed of light is a constant, then E ∝ 1/λ or Eλ = a constant
in other words, the more energy the photon of light has the shorter its wavelength is.
In the case of uranium glass, the absorbed photon of ultra-violet light has a wavelength of about 300 nm, while the emitted photon of green light has a wavelength of about 550 nm.
The wavelength of the emitted photon of light corresponds to the green part of the visible spectrum.
The emission of visible light in this way is known as fluorescence.

Further Reading:
Isotopes
Radioactivity: Properties and Uses
Emission Spectra
Flame Tests

Suggested Study Questions

1. Uranium is found in nature as one of three isotopes, uranium-234, uranium-235 and uranium-238. Explain how atoms of each isotope are:
• the same
• different
2. Atoms of neptunium-234, neptunium-235 and neptunium-238 have been synthesized. Explain the similarities and differences between each of the following pairs of atoms:
   • neptunium-234 and uranium-234
   • neptunium-235 and uranium-235
   • neptunium-238 and uranium-238
3. The value for Planck's constant is 6.626 070 040 x 10^-34 J s and the speed of light is given as 300 000 000 m / s. Calculate the energy of each of the following photons of light:
• ultra-violet light, λ = 300 nm
• green light, λ = 550 nm
4. Using the results of question 3, compare the energy of the photons used to excite uranium atoms and the energy of the photons emitted by uranium atoms and explain the difference.
5. Explain why the same wavelength of light is always emitted when these uranium atoms are exposed to ultra-violet light.
6. Would you expect the uranium glass to fluoresce if it is exposed to infra-red light rather than to ultra-violet light? Explain your answer.
7. Optical brighteners are often used in laundry detergents to make your old, yellowy-looking white clothes look whiter. Typically these compounds absorb ultra-violet light with a wavelength of around 300 nm and emit light with a wavelength of around 450 nm.
   • What colour is the light emitted?
   • What is the energy of the emitted light?
   • Why is the energy of the light emitted not the same as the energy absorbed when the incoming photon hits the "optical brightening compound"?
   • Would you expect a laundry detergent containing "optical brightening compounds" to glow in the dark when exposed to UV light? Explain your answer.

Coral Reef Dissolution

Coral reefs dominate much of the world's tropical coastline, covering about 15% of the seabed shallower than 30 metres.

The largest coral reef in the world is the Great Barrier Reef off the north-east coast of Australia.

What impact will increasing amounts of atmospheric carbon dioxide have on our coral reefs?

Find out in this edition of AUS-e-NEWS!

If you haven't received your copy of AUS-e-NEWS, or if you would like to subscribe to our free quarterly newsletter, AUS-e-NEWS, the email us at

 

Nitrous Oxide Ban

On Saturday 29^th August 2015, Brisbane's Couriermail reported that, "Supermarkets have removed nitrous oxide canisters from their shelves because of the alarming trend of people using the gas to get high".
Nitrous oxide, N₂O, commonly known as "laughing gas", is found as an additive in food (E942). It has been used as an aerosol propellant in whipped cream canisters and cooking sprays, and has also been used as an inert gas to displace oxygen from food packages like potato chips to prevent the food from spoiling. The nitrous oxide canisters being removed from supermarket shelves refer to the small canisters used to re-charge re-usable whipped cream dispensers. Nitrous oxide is soluble in fats and oils so it is pumped into the fatty cream inside the dispenser where it dissolves. When the cream leaves the dispenser, the gas pressure inside the cream is greater than atmospheric pressure, so the nitrous oxide gas leaves the cream quickly, creating a foam. This "whipped cream" has about 4 times the volume of the original cream. However, if the whipped cream is left standing for some minutes, the gas pressure equilibrates with atmospheric pressure and the cream reverts to the "unwhipped" state.
Nitrous oxide has been the preferred choice for whipped cream dispensers because it does not react with the food and prevents it from spoiling. If air were used, the oxygen in the air would accelerate the rate of oxidation causing the cream to spoil. Carbon dioxide gas is not used because it would dissolve in the water present in the cream which would lower the pH and the cream would curdle.

In the laboratory, nitrous oxide can be produced by the thermal decomposition of ammonium nitrate (which is explosive!):

NH₄NO₃(s) → 2H₂O(g) + N₂O(g)

It can also be produced by heating a mixture of sodium nitrate and ammonium sulfate:

2NaNO₃ + (NH₄)₂SO₄ → Na₂SO₄ + 2N₂O + 4H₂O

Nitrous oxide has been used in dentistry as an anaesthetic for more than a century.
The chemistry of how nitrous oxide reacts in the body to produce a "high" is not well understood, but research continues.

Further Reading
Density
Types of Chemical Reactions
Molecular Formula
Name and Formula of Covalent Compounds
Fats and Oils 
Solubility and Le Chatelier's Principle
Mass-mole Calculations
Mass and Moles in Chemical reactions 
Molar Volume of Gases 
Safety in the Laboratory

Suggestion Study Questions:

1. Give the molecular formula for each of the following compounds: 
   • nitric oxide
   • nitrogen dioxide
   • nitrous oxide
   • dintrogen tetroxide
2.  Name each of the following compounds:
   • CO₂
   • CO
   • SO₂
   • SO₃
   • PCl₃
   • PCl₅
3.  Draw possible Lewis (electron dot) structures for each of the following compounds:
   • nitric oxide
   • nitrogen dioxide
   • nitrous oxide
   • dintrogen tetroxide
4.  "..whipped-cream has four times the volume of the original cream", describe what has happened to the density of the cream as a result of the "whipping" process.
5. When I order an "iced-coffee" at a Cafe, they usually top it with some whipped-cream from a canister . Why does the whipped-cream float on top of the ice-coffee drink?
6. If I don't the spoon the whipped-cream off the top of my "iced-coffee" I can stir it into the drink quite easily without it floating to the surface again. Explain why this happens.
7. Explain what is meant by the term "fats and oils" when used by a Chemist and give examples.
8. Most aerosol cans contain a warning to the effect that you should not heat the can. Explain what would happen if you heated a dispenser of whipped-cream containing nitrous oxide. 
9. Imagine placing 10 grams of ammonium nitrate in a 500 mL sealed steel can, which you then (very irresponsively!) throw onto a bonfire.
• Calculate the moles of ammonium nitrate in the can
• Calculate the moles of nitrous oxide gas produced 
• Calculate the volume of this number of moles of gas at 25^oC
• Predict what will happen to the sealed steel can in the bonfire. 
10. Your company, "Ammo-nite", sells ammonium nitrate to farmers for use as a fertiliser. You have been asked to re-design the 100 g package so that it includes relevant safety precautions.