Chemistry Rockets to Mars

NASA is developing the most powerful rocket in history, the Space Launch System (abbreviated to SLS) to launch the spacecraft known as Orion. Orion is expected to carry humans beyond the Moon and on to Mars in the 2030s.
It is well known that engineers, physicists, mathematicians and computer programmers play a quintessential part in the design, development, launch, trajectory and landing of rockets and spacecraft, but what about chemists?
Chemistry also plays an important role in getting rockets off the ground.
Without an understanding of chemistry there would be no fuel, no thrust, no take-off!

Read more in the December 2017 issue of AUS-e-NEWS.

To subscribe to AUS-e-NEWS got to http://www.ausetute.com.au/ausenews.html

The Smell of Freshness

Organic compounds are added to cleaning products and air fresheners to make the air smell fresh and clean. Scientists are taking a closer look at the chemistry behind the use of these compounds to determine whether they are hazardous to human health.

One of the organic compounds that is widely used to provide the "smell of freshness" is a molecule known as limonene (1-methyl-4-(1-methylethenyl)-cyclohexene). The 2-dimensional structural formula of limonene is shown on the right.

Limonene is a colourless liquid at room temperature and pressure and is found naturally in the rind of citrus fruits such as lemons. It is one of the compounds that contributes to the typical odour of citrus fruit.
Commercial quantities of limonene are produced from citrus fruits using centrifugal separation or steam distillation.

Scientists are studying the reactions of limonene closely because the chemical reactions of this molecule with the ozone in the air in your home are the same as the chemical reactions that occur in the atmosphere that produce secondary organic aerosols (SOAs), microscopic particles suspended in the air, which contribute to the visible haze known as smog in densely populated areas.

The researchers tested various different scenarios for the production of SOAs in the home from limonene and found that the concentration of SOAs produced was between 5μg/cm³ and 100μg/cm³. The acceptable level of aerosols in breathable air is about 12μg/cm³.

The researchers suggest that the best way to reduce SOAs in your home is to either use unscented cleaners or to keep windows open while cleaning. 

Reference:
Somayeh Youssefi, Michael S. Waring. Transient Secondary Organic Aerosol Formation from Limonene Ozonolysis in Indoor Environments: Impacts of Air Exchange Rates and Initial Concentration Ratios. Environmental Science & Technology, 2014; 48 (14): 7899 DOI: 10.1021/es5009906

Further Reading:
Empirical Formula
Molecular Formula
2-Dimensional Structural Formula
Condensed Structural Formula
Skeletal Structural Formula
Percentage Composition
Parts Per Million (ppm) Concentration
Molar Mass

Suggested Study Questions:

1. Write the molecular formula for limonene.
2. Give the empirical formula for limonene.
3. Calculate the percentage of
   • carbon in a molecule of limonene
   • hydrogen in limonene
4. Draw a skeletal structural formula for limonene.
5. Limonene has the IUPAC name 1-methyl-4-(1-methylethenyl)-cyclohexene. Draw the 2-dimensional structural formula for limonene and circle each of the following groups:
   • cyclohexene parent hydrocarbon in red
   • methylethenyl branch in blue
   • methyl branch in black
6. Would you classify limonene as a saturated or unsaturated hydrocarbon? Explain your answer.
7. Convert these concentrations in μg/cm³ to concentrations in parts per million (ppm)
• 5μg/cm³
• 12μg/cm³
• 100μg/cm³
8. Calculate the molar mass of limonene.
9. Calculate the mass of limonene in 100 L of air at 25^oC and 100 kPa for each of the following concentrations:
   • 5μg/cm³
   • 12μg/cm³
   • 100μg/cm³

Salts of Drugs a Health Risk

Many studies have shown that excess salt is harmful to heart health, but many commonly prescribed medicines have sodium added to improve their absorption into the body, but the effect of doing this has not been known. For example, 1 Alka-Seltzer tablet contains 324 mg of aspirin (the drug) and 445 mg of sodium.
University of Dundee and College of London researchers have found that a person taking the maximum, daily dose of some medicines would exceed the recommended daily dietary intake limits for sodium. In Australia, the total maximum recommended limit of sodium for adults should be less than 2300 mg per day (less for children). The label on the Alka-Seltzer tablets carries a warning that you should not take more than 8 tablets per day.
In the study, the researchers found that patients taking the sodium-containing medication had a 16% increased risk of a heart attack, were 7 times more likely to develop high blood pressure, and, were 28% more likely to die, compared with patients who took the non-sodium containing versions of the same drug.

So why do we add sodium to drugs if it is potentially harmful?

We do this because many drugs are actually insoluble in water. The cells in your body are made up mostly of water, so if you want to be able to transport a drug around the body, and have it absorbed into cells, it is beneficial if the drug is soluble in water.

How do we add sodium to drugs?

If the drug is, for example, a weak acid like aspirin, then it is not very soluble in water.
Being a weak acid, though, aspirin can undergo a proton transfer (neutralisation) reaction with a base such as sodium hydroxide. The product of a neutralisation reaction are salt and water.
acid + base → salt + water

aspirin + sodium hydroxide → sodium salt of aspirin + water

The sodium salt of aspirin readily dissolves in water by dissociating into positive sodium ions and negative "aspirin" ions.


Reference:
BMJ-British Medical Journal (2013, November 26). High salt levels in medicines increase risk of cardiovascular events. ScienceDaily. Retrieved November 28, 2013, from http://www.sciencedaily.com­ /releases/2013/11/131126191557.htm 

Further Reading
aspirin
mass conversions 
ppm
molarity
neutralisation
proton transfer reactions
acid dissociation constants

Suggested Study Questions: 

1. Convert these masses in milligrams to masses in grams
• 324 mg
• 445 mg
2. The label on the Alka-Seltzer packet recommends dissolving 2 tablets in water. For these two tablets, calculate the mass in milligrams of
• aspirin
• sodium
3. If you were to take the maximum number of tablets, 8, in a day, how much of each of the following substances would you be ingesting?
• aspirin
• sodium
4. Would you be exceeding the recommended daily dietary intake limits for sodium in Australia? Explain your answer.
5. A low salt food is one that contains less than 120 mg of sodium per 100 g of food. If Alka-Seltzer were to be considered a low salt food, what would the mass of each tablet need to be?
6. Aspirin has the molecular formula C₉H₈O₄. What is the molar mass of aspirin?
7. The sodium salt of aspirin has the molecular formula C₉H₇O₄^-Na⁺. What is the molar mass of the sodium salt of aspirin?
8. Calculate the mass of sodium in 1 Alka-Seltzer tablet due to the sodium salt of aspirin.
9. Compare the mass of sodium calculated above to the actual mass of sodium present in 1 Alka-Seltzer tablet according to the package. How would you explain the difference in the two masses?
10. If a person dissolved 2 Akla-Seltzer tablets in 150 mL of water, what is the concentration of sodium ions in the water in
    • mol/L
    • mg/L
    • ppm
11. Recommendations for the daily intake of potassium are higher than those for sodium at 4700 mg day, so one way to alleviate the sodium problem in aspirin tablets might be to replace the sodium with potassium. Describe one way that you could produce the potassium salt of aspirin.

 

Fun Calculations

Practicing the skills of writing chemical formula and calculating relative molecular masses, molar masses and percentage compositions can be a bit, .. well, ... a bit ..... boring (sh, don't tell anyone I said that). But, you can use chemspider to find some interesting molecules for your students to practice their skills on.
ChemSpider is a free chemical structure database run by the Royal Society of Chemistry. It provides access to over 25 million chemical structures, properties and associated information.

Activity:
For each of the molecules below:

1. Use chemspider to find the structural formula.
2. Write the molecular formula..
3. Calculate the relative molecular mass..
4. Calculate the molar mass..
5. Calculate the percentage of carbon present..

Molecules with "interesting names" to practice on:

• olympicene
• ovalene
• performic acid
• traumatic acid
• arabitol
• putrescine
• cadaverine
• nonose 
• syringic acid
• warfarin
• orotic acid
• megaphone
•  moronic acid
• inflatene
• sexithiophene
• arsole
• anol

Further Reading
Calculating Relative Molecular Mass
Molar Mass
Percentage Composition