Spud Lite?

"Spud Lite", the advertising poster said, "25% less carbs", followed in fine print by "than other potatoes".
"How strange", I thought, "I thought you ate potatoes for their carbohydrate (carbs) content so why would you want a potato with less carbohydrate?"
But then I started thinking about what this meant in terms of the chemical composition of the potato. If it contains 25% less carbohydrate, then surely that means something else must have been increased or added? Or are you just getting less potato for your money?

Typically, a traditional potato has the following approximate composition:

nutrient	% by mass
water	79
carbohydrate	17.5
protein	2
fat	0.1

 That is, 100 g of traditional potato contains about 79 g of water, 17.5 g of carbohydrate, 2 g of protein and 0.1 g of fat.

One way to reduce the percentage of carbohydrate in a potato would be to reduce the density of the potato.
If 100 g of a traditional potato had a volume of 92 mL, then the density of the potato would be 1.09 g/mL. 1 mL of traditional potato has a mass of 1.09 g and contains 17.5% by mass (0.19 g) of carbohydrate.
If "spud lite" has a lower density of potato "flesh", say 0.8 g/mL, then 1 mL of "spud lite" has a mass of 0.8 g and contains 17.5% by mass (0.14 g) of carbohydrate.
If we then compare equal volumes (sizes) of potatoes, say 1 mL of traditional potato and 1 mL of "spud lite" we find that "spud lite" contains 100 x (0.19 - 0.14)/0.19 = 26% less carbohydrate (by volume!).
But, if the density of "spud lite" is less, the % by mass composition remains the same, that is, for every 100 g of potato (traditional or "spud lite") there will be 17.5 g of carbohydrate (but the "spud lite" potato will be a bigger potato for your 100 g).

The nutrition label on a packet of "spud lite" potatoes gives the following masses per 100 g of potato:

• fat < 0.1 g
• protein 1.4 g
• carbohydrate: 8.9 g
• sugars: 1.1 g
• dietary fibre:  1.4 g

So, the total carbohydrate content is 8.9 + 1.1 + 1.4 = 11.4 g
(assuming the dietary fibre is cellulose which is also a carbohydrate).
This means that the actual mass of carbohydrate per 100 g of potato has been decreased. That is, "spud lites" are not just less dense than traditional potatoes.

 Another way to decrease the proportion of carbohydrate in your potatoes would be to increase their water content.
Imagine you have 100 g of traditional potato. This potato is made up of 79 g of water and 17.5 g of carbohydrate.
"Spud lite" contains 11.4 g of carbohydrate.

If all the lost mass of carbohydrate in the "spud lite" (17.5 - 11.4 = 6.1 g) was present as water, then the mass of water in "spud lite" = 6.1 + 79 = 85.1 g

And you, the consumer, is just paying for additional water in your potato!

Further Reading
 Experimental Design

 Carbohydrates
Proteins
Lipids (fats and oils) 
Percentage Composition
Density 

Suggested Study Questions:

1. Design an experiment to test the hypothesis that "spud lite" potatoes have a lower density than traditional potatoes.
2. Design an experiment to test the hypothesis that "spud lite" potatoes have a greater percentage by mass of water than traditional potatoes.
3.  For each serving of traditional potato given below, calculate the mass of carbohydrate consumed:
• 25 g of potato
• 75 g of potato
• 135 g of potato
4. Calculate the mass of "spud lite" you would have to consume in order to obtain
   • 1 g of carbohydrate
   • 7 g of carbohydrate
   • 21 g of carbohydrate
5. The density of potato changes as the potato ages on the shelf. The table below shows the results of an experiment in which the mass and volume of the same potato is measured and recorded every 3 days. Calculate the density of the potato on each day.

   Day	Mass (g)	volume (mL)
   1	142	130
   4	140	129
   7	138	128

6. Consider the results of the experiment above. Describe any trends that you see in the data and suggest reasons for these trends.
7. Explain what chemists mean when they refer to "carbohydrates".
8. The nutrition label on "spud lites" lists the mass of carbohydrate, sugars and dietary fibre separately. What do you think the "carbohydrate" is on this label?
9. Add together the percent by mass of all the components listed for a traditional potato.Suggest reasons for why the total percentage is less than 100%.
10. Potatoes are usually classified as high on the glycemic index (GI). What does this mean?

Nanoparticles to Remove Coral Bleaching Oxybenzone

Sunblocks contain a number of different compounds including oxybenzone which acts as a UV filter. The skeletal structural formula of oxybenzone is shown below:

Oxybenzone is soluble in water.
Before you go snorkeling in the Great Barrier Reef to be amazed by the beautiful corals, fascinating fish and other exciting wonders, you smother yourself in sunblock. When you step into the water, the oxybenzone starts to dissolve. Unfortunately, oxybenzone contributes to coral bleaching, the killing off of the tiny, colourful zooxanthellae marine algae that live inside corals. The result is that the coral loses its colour and appears white, as if it has been bleached.

Researchers have found a way to soak up the oxybenzone from the seawater using magnetite nanoparticles.

Magnetite, Fe₃O₄ , is a mineral made up of iron(II) and iron(III) oxides and is one of the main iron ores, that is, magnetite is mined in order to produce iron. Magnetite is ferromagnetic, that is, it is attracted to a magnet. It is the most magnetic naturally occurring mineral on Earth. If you could get the oxybenzone in the seawater to attach to magnetite nanoparticles then you could pull the oxybenzone out of the water using a magnet.

First, the researchers coated the magnetite nanoparticles with sodium oleate. The skeletal structural formula of sodium oleate is shown below:

Next, they oxidised the oleate coating to increase the number of hydroxyl (OH) functional groups:

Since oxybenzone can interact with other molecules via hydrogen bonds, magnetite nanoparticles  covered in a coating rich with hydroxyl functional groups increases the interactions between oxybenzone and the nanoparticles. Once the oxybenzone has hydrogen bonded to the nanoparticle coating, a magnet can be used to extract the particles from water.

Does it work?
One brave researcher applied sunblock, stepped into the ocean, waited 10 minutes, then collected a sample of the surrounding seawater. Back at the lab, chromatography was used to determine the concentration of oxybenzone in the water, 1.3 ppm. This is a disturbing result since it is known that the concentration needed to bleach coral is measured in parts per billion.
Next, the researchers prepared seawater samples. Some had no magnetite nanoparticles added, others had the nanoparticles added. Then they added 30 ppm oxybenzone to  all the samples. The concentration of oxybenzone in the samples with no nanoparticles did not change in an hour. In the samples that contained the nanoparticles, 95% of the  oxybenzone  was removed within the hour.

Reference
American Chemical Society. "Sopping up sunblock from oceans to save coral reefs." ScienceDaily. ScienceDaily, 21 August 2017.

Further Reading
Solutions Concepts
Water as a Solvent
Transition Metals (magnetism)
Fatty Acids
Carboxylic Acids
Nanoparticles and Nanotechnology
Parts per Million (ppm)
Chromatography
Experimental Design
Variables
2-Dimensional Structural Formula
Skeletal Structural Formula
Molecular Formula

Suggested Study Questions

1. For a molecule of oxybenzone:
• draw the 2-dimensional structural formula
• give the molecular formula
2. On the 2-dimensional structural formula of oxybenzone identify and name each functional group present.
3. Use diagrams to explain why oxybenzone is soluble in water.
4. Draw the 2-dimensional structural formula for oleic acid.
5. On your structural formula of oleic acid, identify and name the functional group(s).
6. Suggest a method by which you could change oleic acid into sodium oleate in the laboratory.
7. Suggest a method by which you could oxidise sodium oleate in the laboratory.
8. Explain the term "nanoparticle".
9. Why do you think the researchers chose nanoparticles of magnetite rather than bulk magnetite for this research?
10. Consider the description of the experiment used to determine the effectiveness of the magnetite nanoparticles in removing oxybenzone from seawater:
• What was the hypothesis being tested?
• What was the aim of the experiment?
• What variables need to be considered in this experiment?
• What is the independent variable in the experiment?
• What is the dependent variable in the experiment?
• Which variables are constant variables in the experiment?
• Why did the experimenters add nanoparticles to some samples but not to others?
• Write out a suitable method for this experiment.

Stinky Socks and Shmelly Shirts?

Northumbria University researchers have identified six volatile organic compounds on dirty socks and t-shirts which are responsible for the stench of your dirty laundry. Surprisingly, some of these compounds can survive washing in a machine with detergent at 20°C, that is, washing in cold water will not remove all the compounds responsible for the smell.

The researchers wanted to identify the volatile organic compounds from dirty clothes before washing, after washing while still wet, and after drying, to see which compounds are responsible for bad smells and to see if they were eliminated during the washing process.

6 men and 2 women were each given a new pair of socks. Each person was asked to wash their feet and dry them before wearing the socks for at least 10 hours in a specified type of shoe. Each sock was then placed in a separate bag and stored in the dark overnight. 9 men were each given a t-shirt to wear for 2-3 hours while taking part in a soccer match. After the match the t-shirts were bagged separately and refrigerated.

The researchers smelled each item and graded it on a scale of 0 (no bad smell) to 10 (very bad smell).
Then the items were washed in a Tergotometer, a lab machine made up of several miniature washing machines, at 20°C using non-perfumed detergent. Each item was graded for odour after washing while still wet and then again after drying.

Using analytical techniques like gas chromatography, the team identified 6 main volatile organic compounds that contribute to the smell of dirty laundry:

• butanoic acid (butyric acid); rancid butter odour
• dimethyl disulfide; onion-like odour
• dimethyl trisulfide; powerful, unpleasant odour
• heptan-2-one (2-heptanone); fruity odour like bananas
• nonan-2-one (2-nonanone); herbaceous odour
• octan-2-one (2-octanone); apple-like odour

As the concentration of these volatile organic compounds decreased after each washing, the items became less smelly.


Reference:
Chamila J. Denawaka, Ian A. Fowlis, John R. Dean. Source, impact and removal of malodour from soiled clothing. Journal of Chromatography A, 2016; 1438: 216 DOI:10.1016/j.chroma.2016.02.037

Further Reading:
Scientific Method: http://www.ausetute.com.au/scientificm.html
Experimental Design: http://www.ausetute.com.au/experimentd.html
Writing Lab Reports: http://www.ausetute.com.au/labreport.html
Introduction to Functional Groups: http://www.ausetute.com.au/fungroup.html
Naming Alkanoic Acids: http://www.ausetute.com.au/namalkacid.html
Naming Alkanones: http://www.ausetute.com.au/namalkanone.html
2-Dimensional Structural Formula: http://www.ausetute.com.au/structural2D.html
Condensed Structural Formula: http://www.ausetute.com.au/condensedsf.html
Molecular Formula: http://www.ausetute.com.au/molecularformula.html
Molar Mass Calculations: http://www.ausetute.com.au/moledefs.html
Gas Chromatography (GC) : http://www.ausetute.com.au/gc.html

Suggested Study Questions:

1. What hypothesis was being tested by the researchers in this experiment?
2. Write an aim for the experiment conducted by the researchers.
3. Write a method for this experiment as a series of steps.
4. Tabulate the results of this experiment.
5. Write a suitable conclusion for this experiment.
6. Discuss how you could improve this experiment.
7. Give the 2-dimensional structural formula for each of the following compounds:
• butanoic acid
• heptan-2-one (2-heptanone)
• nonan-2-one (2-nonanone)
• octan-2-one (2-octanone)
8. On each structural formula above, circle the functional group and name it.
9. Classify each of the compounds listed in question 1 on the basis of their functional groups.
10. Give the molecular formula for each of the following compounds:
    • butanoic acid
    • heptan-2-one (2-heptanone)
    • nonan-2-one (2-nonanone)
    • octan-2-one (2-octanone)
11. Give the condensed structural formula for each of the following compounds:
    • butanoic acid
    • heptan-2-one (2-heptanone)
    • nonan-2-one (2-nonanone)
    • octan-2-one (2-octanone)
12. Calculate the molar mass for each of the following compounds:
• butanoic acid
• heptan-2-one (2-heptanone)
• nonan-2-one (2-nonanone)
• octan-2-one (2-octanone)
13. Which of the following do you think would have the longest gas chromatography retention time ? Explain your answer.
    • heptan-2-one (2-heptanone)
    • nonan-2-one (2-nonanone)
    • octan-2-one (2-octanone)
14. Why is gas chromatography (GC) a good choice of analytical technique for this experiment compared to other chromatographic techniques?

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

Scientific Method and Designing an Experiment

AUS-e-TUTE has just added two new resources sets:

• Scientific Method
• Experimental Design

All the Chemistry Syllabus Study Guides in the Test Centre have been updated to include these new resources.