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

Blood Alcohol Concentration

Drinking alcohol impairs your driving ability, so legal limits are set, not for the amount of alcohol you consume, but on the effects of alcohol in your system. In Australia we measure the amount of alcohol in your blood (BAC or Blood Alcohol Concentration) and have set a "maximum legal limit" of 0.05% for most drivers (BAC for learner, provisional and professional drivers is less).
A Blood Alcohol Concentration, BAC, of 0.05% is a weight per volume percentage, w/v%, that is, a BAC of 0.05% is 0.05 grams of alcohol in every 100 mL of blood.
Your Blood Alcohol Concentration, BAC, is effected by the alcoholic beverages you consume. The concentration of alcohol varies between different types of alcoholic beverages, and is given as w/v% concentration as shown in the table below:

Alcoholic Beverage	Typical Alcohol Concentration
light beer	2.7%
ordinary beer	4.9%
wine	12%
spirits	40%
port or sherry	20%

So drinking 100 mL of wine will increase your blood alcohol concentration more than drinking 100 mL of beer.

But drinking alcoholic beverages is not the only way that alcohol can enter your blood stream. Alcohol is also present as an ingredient in other things you might ingest such as in some mouthwashes where it is used for its anti-bacterial properties, for example, original formula Listerine mouthwash contains 26.9% alcohol. Alcohol is also found as the solvent in many over-the-counter and prescription medications, for example, Benedryl has an alcohol concentration of 14% while Benedryl Decongestant has an alcohol concentration of 5%.

The amount of alcohol you ingest will be one factor in determining your blood alcohol concentration, but another factor is the rate at which your body removes alcohol from your blood, and this differs between individuals. There is no way to determine your blood alcohol concentration short of chemical analysis. Since it is not practical for every driver to do this before they set off, guidelines are produced based on the number of "standard drinks" that an "average person" can consume in an hour before he will be "over the legal limit". It should be noted that some people will need to drink less than the guidelines while there are some people who can consume more.
In Australia, a "standard drink" is one containing 10 g of alcohol.
So, in order for you estimate the number of "standard drinks" you have ingested, you need to know the alcohol concentration in your drink and the volume of the drink you drank. Which is not something you are likely to do while standing at the bar ordering your drink!
For this reason, Government authorities issue the guidelines showing the "standard drink" as volumes of different types of alcoholic beverages:

Alcoholic Beverage	Typical Alcohol Concentration	Standard Drink
light beer	2.7%	1 schooner, 425 mL
ordinary beer	4.9%	1 middy, 285 mL
wine	12%	1 glass, 100 mL
spirits	40%	1 nip, 30 mL
port or sherry	20%	1 glass, 60 mL

In order to maintain a blood alcohol concentration under 0.05%, an "average" person can consume 2 standard drinks in the first hour, followed by 1 drink each following hour. If your legal limit is 0.02%, then even just 1 drink can put you over the legal BAC for driving! And, ofcourse, if your "legal limit" is 0%, you cannot ingest any alcohol at all before driving. Be aware that an average person takes about 1 hour to remove the alcohol in 1 standard drink from their blood stream, so it is quite possible for you to be over the "legal limit" hours after you begin drinking!

Further Reading:
Weight/Volume Percentage Calculations: http://www.ausetute.com.au/wtvol.html
Molarity (mol L^-1 concentration) : http://www.ausetute.com.au/concsols.html

Suggested Study Questions:

1. Determine the mass of alcohol in 100 mL of each of the following drinks:
   • light beer
   • ordinary beer
   • wine
   • spririts
   • port
2. Determine the mass of alcohol in 250 mL of each of the following drinks:
   • light beer
   • ordinary beer
   • wine
   • spririts
   • port
3. Calculate the mass of alcohol present in:
   • 425 mL of light beer
   • 285 mL of ordinary beer
   • 100 mL of wine
   • 30 mL spririts
   • 60 mL port
4. Assuming the recommended dose of Benedryl, or Benedryl Decongestant, is 20 mL, what mass of alcohol is present in each dose?
5. How much of each cough mixture above do you need to consume in order to ingest the same amount of alcohol as present in a standard drink?
6. Explain why the volume of a "standard drink" differs for different types of alcoholic beverage.
7. In one hour, Phyl the Physicist drinks 1 schooner of ordinary beer and 1 glass of wine at Science Expo.
   • What mass of alcohol has Phyl consumed?
   • How many "standard drinks" has Phyl consumed?
8. Also at the Science Expo is Bobby the Biologist who mixes herself a Manhattan; 1 nip of vermouth and 2 nips of whiskey, and a dash of bitters, served in a chilled glass with ice and a cherry garnish.
• What is the minimum mass of alcohol Bobby will consume when she drinks this?
• Approximately how many standard drinks is this equivalent to?
9. Sam the Science student has a cold. She takes a 20 mL dose of Bendryl before going to the Expo. In the same hour, Sam drinks 1 middy of light beer at the Expo.
   • What mass of alcohol has Sam consumed?
   • How many "standard drinks" has Sam consumed?
10. Chris the Chemist is the "designated driver" for his team members at the Science Expo. So Chris drinks a 100 mL cup of mulled wine, which is red wine that has been heated with various spices. Chris thinks the alcohol content of his drink must be less than that of 1 "standard drink". Do you agree? Explain your answer.
11. Assuming "alcohol" refers only to ethanol (ethyl alcohol), convert the following concentrations in w/v% to concentrations of ethanol in mol L^-1 (molarity):
    • light beer 2.7%
    • ordinary beer 4.9%
    • wine 12%
    • spririts 40%
    • port 20%
12. Ethanol is a liquid at room temperature and pressure. Why do you think alcohol concentrations are given in units of grams per 100 mL? Explain your answer

Nano-zinc oxide and the Environment

Increasingly, we are making use of nanoparticles because of their unique properties compared to the same substance in bulk material. Many cosmetics, including sunscreens and sunblocks, now contain nanoparticles. When you go swimming or wash, these nanoparticles are washed off. Depending on where the nanoparticles are washed off, the waste water may directly enter a natural water system such as a river or ocean, it may end up in sewerage sludge, and it may eventually end up on land. What scientists do not know is just how many nanoparticles are entering the earth, air and water.

It is estimated that carbon nanotubes, which form part of a composite material in objects such as bicycle frames and tennis rackets, can take 10 years to breakdown and be released into the environment. On the other hand, about half of the cosmetic nanoparticles enter our waste water within one year.

Europe currently produces about 39,000 tons of nano-titanium dioxide per year, and it is estimated that the concentration of these nanoparticles in effected areas is now 61 micrograms per kilogram of ground. For humans, the maximum "safe" levels for exposure to these nanoparticles is set at:

• 2,500 mg/kg/day for oral exposure
• 2.4 mg/m³ for inhalation

While small amounts of zinc oxide are beneficial to plant growth, larger amounts can impair seed germination. Plants take up the free zinc ions in aqueous solution rather than the zinc oxide particles. This zinc becomes incorporated into the plants we eat. Zinc is an essential element in the human diet. The recommended dietary allowance of zinc for men is 11 mg/day, and for women is 8 mg/day. There are concerns that the increasing level of zinc in  plants may lead to accumulation of zinc in humans which will be detrimental to our health. Ingesting more than about 100 mg of zinc per day may lead to chronic toxicity.

Research into the environmental impact of nanoparticles, and their impact on plant and animal health, will continue for a long time.

Reference:
https://www.sciencedaily.com/releases/2016/05/160512084646.htm

Further reading
Nanotechnology: http://www.ausetute.com.au/nanotech.html
Graphene and Fullerenes: http://www.ausetute.com.au/graphene.html
Solutions Concepts: http://www.ausetute.com.au/solutions.html
Weight percent (w/w): http://www.ausetute.com.au/weightpc.html
Parts per MIllion (ppm): http://www.ausetute.com.au/partspm.html

Suggested Study Questions:

1. What is meant by the term "nanoparticle"?
2. If a nanoparticle of zinc oxide has a diameter of 20 nm, what is its diameter in:
   • metres
   • centimetres
   • millimetres
   • micrometres
3. Give an example of one property of bulk zinc oxide that is different to nanoparticles of zinc oxide.
4. Explain why zinc oxide nanoparticles are used in sunscreens.
5. What is a carbon nanotube?
6. Why are carbon nanotubes used in the production of bicycle frames?
7. Why are concentrations of titanium dioxide nanoparticles in soil given in units of micorgrams per kilogram of soil rather than in moles per litre?
8. Convert the following concentrations into parts per million (ppm)
   • 2,500 mg kg^-1
   • 2.4 mg m^-3
9. Using the recommended dietary allowance figures in the article, determine the mass in grams of zinc allowed for a:
   • 58 kg woman each day
   • 79 kg man each day
10. A typical vitamin pill contains 25 mg of zinc. By consuming 1 tablet per day, will the man or woman above exceed the recommended daily allowance of zinc?
11. 6 raw oysters contain 32 mg of zinc. How many oysters can the man and woman above eat before exceeding the recommended dietary allowance of zinc?
12. 85 g of cooked beef contains 7 mg of zinc. What mass of beef can the man and woman above ingest before exceeding the recommended dietary allowance of zinc.
13. 28 g of dry roasted cashews contain 1.6 mg of zinc. What mass of zinc, in grams, is present in 750 g bag of cashews?
14. 1/2 cup of cooked red kidney beans contain 0.9 mg of zinc. How many cups of red kidney beans would our man and woman above need to consume in order to achieve their recomended dietary allowance of zinc?
15. Do you think you should take a daily vitamin pill containing zinc? Justify your answer.

Hidden Salt in Food

Researchers at VicHealth and Deakin University compared how much salt people thought they consumed with how much salt they really had consumed and found that Australians were not only eating too much salt, but were also eating more salt than they thought they were!

Australians were found to be consuming between 8 and 10 grams of salt per day, about twice the amount recommended by the World Health Organisation (WHO) that recommends adults should eat less than 5 g of salt (a bit less than a teaspoon) per day. The "salt" they are referring to is "table salt" which has the chemical name "sodium chloride" and the chemical formula NaCl. Sodium chloride is actually an ionic substance made up of sodium ions (Na⁺) and chloride ions (Cl^-) in a ratio of 1:1 and it is the sodium ions (Na⁺) that are the cause for concern because elevated levels of sodium ions increase a person's risk of high blood pressure, heart disease and stroke. Unfortunately, non-Chemists often refer to this as elevated "sodium" levels rather than as elevated "sodium ion" levels.

If you want to reduce your sodium chloride intake, the first thing you can do is NOT add "table salt" to your food when you eat it. However, only about 20% w/w of our daily intake of sodium ions comes from adding sodium chloride to our food at the table before we eat it. The other 80%  w/w of the sodium ions we consume is already present in our food, either naturally or because it has been added during processing.

Natural sources of sodium ions in our food include:

• milk and cream: 50 mg of sodium ions per 100 g
• eggs: 80 mg of sodium ions per 100 g
• carrot: 69 mg of sodium ions per 100 g
• spinach: 79 mg of sodium ions per 100 g
• green beans, potatoes: 6 mg of sodium ions per 100 g
• pumpkin: 1 mg sodium ions per 100 g
• apple, banana, pear: 1 mg sodium ions per 100 g

By far the greatest source of sodium ions in our diet comes from eating processed foods:

• 1 slice of white bread (30 g) can contain 140 mg Na⁺
• 1 slice of cheddar cheese (20 g) can contain 140 mg Na⁺
• 1 foil pack of butter (7 g) can have 55 mg of Na⁺
• 1 small bowl of breakfast cereal (30 g) can have 140 mg of Na⁺
• 1 small packet of potato chips (45 g) can have about 300 mg of Na⁺
• 1 can (12 fl oz, about 350 mL) diet coke has 40 mg of Na⁺
• tap water contains about 20 mg Na⁺ per 1 L

Food you buy in packets from a supermarket will have a list of ingredients and you can read this to find the amount of sodium ions (Na⁺) present in the food.

However, there are many foods we buy that do not come in a packet which tells us how much sodium ion is present. These foods make up our "hidden salt intake". You may find this information on company websites, such as

• 1 McDonalds Big Mac contains 859 mg of Na⁺
• 6 KFC chicken nuggets with sauce has 1040 mg of Na⁺
• 1 slice (¹/₈ ^th) of medium pan Pizza Hut Meat Lover's pizza has 740 mg of Na⁺
• 1 Taco Bell black bean burrito contains 1030 mg of Na⁺

Many people forget that sodium ions are also present in many medicines. Effervescent medicines contain sodium hydrogen carbonate (or sodium bicarbonate) which helps them dissolve in water.
For example,:

• 1 effervescent Berocca tablet contains about 280 mg of Na⁺ while the film-coated Berocca tablet contains only 1.85 mg of Na⁺
• 1 Gaviscon Advance tablet contains 55 mg Na⁺ but 10 mL of liquid Gaviscon contains 141 mg of Na⁺
• 1 Panadol Actifast caplet contains 173 mg Na⁺ but 1 Panadol soluble tablet contains 428 mg of Na⁺

So, if you want a diet that's low in sodium, eat lots of fresh fruit and vegetables, drink lots of water, and avoid packaged food and "fast food", and, remember to choose "low sodium" medicines.

Reference:
http://www.abc.net.au/news/2016-03-24/reducing-salt-intake-could-save-thousands-of-lives-each-year/7274140

Further Reading:
Mass Conversions
Percent by Mass

Suggested Study Questions:

1. Convert the following masses in grams to masses in milligrams:
   • 5 g
   • 8 g
   • 10 g
   • 30 g
   • 100 g
2. Convert the following masses in milligrams to masses in grams:
• 1.85 mg
• 55 mg
• 69 mg
• 173 mg
• 859 mg
• 1040 mg
3. Calculate the percentage of sodium ions and the percentage of chloride ions in sodium chloride.
4. Use the information in the article to calculate the mass of sodium ions each adult Australian currently consumes as a result of :
   • adding table salt to food before eating it
   • table salt that is naturally present or is added to food during preparation
5. 100 g of milk contains 50 mg of Na⁺ . What is the percentage by mass of sodium in the milk?
6. One 30 g slice  of white bread contains 140 mg Na⁺. What is the percentage by mass of sodium in white bread?
7. For lunch, a student ate a sandwich made up of 2 slices of white bread, 2 foil packs of butter and a slice of cheddar cheese. She also ate a 200 g banana, and washed it all down with 250 mL of plain, unflavoured milk.
   • Calculate the mass of sodium ions the student consumed for lunch.
   • Calculate her consumption of sodium ions as a percentage of the WHO recommended daily intake of sodium ions.
8. A different student consumed a Big Mac, 1 can of diet coke, and a 200 g packet of potato chips.
• Calculate the mass of sodium ions the student consumed for lunch.
• Calculate her consumption of sodium ions as a percentage of the WHO recommended daily intake of sodium ions.
9. For her birthday, a Chemistry Teacher's class gave her a 500 g block of dairy milk chocolate. The label included the information that the block of chocolate contained 82 mg of sodium per 100 g.
   • What is the mass of sodium ions in the block of chocolate?
   • If each person in the class of 22 received an equal share of the block chocolate, what mass of sodium ions would each person consume?
10. In Australia, the maximum recommended dose of paracetamol (the active ingredient in panadol tablets) is 4000 mg per day. 1 soluble Panadol tablet contains 500 mg of paracetamol.
    • What is the maximum number of soluble Panadol tablets per day that an adult Australian should consume?
    • If an adult Australian consumed the maximum recommended dose of soluble panadol tablets in 1 day, what mass of sodium ions would they have consumed?
    • What percentage of the WHO recommended maximum intake of sodium would this amount of panadol be?