Concentration of Acetic Acid in Vinegar

Here's a strange thing. Most adults wouldn't dream of drinking wine that has been oxidized and "gone bad", just the smell is likely to put most people off! The same people, however, probably have no objection to consuming wine that has been deliberately oxidized, bottled, and marketed as vinegar.

Ofcourse, the chemistry of the oxidation of a mixture like wine is quite complex, but the most important constituent of the mixture is acetic acid (also known as ethanoic acid).

Determining the acidity of your vinegar, or how much acetic acid (ethanoic acid) is present in your vinegar, is quite easy. It's just a simple acid-base titration, and AUS-e-TUTE has just added new resources to help you understand how you can use acid-base titrations to find the concentration of acetic acid in vinegar.

AUS-e-TUTE Members have access to the new tutorial, games, test and exam.

If you are not an AUS-e-TUTE, you can take a sneak peek at the tutorial here

Bioethanol Fireplaces

Ethanol burners are becoming very popular in homes in Australia, often sold as "bioethanol" fireplaces. Although how "bio" your ethanol is really depends on which brand of ethanol or methylated spirits you choose to buy.
Having got some advertising mileage out of sticking the prefix "bio" onto ethanol, the glossy advertising brochure then adds some more enticing words like "eco", "friendly", "green" and/or "smart".
But the real selling point of the slick advertising is that you don't need a flue. No chimney, no pipes, just set your "bioethanol" fireplace up where ever you want it in the room.
Which is really very, very, interesting (for all you Chemists out there).

Chemistry of Combustion
Ethanol combusts (burns) by combining with oxygen gas in the atmosphere.
A balanced chemical equation for the complete combustion of ethanol is:

C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

This tells us that for every 1 mole of ethanol (whether it has the "bio" prefix or not), 2 moles of carbon dioxide gas will be evolved (and yes, that's the same carbon dioxide gas that contributes to the greenhouse effect).

According to the brochure, 5 litres of "bioethanol" would last about 10 hours.
That is, 1 litre of bioethanol keeps your fire going for about 2 hours, just enough to watch a movie.
So how much carbon dioxide will be released into your room while you watch the movie?

First we can use the density of ethanol and the volume of ethanol burnt to calculate the mass of ethanol consumed:

• Density of ethanol is 0.79 g cm³ at 25^oC

• If we let 1cm³ = 1 mL

• then the mass of 1 mL of ethanol is 0.79 g

• so the mass of 1 L of ethanol = 1000 x 0.79 g = 790 g

Now we can calculate the moles of ethanol in the 1 L of "bioethanol" we burnt:

• moles = mass/molar mass

• molar mass = 2 x 12 + 6 x 1 + 16 = 46 g/mol

• so moles of ethanol in 1 L = 790/46 = 17.2 mol

Use the balanced chemical equation to calculate the moles of carbon dioxide produced:

• From the balanced chemical equation, 1 mole of ethanol burns to produce 2 moles of carbon dioxide gas.

• Therefore, 17.2 moles of ethanol burns to produce 2 x 17.2 moles of carbon dioxide gas.

• moles of carbon dioxide produced = 34.4 moles

We can then calculate the volume of carbon dioxide released into your room while you watch the movie:

• At 25^oC, 1 mole of gas occupies a volume of 24.79 L

• So, 34.4 moles of carbon dioxide occupies a volume of 34.3 x 24.79 = 853 L

853 L of carbon dioxide gas sounds like lot!
But is it really? What proportion of the "air" in your room will be carbon dioxide after 2 hours?

Let's calculate the volume of a room:

• A small room is about 3m x 3m x 3m

• or 300cm x 300cm x 300cm = 27,000,000 cm³ = 27,000 L

• So the volume of air in the room before you start burning your ethanol is 27,000 L(ignoring loss of volume due to you and the furniture )

And now we can see what proportion of the "air" in your room will be carbon dioxide after 2 hours:

• Assuming there is no ventilation in the room (all the doors and windows are closed), burning 1 L of ethanol adds about 853 L carbon dioxide gas to the room, so the total volume of gas is now 27,853 L.

• The percentage of that due to the carbon dioxide we have produced is 853/27853 x 100 = 3%

Now that's better, 3% sounds a whole better than 853 L doesn't it?
Or does it?

Did you know that at a concentration of about 1%, carbon dioxide will make you feel sleepy.
At a concentration of about 7%, you can suffocate.
Which makes you think you should probably be opening a window!
Except, wouldn't that defeat the purpose of lighting a fire to keep warm in the first place?

Suggested Study Questions:

1. Draw a structural formula for ethanol.
2. Explain the difference between complete and incomplete combustion of ethanol.
3. How you could you tell by observation whether the ethanol in your "bioethanol" fireplace was undergoing complete combustion or incomplete combustion?
4. The glossy brochure states that your "bioethanol" fireplace will not produce soot. What does this tell you about the type of combustion occurring in the fireplace?
5. If the ethanol in the "bioethanol" fireplace was undergoing incomplete combustion, would the amount of carbon dioxide produced be more or less than that produced during complete combustion?
6. Calculate the moles of carbon dioxide gas that would be produced if you burnt 1 L of "bioethanol" fuel in your fireplace in a room that measured 5m x 7m x 3m
7. What volume of the room in question 6?
8. At 25^oC, how many moles of gas are present in this room from question 6?
9. What percentage of gas in this room from question 6 would be carbon dioxide after you burn 1 L of "bioethanol"?
10. One of your friends suggests that you should take a "bioethanol" fireplace with you on your camping trip because it will be a perfect way to heat your tent. Do you agree with your friend or not? Explain your answer.

Naming Esters the IUPAC Way

IUPAC naming of esters is not a bit hard, it's just a bit different to the way you name other organic molecules.

Follow AUS-e-TUTE's step-by-step guide to :

• naming esters
• drawing the structure of ester molecules
• writing the molecular formula for ester molecules

and you'll be amazed at how easily you can name, and draw the structure of, esters.

Then, when you think you've got the hang of that, why not try our ester naming game?
Or, test your skill with our ester test.
Preparing for an exam? We've got you covered! You can use our ester exam to practice your exam technique before you sit your exam.
And remember, AUS-e-TUTE's test and exam questions come with immediate feedback to help you understand where you go wrong and help you get the next question right.

AUS-e-TUTE Members should log-in to use these new resources. 

Not an AUS-e-TUTE Member?
There is currently a "free-to-view" tutorial available at http://www.ausetute.com.au/namester.html

Find out more about AUS-e-TUTE membership at : http://www.ausetute.com.au/membership.html
and you can join AUS-e-TUTE at http://www.ausetute.com.au/register.html

2015 Chemistry Calendar

Yes, the 2015 Chemistry Calendar is here!
Yes, it's free to download (it's a pdf)!
And yes, it has been redesigned, but you'll have to download one to see why the 2015 Chemistry Calendar is the best calendar we've made so far ........

Go to http://www.ausetute.com.au and click on any of the links to the download page.

Naming Alcohols the IUPAC Way

Alcohols are organic molecules that have the OH (hydroxyl or hydroxy) functional group.
Learn how to apply the IUPAC rules for naming different types of alcohols:

• Naming Straight-Chain Alkanols
• Naming Branched-Chain Alkanols
• Naming Straight-Chain Alkanediols

and learn how to classify alcohols as primary, secondary or tertiary at

• Classification of Alcohols

AUS-e-TUTE Members also have access to additional teaching and learning sources.

Find out about AUS-e-TUTE membership here

and when you're ready to start improving your ability to answer Chemistry questions correctly, you can join AUS-e-TUTE here

Writing Chemical Formula

The chemical formula for the ammonium ion is NH₄⁺.
In order to write this formula correctly you MUST show:

• capital (or uppercase) N for the element nitrogen
• capital (or uppercase) H for the element hydrogen
• a subscript number 4 to indicate the presence of 4 hydrogen atoms in the molecule
• a superscript + sign to indicate that the molecule has a positive charge

When you answer a question at ausetute.com.au requiring a chemical formula, you will need to use the buttons on the textbox provided to make a subscript number and a superscript charge sign.

Here is a quick lesson in how to type your chemical formula into the textbox so that it displays the correct formula and not an incorrect formula (like NH4+)

Amides

You spell amine with an "n" and amide with a "d", but what other differences are there?

AUS-e-TUTE has just added new resources for naming primary amides (primary alkanamides).
AUS-e-TUTE Members should log-in to use the new tutorial, game and test.

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

You can find out about how AUS-e-TUTE can help you improve your chemistry results at http://www.ausetute.com.au/membership.html

and when you're ready to start improving your chemistry results you can join AUS-e-TUTE at http://www.ausetute.com.au/register.html