Ooohhh, nearly there…

Wishing you all the best…

(almost there!)

Mrs Elliott

The Periodic Table of Elements according to relative abundance

In honour of our prac today…

116: Livermorium

Interesting question: Would you rather have an element named after you or win a Nobel Prize?

Acid rain revision.

It might pay to start this topic with some revision of acids and bases.  I posted this one last year….

Rain containing dissolved carbon dioxide is acidic.

Rainwater is naturally acidic, with a pH around 5.6.  This is due to the fact that there are gases present in the atmosphere that undergo natural processes to react with water vapour and form acids.  For example, carbon dioxide can form carbonic acid.  The carbonic acid partially ionises to form a low concentration of H+ ions. The H+ ions are what makes the water acidic, and therefore lowers the pH.

CO2 + H2O –> H2CO3

H2CO3 –> H+ + HCO3

HCO3 –> H+ + CO32-

pH is a measure of the concentration of hydrogen ions: i.e. pH = – log [H+].

pH = -log[H3O+]

pOH = -log[OH]

[H3O+] = 10-pH

pH + pOH = 14

There are a few equations that you are just going to have to memorise. A few things to point out if you have forgotten…

  • The square brackets mean ‘concentration of’
  • H3O+ and H+ are both used interchangeably to represent an acid

And theres always the interacive animations that I have posted previously that you can check out…

For some more details on acid rain, its formation and its effects (you need to know about all of these) , check out the following sites:

Cammie-stry

Aus-e-tute

Department of Chemistry, Washington

Buzzle

Photochemical smog revision.

You wanted to know more about ozone…

Ozone, O3, is found throughout the atmosphere.  Ozone is a pale blue gas that is poisonous to human life and plants, even in small concentrations.  It is harmful when it occurs near ground level, but serves an essential function in the upper atmosphere because it absorbs high energy ultra violet radiation.  Without this vital protection this radiation from the sun would eventually destroy life on earth.

A youtube search has found a video by the Periodic Table of Videos.  It has quite a nice summary…

 

Nitrogen oxides lead to the formation of ozone in the troposphere.

And you need to be able to:

Describe and write equations showing the role of nitrogen oxides in the formation of ozone in the troposphere.

The emission of nitric oxide (NO) from engines burning fossil fuels may lead to the formation of ozone, and subsequently photochemical smog in the lower atmosphere.

Nitrogen and oxygen from the air combine in engines (which have high temperatures) to form nitric oxide (NO).

Nitric oxide is an example of a primary pollutantPrimary pollutants are emitted directly into the atmosphere from a source such as a combustion chamber in a car engine or furnace.

Once in the atmosphere, nitric oxide can be converted to nitrogen dioxide.

Nitric dioxide is an example of a secondary pollutantSecondary pollutants are formed in the atmosphere by chemical reactions of the primary pollutants.

Nitrogen dioxide is very reactive in the atmosphere. By absorbing solar radiation it undergoes photochemical dissociation into nitric oxide and atomic oxygen.

NO2 –> NO + O

The atomic oxygen formed is very reactive and then reacts with oxygen molecules to produce ozone.

O2 + O –> O3

My tip to you:

You are required to describe and write equations

  • If you cant remember the equations, this is one of those times that you are going to have to memorise them.
  • Once you have done that, I would explain those equations using words.  That will go towards the describing part.

But there’s more to it:

Nitrogen oxides and ozone in the troposphere are pollutants.

And you need to be able to:

Explain the terms ‘primary pollutants’ and ‘secondary pollutants’ with reference to the harmful effects of nitrogen oxides and ozone in the troposphere.

So….

I have already covered the primary and secondary pollutants part above.  Next you need to be able to explain the harmful effects of those pollutants.

In short:

  • Ozone attacks the double bonds in rubber and polymers.  This causes cracking/perishing.
  • Ozone can cause health problems such as coughing, wheezing, and irritation of the respiratory system.
  • Plants suffer when exposed to ozone. Their leaves yellow, and therefore the photosynthesis rate is reduced.
  • Nitrogen dioxide causes similar effects in plants and animals.
  • Nitrogen oxides are responsible for the formation of acid rain.

But:

It is possible to reduce the quantities of nitrogen oxides generated by cars.

How?

With the use of catalytic converters.

Basically, the catalytic converter removes the pollutants from the car exhaust and changes them to less harmful gasses.

This is explained in more detail in the videos that I have already shown you…

http://videos.howstuffworks.com/tlc/29979-wrecks-to-riches-catalytic-converter-video.htm

http://videos.howstuffworks.com/howstuffworks/50203-stuff-you-should-know-converting-catalytically-video.htm

Some equations that can explain what is going on chemically:

2CO + 2NO –> N2 + 2CO2

CO + H2O –> H2 + CO2

2CO + O2 –> 2CO2

2H2 + 2NO –> 2H2O + N2

Dry cleaning chemistry. And some revision along the way….

Well, I just picked up my dry cleaning in time for the races…

It gave me some inspiration for this blog post – there is plenty of chemistry involved.

Dry cleaning isn’t ‘dry’ as such, a liquid is still used in the cleaning process.  The word ‘dry’ is used to indicate that water isn’t used.

So, using what we know already:

Polar substances are soluble in other polar substances.  That is, polar substances will dissolve in water.  We normally wash in water, so any polar substances should be removed.  Sound reasonable so far?

In the dry cleaning process, a chemical called perchloroethylene is often used.

(Can you give the systematic name for this chemical?)

The next part of your revision… Can you describe the polarity of this molecule?

chimpanzee_thinking_poster.jpg

Well, you might recall the two conditions necessary for a molecule to be polar.

1. Polar bonds must be present

2. The poles created by the polar bonds must be arranged in such a way that they don’t cancel each other out.  That is, the molecule must not have multiple axes of symmetry.

So, back to perchloroethylene. There are polar bonds present, as there is a difference in electronegativity between the chlorine atom and the carbon atom. The shape of the molecule is planar, and there are multiple axes of symmetry.  This in effect cancels out the sight positive charges and slight negative charges (dipoles), resulting in a non-polar molecule. (Or, the net vector sum of the dipoles is zero, as Reece might prefer to say).

In summary, perchloroethylene is non-polar.

So what does this mean in regards to the dry cleaning (that I’m sure you think I’ve forgotten about…)?

Just as polar substances will dissolve in other polar substances, non-polar substances will also dissolve in other non-polar substances.

That is, non-polar substances will dissolve in perchloroethylene.

Which is really handy, as a number of stains in clothing come from grease and other substances that are organic (and therefore largely non-polar).

To watch more about how dry cleaning works, check out this video (that I couldn’t embed for you).

We will also learn more about other cleaning agents and how they work later in the year.

But if you’re interested in some more related reading, check out the following sites:

How Stuff Works – The Chemistry of Cleaning Clothes

RSC – Dry Cleaning and Green Chemistry

PS.  The systematic name of perchloroethylene? Tetrachloroethene. (Don’t be tricked, it’s not going to be 1,1,2,2-tetrachloroethene… There is only one possible way to get tetrachloroethene, so we won’t need the numbers in this case).

Largest molecule ever made…

Well, you did ask me what it was in the hope that you would be able to make it with the molecule kits….

Its a molecule called PG5, and its a synthetically prepared polymer. It is thought that it could be used for delivering drugs.

Unfortunately I don’t think you’ll be making this one with the model kits any time soon… 🙂

Read more about it here…

Ionic bonds.

The Name's Bond, Ionic Bond

Thanks to Ashleigh for locating this image for me…

It led me on a search for other ionic bonding cartoons. Here’s what I’ve come up with…

If you would like to have a go at creating your own, I might be able to upload it to the blog 🙂

Moonshine…

Leading on from our alcohols topic in class…

Moonshine.  White lightning. Mountain dew. Hooch. Rotgut. Bathtub gin. Popskull. Panther’s breath. Jet fuel. Corn liquor. Or just plain old shine…

So what is it?

Moonshine is any kind of alcohol, usually whisky or rum, that is made in secret to avoid high taxes or outright bans on alcoholic drinks.

What is it made from?

Corn, sugar, yeast and water.

Although alcohol can be made from nearly any type of grain, Moonshine is usually made from corn.

And how is it made?

In short: The first process is fermentation and involves yeast breaking down sugar to produce alcohol (like we have learnt in class).

The alcohol is then distilled – we have spoken about this too – whereby the fermentation product is heated. The alcohol evaporates off first (lower boiling point than water… I hope you can explain why…) which separates it from the water and other impurities, before it it is condensed back to a liquid. The result? More concentrated alcohol.

In more detail:

But how is it different to the alcohol from the shops?

Well…

Aside from the obvious differences between something made in a sanitized production facility and something made at night in the woods, the primary difference is aging. When whisky comes out of the still, it’s so clear it looks like water. Moonshiners bottle it and sell it just like that. Commercial alcohols have an amber or golden color to them — this is because they are aged for years in charred oak barrels. The aging process gives them color and mellows the harsh taste. There’s no such mellowing with moonshine, which is why it has such “kick.”

And some more about moonshine that relates to chemistry…

It is not uncommon to create a poisonous batch of moonshine. A few ways this might happen…

  • It usually takes two or three passes through the still to remove all the impurities from the alcohol. One pass may not be enough to create a safe batch.
  • If the still is too hot, more than alcohol can boil off and ultimately condense — meaning more than alcohol makes it into the finished product.
  • Poisonous ingredients are sometimes added (such as  manure, embalming fluid, bleach, rubbing alcohol and even paint thinner) in an attempt to increase the “kick”

People have actually died from drinking moonshine…

Also:

Although methanol is not produced in toxic amounts by fermentation of sugars from grain starches, contamination is still possible by unscrupulous distillers using cheap methanol to increase the apparent strength of the product. Moonshine can be made both more palatable and less damaging by discarding the “foreshot”—the first few ounces of alcohol that drip from the condenser. The foreshot contains most of the methanol, if any, from the mash. Methanol may be present because it vaporizes at a lower temperature than ethanol. The foreshot also typically contains small amounts of other undesirable compounds such as acetone and various aldehydes.

Alcohol concentrations above about 50% alcohol by volume are flammable and therefore dangerous to handle. This is especially true during the distilling process in which vaporized alcohol can accumulate in the air if there is not enough ventilation.

Hope this covers what you were after…

Sources:

How Stuff Works – How Moonshine Works by Ed Grabianowski

Wikipedia – Moonshine

Also related and worth a look (although not much chemistry):

Discovery channel – Moonshiners (online videos here)

The Dukes of Hazzard (just for fun!)

 

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