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8/6/2019 Ideal Gases Etc
1/22
Resource Guide- Ideal Gases/Acid rain & the
Greenhouse Effect
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Contents
Title Page 1
Contents Page 2
Student learning outcomes Page 3
States of Matter Page 4
Introduction to Ideal Gases Page 58
Convection currents Page 9
Introduction to Acid Rain Page 10 & 11
Introduction to The Greenhouse Effect Page 12 & 13
Experiment 1: Convection Currents Page 14 - 16
Experiment 2: Making Acid Rain Page 17 - 20
Experiment 3: The Albedo Effect Page 21
Glossary Page 22
References Page 22
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Student learning outcomes
- What is a gas?- The ideal gas laws and how to use them.
- What is acid rain?- How is acid rain formed?
- What is the greenhouse effect?- What are the greenhouse gases and what do they do?
- Density based on temperature within a state of matter.
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States of Matter
The three main states of matter are Gases, Liquids and Solids.
Gases, liquids and solids are all made up of tiny particles. These particles act
differently in the three phases. The images below show these different behaviours.
Microscopic view of a
gas.
Microscopic view of a
liquid.
Microscopic view of a
solid.
Particles in a - gas are well separated with no regular arrangement. They vibrate and
move freely at high speeds.Pressure is due to the gas molecules
colliding with the walls of a container.
- liquid are close together with no regular arrangement. They vibrate,
move about, and slide past each other.
- solid are tightly packed, usually in a regular pattern. They vibrate
(jiggle) but generally do not move from place to place.
(Purdue University, 2010)
The following table describes the properties of the 3 above mentioned states of
matter:(Purdue University, 2010)
Some Characteristics of Gases, Liquids and Solids and the Microscopic
Explanation for the Behaviour
Gas Liquid Solid
Takes on the shape and
volume of its container
particles can move past
one another
Takes on the shape of the
part of the container
which it occupies
particles can move/slide
past one another
Maintains a fixed volume
and shape
rigid - particles locked
into place
Compressible
lots of free space between
particles
Not easily compressible
little free space between
particles
Not easily compressible
very little free space
between particles
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Ideal Gases
What is an Ideal gas?For a gas to be considered ideal it must possess both of the following traits:
1. The space the gas molecules occupy is insignificant when compared with the space
in between the gas molecules.(Bellevue College, 2010)
This statement follows that the volume of space that the particles dwell in is
practically nonexistent in comparison to the mass amount of space around andbetween each particle. So although the gas molecules do have a volume, it is so smallcompared to the volume in between gas molecules that it really doesn't matter.
2.Intermolecular forces between gas molecules are negligible. (Bellevue College, 2010)
This statement follows that gas molecules are moving so rapidly that they zip past
each other before having time to be attracted or repelled by one and other. Therefore,
even if certain gas molecules are attractive or repulsive to each other, it doesn't matterbecause they move past each other too quickly to notice it.
When is a gas not ideal?
At exceptionally high pressures, the first above listed trait fails. When gases are
packed under a great deal of pressure, the space between them becomes small. It's
like the difference between having 100 balloons in a large room, and then forcing
them into a much smaller room. Because at this stage their volume cannot be ignoredas it is not so small in comparison to the space around them.
When exposed to extremely low temperatures, gas particles move much slower. In
fact, they move so slow that they no longer zip past each other too quickly to notice
the attractions or repulsions that might exist. So this is when the second above listedtrait fails.
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What is the ideal gas equation?
PV=nRT
This equation has the ability to link all the essential properties of gases together.
P is the pressure (measured in atm) V is the volume (measured in litres) n is the number of moles (measured in moles) R is the ideal gas constant (0.08206) it is not a variable and therefore never
changes T is the temperature in Kelvin (Degrees Celsius + 273). P is pressure (often measured in atmospheres (atm), but can also be measured
in Pascals).
Where does the ideal gas equation come from?
The Ideal gas equation was derived from a combination of several different gas laws.
Boyle's LawBoyles law refers to the relationship between absolute pressure and volume of a gas.
It states the volume of a definite quantity of dry gas is inversely proportional to thepressure, provided the temperature remains constant (Oracle, 2010).
This law can be expressed as P1V1 = P2V2
V1 is the original volume V2 is the new volume P1 is original pressure P2 is the new pressure
Eg. If you have a gas with a volume of 45.0 ml and a pressure of 760mm. If the
pressure is increased to 800mm and the temperature remains constant then according
to Boyle's Law the new volume is 42.75 ml.
- (760mm)(45.0ml) = (800mm)(V2)- V2 = (760mm)(45.0ml) / (800mm)- V2 = 34200 / 800- V2=42.75ml
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Charles's Law
Charless Law refers to the relationship between temperature and volume. He noticedthat as the temperature of a gas increased, the volume increased
This law states that the volume occupied by any sample of gas at a constant pressureis directly proportional to the absolute temperature. (Oracle, 2010)
This law can be expressed as V / T = constant
V is the volume T is the absolute temperature (measured in Kelvin)
Charles's Law can be rearranged into two other useful equations.
V1 / T1 = V2 / T2
V1 is the initial volume T1 is the initial temperature V2 is the final volume T2 is the final temperature
V2 = V1 (T2 / T1)
V2 is the final volume
T2 is the final temperature V1 is the initial volume T1 is the initial temperature (Oracle, 2010)
Avogadro made, perhaps, the most obvious correlation by linking n with V. He
showed that as the number of moles increased, the volume they occupied increased.
Again, this makes perfect sense. The more of anything you have, the more space itwill require. In other words, V= constant x n.
Avogadro's LawAvogadros Law refers to the relationship between n and V or moles and volume,
showing that as the number of moles increased, the volume they occupied also did.The easiest way to quantify the amount of gas is as a mass.
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Calculations using the ideal gas equation
1. Calculations where one variable is missing.
These equations are normally worded along the lines of:
"A gas cylinder of volume ___ contains ___ moles of an ideal gas at ___
temperature. What is the pressure inside the cylinder."
Alternatively, you may be provided with T, P, and n, and ask for V, or any
combination thereof.
For this type of question as you have three of the four variables, you simply need to
solve for the fourth. It's just a case of plugging your given values into the equation.
Start by writing "PV=nRT" and then fill in the values you have been given or already
know (such as that R will always be 0.08206) and then solve for the one that's still
missing. It is important to keep track of units as you do this, as it is easy to make a
mistake here.
2. Calculations where two variables are changed.
In this case, there is a "before and after" situation. Two of the variables are kept the
same, and two are changed. The simplest way to go about solving such an equation is
to group the things that change on one side of the equation, and the things that don'tchange on the other side.
Example: A box containing a sample of gas at 1.00 atm is heated from 270K to
300K. What happens to the pressure inside the box?
Answer: the volume of the box (V) and the number of moles inside the box have not
changed. The temperature and the pressure have changed. So re-write PV=nRT
rearranged such that these two sets are grouped on either side . . . P/T = nR/V. Now,since the entire expression nR/V does not change, P/T for the "before" situation must
equal P/T for the "after" situation. (AUS-e-TUTE, 2011)
Another way to write this equation mathematically is P1 x T1 = P2 x T2
Then when we plug in our given values, we have the equation
- (1.00 atm)/(270K) = (P2)/(300K)- P2 = [(1.00 atm)/(270K)] x 300K- P2 = 1.11atm
To double check your answer you should always consider does your answer make
sense given the situation? So since the temperature has been raised, as a result thepressure should go up. This is the case as we are following one of the abovementioned gas laws where, a rise in temperature must correspond with a rise inpressure.
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Convection currents
Convection currents are a cyclic process of the flow of heat through a movement of
matter from a hot region to a cool region.
For example, if we were to heat up a region of air, as this air heats, the molecules
spread out, causing this region to become less dense than the surrounding, unheated
air. When air is less dense it is also less heavy and therefore rises. As it rises, it
reaches cooler regions and thus begins to cool itself. Eventually with the cooling of
the air, it starts to become more dense and therefore heavier and so it will begin to
fall. But in the mean time other air molecules have been heated and have began to
rise taking the original rising molecules place in a continuous cycle where they will
then eventually cool and fall as well.
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Acid rain
"Acid rain" is a broad term referring to a mixture of wet and dry deposition
(deposited material) from the atmosphere containing higher than normal amounts of
nitric and sulfuric acids. (EPA, 2007)
The formation of acid rain is a result of both natural causes and manmade, but
ultimately is when rain is made acidic by pollutants in the air. Some natural sources
include volcanoes and decaying vegetation. The manmade sources, are mainly
emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx). through the burning of
fossil fuels (such as coal to produce electricity) or the exhaust from vehicles.Acid rain occurs when these gases react in the atmosphere with water, oxygen, and
various other chemicals to form different acidic compounds.
Sulphur and nitrogen oxides produced when oil, coal, natural gas or peat were
burned could be converted in the atmosphere into sulphates and nitrates, and then into
acids, which could return to earth in contaminated rain, snow, hail, fog or mist.
McCormick, J, (1954. Pg 1)
Wet Deposition
Wet deposition refers to acidic fog, snow, and rain. If the acid compounds in the air
are blown into areas where the weather is wet, they can fall to the ground in the formof rain, snow, fog, or mist. As this acidic water flows over and through the ground, itaffects a variety of plants and animals.
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Dry Deposition
In areas where the weather is dry, the acid chemicals may become incorporated intodust or smoke and fall to the ground through dry deposition, sticking to the ground,
buildings, homes, cars, and trees. Approximately 50% of the acidity in the
atmosphere returns back to the earth through dry deposition.
What is acidity?Acidic and basic are two ways that we describe chemical compounds. Acidity is
measured using a pH scale. A pH scale runs from zero (the most acidic) to 14 (the
most basic or alkaline). A substance that is neither basic or acidic is called "neutral",and this has a pH of 7. (EPA, 2007)
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The Greenhouse Effect
The term 'greenhouse gases' is used to refer to the gases in the atmosphere that havethe ability to absorb the radiations released off the earths surface from the sun. The
most prominent greenhouse gases in the Earth's atmosphere are water vapour, carbon
dioxide, methane, nitrous oxide, ozone and CFCs.
Greenhouse Effect
The greenhouse effect warms the Earth naturally. To warm the Earth, it relies on the
Sun's energy. When the Sun's energy reaches the Earth's surface, around 49% of it is
absorbed and the rest is reflected back to space. This absorbed energy warms the
Earth's surface, which in turn radiates heat energy back towards the space. While this
warm energy is travelling towards space, it is partially trapped by greenhouse gases.
The trapped energy is then released in all directions, warming the earth's surface and
atmosphere. This process of warming the Earth is known as the greenhouse effect.
Without the greenhouse effect the earth would be around 33 degrees Celsius cooler
than usual. (Buzzle, 2011)
But the greenhouse effect isnt all good. Although it heats up the surface of the
Earth, it simultaneously cools the stratosphere, which eventually triggers ozone layer
depletion. The Ozone layer is very important to human life, considering the vital role
it plays by protecting the earth from UV rays entering the atmosphere.
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Besides the above-stated factors that affect the greenhouse effect, the sunlight's first
encounter with the type of Earth surface, also impacts the greenhouse effect. The
percentage of the heat reflected and radiated back by different Earth surfaces like the
grasslands, forests, glaciers, deserts, cities including the industrial areas, and clouds is
defined as albedo, by atmospheric scientists. The levels of heat radiation range
depends upon the type of Earth's surface, it has reflected back from into the
atmosphere. Cloud cover also plays a vital role by reducing both; the amount of solar
radiation reaching the Earth's surface and the amount of radiation energy emitted
back into the space. (Buzzle, 2011)
Greenhouse Gases
Water Vapour: Water vapour is the gaseous form of water and is produced due to
watersevaporation. It makes up about 33 to 66 percent of greenhouse gases and is
therefore the most prominent constituents of the greenhouse gases list.
Carbon Dioxide: Carbon dioxide is a chemical compound with the chemical formula
CO2. Carbon dioxide is produced in several processes such as, respiration in plants,
animals and humans and combustion of fossil fuels. This gas makes up 9 to 26percent of greenhouse gases.
Methane: Another prominent greenhouse gas is methane. Its molecular formula is
CH4. The ability methane possesses to trap heat is 20 times more than that of carbon
dioxide. It's assumed that the Earth's crust contains huge deposits of methane gas, a
part of which is let out in the process of mining, thus adding to the greenhouse effect.
Methane makes up 4 to 9 percent of greenhouse gases.
Nitrous Oxide: Nitrous oxide is another important greenhouse gas, which can cause a
high impact on global temperatures. The chemical formula of nitrous oxideis N2O.
This gas is an important, naturally occurring regulator of the stratospheric ozone,
which tends to react with the ozone and contribute to greenhouse effect.
Ozone: Another main greenhouse gas is ozone, making up approximately 3 to 7
percent. Ozone, in upper troposphere acts as a greenhouse gas, while at ground level
it acts as an air pollutant. As a greenhouse gas, ozone absorbs the infra red energythat is emitted by the earth.
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Experiment 1 : Convection Currents
Aim: To show that warm air is less dense and therefore less heavy than cold air
Materials:
1 x Small aquarium
4 x Polystyrene cups
4 x Bulldog clips
1 x Needle
Ice water
Tap waterWarm water
Boiling water
Green dye
Blue dye
Yellow dye
Red dye
Method:
Step 1: Half fill the small aquarium with tap water.
Step 2: Using the bulldog clips, attach each of the 4 cups to one of the corners of
the aquarium each. (Make sure the cups are not sitting in the water, but
are just above its surface)
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Step 3: Fill the first cup with ice water and mix in the green dye
Step 4: Add some tap water to the next cup and mix in the blue dye
Step 5: To the third cup add some warm water and mix in the yellow dye
Step 6: For the fourth cup add some boiling water and mix in the red dye
Step 7: Take the needle and poke a small hole into the bottom of each cup so
that the colour solutions can leak into the aquarium
Step 8: Observe the colour distribution. There should be a layering effect
occurring, with the hottest solution on top and the coldest solution on the
bottom
Worksheet:
1. Explain how you think a convection current would work in theatmosphere.
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
___________________________________________________
2. Draw the layering effect that should have occurred in the experiment.
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Worksheet Answers:
1. Explain how you think a convection current would work in theatmosphere.
As hot air rises due to its lower density, it starts to cool as the temperature
drops at higher altitude and so it therefore becomes denser and starts to
want to fall. In the meantime other hot air would be rising and continuing
the cycle.
2. Draw the layering effect that should have occurred in the experiment.
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Experiment 2 : Making Acid Rain
Aim: To show how acid rain is formed and the effect it has on the environment.
Materials:
Red cabbage
Clear plastic bag
30ml Ethanol
Filter paper
Water tank
2 x Tripod
2 x Gauze mat
Shavings of PVC piping
Top of a tin can
Piece of tin
Piece of wood
Flask
100ml of water
Piping to direct water vapour
Plastic ice tray
Ice
Bunsen burner
Matches
Method:
Step 1: Tear several leaves of red cabbage into small pieces and place them in a clear
plastic bag. Pour in 30ml of ethanol and knead the bag for about 1 minute. (The
leaves will lose their purple colour)
Step 2: Grab some filter paper and add it to the cabbage extract. Once it has taken on
the colour remove it and allow it to dry for 5 minutes. Repeat the process until the
paper is saturated with the colour.
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Step 3: Prepare the materials in the following set up:
Step 4: Place some ice in the ice tray, place the filter paper on the inside tripod andgauze mat and add 100ml of water to the flask outside the tank and begin to boil it.
Step 5: with everything in position, use a match to ignite the PVC shavings (acid rain
source)
Step 6: Once the PVC has completely burnt, gently tap the plastic tray. The droplets
that have formed through condensation should fall and hit the filter paper.
Step 7: Take note of any colour changes.
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Worksheet:
1. Why do you think the filter paper changed colour as the water dropletslanded on it?
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
2. What do you think would happen if the same experiment was donewithout burning the PVC shavings?
_________________________________________________________
_________________________________________________________
_________________________________________________________
________________________________________________________
3. What do you thing the filter paper is representing in this experiment forin the natural environment?
__________________________________________________________
__________________________________________________________
__________________________________________________________
__________________________________________________________
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Worksheet Answers:
1. Why do you think the filter paper changed colour as the water dropletslanded on it?
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
_____________________________________________________________
2. What do you think would happen if the same experiment was donewithout burning the PVC shavings?
It would just be a small scale model making normal rain!What do you think the filter paper is representing in this experiment for in
the natural environment?
The plants that are effected by acid rain, and lose their pigmentation due to
the chemical reaction.
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Experiment 3 : The Albedo Effect
Aim: To show that the surface the incident radiation hits on the earth affects the
reflected radiation.
Materials:
2 x Aluminium pans (approx. 15 x 25 x 3cm) one painted black and the other white
1 x Small torch
1 x Retort stand
1 x Clamp
1 x 50cm piece of string1 x Protractor
1 x Lux metre
Method:
Step 1: Starting off with the white pan, set up the retort stand to hold the torch
so that it is focussing on the centre of the pan.
Please note: The light must be at a 30 degree angle from the location of
the clamp, and the distance from where the light shines from the torch to
the pan must be 50cm.
Step 2: Using a Lux metre measure the incident radiation and record the value.
The position you choose to measure this vale must be used throughout
out all recordings in this experiment.
Step 3: Move the Lux metre so that you can record the reflected radiation (Dont
forget to flip the Lux metre over for this recording)
Step 4: Repeat steps 2 and 3 for a few different surfaces, first the black pan, then
the black pan filled with 2 centimetres of water and finally with crushed
ice. Make sure you record all readings to determine and compare the
Albedo.
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Glossary
Atmosphere: The air or gases that surround the Earth
Base: Any of a large group of chemicals with a pH greater than 7. Examples are
ammonia and baking soda.
Emissions: The gases that are released when fossil fuels are burned.
Neutral: A substance that is neither an acid nor a base and has a pH of 7. Neutral
substances can be created by combining acids and bases.
References
- AUS-e-TUTE, 2011, Chemistry Tutorial : Ideal Gas Law, viewed 5th June2011
- Bellevue College, 2010, Science DivisionIdeal Gases, viewed 7th June 2011http://scidiv.bellevuecollege.edu/bg/ideal.html
- Buzzle, 2011, Greenhouse Gases, viewed 4 th June 2011,http://www.buzzle.com/articles/greenhouse-gases-list.html
- McCormick, J.1954,Acid EarthThe global threat of acid pollution, 2nd edn,Earth Publications Limited, London
- Oracle - Think quest, 2010, ChemWeb, viewed 7th June 2011
- Purdue University, 2010, States of Matter, viewed 5th June 2011
- Taylor, F.W 2005,Elementary Climate Physics, 1st edn, Oxford UniversityPress Inc., New York.
- EPA, 2007,Acid Rain, viewed 4th June 2011http://www.epa.gov
By Katherine Strangos
http://scidiv.bellevuecollege.edu/bg/ideal.htmlhttp://scidiv.bellevuecollege.edu/bg/ideal.htmlhttp://www.buzzle.com/articles/greenhouse-gases-list.htmlhttp://www.buzzle.com/articles/greenhouse-gases-list.htmlhttp://www.epa.gov/http://www.epa.gov/http://www.epa.gov/http://www.epa.gov/http://www.buzzle.com/articles/greenhouse-gases-list.htmlhttp://scidiv.bellevuecollege.edu/bg/ideal.html