Name 1 ______________________________ Name 2_____________ ______________________
GEOS 110 Lab 2: Introduction to Properties of Gases and Liquids
This lab has several parts, including this “hands-on” part which deals with properties of fluids – gases to represent the atmosphere , and water to represent the ocean .
1. Gases
The aim here is to investigate some of the properties of gases, using simple equipment.
Materials
Large balloons , Fine thread, meter stick, 1-L beaker, three 50- or 100-mL beakers, 250-mL Erlenmeyer flasks, ring stand, clamp, wire gauze, ring, empty soft drink bottle, 2 drinking glasses , empty pop cans, pieces of cardboard, index cards or wax paper, clean plastic bottle with lid, empty aluminum soft drink can, bottle of perfume, 100 mL concentrated ammonia, NH
3
(aq)phenolphthalein, 10 mL concentrated hydrochloric acid, HCl (aq) iodine crystals, printer paper, 2 petri dishes, clear, empty wine bottle, tight-fitting cork, rubber hoses, hair dryer guns (hand held), paper matches, small plastic (lightweight) balls
Part 1. Is air really matter? Does it have mass and occupy space?
1: Weight is the force on an object due to gravity; W=mg Demo: We’ll balance two ~equally filled balloons by hanging them from a meter-stick balance. Note the direction of the balance’s tilt after we pop one balloon.
What does this demonstrate?
2: Lower an “empty” glass, open end downward, into a larger beaker (or pot) of water. Does water fill up the “empty” glass? Tilt the glass.
What happens and what does this demonstrate?
Part 2. What is air pressure all about?
4: Select a balloon that is easy to blow up. Insert the bottom of the balloon partway into an empty soft drink bottle, stretching its neck over the bottle mouth. Try blowing up the balloon so it fills the container.
Explain the result.
5: Place 10 mL of water in a 250-mL Erlenmeyer flask. Place the flask on a hot plate and bring the water to boiling. Do not boil the flask dry . Remove the flask from the source of heat and quickly and carefully place an empty balloon over the mouth of the flask. (It helps to pre-stretch & blow up the balloon once before it is used.)
Record what happens and explain the result .
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6: Air exerts pressure upward and in all directions . Fill a glass to the rim with water, then cover it with either wax paper or a piece of plastic or cardboard. Press down along the edges to make a tight seal, turn the glass upside down over a sink , and let go of the cover. It may take a few attempts, but it is possible to have the water supported without the water coming out. Note that: water has an approximate density of 1.00 g/mL, 1 atmosphere=760 mmHg or 101,325Pa (1Pa = 1N/m
2
), g=980 cm/s
2
(9.8 m/s
2
).
One Newton is the force required to accelerate a mass of one kilogram at a rate of one metre per second squared F = ma , m (kg) by a (m/s 2 ) . A column of the atmosphere one square centimeter in cross-section, at sea level, has a mass of about a kilogram and a weight (force) of about 9.8 N (9.8 kg m/ s
2
).
1. There are two forces acting on the index card; one pushes up and one pushes down (see the arrows in the above diagram). a. What is producing the force that is pushing down on the card? b. What is producing the force that is pushing up on the card? c. Which force is greater? How do you know?
2. Consider varying the size of the cup and amount of water it can hold. Use the info provided above to answer:
If the cup were 30 cm tall, would this still work? ______ What about 300 cm? ______ What about 3000 cm? _____
Repeat the process without filling the glass completely. Explain what happens.
Part 3.
Diffusion of gases - Demonstration.
Materials: Ammonia or very strong perfume or.. (2-isoButyl-3-methoxypyrazine...C9H14N2O is detectable at 0.002 ppb; Mercaptan / methanethiol is also detectable as low as 0.002 ppm but smells much worse).
7: Diffusion of gases. At the front of the classroom, we’ll open a bottle of with safe, odoriferous substance with high vapor pressure. Raise your hand as soon as the odor is detected.
What does this demonstrate about the motion of gas molecules?
8: Demonstration on diffusion rates of gases. We’ll place two small beakers (one containing ammonia, the other, water and phenolphthalein) under a large sealed plastic or glass container. Do not allow ammonia fumes to escape. Note: NH
4 g
+ H
2
O l
 
(NH3
+
) aq
+ (OH
-
) aq
, The OH
-
2

(hydroxyl) ions react with phenolphthalein. Placing the setup on an overhead projector makes it more visible, and the heat causes the diffusion to occur faster. We’ll perform a similar demonstration using hydrochloric acid and ammonia (to produce ammonium chloride – it’s a nifty reaction).
HCl g
+ NH
4
OH aq
 
NH
4
Cl s
+ H
2
O l a.
What do you observe in each experiment?
b.
One way to “clean-up” ground water contaminated by organic solvents like gasoline is to spray the water into the air then collect the runoff for reinjection. In hot arid areas, saline ground water can be sprayed into the air to separate the salt which precipitates out. We routinely use smokestacks to disperse combustion products. Comment on the fate of volatile chemical compounds from smokestacks.
Part 4. Air pressure, mass and motion. Is air heavy?
9: Different gases have different densities . Compare and contrast the behavior of equal-sized balloons filled with available gases such as natural gas from a burner jet which is mainly methane, “air”, or carbon dioxide by attempting to throw the balloons carefully . Which has the greatest and least mass?
Part 5.
To demonstrate Bernoulli’s Principle
and explain its relation to air pressure differences and what happens because of these differences (winds, storms, weather…)
Bernoulli's Principle says that the pressure decreases inside a stream of faster flowing air relative to slower-moving surrounding air. This explains lift, entrainment and how some pumps work.
10. Materials: Paper - Standard letter-size paper will work fine, though heavier paper stock like resume paper or construction paper will work better.
1. Fold the piece of paper in half. 2. Then place it on the very edge of a table, so that the paper “tunnel” points off the edge of the bench. 3. Blow a steady stream of air through the tunnel. Try to aim so you’re blowing down by the table surface, in the center of the paper. What happens? Draw this experiment and label the forces.
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11.
Rinse out two aluminum juice/pop cans of the same size: 1. Place the two empty cans lying down a few inches apart on a flat surface. 2. Blow air downwards between the two cans from directly above them and observe and draw or describe what happens. Try it with the two cans very close together.
12.
Cans: Set the cans up again as in step one and blow between the cans horizontally from the level of the flat surface. Observe, draw and label what happens. Explain the observation.
13. Bouncing Balloon in an airstream (lift in updrafts).
Equipment:
1.
Blow up a balloon and tie off the end.
2.
Hold the balloon out at arm’s length and let go of it. Does it stay there, or drop?
3.
Hold the balloon above your head at arm’s length, then blow hard up at it as you let go. Can you keep the balloon in the air?
4.
Hold the air dryer in one hand (use the cold air setting) and point it up toward the ceiling. Observe what happens when you let go of the balloon in the stream of moving air. Does the balloon fall to the ground or stay up? Why does this happen?
5.
Experiment further with the hair dryer. If you tilt the nozzle slowly a little to one side, does the balloon stay in the air stream? Can you bring the nozzle back to vertical and make the balloon follow? How far can you tilt the nozzle before the balloon falls? What causes the balloon to stay in the stream of moving air?
)
6.
Try placing a small ball in the air stream created by the hot air gun. If your hot air gun is powerful enough, the ball will float in the stream just like the balloon? Birds have much more hollow bones
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than you do, to reduce the mass that the lift of air has to carry in flight. Can you place both the balloon and the table tennis ball in the air stream at the same time? Which of the 2 objects must be placed on top for them to both remain floating? Why is this the case?
7. Would you expect to be able to keep the ball up using a rubber hose with air flow from taps on the bench? Try it and describe your results.
Part 6. Air compressibility
14. Match-head hydrometer in the Bottle
1. Obtain a tall empty bottle - such as a wine bottle, a tight fitting cork, and a paper match and some water.
2. Fill the bottle up with water up to the neck near the top.
3. Drop the match into the water. It ought to float vertically in a moment with the head pointing upwards. You may need long tweezers to get it to sit correctly. It might help to wet the match first.
4. Force the cork part way into the bottle. What happens? Move the cork in and out. See if you can even get the match to stop halfway down and rest in one place. Eventually the match will water-log and the sulfur top will start to disintegrate so don't push your luck on this one. Water does not compress much but the match has many very small air pockets. Why do you think the match sinks? Hydrometers are manufactured devices that float like this and are calibrated to measure the density of the liquids that they sit in. What kind of animals do you think take advantage of air compressibility?
2. Liquids
Here we will do some simple experiments on conduction and convection in liquids, using oil water, ice, salt, heat.
1.
Convection and Conduction of heat
Convection occurs in water, as we will see in later experiments, but firstly we show convection using oil which is more viscous (flows less readily than water). This slows it enough for better visualization.
Equipment: Hot plate, aluminum disc to distribute heat, frying pan, silicone oil or vegetable oil (or other low viscosity oil), aluminum flakes or iron filings or other particles to aid visibility.
1.
Pour a layer of oil, laced with aluminum flakes for visualization, into the fry pan.
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2.
Use the aluminum disc to more evenly distribute the heat.
3.
Turn the hot plate on to low or medium .
4.
Repeat, change layer depth by adding more fluid, or tilt the pan, to show that cell size is proportional to depth.
Draw and label what happens:
2.
Heat transfer in a fluid; directional effect
Now consider heat movement through a fluid. You already know from Lab 1 that the density of water varies with its heat content (temperature).
Equipment: Bright incandescent lamp, 250 ml beakers (without spouts), dark metal plates, alcohol thermometers, Thermometer clamp, ring stand, wire mesh
1.
Fill a 250mL beaker with water and place on the bench or base of the ring stand.
2.
Place the dark metal plate horizontally on top so that the plate is in contact with the water.
3.
Shine the lamp on the dark metal plate for several minutes (the plate is there to heat the water while preventing the light from heating the whole beaker.)
4.
Record the temperature at two depths (near the top and near the bottom) vs. time. Think about where the warmer water should be and comment on how this agrees with your data.
Depth (cm) Time (mins)
5.
Change the above experiment by heating the bottom of the beaker of water, shining the light from below with a dark material below the bottom of the beaker to absorb the light, and warm up the water from below only. Again measure temperatures in the beaker vs. time. Think about where the warmer water should be and comment on how this agrees with your data.
Depth (cm) Time (mins)
6. Explain the results and differences between 4 and 5 above in words or labeled sketches and interpret the directionality of heat transfer in fluids and how this might influence natural lakes, oceans.
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3. Simulation of global ocean thermohaline circulation.
The entire global ocean has a circulation that involves sinking at high latitude, and rising elsewhere.
This circulation, sometimes known as a ‘conveyor belt’, transfers energy, sediment and nutrients around the planet, and plays a major role in determining the distribution of ocean life.
A fundamental property of the ocean is the ‘layering’, with dense (cold or salty) waters at the bottom and buoyant (warm or fresh) waters at the top. This is a vertically stable pattern and it is difficult for water to move against this density difference.
In the experiment we want to observe the form of the ocean circulation when the water at the surface is made dense or less dense by cooling and heating or by ‘rainfall’ and evaporation.
Equipment: fish tank/ flume, tap water, crushed ice, stop watch, salt solution, food colouring, powdered clay, disposable pipettes, large ruler and lab tape.
Partially fill the tank as described below. One of the simplest ways to begin is to use a small amount of crushed ice to cool the surface of the water and observe the circulation that follows, using colored dyes, or small suspended, wetted clay particles in the water.
1.
Gently fill the tank or section of the flume with tap water to within about 5cm of the top.
2. Allow the water to stabilize and mark off the length & depth with numbered tabs of lab tape as a grid.
3.
Gently add ice to the surface only at one end , without initiating turbulence. Dropwise, add food colouring or droppers of pre-wetted clay slurry.
4. Use a stop watch to measure the rates of circulation (as well as internal wave motions, where regions of different density move as an internal wave front in a ‘silent surf.’)
5. Make a data table to record your data as times for motion/arrival of wave front.
Distance
Depth______
Depth______
Depth______
Depth______
Depth______
______ ______ ______ ______ ______ ______ ______ ______ ______
-Describe how the colouring or particles moved and interpret the reason(s) for the motion. It may help to contour the times in your table above.
5.
Distribute ice more evenly across the surface and observe the circulation (see question 11)
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6.
Remove any remaining ice.
7. Put saline water (made by dissolving 10 g of salt per 100 g of water) in a spray bottle.
Its density will be close to 10% greater than fresh water.
8.
Spray this water on the surface of the tank near one end, and use dyes to qualitatively trace the circulation that develops.
-Is this circulation similar to that developed with the ice? Describe or draw and interpret this flow.
Please be careful not to spray the salt water anywhere but in the tank, and wipe up salt
crystals which appear elsewhere.
9.
Note the vertical motion of the fluid, comparing and contrasting the sinking regions with the regions of rising water. This is an appropriate model of the global ocean thermohaline circulation, and its form largely controls where the biological communities in the world’s oceans can exist.
- The addition of salt water simulates evaporation at the sea surface as evaporation removes water only and leaves salt behind (consider the opposite effect of fresh buoyant rainfall or runoff on the surface salinity). How can these salinity/density inputs at the top of the ocean drive or otherwise influence deepocean circulation?
10.
Examine and describe or draw and label the competing effects of heat and salt on the ocean circulation.
11.
The observation that the oceans are cooled at one end of the ‘tank’ is of great importance. Observe the character of the circulation when the crushed ice is uniformly distributed along the surface.
12.
Compare this with circulation which develops by placing all of the ice near one end of the tank.
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