Experiment 2 Acquaintance with Matter Safety Instructions
For your safety you need to take the following precautions: Use your safety glasses throughout the entire experiment. Use safety gloves while handling chemicals. It is recommended to use laboratory robes to protect your clothes. Do not use materials that are not listed in the procedure of the experiment. Read each part of the experiment from beginning to end before starting to perform the experiment.
I.
The Wonders of Matter
Introduction
States of matter in general are solid, liquid and gas. Gases occupy the volume and take the shape of the container in which it exists. Gas density is very low compared with the same quantity of liquid or solid at 25oC and 1atm pressure. Liquids take the shape of the container but cannot expand to fill it. Solids have definite shapes; for most materials, their solid state is more dense than their liquid state (water is exceptional). The parameter that is responsible for the state of matter is the physical interaction between its particles. Weak physical interaction is present in gases, while the strongest physical interactions are present in solids. A substance can change its state; this change is a physical change. Liquid can be converted into solids by cooling (freezing). Solids convert to liquid by heating (melting). Liquid converts to gas by heating (evaporation). Gas converts to liquid by cooling (condensation). Solids may convert to gas without passing through the liquid state (sublimation). For example: heat
I2(s)
I2(g)
Certain materials are used for cooling, such as N2 liquid, which can be isolated from air through fractional distillation by cooling and applying pressure. The following table gives the boiling points of some gases:
Gas CO2
M wt [g/mol] 44
Boiling Point [C] -78.5 [sublimation]
Xe Kr O2 Ar N2 He
131.1 83.8 32 39.9 28 4
-108 -153 -183 -186 -196 -269
Nitrogen is an inert substance [N≡N] because of the triple bond; it takes a lot of energy to break it. Solid CO2 also can be used for cooling. CO2(s) is called dry ice; "dry" because when it is heated it converts to gas without passing trough the liquid state and "ice" because it is very cool. Evaporation is not the same as boiling. Evaporation is the process in which liquid converts to gas and this can occur at any temperature. Different factors affecting evaporation, which include: temperature, surface area of liquid, continuous shaking of liquid, continuous removal of vapors and the surrounding pressure. Boiling point is the temperature at which the vapor pressure equals atmospheric pressure. At the boiling point the whole liquid has enough energy to become a gas. The boiling point depends on: 1. The type of intermolecular forces between the particles of the substance; the stronger the intermolecular forces are, the higher is the boiling point. 2. The surrounding pressure; as pressure increases, the boiling point also increases.
Pure substance boils at constant temperature at a given pressure, so boiling point is a physical constant from which we can identify a certain liquid. We can know that a liquid substance reaches its boiling point when we see a rapid and continuous stream
of bubbles emerging from the body of the liquid. Boiling point can be determined by different methods: By distillation. By the micro boiling point method, in which a glass capillary is used.
1)
A
Teacher's
Demonstration
with
Liquid
Nitrogen
In front of you is a beaker containing a liquid. Observe the liquid. 1. Do you think that the temperature inside the beaker is higher or lower then the room temperature? Explain.
The beaker contains liquid nitrogen. 2. Write in a scientific way the contents of the beaker 3. 4. What do you think will happen if we place inside the beaker
A Balloon filled with oxygen gas?
A balloon filled with CO2 gas?
A balloon filled with helium gas?
5. Observe the teacher's demonstration 6. Write down your observations.
7. Were your hypotheses confirmed?
8. Try to give explanations for the phenomena you have observed. You can use the following table to help you: The Material Nitrogen Oxygen CO2 Helium Boiling point in ºC - 198 - 183 -78* - 269 * Temperature of Sublimation - 270 Freezing point in ºC - 210 - 220
9. Observe the teacher's demonstration. Write your observations using clear scientific language: a. What happens to the egg which was "fried" in liquid nitrogen?
b. How does the egg look after half an hour?
c. What happens to a rubber ball when put in liquid nitrogen?
d. What happens to a chewing gum when put in liquid nitrogen?
e. What happens to a plant when put in liquid nitrogen?
f. What happens to a banana when put in liquid nitrogen?
g. What happens to a rubber tube when put in liquid nitrogen?
2) Acquaintance with Dry Ice
Materials & Equipments:
Washing bottle Dry ice Graduated cylinder 50 mL 300 mL graduated cylinders containing NaOH 0.1M + phenolphthalein 300 mL graduated cylinders containing NaOH 0.1M + methyl orange 300 mL graduated cylinders containing NaOH 0.1M + universal indicator 3 erlenmeyer flasks 50 mL
Experimental procedure
BEWARE: Put your safety glasses on, and do not touch the dry ice with your fingers or you can get burned.
In front of you is dry ice in a polystyrene cup. 1. Fill a 200 mL beaker with 100 ml of water. Use a teaspoon to transfer a small piece of dry ice into the water. a. What happens? (Observe what happens in the surroundings of the dry ice, and the water surface) Write your observations using clear scientific language.
b. Try to explain what happens (use terms such as sublimation, freezing, condensation, evaporation)
2. What do you think will happen if you will add dry ice to hot water?
3. Add dry ice to a beaker containing hot water c. Was your hypothesis confirmed? d. Try to explain what happens.
4. Place a lit candle near the beaker. e. What happens? f. Try to explain what happens.
5. Pour 30 ml water into the graduated cylinder. Add 10 drops of soap water and 10 drops of liquid paint. Put a small piece of dry ice into the graduated cylinder. g. What happens?
h. Try to explain what happens.
6. Place a white page on top of the graduated cylinder. i. What happens?
j. Try to explain what happens.
3) A Teacher's Demonstration with Dry Ice
The teacher will put a small piece of dry ice inside a washing bottle containing water and place it near the graduated cylinder. Observe what happens. a. What happens?
b. Try to explain what happens.
1. The teacher will put a piece of dry ice inside each of the 3 graduated cylinders containing colored solutions. What happens?
Explanations for those phenomena require further chemistry studies. 2. The teacher will prepare some tasty ice cream. Watch the procedure and explain: Why is the ice cream so soft and smooth and not hard and solid like a popsicle?
3. Write at least 3 properties of dry ice that you have discovered today. Try to find some creative use for dry ice.
II. Determining the Boiling Point of a Liquid
Materials: Ethanol Acetone Very hot Water (nearly boiling) Equipments: Pasteur pipets Glass capillary Matches Rubber band Thermometer 100 mL beaker Wooden clip Metal cutter for the glass For the alcohol burner: small bottle (1-10 ml), filtering paper (2 cm x 4 cm)
Preparations of tools: 1) Preparing the alcohol burner Roll the paper into a graduated cylinder to form a thread. Pour alcohol into the small bottle and put the thread inside such that 1 cm of it is left out. Wait 2 minutes for the thread to soak the alcohol and light the burner. If the procedure does not work the first time, try it again.
2) Preparing a small test tube Use the burner you prepared to warm the thin side of a Pasteur pipette. Move it in the flame in a cyclical motion. When the pipette starts to soften – stretch it and take away the thin part. Keep stirring the wider side in the flame until it closes. You have just created a small test tube. Let it cool. BEWARE: The glass is very hot. Do not touch it with your fingers.
3) Preparing a capillary tube Take the glass capillary and close it in the flame. Break the capillary 1 cm from the edge, using a metal cutter. 4) Determining the boiling point a. b. c. d. e. f. g. Put the capillary you prepared inside the small test tube, open end down. Use a dropper to add 0.5 mL of ethanol to the small test tube. Use a rubber band to connect the thermometer to the test tube. Hold the pair with a wooden clip. Place the pair inside a 100 mL beaker containing hot water. Let the system cool. Watch the bubbles going out from the capillary until they stop and the capillary suddenly is filled with liquid: This is the boiling point. h. i. j. The condensation temperature of ethanol is: Repeat the process again with acetone. The condensation temperature of acetone is:
Please answer the following questions: 1. Explain why the temperature measured is the condensation temperature.
2.
How does the boiling point relate to the condensation point?