Unit 8 Lesson 5: Electrical Bonding Investigation Evidence
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temperature
a measure of the average kinetic energy of the particles of a substance
boiling point
temperature at which a substance changes state from a liquid to a gas
trial
one of a number of attempts of a repeated procedure
There are different ways to investigate the electrostatic forces between molecules in a substance.
Both the melting point and boiling point are indications of the strength of these forces, as are the surface tension and vapor pressure of substances.
To conduct an investigation to measure these properties, you need to make sure you have a sound experimental design. Things to consider include:
• Determining what data to collect • Deciding how many trials to perform • Determining the procedure • Collecting the appropriate experimental equipment
What factors must be considered when designing an investigation?
Determine what data to collect, decide how many trials to perform, develop a procedure, and collect the appropriate materials and equipment.
Why is measuring the melting point of ice easier than measuring the freezing point?
The melting point can be measured by melting water ice in a pool of water, which can be done in a room-temperature environment. Determining the freezing point requires that water be cooled down to freezing in some way, and also requires care that it does not become supercooled.
Design an investigation to measure the boiling point of water compared to that of ethanol. Describe the data to collect, equipment needed, and procedures to follow.
Using a glass beaker, water and ethanol, a thermometer, and a heat source, such as a Bunsen burner, measure the temperature of each liquid as it is heated to boiling. Record the boiling temperatures. Repeat 3–4 times and take the average of the measurements. Additional equipment that may be needed includes tongs for holding hot beakers, hot pads, and a source of fuel for the burner.
Design an experiment for determining the surface tension of water compared to ethanol. Describe what data you will collect, what equipment you need, and what procedure you will follow.
Place equal samples of each liquid in identical containers with large openings on the top. Place successively heavier materials on the surfaces of each liquid and determine whether the surface tension is able to hold the material. Examples of materials may include hair, tissue paper, feathers, or paperclips.
Published boiling points are generally given at standard atmospheric pressure, which is
1 atm (=1 bar) .
What does it mean to boiling points if atmospheric pressure is lower than at sea level
If atmospheric pressure is lower than that at sea level, such as occurs at higher elevations, boiling points are lower.
What happens if we extend this to the extremes? Suppose you place a glass of room temperature water in a vacuum chamber and slowly remove the air, reducing the pressure. What will happen
Once the pressure is low enough, it is possible for water to boil, even at room temperature!
Now suppose you bring that glass of water out into the vacuum of space.
Not only is space a nearly perfect vacuum (0 pressure), but it is also extremely cold (approximately −270°C ).
Now suppose you bring that glass of water out into the vacuum of space. Will water boil due to the extremely low pressure, or will it freeze due to the extremely low temperature?
It turns out that it does both. It takes time for water to freeze, even in the coldest of environments. It is not an instantaneous process. So, for a brief moment, this water will indeed boil before quickly freezing into diffuse ice crystals. (Fun fact: This has been verified by astronauts who have observed this phenomenon when discharging their urine into space.)
Describe how atmospheric pressure can affect experimental results of boiling point measurements.
If the atmospheric pressure is higher than standard, the boiling temperature is also higher. If the pressure is lower than standard, the boiling temperature is lower.
Describe the role of vapor pressure in the boiling of a liquid.
A liquid boils when the vapor pressure equals the atmospheric pressure.
Describe how you would conduct an investigation using a vacuum chamber to determine the effect of air pressure on the boiling point of a given liquid.
By using a vacuum chamber and setting up an experiment to measure boiling temperature, you can vary the pressure and measure the boiling temperature each time. This requires having a means to heat the liquid when it is in the vacuum chamber. An electric heat source is probably best. Data that should be taken include boiling temperatures for different pressures. Multiple trials should be conducted and the values averaged.
It is possible to supercool liquids, which means their temperature can be below the freezing point before they form ice crystals. It is also possible to superheat liquids, which means to raise their temperature above the boiling point before they boil. Either can happen if the water is free of impurities and left undisturbed while undergoing a temperature change, or in the case of supercooling, if the temperature change occurs so rapidly that the formation of ice crystals does not have time to occur. Supercooled water can then be made to freeze instantly upon disturbing it, and superheated water can be made to instantly boil upon being disturbed. How likely do you think it is that supercooling or superheating of a liquid during an investigation to measure the freezing or boiling point would occur and affect the results? Explain your reasoning.
Since it is unlikely that the liquid is super pure or undisturbed during such an investigation, it is unlikely that supercooling or superheating would occur. However, it is more likely that the temperature could be lowered too quickly when measuring freezing temperature, and supercooling could occur. This can interfere with results.