Lab #1.1 Water: Particle Model to Explain Water as a Solid, Liquid and Gas
Purpose: To visualize a particle model to differentiate between solids, liquids and gases.
HOLT Textbook Reference- chapter 1-1 page 6-7
KOTZ Chapter 1.5 and 6.1 - 6.3 and 13.1 - 13.5
Procedures:
A. Use the closed-end syringes to compress both water and air. Record your observations. Remember this from IPS
B. Compare the behavior of solids, liquids and gases when placed in a new container.
C. Observe the behavior of water drops on wax paper. Focus on their shape and behavior when dragged near another drop.
Analysis:
1. Compare and contrast the spacing of particles in solids, liquids and gases. Use your observations of compression to support your position.
2. Compare and contrast the freedom of movement of particles in solids, liquids and gases. Use your observations of pouring, shape, and objects passing through it to support your position.
3. Describe the modes of kinetic energy in solids compared to liquids and gases.
4. a. Describe the interaction of charges that result in attractions due to electrical force.
b. Describe the interactions that result in repulsion.
c. What two factors affect the magnitude of electrical force between two charges?
5. A Water Molecule.
a. Describe the oxygen and hydrogen atoms in a water molecule. Include number of protons and electrons.
b. Which atom pulls harder on electrons? Explain your reasoning.
c. Describe the covalent bond that holds together the hydrogen and oxygen atoms in a water molecule. How are the electrons shared? How does this explain the polarity of the molecule: the oppositely-charged ends?
6. Write a CLE paragraph to support the claim of water to water particle attraction. Describe at least three pieces of evidence. Remember IPS- water drops.
7. Describe the dipole-dipole attraction (hydrogen bonding) that accounts for the observed water to water particle attraction.
8. Think about changing phases- ICE MELTS:
a. When solid water (ice) melts to become a liquid, what happens to the molecules of water? What bonds were broken? What bonds were not broken?
b. ENTHALPY- Describe the direction of energy transfer. Is this reaction endothermic or exothermic? Did enthalpy (energy contents) increase or decrease? Draw an energy graph to represent the change.
c. ENTROPY- What happened to the disorder (entropy)- increase or decrease? Explain.
d. When the process is reversed, (freeezing) how does the enthalpy and entropy change?
9.Think about changing phases- WATER BOILS:
a. When liquid water boils to become a gas, what happens to the particles? Write an equation to show the change. What bonds were broken? What bonds were not broken?
b. ENTHALPY- Describe the direction of energy transfer. Is this reaction endothermic or exothermic? Did enthalpy (energy contents) increase or decrease? Draw an energy graph to represent the change.
c. ENTROPY- What happened to the disorder (entropy)- increase or decrease? Explain.
d. When the process is reversed, (condensation) how does the enthalpy and entropy change?
Lab #1.2 Water: Adding Heat Energy to Solid Water
Purpose: To use the particle model to explain phase change (liquids and solids) and energy transfers. To experimentally measure the heat of fusion of water.
Procedures: A measured quantity of ice will be melted in bag in a Styrofoam cup with 100 mL of warm water. The heat absorbed from the water by the melting ice will be measured and calculated. The heat of fusion will be calculated as Joules per gram to melt solid to liquid.
Construct two tables to record both measured and calculated values.
MEASURED VALUES: Construct a Data Table for Measured Values.
A. Measure and record the mass of an empty bag and empty Styrofoam cup.
B. Measure 100 mL of hot water. Pour into the Styrofoam cup.
Measure and record the mass of the cup with hot water.
C. The following must be done quickly by cooperating with your lab partner.
- Fill the empty bag with a handful of ice.
- Measure and record the temperature of the hot water immediately before adding the ice.
- Quickly place the bag with the ice into the cup of hot water.
D. Allow the ice to completely melt. Measure and record the final temperature of the water in the cup as soon as the ice has melted.
E. Measure and record the mass of cup, water and the bag after melting.
CALCULATED VALUES: Construct a Table for Calculated Values.
F. Calculate the mass of the hot water, the mass of the ice, and the change in temperature of the hot water. Express your calculation to appropriate number of significant digits.
G. Calculate the total heat transferred from the hot water to the ice in the bag in Joules. Remember heat transfer can be calculated using the equation q= mC∆T. Specific Heat (Cp) for water is 4.18J/g˚C. Express your calculation to the appropriate number of significant digits.
H. Calculate the calories absorbed per gram of ice. Calculate the Joules/gram of ice. Express your calculation to appropriate number of significant digits.
I. Report your measured value for the heat of fusion. Copy the class data set.
Analysis:
1. Precision. Precision is a measure of the reliability or reproducibility of the measurement.
a. What is the range of data for the class sample?
b. Calculate the average of the class data set.
c. How close are the measurements to the average? Do the results appear to be precise?
d. Give an example of a team’s data set that was very precise and one that was not precise.
2. Accuracy. Accuracy is a measure of degree of error compared to an established value.
a. Calculate the percent error of your measured heat of fusion.
The accepted value for the heat of fusion of water is 334 Joules/gram.
b. Calculate the percent error for the class average.
c. Which results are more accurate? Justify your selection.
3. Exactness. Exactness reflects the number of digits actually measured.
a. How many digits did you measure for the masses?
b. How many digits did you measure for the volume of water?
How is your mass measurement for the water more exact than the volume measurement?
c. How many digits did you measure to determine the temperature?
d. How many significant digits should be reported in calculated value of the mass of the ice, mass of hot water, temperature change of the hot water, and heat?
4. Temperature.
a. Define temperature.
b. When the temperature increases, what happens to the speed and kinetic energy of the particles?
c. The temperature of the hot water (the surroundings) outside the ice (the system) decreased. What does this tell you about the kinetic energy of the water molecules in the hot water? What does it tell you about the direction of the energy transfer?
d. While the ice melts, the temperature of the ice remains at 0˚C. What does this indicate about the water molecules?
5. Energy Transfers. Energy transfers lead to a change in the internal energy of the system. Energy may be transferred in the form of heat.
Heat is the transfer of energy from hot to cold.
a. Compare the particles of the hot and cold areas. Include motion and kinetic energy.
b. The energy transfer may lead to a change in either kinetic energy or potential energy. Compare both forms of energy. What parameter is changed?
6. Visualizing and Explaining the Change and Energy.
Sketch the ice in the bag within the styrofoam cup. Label the system and the surroundings.
Draw an arrow to show the energy transfer.
a. Explain the change in temperature of the hot water in the cup. What happened tot eh kinetic energy of the water in the cup. Which way was energy transferred? (into the system from the surroundings or the out of the system to the surroundings)
b. Use your direction of heat transfer to explain whether the energy content (enthalpy) of the system increased or decreased.
c. When the ice melts, is the process endothermic or exothermic?
d. Sketch an energy graph to show the change in energy.
e. Based upon the change in energy is the product (liquid water) more or less stable? Explain.
c. Is this favored based upon enthalpy?
d. Based upon enthalpy alone, would you expect ice to melt when left on the kitchen counter? Explain. Include entropy in your description to explain why it melts.
Additional Procedures- An additional sample of a liquid/solid phase change
- Obtain a liquid-filled plastic pack.
- When your team is ready to make observations of the changes, bend the metal disc within the pack.
- Record observations of the changes that occur.
- After you have completed your observations, carefully place the pack in the hot water.
Additional Analysis:
- Liquid to Solid Phase Change
- Describe the change at the particle level.
- Describe the direction of energy transfer. Define the system and surroundings in your description.
- Did the internal energy of the system increase or decrease? Explain your reasoning.
- Is the reaction favored based upon enthalpy? Justify your answer with stability.
- What happened to the entropy? Justify your answer by describing the particle changes.
- Explain what happens to the pack in the boiling water. Include a description of the particle changes and the energy transfer.
Lab #1.3 Water:Adding Heat Energy to Liquid Water
Purpose: To use the particle model to explain phase change (liquids and gases) and energy transfers.
Procedure:
Sketch the set-up for the distillation of water. Record your observations.
Record the temperature changes that occur.
Describe the energy transfers occurring on both sides. Include observational evidence.
Visualize.
How are these observed energy transfers related to changes in water molecules you cannot see?
Analysis:
1. BOILING WATER- VAPORIZATION. Write the equation.
a. Before the water boils, what happens to the temperature of the liquid water as heat is added? How does the transfer of heat into the flask from the surroundings affect the particles? Do the particles gain kinetic energy or potential energy? Justify your answer.
b. The temperature of the boiling water stays constant at 100˚C, even though heat is still being transferred into the flask. Are the particles moving any faster as a result? Explain your thinking. How does the transfer of heat into the flask from the surroundings affect the particles? Do the particles have more kinetic or potential energy as a result of the added heat? Justify your answer.
c. After heating the boiling water, what is the gaseous product? What has happened to the water molecules? What attractions broke? What attractions did not break? (Hint: Do you still have water molecules?)
d. Sketch the water molecules in the liquid to show the spacing of the particles.
Sketch the water molecules in the gas to show their spacing.
Label the force that acts between the molecules.
Label the force that acts between the atoms within the water molecules.
Label the particle arrangement with more potential energy and with less potential energy.
Include a label to show when they have more PE.
e. Enthalpy. Explain whether the boiling reaction is endothermic or exothermic. Explain in terms of energy transfer, systems and surroundings. What happens to the energy content of the system? When is there more potential energy? Explain why. Construct an energy graph to show the relative energy levels of the liquid and gaseous water and the energy change. Based upon the change in enthalpy is this reaction favored to occur in this direction?
f. Entropy. Explain whether entropy increases or decreases in this reaction. Based upon the change in entropy, is this reaction favored to occur in this direction?
2. CONDENSATION. Write the equation.
a. When the water condenses, what happens to the molecules of water? Compare the change at the particle level to the stretch and release of a spring. Include potential energy and kinetic energy in your description.
b. The water condensed in the flask, the system, placed in an ice bath, the surroundings. Over time the ice outside the flask, the surroundings, melted and the temperature of the melt water increased. What does this suggest about the energy transfer- from the system out to surroundings or from surroundings into the system? Justify your answer.
c. In order to boil water, 2257 Joules (540 calories) of heat must be absorbed per gram of water. Is energy absorbed or released in the condensation of 1 gram of water. Explain your reasoning. How much energy? Is condensation an endothermic or exothermic process?
d. Based upon the change in entropy, is this reaction favored to occur in this direction? Explain.
3. PHASE CHANGE DIAGRAM.
Draw a phase change diagram to show the effect of temperature on water from a solid to gas- with temperature on the y-axis and added heat on the x- axis. Label the heat of fusion, heat of vaporization, solid, liquid and gas.
a. Explain the areas of the graph that show where adding heat leads to an increase in temperature.
How does the transfer of energy as heat affect the particles?
b. Explain the areas of the graph that show where adding heat does not change the temperature.
Explain why the transfer of heat does not increase the temperature?
What is happening to the particles?
4. EVAPORATION. Describe evaporation at room temperature. Which particles tend to escape? Explain your thinking. What happens to the temperature as a result?
5. BOILING VS EVAPORATION. Compare and contrast boiling and evaporation. Where do they occur in the water? At what temperature do they occur?
Procedures: Second Demonstration.
Record observations of the boiling water in the inverted flask.
6. BOILING AND VAPOR PRESSURE.
a. How is boiling related to vapor pressure? Address the formation of bubbles.
b. Explain why the vapor pressure of a liquid increases as temperature increases. Include KE and attractions in your explanation.
c. Describe the relationship between the boiling point and temperature, vapor pressure, and the external pressure?
d. Why did the water in the flask boil when ice was placed on the inverted flask?
7. VAPOR PRESSURE EQUILIBRIUM occurs in closed container.
A reversible reaction in a closed system will eventually reach equilibrium.
a. When the container is first closed, describe vaporization at the particle-level. Write an equation for this reaction. What happens to number of water molecules in the air above the liquid as vaporization continues?
b. As the number of water molecules in the air above increases, describe the reverse reaction that is also occurring. Write an equation for this reverse reaction.
c. As the number of water molecules in the air above the liquid increases,
What happens to the rate of the reverse reaction (condensation: gas liquid)?
What happens to the rate of the forward reaction (vaporization: liquid gas)?
d. Eventually the forward reaction occurs at a rate equal to the rate of the reverse. Describe this state of equilibrium. Write a reversible equilibrium equation to show the equilibrium. What happens to the number of water molecules in the air above the liquid when the system is at equilibrium? How is this state related to the rates of the two reactions?
e. If the system in a closed container at equilibrium is left undisturbed, it will remain at equilibrium. If the temperature changes the equilibrium will be disturbed. If the temperature of the liquid increases, what happens to the water molecules in the liquid? What will happen to the number of water molecules above the liquid? How is this related to the relative rates (Which reaction is temporarily faster?) How does this show that the system is no longer at equilibrium?
f. Are vapor pressure and temperature directly or inversely related? Explain why using your definition of temperature and vapor pressure.
g. Boiling occurs when the vapor pressure of the liquid is equal to the external atmospheric pressure. The vapor pressure of the particles in the bubbles is equal to external pressure, thus bubbles form and maintain their shape until they rise to the surface. If the atmospheric pressure is lower (like at high altitudes), will the water boil at a lower or higher temperature? Explain your reasoning.
Lab #1.4 Water:Adding Electrical Energy to Liquid Water
Purpose: To observe and explain the decomposition and synthesis of water
Procedures:
A. Add electrical energy to water.
Sketch the electrolysis set-up. Label the positive and negative terminals.
Record the volume of both gases, as well as observations of the reaction.
B. Capture and identify the products. Record your observations.
Analysis:
1. After the electrolysis of water do you have the same substance- water molecules?
Clearly support your answer with evidence from the lab.
2. Write a balanced equation to summarize the reaction.
3. Explain why this is a chemical reaction and the boiling of water is a physical change.
4. How is the electrolysis or decomposition of water observed in this part of the lab different from the boiling of water? What happened to the water molecule in each reaction? What bonds or attractions broke in each reaction?
5. Complete an analysis of the reaction to describe the changes that occur in the reaction.
a. Describe the water molecule – the reactant.
Describe the polar covalent bond and how the electrons are shared.
b. Describe the molecules in the products. Describe the nonpolar covalent bonds.
c. What bonds were broken and formed? What happened to oxygen’s share of electrons? What happened to hydrogen’s share electrons?