CHANGES

Engage

Investigate: Steam and Ice

  1. Observe the setup of the apparatus at your table. Discuss your observations with your group.
  2. Discuss the following questions in your group and record in your journal
  • Describe your observations.
  • What is a reasonable explanation for your observations?
  • What are the similarities and differences between evaporation and boiling?
  • What are the similarities and differences between freezing and melting?
  • What is the relation between boiling temperature and condensation temperature?
  • What kind of change did you observe? How do you know?

Explore/Explain 1

Investigate: Changes in a Bag

Part A

Safety

Study the MSDS for the chemicals used in Part A. Discuss safety precautions that must be used and list them in your journal.

Procedure

  1. Place 1.0 g of sodium bicarbonate into one corner of a plastic bag.
  2. Place 1.5 g of calcium chloride into the other corner of the same bag.
  3. Fill two disposable pipettes with water and place them in the plastic bag. Seal the plastic bag.
  4. Observe the contents of the bag and record observations in your journal in a table like the one pictured below:

Before addition of water / After addition of water
Sodium bicarbonate description
Calcium chloride description
Water description
Mass of system
  1. Carefully place the sealed bag in a plastic cup. Place the cup with its contents on a balance. Measure the mass of the system and record this mass in the table.
  2. Lift the bag and, from the outside, gently squeeze the pipettes inside the closed bag. Spill the water into the sealed bag and place the bag onto a tabletop. Mix the substances in the bag by squeezing gently.
  3. Observe all changes inside the plastic bag and write down your observations in the table.
  4. Place the sealed bag in the same plastic cup and measure the mass of the system once again and record the mass.
  5. Clean up by disposing of the sealed bag in the trash.
  6. Proceed to Part B of the investigation.

Part B

Safety

Study the MSDS for the chemicals used in Part B. Discuss safety precautions that must be used and list them in your journal.

Procedure

  1. Place 1.0 g of sodium bicarbonate into one corner of a plastic bag.
  2. Place 1.0 g of citric acid into the other corner of the same bag.
  3. Fill two disposable pipettes with water, place them in the plastic bag, and seal it.
  4. Carefully place the sealed bag in a plastic cup. Place the cup with its contents on a balance, measure the mass of the system and record in your journal in a table like the one below:

Before addition of water / After addition of water
Sodium bicarbonate description
Citric acid description
Water description
Mass of system
  1. Lift the bag and, from the outside, gently squeeze the pipettes inside the closed bag. Spill the water into the sealed bag and place the bag onto a tabletop. Mix the substances in the bag by squeezing gently.
  2. Observe all changes inside the plastic bag and write down your observations in the table.
  3. Place the sealed bag in the same plastic cup and measure the mass of the system once again and record the mass.
  4. Clean up by disposing of the sealed bag in the trash.
  5. Discuss the questions in your group. Make section labeled analysis in your journal and record your responses.

Analysis and Conclusions: Parts A and B

  1. Was the change in Part A a physical or chemical change? How do you know?
  2. Was the change in Part B a physical or chemical change? How do you know?
  3. Define physical change and chemical change in your own words.
  4. What are some indicators of a chemical change?
  5. Were the changes endothermic or exothermic? How can you tell?
  6. How did the mass before mixing of the contents in the bag compare with the mass after mixing?

Application: Physical and Chemical Changes

  1. In your journal, identify the following changes in each scenario described below as physical or chemical and endothermic or exothermic. Give reasons for your identification.
  1. When two clear colorless liquids are mixed, a yellow precipitate forms and settles to the bottom of the test tube. There is no significant change in temperature.
  2. When two clear colorless liquids are mixed, gas bubbles escape out of the test tube. There is no significant change in temperature.
  3. When two clear colorless liquids are mixed, a clear colorless liquid is formed. There is a decrease in temperature.
  4. When two clear colorless liquids are mixed, a clear pink solution forms. There is no significant change in temperature.
  5. A warm, clear liquid changes to a clear crystalline solid at room temperature.
  1. In which type of change is mass conserved?
  2. Describe a situation when observations may indicate that mass is not conserved in the change. (diagrams allowed)

Explore/Explain 2

Investigate: Phase Change

Safety

Study the procedure that you will follow. Discuss safety precautions that must be used and list them in your journal.

Procedure

  1. Place 4-5 ice cubes (less than 100 g) in a 250 ml beaker.
  2. Connect the graphing calculator (TI-84) to CBL 2 using the link.
  3. Insert the temperature probe into Channel 1.
  4. Select the Easy Data® program from APPS for data collection.
  5. Complete setup of the calculator program for data collection as instructed by your teacher.
  6. Place the temperature probe in the ice-water mixture.
  7. Place the beaker with the ice-water mixture and thermometeron a hot plate.
  8. Turn on the hot plate and begin stirring with the temperature probe.
  9. Stir continuously recording the temperature every 30 seconds until the water is boiling and the temperature does not change over a 2 minute period.
  10. Identify the independent and dependent variables, then make graph using 30 second intervals for time.

Analysis and Conclusions

Make an Analysis section in your journal and answer the following:

  1. In your investigation, what was the independent and dependent variables?
  2. How does the temperature of the ice-water mixture vary as it is continually heated?
  3. What do the different sections of the graph represent?
  4. From your graph, identify the melting temperature of ice and the boiling temperature of water.
  5. Predict the shape of the graph if you cooled steam continually to change it to ice. Draw the predicted shape of the graph in your journal. Identify the condensation temperature and the freezing temperature on the graph.
  6. Why do you think the temperature stayed constant as the ice melted into water?
  7. Why do you think the temperature stayed constant as the water boiled?
  8. What is the difference between evaporation and boiling?

Change / Physical or chemical / Endothermic or exothermic / Reason
Melting
Freezing
Boiling
Condensation
Evaporation
  1. Classify the following changes as physical or chemical and endothermic or exothermic and give reasons for your classification.

Application: Phase Change

Two students conduct phase change experiments for a certain chemical using a graphing calculator and probes. One student works on the heating curve of the solid while the other student works on the heating curve of the solid while the other student works on the cooling curve of the liquid. Both students decide to take temperature readings in Celsius every minute for 15 minutes. The two sets of graphs obtained by the students are shown below.

  1. What is the independent variable in the experiment? What is the dependent variable?
  2. Which set of graphs represents the heating of the solid? Which set of graphs represent the cooling of a liquid? How do you know?
  3. Color or mark the melting point and the freezing point on the respective graphs. What are the melting temperature and the freezing temperature of the substance?

Elaborate

Investigate: Changes

Safety

Conduct the following investigations with attention to chemical and laboratory safety. Assume that the chemicals used in the investigations are toxic and corrosive. List the safety precautions in your journal.

Procedure

Create the table below in your journal (leave off the directions). Add one substance to another as directed in the table. Observe carefully and record your observations. Classify the changes as physical or chemical and state your reasons for the classification. Be prepared to discuss your observations, analyses, and conclusions with the class.

Investigation / Observation / Physical/Chemical How do you know? / Exothermic/Endothermic How do you know?
1 / Place about 2 ml of Liquid B in a test tube. Add a very small amount of Solid A to Liquid B
2 / Place about 2 ml of Liquid C in a test tube. Add a few drops of Liquid D to Liquid C.
3 / Place about 2 ml of water in a test tube. Add a pea-sized scoop of Solid E to the water in the test tube.
4 / Fill a small beaker half-full with water. Obtain Liquid F from instructor. (Caution: This liquid may be hot.) Carefully pour the hot Liquid F into the water in the beaker.
5 / Place about 2 mLs of Liquid G in a test tube. Add an equal amount of H to the test tube.

Analysis and Conclusions

Make an Analysis section in your journal and answer the following:

  1. In which investigation is mass conserved?
  2. In which investigation would you expect to observe a reduction in mass? Why?

Evaluate

A student’s experimental procedure and observations are diagrammed below. Study diagrams A through F and answer the questions below in your journal.

  1. If there was a change, was it a physical change or chemical change? Explain.
  2. Was the process endothermic or exothermic? Explain.
  3. Was mass conserved in this process? Explain.

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