CHEMISTRY:
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Engage
Investigate: Steam and Ice
1. Observe the setup of the apparatus at your lab table. Discuss your observations with your group.
2. Discuss the following questions in your group and record in the space below.
• Describe your observations.
• What is a reasonable explanation for your observation?
• 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?
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Explore/Explain 1
Investigate: Changes in a Bag Part ASafety
Study the MSDS for the chemicals used in Part A. Discuss safety precautions that must be used and list them in the space below.
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 the table below.
5. 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 below.
6. 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. 7. Observe all changes inside the plastic bag. Write down your
observations.
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Observations
Before addition of water After addition of water
Sodium bicarbonate description
Calcium chloride description
Water description
Mass of system
Part B
Safety
Study the MSDS for the chemicals used in Part B. Discuss safety precautions that must be used and list them in the space below.
11. Place 1.0 g of sodium bicarbonate into one corner of a plastic bag. 12. Place 1.0 g of citric acid into the other corner of the same bag. 13. Fill two disposable pipettes with water and place them in the plastic
bag. Seal the bag.
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15. 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. 16. Observe all changes inside the plastic bag. Write down your
observations.
17. Place the sealed bag in the same plastic cup and measure the mass of the system once again. Record this mass.
18. Clean up by disposing of the sealed plastic bag.
19. Discuss the questions in your group and record responses in the analysis section.
Observations
Before addition of water After addition of water
Sodium bicarbonate description
Citric acid description
Water description
Mass of system
Analysis and Conclusions: Parts A and B
1. Was the change in Part A a physical or chemical change? How do you know?
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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?
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Application: Physical and Chemical Changes
1. Identify the change in each scenario described below as physical or chemical andendothermic or exothermic. Give reasons for your identification.
Scenario Physical or Chemical Endothermic or Exothermic
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 an increase 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
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2. In which type of change is mass conserved?
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Explore/Explain 2
Investigate: Phase ChangeSafety
Study the MSDS for the chemicals used in Part A. Discuss safety precautions that must be used and list them in the space below.
1. Place 4–5 ice cubes (less than 100 g) and about 50 mL of water 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 “DataMate” program from APPS for data collection.
5. Follow the instructions as directed by the program. 6. Set the program in “time graph” data collection mode. 7. Set the program to collect samples every 10 seconds.
8. Set the total number of samples as 90. This should be a total of 15 minutes.
9. Place the temperature probe in the ice-water mixture.
10. Place the beaker with the ice-water mixture, thermometer, and magnetic stirrer on a hot plate.
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13. When data collection is complete and the graph is displayed, analyze and discuss it with your lab group.
14. Data and graphs from the calculator may be transferred to a computer using an interface program such as TI-Connect™. The investigation report may be then printed out.
OR Data may be transferred manually to the data table, and graphs may be constructed.
Note
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then
Select DataMate to enter the
data collection program
then
to clear previous data
Check that temperature is displayed in Celsius (if not, ask for assistance from your instructor)
Press 1 for SETUP
to change the time graph
If temperature in Celsius is not displayed, check
links, then .
Sometimes calibration may be needed.
Scroll down using the arrow
keys to Mode: TIME GRAPH
then
Press 2: TIME GRAPH to
change the mode of the time graph
Press 2: CHANGE TIME
SETTINGS to change the time
settings
Using the number keys, enter
10 seconds as the time between
samples
then
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Using the number keys, enter
90 as the total number of
samples, then to see the
TIME GRAPH SETTINGS. Your
data collection should take no more than 900 seconds.
Press 1: OK to confirm changes
to data collection settings
Press 2: START to start data
collection
Graph will be displayed after data collection is complete
then to get to main
screen
Press 6: QUIT then to
return to calculator screen
Disconnect calculator from CBL 2™
Press to study and
analyze the graph of data
Data-collection is complete.
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Data (for Manual Data Collection)
Time (30 sec
intervals) Temp (°C)
Time (30 sec
intervals) Temp (°C)
Time (30 sec
intervals) Temp (°C)
Time (30 sec
intervals) Temp (°C)
0 25 50 75
1 26 51 76
2 27 52 77
3 28 53 78
4 29 54 79
5 30 55 80
6 31 56 81
7 32 57 82
8 33 58 83
9 34 59 84
10 35 60 85
11 36 61 86
12 37 62 87
13 38 63 88
14 39 64 89
15 40 65 90
16 41 66 91
17 42 67 92
18 43 68 93
19 44 69 94
20 45 70 95
21 46 71 96
22 47 72 97
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Analysis and Conclusions
1. In your investigation, identify the independent and the 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.
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6. Classify the following changes as endothermic or exothermic and give reasons for your classification.
Change Endothermic or Exothermic Reason
Melting
Freezing
Boiling
Condensation
7. Why do you think the temperature stayed constant as the ice melted into water?
8. Why do you think the temperature stayed constant as the water boiled?
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10. Classify the following changes as physical or chemical and exothermic or endothermic. Give reasons for your classification.
Change Physical or Chemical Exothermic or Endothermic Reason
Melting
Freezing
Boiling
Condensation
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Application: Phase Changes
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 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. Study the graphs carefully and answer the questions 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 represents the cooling of the 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?
A
P
B
Q
C
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Elaborate
Investigate: Changes SafetyConduct 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 the space provided.
Add one substance to another as directed in the table below. 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 How do you know?Physical/Chemical EndothermicExothermic/ 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 small amount of
Solid E to the water in
the test tube.
4
Fill a small beaker half full with water. Obtain
Liquid F from your
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Analysis and Conclusions
1. In which investigation is mass conserved?
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Evaluate
A student’s experimental procedure and observations are diagrammed below. Study diagrams A through F and answer the questions below.
mass of empty test tube = 32.5 g white powder added
mass of test tube with powder = 33.6 g
temperature of clear liquid in beaker = 25.1 °C 10.0 g of clear liquid is poured
into the white powder.
Gas bubbles were given off. temperature of liquid in test tube
= 23.3 °C
mass of test tube with liquid = 41.8 g
1. If there was a change, was it a physical change or chemical change? Explain.
2. Was the process endothermic or exothermic? Explain.
A
D
B
E
C
