Unit 3 - Section 6.2 - Conservation of Mass Lab 2014

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Grade 9 Academic Science - Chemistry
Laboratory: Conservation of Mass
Section 6.2
Purpose
The Law of Conservation of Mass states that the mass of the products must equal the mass of
the reactants in a closed system. In other words, mass is not lost, created or destroyed during a
chemical reaction. In this laboratory, you will test whether mass changes after a chemical
reaction occurs.
Hypothesis (ask your question for this investigation) ---Materials
 Goggles
 Two small test tubes (<10mL)
 Two Erlenmeyer flasks (250 – 500mL)
 5 mL Iron III chloride solution (FeCl3(aq))
 5 mL Sodium hydroxide solution (NaOH(aq)),
 2 g Sodium bicarbonate (NaHCO3(s))
 30 mL Hydrochloric acid (HCl(aq))
 2 g calcium chloride (CaCl2(s))
 Distilled Water (H2O)
 100 mL Graduated cylinder
 2 -100 mL beakers
 Scoopula
 Measuring glass
 Electronic balance
 Rubber stopper
 Empty 500mL plastic pop bottle and lid
 Tongs
Methods
Part A: IronIII chloride (FeCl3) and sodium hydroxide (NaOH)
1. Practice holding the empty test tube with tongs and sliding it into an empty Erlenmeyer flask.
Seal the flask to check that the test tube fits and the stopper forms a tight seal.
2. Make observations of the substances before and after the reaction (e.g., colour, state).
3. Measure 5 mL of NaOH solution in the 10mL graduated cylinder. Pour this solution into the
flask.
4. Measure 5 mL of FeCl3 solution. Pour this solution into the test tube.
5. Tilt the flask and carefully slide the test tube into the flask using the tongs. DO NOT allow the
test tube’s contents to spill.
6. Seal the flask with the stopper.
7. Place the flask on a balance and determine the TOTAL MASS of the flask and the unmixed
chemicals.
8. Mix the contents in the flask by tilting the flask so that the FeCl3 solution mixes with the NaOH
solution.
9. Measure the mass of the flask and the mixed chemicals.
10. Record any other observations of chemical change (e.g., colour change, gas formation, heat
produced, light produced).
11. Calculate any change in mass between pre- and post-mixing of chemicals.
12. Record your data on the class results list.
Part B: Sodium bicarbonate (NaHCO3) and Hydrochloric acid (HCl)
1. Using the electronic balance, measure out 1 g of NaHCO3 and place it into a flask.
2. Make observations before the reaction (e.g., colour, state).
3.
4.
5.
6.
7.
8.
9.
10.
Using the graduate cylinder, measure out 15 mL of HCl and place it into a test tube.
Place the test tube into the beaker. Do not put a stopper on the flask.
Place the flask on a balance and determine the mass of the flask and the chemicals.
Mix the contents in the flask by tilting the flask so that the NaHCO3 mixes with the HCl.
Shake vigorously to ensure a complete reaction.
Record any other observations of chemical change (e.g., colour change, gas formation, heat
produced, light produced).
Measure the mass of the flask and the mixed chemicals.
Calculate the change in mass pre- and post-mixing of chemicals.
Record your data on the class results list.
Part C: NaHCO3 and HCl
1. Using the electronic balance, measure out 1 g of NaHCO3 and place it into a pop bottle.
2. Using the graduate cylinder, measure out 15 mL of HCl and place it into a test tube.
3. Place the test tube into the pop bottle AND screw on the cap.
4. Place the pop bottle on a balance and determine the mass of the pop bottle and the
chemicals.
5. Mix the contents in the pop bottle by tilting the pop bottle so that the NaHCO3 mixes with the
HCl. Shake vigorously to unsure complete mixing.
6. Record any other observations of chemical change (e.g., colour change, gas formation, heat
produced, light produced).
7. Measure the mass of the pop bottle and the mixed chemicals.
8. Calculate the change in mass pre- and post-mixing, and record the difference.
9. Slowly unscrew the cap from the pop bottle and allow the gas to escape.
10. Measure and record the mass of the pop bottle and the mixed chemicals with the lid off.
Part D: CaCl2 and NaHCO3
1. Measure 2 g CaCl2 and 2 g NaHCO3 with the electronic balance
2. Use a graduated cylinder to add 20 mL H20 to each beaker.
3. Add 2 g of calcium chloride to the water in one beaker. Swirl until as much of the calcium
chloride dissolves as possible.
4. Add 2 g NaHCO3 to the water in other beaker. Swirl until as much of the NaHCO3 dissolves as
possible. There may be some undissolved NaHCO3.
5. Carefully pour the NaHCO3 solution into the CaCl2 solution. Try not to pour in any undissolved
NaHCO3.
6. Observe and record
Results
Table 1. << Insert an appropriate descriptive title >>
Reactants
Iron III chloride
(FeCl3) solution
Description of
Reactants
Total mass
before
(g)
Description of
products
Total
mass
after
(g)
Total mass
after cap
removed (Part
C only) (g)
Mass
Difference (g)
N/A
Sodium hydroxide
(NaOH) solution
Sodium
bicarbonate
(NaHCO3)
N/A
Hydrochloric acid
(HCl)
Sodium
bicarbonate
(NaHCO3)
Cap on
Hydrochloric acid
(HCl)
Cap off
Sodium
bicarbonate
(NaHCO3)
N/A
Calcium carbonate
(CaCl2)
Discussion
<< Explain your results … think for Part A – Mass vs Density / Part B-C – Closed vs Open systems –
Illustrate and demonstrate your understanding of (1) the Law of Conservation of Mass, (2) what is mass and
(3) Physical and Chemical Change >>
Also answer the following questions
1. Answer “Analyze and Evaluate” questions a-j on page 229 in your textbook.
2. Write the word equations to describe the two reactions.
3. State the Law of Conservation of Mass and explain why it is difficult to apply to a reaction in
which a gas is produced?
Mass Reactants (g)
Part A: Iron III chloride and sodium hydroxide
Class Results
Investigation – Conservation of Mass
Mass Products
Mass change (g) (+ or -)
175.98
175.98
No change
192.70
192.70
No change
175.98
175.98
No change
186.07
185.93
-0.14
111.60
111.61
+0.01
191.86
191.81
-0.05
271.00
271.00
No change
Average change
Part D: Calcium chloride and Sodium bicarbonate
Class Results
Investigation – Conservation of Mass
Mass Reactants (g)
Mass Products
Mass change (g) (+ or -)
Average change
Part B: Sodium bicarbonate and hydrochloric acid (Open System)
Class Results
Investigation – Conservation of Mass
Mass Reactants (g)
Mass Products
Mass change (g) (+ or -)
156.62
156.01
-0.61
138.03
137.72
-0.31
156.62
154.44
-2.18
141.0
141.0
No change
138.02
137.72
-0.31
149.54
148.88
-0.62
159.92
159.44
-0.48
Average change
Part C: Sodium bicarbonate and hydrochloric acid (Closed System)
Class Results
Investigation – Conservation of Mass
Mass Reactants (g)
143.07
Mass Products (g)
With Cap on
Without Cap
143.07
142.60
Mass change (g) (+ or -)
Cap On
No change
Cap Off
-0.47
152.86
152.86
152.56
Cap On
No change
Cap Off
-0.30
142.22
142.21
138.80
Cap On
-0.01
Cap Off
-3.42
143.07
143.07
142.65
Cap On
No change
Cap Off
-0.42
152.86
154.95
152.56
Cap On
+2.09
Cap Off
-0.30
144.64
144.64
144.07
Cap On
No change
Cap Off
-0.57
Average change
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