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Transcript of Stoichometry Lab
a. Key Question or Purpose
The purpose of this lab is to determine the mass and mole relationships of the given reactants; The base NaOH and an unknown acid. We are supposed to determine the best mole ratio between the reactants that make the chemical reaction more productive.
b. Hypothesis and Prediction with Justification
a. Materials -
- 225 mL of 1 M sodium hydroxide in a 250-mL beaker
- 225 mL of 1 M Unknown Acid in a 250-mL beaker(assigned by teacher)
- 2 foam cups
- 10-mL graduated cylinder
- 100-mL graduated cylinder
- 400-mL beaker
- wash bottle with distilled water
- paper towels
b. Sketch of Lab apparatus -
c. Safety Concerns
- It is important to use protective lab gear such as aprons/coats, safety goggles, and gloves.
- The chemicals needed for the experiment are corrosive so extra caution is required while handling the materials.'
- If the chemicals spill on your skin you must wash the area thoroughly, especially if the chemicals got on your face. This is why the safety goggles are requires.
- If you accidentally break the glass apparatus, such as graduated cylinders or beakers, proceed with caution and do not touch the broken shards.
1. Measure the temperature of the 1 M sodium hydroxide and the temperature of your unknown acid. Record the data in the appropriate data table. If the solutions are not the same temperature, then you must make a correction for the temperature difference..
2. Rinse the thermometer with distilled water, and thoroughly dry it.
3. Create a reaction chamber by nesting the foam cups one inside the other, and then placing them in a 400-mL beaker. Place the lid on the foam cup, with the thermometer inserted through the lid. This will help insure the heat liberated by the reactions is not lost to the atmosphere during the experiment.
4. Using the appropriate graduated cylinder, measure 45 mL. of 1 M sodium hydroxide and pour it into the foam cup.
5. Using the appropriate graduated cylinder, measure 5 mL of the unknown acid and add it to the 1 M sodium hydroxide in the foam cup.
6. Carefully stir the mixture by moving the 400-mL beaker in a gentle circular motion on the lab table. Record the maximum temperature reached as the reaction occurs. Record the maximum temperature in the data table.
7. Follow your teacher's instructions for proper disposal of laboratory wastes.
8. Rinse the foam cup and thermometer with distilled water and dry them.
9. Measure the indicated ratios, given in the data table for your unknown acid, for the reaction of sodium hydroxide and the unknown acid.
10. Repeat step 3-*8 fr the remaining reactions. Record the maximum temperatures in Data Table 1 or Data Table 2, depending on which acid you are working with.
11. Calculate the change in temperature for each reaction. Exchange data with a group that performed the experiment with the other unknown acid. Record that group's data in the appropriate data table.
b. Pre-lab questions -
1. What observations can be made that indicate a chemical reaction has occurred?
- Color change, temperature change, odor change, solute forming, or gas forming.
2. Calculate the mass of solute. If you know that 5 mL of 2 M calcium chloride is used in a chemical reaction.
- 5 mL/1000 L = 0.005 L X 2 M = 0.01 moles CaCl X 110.98 g CaCl = 1.1098.
3. Define the term "limiting reagent"
A limiting reagent is a reactant that is completely used up in a chemical reaction
4. Determine the limiting reagent in the ff. reaction if 6 mL of 1 M sodium hydroxide is added to 4 mL of copper sulfate.
NaOH is the limiting reactant.
5. 30 mL X 30 degrees C
+ 20 mL X 35 degrees
/50 mL= 32 degrees C
a. Table - Data Table 1: Unknown acid A
b. Graphs - 1 M NaOH
and unknown acid A
x-axis; mL 1M NaOH & Acid
3 temperatures undetermined.
b. Data comparison with other groups.
c. Lab issues: My group wasn't able to finish the experiment on time and are missing data on the table and graph
d. Post-Lab Questions -
1. Graph the temp. change versus the vol. of reactants for unknown acid A
2. For both graphs; Draw the best-fit lines indicated by the data and extend them until they intersect. At this point, what is the volume of sodium hydroxide and unknown acid A?
-Volume of NaOH = 20 mL
-Volume of Acid - 30 mL
3. Name the limiting reagent along the ascending line and along the descending line on each graph.
-Ascending line - Sodium Hydroxide
Descending line - Unknown Acid
4. Determine the mole ratio for the reaction of NaOH
Mole ratio is 1 : 1
4b. Because if you determine the mole ratio using the ratio associated with the greatest temperature change, you wouldn't get the exact ratio and you would actually need more or less of the reactants to make a balanced equation.
-NaOH(aq) + HCl(aq) ---> NaCl(aq) + H2O(l) ; 1:1
-H2SO4 + 2NaOH = 2H20 + Na2SO4; 2:1
-H3PO4 + 3NaOH = Na3PO4 + 3H2O; 3:1
5b - Unknown acid A is Hydrochloric acid
6. NaCl 225 mL, 1 mole, 58.43 grams
HCl - 225 mL, 1 mole, 36.46