Lab Manual- Chapter 13
Complete the calculation required to appear on the Report Sheet.
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A thermometer is not present in the space (or volume) in which the CO2 is collected in this experiment. How then is the temperature of the CO2 determined?
It's based on the temperature of the water in the pan.
Purpose
To determine the percent calcium carbonate in a heterogeneous mixture. To determine the molar volume of carbon dioxide at 273 K and 760 torr
Molar Volume of CO₂
To make determinations, two important measurements are made: 1. The CO₂ gas evolved from the reaction is collected and its volume is measured. 2. The mass difference of the CaCO₃ mixture, before and after the reaction is also measured.
If a large amount of calcium sulfate is present in the original sample, how does it affect the reported a. molar volume of the CO2? b. percent CaCO3 in the sample?
Too low because gas is not being formed.
The Table (???)
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Needed Calculations
1. DALTON'S LAW OF PARTIAL PRESSURES: Because the gas is being evolved over water, we must take into account that it is wet (saturated with water vapor. Dry Carbon Dioxide=Pressure Total- Pressure H₂O 2. VOLUME OF CARBON AT STP: This is a mixture of Boyle's Law and Charles's Law. Volume Carbon Dioxide (at STP)= Volume of CO2 (experimental value) x (Pressure CO2 (experimental value in torr)/760 torr) x (273 K/ Temperature of CO2 (experimental value in K)) 3. MOLAR VOLUME OF CO2- the mass loss of the CaCO3 mixture is due to the mass of the arbion dioxide evolved in the reaction. The volume of CO2 collected over water under the temperature/pressure is calculated. Molar volume of CO2= Volume of Carbon At STP/ moles of Carbon dioxide
The water level in the CO2 collection cylinder is higher than the water level outside the cylinder. a. IS the wet CO2 gas pressure greater or less than atmospheric pressure. Explain. b. An adjustment is made to equilibrate the water levels. Will the volume of wet CO2 gas increase or decrease? c. The student chose not to equilibrate the inside and outside water levels. Will the reported number of moles of CO2 generated in the reaction be too high, too low, or unaffected?
1. If the water level is higher inside the cylinder, than the resulting wet CO2 gas pressure would be less. 2. If the water levels were changed so that the two were now even, the wet pressure of CO2 would also increase. 3. If the student was careless, than the reported number of moles would be affected, but it would depend on which level was higher/lower.
Procedure
1. Saturate 1000 mL of water with CO₂ 2. Calculate mass of CaCO₃ needed to produce ~40mL of CO₂ at STP 3. Set up the CO₂ generator (3M HCl with the sample inside a testube.) 4. Twist cylinder that will measure CO₂ output upside down and mark initial waterline values. Attach CO2 generator to a stand and than mix the sample with the HCl. 5. Determine CO₂ volume by drop in water level
In some solid calcium carbonate samples, calcium bicarbonate is also present. Write a balanced equation for its reaction with hydrochloric acid.
Ca(HCO3)2 + 2HCl → 2H20 _ 2CO2 + CaCl2
Explain how a water-filled graduated cylinder is inverted in a pan of water
Fill the graduated cylinder with CO2 water by laying it horizontally ad then setting it upright.
The water for the pan is not saturated with CO2. Wil the reported percent CaCO3 in the original sample be too high, too low, or unaffected?
IF the water in the pan is not saturated with carbon dioxide, the reported percent of calcium carbonate will be too low due to the fact that the water will absorb the CO2, making the value seem smaller than what it really is.
A few drops of HCL spilled over into the CaCO3 sample prior to firmly seating the stopper and prior to collecting any CO3. As a result of this poor technique, what will happen to the reported CaCO3 in the sample?
If a few drops of HCl spilled into our sample prior to experimental procedure B.2, than our reported percent of calcium carbonate would be too low because some of the reaction would have taken place without ever being measured.
An air bubble accidentally enters the CO2 collection graduated cylinder after the completion of the reaction. How does this error affect the reported moles of CO2?
If an air bubble enters the CO2 collection, than the reported volume of CO2 would be too high to due the increased gas.
The rubber stopper has a small crack resulting in a not tight seal. How will this affect the calculated molar volume of CO2?
If the rubber stopper has a crack in t, this technique error will cause some the CO2 to leak out from the container, meaning we will have a lower reported molar volume.
The mass of a gas is elusive. How is the mass of CO2 collected over water determined in this experiment?
The mass of the CO2 is measured using the initial and final values of the water present in the inverted beaker. As the water levels drop, the more carbon dioxide is present and the value is determined from that.
Suppose 6 M HCl is substitute for the 3 M HCl in the procedure. What would be the consequences of this substitution? Explain.
The mole ratios would be higher because the acid is more concentrated and would speed up the reactiom
Standard Temperature and Pressure (STP)
273K and 1 atmosphere (760 torr) One mole of an ideal gas occupies 22.4 L.
What is the proper procedure for inserting a piece of glass tubing into a rubber stopper?
Make sure there are no cracks, use a lubricant and a gentle twisting motion.
Molar Volume
Volume occupied by one mole of gas at a define temperature and pressure conditions.
How is the volume of the CO collected over water measured in the experiment?
When no further CO2 is collected, adjust beakers so that the water levels in and out of the graduated cylinder are even.
