Please Help with my chem lab

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Lab Score: _______ Unknown Score: _______

DETERMINATION OF THE GAS CONSTANT

This experiment will rely heavily on your GCN and Lab Notes. This experiment will not tell you when you need to record data. Look at the data table closely, and think about the relevance of the data you are collecting as an indication about the need to record the data.

It is critical to follow instructions exactly as indicated in this experiment, as it can be very dangerous. To ensure safety, there are many places for instructor initials. DO NOT PROCEED past these points until signed, or there will be a major point deduction and possible removal from the lab for the day. You may be verbally tested the next period by your instructor before being allowed to move on. Please sign below showing that you understand the importance of these instructions: Signature: ____________________ Instructor’s Initials: _______

PROCEDURES Sample Preparation Weigh a large, clean and dry test tube on an analytical balance. The test tube must be free from contaminants or an explosion might occur. Use a top loader balance to weigh out about 3 g of KClO3 onto a piece of weighing paper (this mass is not critical to your calculations). Transfer the KClO3 into the tt, without getting any solid on the side near the top of the tt. Heat the tt, using your wire test tube holder to hold it, until all of the solid is melted (to drive off any water). Keep the tt in the tt holder at an angle as the KClO3 resolidifies as indicated in the diagram. Once solidified, let the tt cool in your test tube rack for approximately 30 minutes. While cooling, continue to the next section (glassware preparation), and then return to finish this section after 30 minutes. When the tt containing the resolidified KClO3 is at room temperature, weigh it on an analytical balance. Using a top loader balance, measure about 0.1 g of MnO2 on a piece of weighing paper (this mass is not important to your calculations). Add the MnO2 to the tt, covering the solid, and weigh it on an analytical balance. Insert a dry rubber stopper into the tt to prevent the adsorption of moisture. Bring the tt and your Data Sheet to your instructor to be checked. Instructors approval

Glassware Preparation Your instructor will be periodically performing 10 minute demonstrations on glass scratching and bending, fire polishing and safety. Attend the next one of these and have your instructor check you off. You will practice these techniques under the hood and then be tested on them. Instructors Initials Obtain a short piece of glass tubing and a glass scratcher from the hood. Show your instructor the proper procedure for scratching and breaking the glass tubing.

Instructors approval

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Obtain a medium piece of glass tubing from your instructor. Fire polish both ends of the glass tubing in the hood and make a 90o bend. Once the glass is cool, show it to your instructor. Instructors approval

Demonstrate the proper and safe use of the rubber safety grips for inserting glass tubing into stoppers to your instructor. Instructors approval

Study the diagram for the apparatus for this experiment. Using your glassware, stoppers and a meter stick, estimate the approximate lengths of glass tubing (in cm) needed for each piece and record these below:

I: Tubing in the stopper in the tt: ____________ II: Short tubing in the stopper in the flask: ____________ III: Long, bent tubing in stopper in the flask: ____________ IV: Tubing in the beaker: ____________

Instructors approval

Obtain a long piece of glass tubing from your instructor, which will be used for this experiment and the next one (Zn unknown). This is your only piece of tubing, so if any more is required, a small point deduction will be incurred. Prepare the glass tubing pieces needed for this experiment according to the diagram and instructions in your Lab Notes. Once complete, take all the cool glass tubing to your instructor for inspection of your lengths, bends and fire polishing. Instructors approval

If you have not already finished the Sample Preparation section before this, do so now.

Assembly of the Apparatus Assemble the apparatus according to the diagrams and instructions in your Lab Notes. Your apparatus must be in compliance with all of the items listed. In particular, glycerol should be used to lubricate all of the stoppers before inserting glass tubing EXCEPT for the stopper that goes into the test tube. The tt stopper must not have any glycerol! Glycerol in contact with hot potassium chlorate could cause an explosion. Do not use glycerol in the rubber connectors. Remove and gently heat the glass tubing and stopper in the tt while aspirating to dry the tubing. Have your instructor show you this technique if you are not familiar with it. Once cool, weigh the tubing and stopper on an analytical balance. Do not include the rubber connector in the measurement.

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Preparation of the Apparatus

If there is not enough time to run the experiment (~ 1 ½ – 2 hours), it is worthwhile to practice the assembly and pressure adjustments, so that the experiment will run efficiently and safely next lab period. Without the tt connected, fill the Florence flask full, and the beaker half full, with tap water. In order to fill the siphon tubing that runs from the flask to the beaker with water, cup your hand around the rubber tubing connector on top of the flask, and blow air into the flask (your lips should touch your hand, not the connector) until no more bubbles go into the beaker. Raise the beaker to force water back into the flask until the water level in the flask is within 2-3 cm of the stopper, but below the bottom of the short piece of glass tubing. Close the pinch clamp and then lower the beaker to the bench top. Place the rubber stopper with the glass tubing into the tt, connect the glass tubing to the rubber connector on the flask and make sure that all stoppers and connections are tightly sealed. Open the pinch clamp above the beaker to see whether the level of water in the flask continues to drop. If it does, there is a leak somewhere in the system, so tighten all the connections and try again. If there is no leak, test the fitting of the stoppers since even a small leak may require a repeat of the experiment. With the clamp open above the beaker, remove the glass tubing and set it on the counter. Support the test tube and press the stopper in more tightly. If water comes out of the tubing, then the stopper was not seated as firmly as it could have been. Repeat this with the stopper in the flask, pressing down with both thumbs.

With no leaks and the pinch clamp still open, notice the difference in the water levels between the beaker and the flask. The level is higher in the flask because there is a greater pressure on the top of the water in the beaker (atmospheric pressure) than there is on top of the water in the flask. This means that the pressure inside of the tt is less than atmospheric pressure. To accurately know the pressure inside the tt, and above the water in the flask, the pressure inside the apparatus must be equalized to atmospheric pressure. To do this, raise the beaker (pinch clamp is still open) until the top surface of the water in the beaker and the flask are at the same level. While the beaker is being held in this position, close the pinch clamp and set the beaker down. The pressure inside the apparatus should now be equal to atmospheric (barometric) pressure since the liquid surfaces are at the same height.

Carefully remove the tubing from the beaker (don’t dislodge any water from it) and allow it to hang in the sink. Empty the beaker, dry it inside and out, and weigh it on a top loader balance. Put the tubing back in the beaker, leaving the pinch clamp closed. Check all of the requirements for the apparatus listed in the GCN, and then have your instructor approve your apparatus. Note that if you have to repeat this procedure, you should have your instructor approve your apparatus EACH time. Instructors approval

Notice that a small amount of water flowed into the beaker when your instructor removed the pinch clamp. This was supposed to happen, and that water must be left in the beaker. Be sure to leave the pinch clamp open as you begin heating, as described in the next part of the experiment.

The remainder of the experiment requires slightly more than one hour. If sufficient time is not available, disassemble your apparatus by disconnecting the rubber connectors and then removing both stoppers. Empty the flask and drain the water from the tubing by opening the pinch clamp. Stopper the tt with a clean, dry solid rubber stopper. At the beginning of your next period, reassemble your apparatus and have your instructor check it again.

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Generation of Oxygen Using a small flame from a Bunsen burner, gently heat the tt, carefully following the steps outlined in your GCN. Holding the burner by the base, direct the flame at the solid (keep the upper end of the tt as cool as possible). Melt the solid in approximately two minutes, then reduce the heat so that the mixture remains just melted. The objective is to have a slow and continuous release of oxygen until about 300-400 mL is obtained in about 25 minutes (determine roughly how many mL you should obtain every 5 minutes for a constant rate of O2 generation). Do not overheat, and do not allow the water level in the flask to drop below the bottom of the long glass tube. When the desired volume of gas has been obtained, turn off the burner and allow the system to cool undisturbed for 30 minutes.

Carefully make these observations:

a) Did you see any white smoke in the flask? . b) Is there a white deposit on the glass tubing connected to the tt? . c) As the system cools, what happens to the temperature of the gas? ________ . d) As the system cools, what happens to the volume of the gas? ___________ . e) As the system cools, would you predict water to flow into or out of the flask? _________ . While the system is cooling, read the barometer mounted on the wall, following the instructions in your GCN. Record the barometric pressure and the temperature of the barometer.

After the system has reached room temperature, measure the height of the water in the beaker by placing a half-meter stick next to the beaker.

Height: _______ .

Leaving everything connected, lower the beaker into the sink until the liquid levels in the beaker and the flask are equal, and pinch the clamp securely over the rubber tubing. Should the volume of gas increase or decrease as the beaker is lowered? (Circle one)

Measure the height of the water in the beaker again: ________ .

Remove the glass tubing from the beaker and let it hang in the sink. Carefully disconnect the rubber stopper from the tt, without losing any solid. Carefully tap down any white solid into the tt, then lay the tt down for 15 minutes (to allow for exchange of oxygen and air). If oxygen in the tt where not replaced by air, would the measured mass of the tt be too big, too small or not affected? (Think about the molar masses and densities of oxygen vs. nitrogen) ________ .

Dry the bottom of the beaker and weigh it (with water) on the top loader balance. Measure the temperature of the water. Weigh the tt and then the glass tubing with rubber stopper. Retain the materials needed for the set-up until after the calculations have been accepted.