Unit 21 Charles's Law Charles's Law was discovered by the French physicist, Jacques Charles in 1787 and can be simply stated as follows: OR: V1 V2 ---- = ---- T1 T2 V = kt In this experiment we will explore the variation in volume with temperature of a gas. We will heat a gas in a boiling flask and then cool the flask in a water reservoir. By knowing the volume of the empty flask (V1), the volume of water drawn into the flask after cooling and the temperature of the cooling water reservoir T(2) we will be able to calculate the temperature of the hot gas. With the temperature of the hot gas we will be able to calculate two values for the Charles's Law constant "k". Procedure 1. Obtain a water reservoir. This can be a large container of water or a filled sink. 2. If a one-hole stopper with a bent glass tubing is not supplied, make one using the following procedure: Cut a 4-6 inch piece of glass tubing using a file to make a scratch and carefully snapping the glass tubing away from you. Using a burner, fire polish the ends of the cut glass tubing and make a 90 o bend by heating a 1 inch section of the tubing continually with a burner on maximum heat (maximum air). Let the tubing cool for about 5 minutes and then place the tubing under cold water to cool. Apply glycerin, or other suitable lubricant to the hole of an appropriate sized one-hole stopper that fits the boiling flask that you will be using. Apply the lubricant to the end of the
Unit 21 Charles s Law glass tubing along about the last inch or two of the tubing. Carefully insert the tubing into the stopper. It should slide in easily. If it does not see your instructor. DO NOT FORCE THE TUBING! It can easily break and cause serious injury to your hand. 3. Place the one-hole stopper with the 90 o glass tubing onto the boiling flask and clamp the flask to a ring stand. Place a wire gauze onto a ring clamp just below the flask. Heat strongly for about 1 minute. 4. Be careful in handling hot equipment. Carefully remove the clamp, still attached to the flask, from the ring stand and carefully place it in the water reservoir with the bent glass tubing pointing down. Be sure the opened end of the glass tubing enters the water before the flask. Be sure, also, that you insert the flask into the water slowly so as not to cause such a temperature differential as to break the flask. Observe the water from the reservoir being withdrawn into the flask as it cools. The flask should remain completely submerged in the water until no more liquid withdraws into the flask. 5. Measure the temperature of your water reservoir and record on your lab report. Be sure to use the Kelvin temperature scale. 6. Remove the flask, carefully remove the stopper and bent glass tubing, and pour the contents of the flask into a graduated cylinder to measure the amount of water withdrawn into the flask. Record the water withdrawn onto your lab report. 7. Fill the flask with water to level just below where the stopper reached in the flask. Pour the contents into a graduated cylinder to measure the volume of the empty flask and record on your lab report. 210
Unit 21 Charles s Law 8. Use Charles's Law to calculate the temperature of the hot gas in the empty flask before cooling. Also, using the two sets of data (one for the hot gas and one for the cooled gas) determine the two values for the Charles's Law constant and average them. 211
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Unit 21 Charles s Law Prelab Exercises for Unit 21 Name Section Date 1. State the two versions of Charles's Law. 2. If you measured the volume of an empty flask to be 280 ml, you heated the gas stoppered with a bent glass tubing, cooled it in a 21 o C water reservoir, and then obtained 85 ml of water withdrawn into the flask when cooled, what was the temperature of the hot gas? 3. What would be the average Charles's Law constant for the experiment in question 2? 213
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Unit 21 Charles s Law Lab Report for Unit 21 Name Section Date volume empty flask volume water withdrawn volume of cold gas temp. of water reservoir temp. of cold gas temp. of hot gas Charles's Law constant avg. Charles's Law constant show calculations: 215
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