Determination of the Chemical Formula

Transcription

1 Determination of the Chemical Formula Place pre-lab report on table for the TA to sign Hand in Lab Safety Certification and Identification with photo Collect laboratory equipment: Clean and oven dry one large test tube and a drying tube 250 ml Erlenmeyer flask, thistle tube and rubber tube Alcohol lamp, matches, and wind shields Ring stand, two extension clamps Prepare personal equipment: One clean 100 ml beaker (take 40 ml of 6 M HCl) 10 test tubes (collecting hydrogen gas over water) (2015/09/23 revised) 1

2 Objective Objective: determine the empirical formula of copper oxide by the analytical method. Techniques: -Weighing chemicals -Preparing and collecting hydrogen gas over water -Using an alcohol lamp Chemical reactions: Zn (s) + 2 HCl (aq) ZnCl 2(aq) + H 2(g) H 2(g) + CuO (s) Cu (s) + H 2 O (l) Cu : O (Mole ratio) 2

3 Equipment and Setting-up Drying tube Cotton Extension clamp Copper oxide Thistle tube Collecting gas over water Clamp Ring stand Zinc granules Hydrogen gas generator Plastic basin 3

4 Procedure 1: Prepare the Drying Tube Stuff both ends of the drying tube with small amounts of cotton to keep CaCl 2(s) from falling Prepare the drying tube on the plastic plate to prevent CaCl 2 from falling Cotton and CaCl 2(s) must not be stuffed too tightly to obstruct hydrogen gas flow Put the cap of CaCl 2 back on the bottle after use 4

5 Procedure 2: Filling Large Test Tube with Copper Oxide Clean, oven dry, and cool the large test tube Weigh and record the accurate weight of the tube Use the small end of the spatula to put 1 g of copper oxide in test tube Copper oxide should be placed in the middle of the test tube Accurately weigh again Note 1: use the same analytical balance throughout the experiment Note 2: Avoid the test tube touching the wind shield that cause error in weighing 5

6 Procedure 3: Set Up the Apparatus Add 15 g of zinc granules into flask Use the clamp to hold the test tube and Erlenmeyer flask Avoid clamping the test tube where the copper oxide is placed The thistle tube should be as close to the bottom of the flask as possible 6

7 Procedure 4: Preparation Collecting Gases over Water Fill the plastic basin with 2/3 water Fill 6-8 test tubes with water and place into water Hold the end of the test tube, keep the opening of the test tube under water, and avoid the air getting into tube 7

8 Check the Setting Up by TA Proper filling of drying tube Firmly connection of apparatus Suitable position of two clamps Airtight fitted of 3 rubber stoppers 8

9 Procedure 5: Generate Hydrogen Gas Use 100-mL beaker to take 20 ml of 6 M HCl Pour the HCl(aq) through the thistle tube all at once The end of the thistle tube should be immersed underneath the liquid Collect gases over water at once Notice HCl(aq) is strong acid. This experiment evolves hydrogen gas that is explosive. Do not close the windows or safety doors. 9

10 Procedure 6: Collect Gases over Water Collecting Gases Over Water: Reverse the filled test tubes in water Put rubber tube into test tube to collect gas over water When test tube is filled with gas, stand test tube upside down on table (opening pointed downward) Collect 6-8 test tubes, use matches to bring flame to the opening of the tube and test for pop sound Loud pop sound in the beginning (Mixture of air and hydrogen gas) Pop sound should become less and less noticeable * When the pop sound becomes unnoticeable, it means the air in the system has been pushed out by the hydrogen gas. * Notice: start heating only after this step is completed. 10

11 Procedure 7: Heat and Start the Reaction Add another 20 ml of 6 M of HCl(aq) to ensure the continuous production of hydrogen gas Add about 2 times (40 ml) Do not take too much HCl(aq) to prevent wasting of chemicals Light the alcohol lamp to begin heating Take rubber tube out of water to prevent the water flow into system Check the length of the wick of alcohol lamp Put out the fire first and use a funnel when adding alcohol The alcohol should be half filled 11

12 Procedure 8: Heat Evenly Heat the reacting test tube from right to left evenly Heat evenly to eliminate the water condensed inside test tube Do not burn the rubber stopper and the clamp Use the wind shield to shield the wind Heat until there are no more visible changes in its content Stop heating, keep hydrogen gas flowing, and cool the system 12

13 Procedure 8: Weighing after System Cools Hydrogen gas flow should be maintained throughout cooling Disconnect the test tube after cooling Accurately measure the weight with the same balance Calculate the weight of Cu and O, separately Recycle: cotton, CaCl 2, zinc granules (wash with water), the copper produced thrown into chemical recycling bin 6 M HCl: recycled into recycling bin for heavy metals References: 13