Lab+2+The+Formula+of+a+Hydrate

Title/date: The Formula of a Hydrate 11/7/11

Purpose: To learn about hydrates and to determine the number of waters of hydration in a hydrate. Teacher Comment: More detail in purpose. List of Materials: small hot plate 10 culture tubes wire test tube clamp glass stirring rod thin-stem transfer pipet Bunsen burner calcium sulfate cobalt (2) chloride copper(2) chloride copper (2) sulfate nickel (2) chloride potassium carbonate potassium chloride unknown hydrate

Safety Considerations: Safety goggles must be worn during the lab to protect your eyes from chemical splash. Also, wash your hands thoroughly before leaving the laboratory because of the moderately toxic cobalt. Be careful handling hot glassware. For disposal, all of the substances except cobalt chloride can be flushed down the drain. Cobalt chloride should be placed in a receptacle provided. Clean the glassware after use.

Procedure: In seven test tubes, place seven different solids, one for each tube. Heat the coumpounds over a hotplate and record any color changes or moisture collection. After the compounds are colled, add a milimeter of water and observe and record if the substance dissolves and changes color close to the original color of the substance. For part B, weigh three marked test tubes and add an unknown hydrate to each tube. Record the mass of each tube. Hold each one over a bunsen burner for 15 minutes or longer and then let them cool. Record the weight of each tube.

Data Table:
 * Reagents || moisture collection/color || dissolve/color ||
 * calcium sulfate || no/no clor change || dissolved/white ||
 * cobalt(II)chloride || yes/green --> brown || dissolved/green ||
 * copper(II)chloride || yes/purple --> blue || dissolved/purple ||
 * copper(II)sulfate || yes/blue --> green || dissolved/blue ||
 * nickel(II)chloride || yes/green --> orange || dissolved/green ||
 * potassium carbonate || yes/white --> clear || dissolved/clear ||
 * potassium chloride || no/no color change || dissolved/white ||


 * Tube || mass of tube || mass w/ substance || cooled mass ||
 * Tube 1 || 18.548 g || 18.999 g || 18.222 g ||
 * Tube 2 || 21.834 g || 22.212 g || 21.933 g ||
 * Tube 3 || 21.069 g || 21.514 g || 21.124 g ||

Questions/Problems: Pre-Lab 1) A hydrate is an ionic compound bonded to a certain amount of water molecules. The dot indicates the amount of water molecules bonded to the salt. When calculating the molar mass of a hydrate, the dot is treated as an addition sign. 2) The term "anhydrous" means water free. 3) If the unknown hydrate in part B is not heated enough, the waters will not be driven off and there would be too many waterleft over and the mass calculated would turn out too high.

Analysis/Conclusion 1) Cobalt (2) chloride, copper (2) chloride, copper (2) sulfate, nickel (2) chloride, and potassium carbonate are all hydrates because water collected on the test tube during the process of heating. The other reagents are not hydrates because water did not collect while heated. 2)a) Tube 1: mass of sample = 0.451 g mass of water lost = 0.125 g Tube 2: mass of sample = 0.378 g mass of water lost = 0.279 g Tube 3: mass of sample = 0.445 g mass of water lost = 0.390 g Teacher Comment: Please type the answers in a way that I can tell the question. (Or type the question.) b) % by mass = part/ whole x 100 Tube 1: % by mass = (0.125 g / 0.451 g) x 100 = 27.7 % Tube 2: % by mass = (0.279 g / 0.378 g) x 100 = 73.8 % Tube 3: % by mass = (0.390 g / 0.445 g) x 100 = 87.6 %

3) Molar mass of Al(NO3)3 = 213.01 g/mol molar mass of Al(NO3)3 * 9H20 = 375.154 g/mol a)Tube 1: 0.125 g x (1 mol 9H2O / 162.144 g) = 7.71 x 10^ -4 mol H2O Tube 2: 0.279 g x (1 mol 9H2O / 162.144 g) = 1.72 x 10^ -3 mol H2O Tube 3: 0.390 g x (1 mol 9H2O / 162.144 g) = 2.41 x 10^ -3 mol H2O

b) Tube 1: 0.326 g x (1 mol Al(NO3)3 / 213.01 g) = 1.53 x 10^ -3 mol Al(NO3)3 Tube 2: 0.099 g x (1 mol Al(NO3)3 / 213.01 g) = 4.65 x 10^ -4 mol Al(NO3)3 Tube 3: 0.055 g x (1 mol Al(NO3)3 / 213.01 g) = 2.58 x 10^ -4 mol Al(NO3)3

c) Tube 1: (7.71 x 10^ -4 mol H2O / 1.53 x 10^ -3 mol Al(NO3)3) = (x mol H2O / 1 mol Al(NO3)3) x = 0.504 mol H2O / 1 mol of annhydrous solid Tube 2: (1.72 x 10^ -3 mol H2O / 4.65 x 10^ -4 mol Al(NO3)3) = (x mol H2O/ 1 mol Al(NO3)3) x = 3.70 mol H2O / 1 mol of annhydrous solid Tube 3: (2.41 x 10^ -3 mol H2O / 2.58 x 10 - 4 mol Al(NO)3) = (x mol H2O / 1 mol Al(NO3)3) x = 9.34 mol H2O / 1 mol of annhydrous solid

4) a) Tube 1: 1 mol of water / 1 mol of salt Tube 2: 4 mol of waters / 1 mol of salt Tube 3: 9 mol of waters / 1 mol of salt b) Tube 1: Al(NO3)3 * H2O Tube 2: Al(NO3)3 * 4H2O Tube 3: Al(NO3)3 * 9H2O Teacher Comment: Always explain suc wide results right away. 5) Any non-whole number experimentl calculations could have been the result of the open window. The balance could have been thrown off and the salt could have rehydrated from the moisture from the air coming in through the windows.

6)a)The two hydrated copper compounds were colored purple (copper(2)chloride) and blue (copper (2) sulfate). b) The annhydrous forms were colored blue and green. c) Sodium chloride and potassium chloride are white. d) Teacher Comment: Some questions lacking Analysis/ Summary: The observations reveal that if a substance is a hydrate, water should collect when heated on the sides of the container, and the substance should change colors. Also, you can fiind the formula of the hydrate by weighing the substance before and after heating it to drive the waters away. The experiment works if it is dont precisely and accuratly. It must be done carefully. The theory that finding the formua of a hydrate using heating and masses was demonstrated. The majority of the results were too low because tube 1 and2 in part B ened up after calculations having a lower amount of moles than the hydrate actually has. A source of error ould have been that the masses were off because the open window next to the scales was blowing wind and throwing them off. Also, the moisture from the outside air could have bonded to the hydrate while it was cooling and when it was weighed and the number of waters was calculated, the moles of waters was off. To prevent this, the window could have been closed. Teacher Comment: Just a few errors along the way. Overall not bad. 46/50