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Precipitation Reaction and General Solubility Rules
Materials: BaCl2, Na2CO3, K2CrO4, NaOH, MgCl2, Na2SO4, AgNO3, Pb(NO3)2, KNO3, 96-well plate, micro-tip pipettes
Using a 96-well plate mix all of the possible solution combinations.
Place 2 drops of each solution in the well. In the upper right, write R if a precipitate forms or NR if no precipitate forms.
Write the formula for the precipitate in the box.
Write the balanced net ionic equation for each precipitation reaction.
Develop some general rules for solubility based on your results. (ex. All chlorides are soluble except...)
Using your rules, what could you add to separate the following pairs of ions.
a. Mg2+ and Ba2+
b. Ag+ and Pb2+
c. K+ and Mg2+
Comparinbg Activties of Selected Metals
Materials: copper, lead, iron, magnesium, calcium, zinc, silver, 0.1 MN solutions of Cu(NO3)2, Pb(NO3)2, Fe(NO3)3 , Mg(NO3)32, Ca(NO3)2 , Zn(NO3)32, AgNO3
Using a 96-well plate, microtip pipette.
Place 5-6 drops of each solution in the well lettered rows A-G Cu(NO3)2, Pb(NO3)2, etc.), columns 1-7
Please metal into each column 1-7. (Column 1 copper, 2 lead, etc.)
After 10 minutes, remove the metal from each well. Indicate whether a reaction has occured and record any observations. Evidence of a rection may be a change in color, evolution of a gas, or formation of a precipitate.
Did all of the metals react in the same way? Explain.
Were there any metals that did not react at all? Explain.
Determine the number of reactions of each metal. Record the results.
Attance the metals in order or reactivity from highest to lowest. Which metal is the most active? Which is the least active?
How did your results compare with a table of metal activities in a reference book?
A magnesium rod is usually found inside a hot warter header. Whgat purpose do you think the rod serves?
Colligative Properties -- Boiling point elevation
Materials: “unknown” solid (urea) supplied by instructor; 6x1-in. test tube fitted with two-hole no. 4 stopper, thermometer, stir rod, boiling chip
Procedure: Caution! Ethanol is flammable! Keep away from all flames. Use hot plates to heat water baths.
Prepare a 90°C water bath by heating 250–300 mL of water in a 400 mL beaker (use hotplate setting number 5 to 6).
Obtain the clean, dry 6x1-in. test tube from the instructor. Stand the test tube in a 150 or 250 mL beaker and place the beaker and test tube on the balance. Tare the balance and once the balance has re-zeroed, add 19 to 20 grams of ethanol to the test tube using the squirt bottle provided. Record on the data sheet to the nearest 0.01 gram the mass of ethanol used. Convert this value to kilograms and record the value on the data sheet.
Place a boiling chip (an inert porcelain chip designed to promote smooth boiling) in the test tube containing the ethanol. Fit the test tube with the two-holed no. 4 stopper-thermometer-glass tubing assembly supplied by the instructor. Carefully adjust the thermometer to make sure that the end of the thermometer is about 1 inch below the surface of the ethanol.
Clamp the test tube to a ringstand and immerse the tube in the water bath to a depth of about 1 inch. When the ethanol begins to boil gently, as indicated by a steady stream of bubbles from the boiling chip, read the temperature to the nearest 0.1°C for several minutes until a constant value is obtained. This is the boiling point of ethanol. Record this value to the nearest 0.1°C. NOTE: Vigorous boiling should be avoided since this can lead to the loss of solvent through the glass tubing. Watch carefully for the appearance of vapor in the tubing. If it rises more than half way up the tubing, remove the test tube from the hot water bath.
Once you have determined the boiling point of pure ethanol, raise the test tube out of the bath and allow it to cool for several minutes. Carefully remove the stopper and add about 2.5 grams of the unknown solid to the test tube using a powder funnel. Make sure that you record the actual mass (to the nearest 0.01 gram) of the unknown used. Replace the stopper and allow the solution to boil gently for several minutes until all of the solid has dissolved. (NOTE: Observe the solution carefully while it is reheating. If no bubbles are observed coming from the boiling chip as the temperature nears the normal b.p. of ethanol, gently remove the test tube from the water bath, allow it to cool and notify the instructor. It is possible that the solution is superheating and may “bump,” leading to a rapid loss of solvent and solute out the glass tubing!). Record the boiling point of the solution. Remove the test tube from the hot water bath. Discard the warm ethanol solution in the beaker provided by the instructor. Rinse the test tube and thermometer under the tap to clean and return these items to the instructor.
Data and calculations:Name and formula of "unknown" solid
Urea, CO(NH2)2
Mass of unknown solid (grams)
Mass of ethanol used (grams)
Mass of ethanol in kilograms
b.p. of pure ethanol
b.p. of ethanol/unknown mixture
∆Tbp
calculated molality = ∆Tbp/Kbp
calculated number of moles of solute*
experimental molar mass (g/mol)
theoretical molar mass (from chemical formula)
experimental error†
% error‡
* number of moles of solute = molality of solution (mol/kg solvent) x mass of solvent (kg
† Experimental error = [Experimental value – Theoretical value]
‡ Percent error = [(Experimental error)/(Theoretical value)] x 100
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