Double Replacement Reaction

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Unit 3 – Virtual Labs
Letizia Schianodicola
Lab #1 – Atomic Weight of Magnesium
1. Moles of hydrogen evolved, from chemical property dialog for beaker: a. 0.000411 mol H2
2. Calculate the atomic weight of Magnesium. Atomic weight of Mg = weight of Magnesium/moles of H2. b. 59,136.253 g/mol Mg
(24.305 - weight of Mg / 0.000411 mol H2)
3. Calculate the # of molecules of H2 that were produced in the reaction – use Avagadro’s number – remember units! c. 2.47510016 × 1020 # of molecules of H2 (Avagadro’s number * moles of H2)

4. Calculate the # of atoms of Magnesium that were involved in the reaction – use Avagadro’s number – remember units! d. 2.47510016 × 1020 # of atoms of Mg (Each atom of Mg produces 1 molecule of H2, so number remains the same)

The most important concept I learned during this lab was how and when to use Avagadro’s number. I learned that you use Avagadro’s number for calculating a mass when you have a mole of an element. One mole is equal to Avagadro’s number. I also learned that by measuring the amount of hydrogen gas evolved when reacted with magnesium, you can find the atomic weight of magnesium. Lab #2 – Double Replacement Reaction

1. Record weight of lead (II) iodide solid + watch glass (grams): a. __________g
2. Record weight of watch glass (grams):
b. __________g
3. Take the difference of the two values to determine the mass of lead (II) iodide solid (grams): c. __________g
4. Calculate % yield for the reaction:
d. __________%
5. Finally, the % yield now may be calculated:
% yield = (actual yield / 9.22 g PbI2) x 100%
e. % yield = __________%

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