Stoichiometry is the branch of chemistry that deals with the calculation of the quantities of reactantsand products involved in a chemical reaction.
A mole is the quantity of a given substance that contains as many molecules or formula units as the number of atoms in exactly 12 grams of C-12.
The limiting reactant is the reactant that is entirely consumed when a reaction goes to completion. The excess reactant is the reactant that is not completely consumed, and is left over. The moles of the product are always determined by the starting moles of the limiting reactant.
Facilitate the following procedures for students. Circulate around the laboratory to ensure safety of all students, as well as to make sure they are conducting the experiment without tremendous error.
Pre-Lab (homework from the night before)
Note: Usual lab groups should have picked out a number from a hat during the previous day. The number indicates the amount of aluminum and copper (II) chloride dihydrate (in grams) they will be working with in the lab.
Using the chart below, select your group number and the mass of aluminum metal and copper (II) chloride dihydrate that you will be using in this activity.
Mass of Al (g)
Mass of CuCl2·2H2O (g)
Include a brief introduction, data, the balanced reaction equation, and calculated results (including work). Determine the relative size of any error between your predicted post-reaction mass of the Al and its actual mass. Discuss the possible causes for errors; be certain that the causes you discuss would result in the error you experienced, i.e. the actual post-reaction aluminum mass being larger or smaller than predicted.
Percent Error = abs value (accepted value - experimental value)/(accepted value) * 100
Show all work in your lab notebook. Note: when calculating the molar mass of the copper (II) chloride dihydrate, don’t forget to add the mass of 2 moles of water!
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