Introduction
This experiment is the culminating experiment for all the previous experiments involving stoichiometric explorations. In experiment 4 we explored the 1:1 reaction between sodium bicarbonate and carbon dioxide, i.e. for every one mole of sodium bicarbonate that reacted, one mole of carbon dioxide was formed. 1:1 reactions are very simple mathematically and thus a good starting point for stoichiometric investigations. In this experiment we expand our knowledge by working with a reaction between copper (II) nitrate and potassium iodide, a reaction that does not have one-to-one stoichiometry.

In addition to stretching our ability to calculate product and reactant amounts using reaction stoichiometry, we will also be exploring the concept of limiting and excess reagents. It is not always obvious from gram amounts which reactant will run out first when a reaction occurs. Two factors complicate the prediction: 1) chemical equations are balanced in moles not grams; and 2) moles are based on molecular weights. Thus 100 grams of O2 is a lot fewer moles than 100 grams of H2.

In addition to practicing stoichiometry, we will also learn about two new devices: the centrifuge and the dessicator.

The centrifuge is a device that uses centrifugal force to separate solids (often called precipitates) from solution. 
 

A desiccator is a piece of laboratory equipment used to protect chemicals from moisture. 

In the last lab we mentioned substances called hydrates. A hydrate is a compound that has water molecules incorporated into its crystal structure. A desiccant is a hydrate that has been stripped of all its water molecules, making it very "hungry" for water. If a desiccant is placed in a sealed container, the container is then called a dessicator, since anything placed inside it will be stripped of its moisture by the desiccant.