Stoichiometry LabStoichiometry Lab

Mass-Mass and Limiting Mass-Mass and Limiting ReactantReactant

PurposePurpose

• In this lab, you will determine the reaction In this lab, you will determine the reaction for mixing two reactants together.for mixing two reactants together.

• You will then measure out 0.005 moles of You will then measure out 0.005 moles of each reactant. You will dissolve, mix, and each reactant. You will dissolve, mix, and react them to make products.react them to make products.

• You will compare the amount you You will compare the amount you produced at the end with the amount you produced at the end with the amount you expected to get using stoichiometry. expected to get using stoichiometry.

Put on your safety goggles!Put on your safety goggles!

Obtain the reactants.Obtain the reactants.• Put the lid back on the Put the lid back on the

bottle! Use a clean bottle! Use a clean spatula from your box to spatula from your box to dip into the chemical! dip into the chemical! Never touch lab chemicals Never touch lab chemicals with your hands!with your hands!

• Be sure to wait after you Be sure to wait after you push the ZERO button push the ZERO button until it reads 0.0000 g until it reads 0.0000 g before you make a before you make a measurement (don’t hit measurement (don’t hit CAL!)CAL!)

Obtain the reactants.Obtain the reactants.

• You can either 1) zero the You can either 1) zero the balance with the weighing balance with the weighing paper, or 2) get a mass of the paper, or 2) get a mass of the weighing paper and subtract.weighing paper and subtract.

• Don’t waste time trying to get Don’t waste time trying to get the exact amount needed… the exact amount needed… instead get close BUT WRITE instead get close BUT WRITE DOWN THE ACTUAL AMOUNT!DOWN THE ACTUAL AMOUNT!

• Keep the balance and the desktop clean of lab chemicals! Clean up the SLIGHTEST spill with a paint brush and dispose of it properly!

Obtain the lead (II) nitrate.Obtain the lead (II) nitrate.

Obtain the potassium Obtain the potassium chromate.chromate.

Be sure to get the mass of the EMPTY beaker before you dump the potassium chromate into the beaker!

Dissolve the reactants in Dissolve the reactants in water.water.

Dissolve the lead (II) nitrate in a beaker with a specified amount of water. In another beaker, do the same with the potassium chromate.

Slowly mix the chemicals.Slowly mix the chemicals.

• Be sure to pour INTO Be sure to pour INTO the beaker that you the beaker that you massed, while massed, while stirring.stirring.

• Assemble a ring Assemble a ring stand and bunsen stand and bunsen burner as shown burner as shown here.here.

• SLIGHTLY warm the SLIGHTLY warm the mixture for a few mixture for a few minutes.minutes.

When is it done?When is it done?

• The reaction should The reaction should be complete when be complete when the color is orange the color is orange rather than bright rather than bright yellow.yellow.

• The solid may “poof” The solid may “poof” a little during a little during heating like in this heating like in this picture. If the picture. If the reaction is gurgling, reaction is gurgling, TURN OFF THE HEAT!TURN OFF THE HEAT!

Filter the products.Filter the products.

• One of the products is an One of the products is an orange precipitate (a solid that orange precipitate (a solid that forms by mixing two liquids).forms by mixing two liquids).

• The other product is soluble in The other product is soluble in water. You will not be able to water. You will not be able to see this product.see this product.

• Separate the two products by Separate the two products by filtering through a paper filtering through a paper funnel. The liquid will pass funnel. The liquid will pass through, but the solid will not.through, but the solid will not.

• Be sure to get the mass of the Be sure to get the mass of the filter paper BEFORE you filter!filter paper BEFORE you filter!

FilteringFiltering

The trick to fast filtering is to keep all the solid in the beaker as possible. Let the solid settle to the bottom, and pour the water through the paper funnel. Catch the liquid in an Erlenmeyer flask, as shown here. The paper will catch any solid that accidentally gets away from you. If you try to pour all of the solid in, it will take HOURS for you to filter.

FilteringFiltering

This is what it should look like when you are finished filtering.

Combine the orange Combine the orange product.product.

Remove the filter paper from the funnel with your forceps. Drop it into the beaker with the rest of the orange precipitate.

Save your product and Save your product and filtrate.filtrate.• Place your beaker with Place your beaker with

the precipitate and the precipitate and filter paper into the filter paper into the oven to dry overnight.oven to dry overnight.

• Put a cork or rubber Put a cork or rubber stopper in the flask stopper in the flask that holds the filtrate that holds the filtrate (liquid). Label it, and (liquid). Label it, and store until the next lab store until the next lab session.session.

Day TwoDay Two

• Get the mass of the Get the mass of the beaker with the filter beaker with the filter paper and precipitate. paper and precipitate. Use the SAME balance Use the SAME balance as before.as before.

• Evaporate PART of Evaporate PART of your filtrate using an your filtrate using an evaporating dish on a evaporating dish on a ring stand. Note there ring stand. Note there is a second product! is a second product! With the water all With the water all evaporated, you can evaporated, you can see the other product see the other product in solid form!in solid form!

% error% error

Experimental yield – Theoretical yieldExperimental yield – Theoretical yield

Theoretical yieldTheoretical yieldX 100 = % error

What YOU got in the experiment

What you predicted you would get (use stoichiometry)

% yield% yield

Experimental yieldExperimental yield

Theoretical yieldTheoretical yieldX 100 = % yield