Experiment Overview

Inorganic synthesis often involves preparing a desired compound and then separating, purifying, drying, and weighing the product. A variety of laboratory techniques such as reflux, filtration, distillation, washing, and drying are used to maximize yield and purity.

What This Experiment Demonstrates

• Reaction control using heating under reflux
• Separation of solids and liquids using filtration and distillation
• Purification of products through washing and drying
• Determination of reaction yield

Apparatus Required

• Round-bottom flask
• Reflux condenser
• Heating mantle or hot plate
• Büchner funnel
• Side-arm filter flask
• Vacuum pump or aspirator
• Filter paper
• Distillation apparatus
• Thermometer
• Receiving flask
• Watch glass or weighing boat
• Analytical balance

Chemicals Required

The chemicals required depend on the synthesis being performed. Solvents such as water, ethanol, or acetone may be used for reaction, washing, and purification steps.

Theory

Inorganic synthesis frequently requires controlled heating to ensure that reactants undergo complete reaction. Reflux is used when prolonged heating is required while preventing solvent loss. Vapours rise into a water-cooled condenser, condense, and return to the reaction flask, allowing the reaction mixture to remain at a constant volume.

Once a reaction is complete, the desired product must be separated from impurities. If the desired product is a liquid, gravity filtration may be used to remove insoluble solids. If the desired product is a solid precipitate or crystal, vacuum filtration allows rapid collection and partial drying.

Simple distillation can be used to separate a volatile liquid from non-volatile impurities or from another liquid with a sufficiently different boiling point. The liquid is vaporized, condensed, and collected separately.

After isolation, solid products are washed to remove dissolved impurities and dried before weighing. Accurate weighing is essential for determining the actual yield of the reaction.

Percentage yield are calculated using stoichiometric relationships:

\[\%\text{Yield} = \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100\]

Part A: Heating Under Reflux

1. Place reactants and a stir bar or boiling chips into a round-bottom flask.
2. Attach a vertical condenser.
3. Connect water to the lower inlet and allow it to leave from the upper outlet.
4. Start a slow water flow.
5. Begin heating the reaction mixture.
6. Adjust heating so the vapour ring remains below halfway up the condenser.
7. Begin timing once condensed liquid is observed dripping steadily back into the flask.

Video courtesy of CapilanoUChemlab (YouTube). Video used for educational purposes under YouTube’s embedding policy.

Part B: Gravity Filtration

1. Fold filter paper into a cone or flute and place it in a funnel.
2. Wet the paper with a small amount of solvent.
3. Pour the liquid carefully through a glass rod.
4. Transfer remaining solids using a rubber policeman.

Part C: Vacuum Filtration

1. Place filter paper in a Büchner funnel.
2. Wet the paper with cold solvent.
3. Apply vacuum to secure the paper.
4. Pour the mixture into the funnel.
5. Wash the collected solid using small portions of ice-cold solvent.
6. Continue suction for several minutes to partially dry the product.

Video courtesy of Professor Dave Explains (YouTube). Video used for educational purposes under YouTube’s embedding policy.

Part D: Simple Distillation

1. Fill the distilling flask one-third to one-half full.
2. Add boiling chips.
3. Position the thermometer bulb just below the side-arm opening.
4. Start condenser water flow.
5. Heat gradually and collect distillate at approximately one drop per second.
6. Record the boiling point range.
7. Stop before the flask becomes dry.

Video courtesy of Professor Dave Explains (YouTube). Video used for educational purposes under YouTube’s embedding policy.

Part E: Washing, Drying and Weighing

1. Wash the collected solid using small portions of cold solvent.
2. Dry the product by continued vacuum filtration, air drying, or oven drying.
3. Allow the product to cool to room temperature.
4. Transfer the dry product to a weighing boat.
5. Record the mass using an analytical balance.

Critical Rules

• Add boiling chips before heating and never to hot liquid.
• Ensure condenser water enters from the bottom and exits from the top.
• Always wet filter paper before filtration.
• Wash solids using small portions of cold solvent rather than one large wash.
• Never wash collected solids with hot solvent.
• Do not weigh warm products.
• Stop distillation before the flask runs dry.

Observations

During reflux, condensed liquid continuously returns to the reaction flask. During filtration, solids separate from liquids. Distillation produces a collected liquid distillate, while drying removes residual solvent from solid products.

Calculations

• Determine the limiting reactant.
• Calculate the theoretical yield of product.
• Measure the actual mass obtained.
• Calculate percentage yield.

Result

The desired product is synthesized, isolated, purified, dried, and weighed. The efficiency of the synthesis is evaluated using the percentage yield.