Indirect Gravimetric Determination of the
Empirical Formula of a Hydrate
Gravimetric analysis is a method of determining masses that uses the gravimetric balance
as the primary measuring tool. You will use this process to determine the empirical
formula of a hydrated compound.
Pre Lab Questions:
Solve problems 3.49 and 3.50 from your text.
Information for Procedure Writing (Technical Information for
Using a Crucible)
1. The container in which a sample is to be heated must be clean and dry. “Dry”
means that it must have been heated as hot as it will be heated during the
experiment before it is weighed the first time. Otherwise, the moisture that
adheres to most surfaces at room temperature will be lost while the sample is
being heated, and this weight loss would be attributed to the sample.
2. Caution must be exercised in handling containers after they have been heated
because perspiration and oil from your skin will adhere to containers and cause
errors. Use crucible tongs to pick up the crucible and lid after both have been
cleaned, heated and cooled.
3. Always allow items that have been heated to cool slowly on a wire gauze. By
putting you hand near but not ON the items, you can determine whether or not it
is hot.
4. Support a clean porcelain crucible and its cover on a clay triangle (as shown in
figure A). Heat them in the hottest portion of a burner flame.
5. There must be agreement among measurements, meaning that processes
(excluding the initial heating and cooling of the empty crucible and lid) must be
conducted more than once. If the difference in successive weights is greater than
0.002 g, the process must be repeated.
6. Heat the compound slowly. The sample will be adequately heated when the
bottom of the crucible glows red for 5 minutes. Reduce the heat if splattering or
smoking occurs at any point, and then gradually increase the intensity of the
flame.
Requirements
All parts of the standard lab report are expected. Show all calculations and write the
empirical formula for the hydrated compound. Use Equation Editor.
Timeline
Period 1: Solve Pre Lab Questions and develop procedure; submit it to be checked by the
teacher for major safety issues
Periods 2 and 3: Perform lab