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C-4
1.
Read the sections at the beginning of this laboratory manual that relate to the use of a Bunsen burner
(p.23 and 24).
2.
What determines if a hydrate effloresces?
Answer: A hydrate effloresces if the vapor pressure of water exerted by its solid is greater than the
(partial) pressure of water in the surrounding atmosphere.
3.
A sample of an unknown hydrate, having a mass of 5.768 g was heated until all the water was driven
off. The mass of the anhydrous residue was 3.248 g. Qualitative tests identified the ions as Zn²
+
and
SO
4
2-
, so the anhydrous compound is ZnSO
4
. Calculate the mass percent of water and the empirical
formula of the hydrate.
Answer: 43.69% H2O; ZnSO
4
•7 H2O.
4.
Which of the chemicals in the reagent list given on page C-4 are corrosive?
Answer: HCl, H2SO
4
, NaOH, and HNO3
5.
(a)
Write a chemical equation for the complete decomposition of sugar:
Answer:
(b)
If decomposition is incomplete, a brown liquid caramel might form first. Then, as heating
continues to complete decomposition, a brown/black solid is formed. What would be the major
component of this solid?
Answer: carbon
6.
If you carried out the flame test on your hydrate and observed a violet flame, what cation might be
present? What cation might be present if a green flame had been observed?
Answer : violet might be potassium and green might be copper
