Video Transcript
Colloidal sulfur can be prepared
through the condensation method. This involves reacting hydrogen
sulfide with sulfur dioxide. Which of the following is the
correct chemical equation for this reaction? (A) SO2 aqueous plus H2S aqueous
react to form S(OH)2 aqueous plus S solid. (B) SO2 aqueous plus four HS
aqueous react to form five S solid plus two H2O liquid. (C) SO2 aqueous plus two H2S
aqueous react to form three S solid plus two H2O liquid. (D) SO aqueous plus two HS aqueous
react to form three S solid plus H2O liquid. Or (E) two SO3 aqueous plus six H2S
aqueous react to form eight S solid plus six H2O liquid.
Condensation methods make colloids
by taking small particles and making them bigger. Typically, they have a particle
size of less than 1000 nanometers. One example of condensation is the
formation of fog or clouds. Here, tiny water droplets in the
air combine to form larger particles that form a visible colloid, what we would
typically call a cloud.
In common industrial processes,
there are multiple types of condensation reactions that are used. One example would be to change a
substance with carefully controlled methods, like going from solution phase to the
solid phase. One common example is the formation
of colloidal sulfur through the condensation method. The chemical equation for this
process is shown. SO2 aqueous plus two H2S aqueous
react to form three S solid plus two H2O liquid.
You’ll notice that this reaction is
balanced with four hydrogen atoms, three sulfur atoms, and two oxygen atoms on both
sides of the reaction equation. And the solid sulfur particles that
are formed in the reaction are a larger aggregate than the aqueous hydrogen sulfide
and sulfur dioxide reactants. And at this point, we should be
able to revisit and answer the question. Which of the following is the
correct chemical equation for the preparation of colloidal sulfur through the
condensation method?
Because we know this equation must
have hydrogen sulfide and sulfur dioxide as starting materials, we can immediately
eliminate answer choices (B), (D), and (E), because they do not contain the required
starting materials. Answer choice (A) cannot be correct
because the reaction between sulfur dioxide and hydrogen sulfide does not form
S(OH)2 as a product. And it is in fact a highly reactive
sulfur intermediate that is formed in unrelated chemical reactions. And so we can correctly choose
answer choice (C). SO2 aqueous plus two H2S aqueous
react to form three S solid plus two H2O liquid.
