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Chemistry Review
1) In my lab, I have an unknown solution in a beaker that could possibly have ions of
silver, strontium or iron(III). I added rubidium iodide and nothing precipitated out. I
added a solution of sodium hydroxide and received a precipitate. I finally added a
solution potassium sulfate and a precipitate fell out. Using balanced chemical equations,
show work to find out what ion or ions were in my solution.
2) A 1.42-g sample of a pure compound, with formula M2SO4 , was dissolved in a water
and treated with an excess of aqueous barium chloride, resulting in the precipitation of all
the sulfate ions as barium sulfate. The precipitate was collected, dried, and found to
weigh 2.33 g. Determine the atomic mass of M, and identify M.
(Hints: What is charge on M? Make M a variable in a calculation)
3) A lake may be polluted with Pb2+ ions. What precipitation reaction might you use to
test for the presence of Pb2+?
4) Methane (CH4) is the main component of marsh gas. Heating methane in the presence
of sulfur produced carbon disulfide and hydrogen sulfide as the only products. (Sulfur gas
is diatomic. Sulfide has a charge of 2-.)
a) Write a balanced chemical equation for the reaction of methane and sulfur.
b) Calculate the theoretical yield of carbon disulfide when 120. g of methane is reacted
with an equal mass of sulfur.