Competitive Exams: Chemistry MCQs (Practice-Test 12 of 31)

  1. In recitation, you saw that silver tarnish (Ag2S (s) ) can be converted to silver metal (Ag (s) ) by placing the tarnished silver piece in a dilute solution of baking soda contained in an aluminum pan. The following half-reactions are thought to be involved, Ag2S (s) + 2H3O + (aq) + 2e- ⇔ 2Ag (s) + H2S (g) + 2H2O (l) Al3 + (aq) + 3e- ⇔ Al (s) Which of the following statements is TRUE?

    1. As the silver piece is being cleaned, H3O + ions are produced and H2S gas is consumed.

    2. It is necessary that the silver piece and the aluminum pan touch so that electrons can be transferred.

    3. As the silver piece is being cleaned, Al3 + ions in the solution are reduced to Al metal.

    4. The silver piece being cleaned functions as the anode.

    5. All of the above are TRUE.

  2. Calculate the cell potential (in V) at 25oC for a copper concentration cell in which the Cu2 + concentration in one half-cell is equal to 0.050 M and the Cu2 + concentration in the other half-cell is equal to 1.5 M. Note: The number of moles of electrons transferred is equal to 2.

  3. Which of the following is a correctly balanced oxidation/reduction reaction.

    1. Fe2 + + Au3 + ⇔ Fe3 + + Au

    2. 2 Fe2 + + Au3 + ⇔ 2 Fe3 + + Au

    3. Fe2 + + 3 Au3 + ⇔ Fe3 + + 3 Au

    4. 3 Fe2 + + Au3 + ⇔ 3 Fe3 + + Au

    5. The correct response is not given.