NET, IAS, State-SET (KSET, WBSET, MPSET, etc.), GATE, CUET, Olympiads etc.: Chemistry MCQs (Practice_Test 13 of 31)
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- In acid solution, dichromate ion oxidizes ferrous iron to ferric iron as illustrated in the partial equation: Fe2 ++ Cr2O72- ⟺ Fe3 ++ Cr3 + When this equation is balanced, the right side of the equation will be as follows:
- ⟺ Fe3 ++ 2 Cr3 ++ 7 H2O
- ⟺ 6 Fe3 ++ 2 Cr3 ++ 7 H2O
- ⟺ 3 Fe3 ++ 2 Cr3 ++ 7 H2O
- ⟺ Fe3 ++ 2 Cr3 ++ H2O
- The correct response is not given.
- You have observed all of the reactions listed below. Which of these reactions IS a reduction-oxidation reaction?
- HCl (aq) + H2O (l) ⇾ H3O + (aq) + Cl- (aq)
- Fe2O3 (s, iron oxide) + 2Al (s) ⇾ 2Fe (s) + Al2O3 (s, aluminum oxide)
- Cu2 + (aq) + 4NH3 (aq) ⇾ Cu (NH3) 42 + (aq)
- NH4NO3 (s, ammonium nitrate) ⇾ NH4 + (aq) + NO3- (aq)
- None of these is a reduction-oxidation reaction.
- In an electrochemical process called “electrolysis” H2 gas and O2 gas can be obtained by passing an electric current through liquid water, 2H2O (l) ⇾ 2H2 (g) + O2 (g) Which species is the OXIDIZING AGENT and which species is the REDUCING AGENT in this reaction, respectively?
- H2O (l) ; H2 (g)
- O2 (g) ; H2O (l)
- H2O (l) ; H2O (l)
- O2 (g) ; H2 (g)
- H2 (g) ; H2O (l)
- 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 involved, Ag2S (s) + 2H3O + (aq) + 2e________ > 2Ag (s) + H2S (g) + 2H2O (l) Al3 + (aq) + 3e ⇾ Al (s) Which of the following is the correct overall balanced equation for the reaction?
- Ag2S + 2H3O ++ Al ⇾ 2Ag + H2S + Al3 ++ 2H2O
- 6Ag + 3H2S + 6H2O + 2Al3 + ⇾ 2Al + 3Ag2S + 6H3O +
- Ag2S + Al ⇾ Ag + Al3 +
- 2Al + 3Ag2S + 6H3O + ⇾ 6Ag + 3H2S + 6H2O + 2Al3 +
- Ag2S + 2H3O ++ Al ⇾ 2Ag + H2S + 2H2O + Al3 ++ e-
- Which of the following statements about porous disks in voltaic cells is TRUE?
- Free electrons flow through the porous disk to maintain electrical neutrality in the two half-cells.
- Ions present in the two half-cells flow through the porous disk to maintain electrical neutrality in both half-cells.
- A porous disk contains a strong electrolyte like potassium chloride (KCl) .
- The wire must be connected directly to the porous disk in order for the porous disk to be able to maintain electrical neutrality in the two half-cells.
- In some cases, a porous disk functions as the cathode.
- In the Standard Hydrogen Electrode, a platinum wire is used as the electrode. Consider the following standard reduction potentials, half reactionEo, V Zn2 + (aq) + 2e________ > Zn (s) -0.76 2H3O + (aq) + 2e ⇾ 2H2O (l) + H2 (g) 0.00 Pt2 + (aq) + 2e ⇾ Pt (s) 1.20
- Which of the following statements best describes what would happen if the platinum wire in the Standard Hydrogen Electrode were replaced with a zinc wire? Note: Assume that this is the only change made to the half-cell.
- Zinc ion in the solution would be reduced; the mass of the zinc electrode would increase.
- The pH of the solution would decrease.
- The zinc electrode would be oxidized; the mass of the zinc electrode would decrease.
- This change would have no effect-the Standard Hydrogen Electrode would continue to function properly.
- It is impossible to tell.
- In recitation, you examined a diagram of a voltaic cell constructed from zinc and copper in which a tube containing a porous disk and a solution of KCl was placed in each half-cell (recall, the two tubes were not connected) . Which of the following statements best describes why this cell has a cell potential of 0.00 V?
- The sum of the zinc and copper half-cell potentials is equal to 0.00 V.
- Electrical neutrality cannot be maintained in the half-cells and the KCl tubes.
- All voltaic cells which use zinc in one of the half-cells have a cell potential of 0.00 V.
- The tubes needed to contain a weak electrolyte, like AgCl, in order for the cell to function.
- There was not enough information given to solve the problem.
- Which of the following statements best describes what will happen when magnesium metal is added to an aqueous solution containing 1.0 M ferric ion (Fe3 +) at 25oC? half reactionEo, V Mg2 + (aq) + 2e________ > Mg (s) -2.375 Fe3 + (aq) + 3e ⇾ Fe (s) -0.036
- Mg (s) will be oxidized; Fe3 + (aq) will be reduced; the standard cell potential will be 2.339 V.
- Mg (s) will be oxidized; Fe3 + (aq) will be reduced; the standard cell potential will be-2.339 V.
- Fe3 + (aq) will be oxidized; Mg (s) will be reduced; the standard cell potential will be-2.339 V.
- Fe3 + (aq) will be oxidized; Mg (s) will be reduced; the standard cell potential will be 2.339 V.
- There is not enough information given to answer the question.
- In recitation, you explored the electrochemistry of the “fruit clock” Which of the following statements best describes why the clock functions best when citrus fruits (i.e. … lemons, oranges, limes, etc.) are used?
- Citrus fruits work best because they are often brightly colored.
- Only fruits and vegetables that grow on trees can be used to power the fruit clock.
- Citrus fruits contain very high concentrations of copper ion.
- Acid is a product in one of the half-reactions involved.
- Acid is a reactant in one of the half-reactions involved.
- Suppose you have been given the task of selecting a metal to be used as the sacrificial anode for the cathodic protection of a buried iron fuel tank. Considering the following standard reduction potentials, half reactionEo, V Pd2 + (aq) + 2e________ > Pd (s) 0.99 Ag + (aq) + e ⇾ Ag (s) 0.80 Cu2 + (aq) + 2e ⇾ Cu (s) 0.34 Ni2 + (aq) + 2e ⇾ Ni (s) -0.23 Fe2 + (aq) + 2e ⇾ Fe (s) -0.41
- which of the following metals could be used as the sacrificial anode in this application?
- Pd
- Ag
- Cu
- Ni
- None of these.
- In lecture, one area of current research in electrochemistry was described: The development of improved batteries for use in electric cars. Which of the following properties of batteries are researchers currently trying to improve?
- range (the number of miles that can be driven before the batteries must be recharged)
- cost
- lifetime (the number of times the batteries can be recharged before they must be replaced)
- recharge time (the time required to fully recharge the batteries)
- Researchers are currently trying to improve all of the above:
- Use the Standard Reduction Potentials given below to calculate Kf for Zn (NH3) 42 + at 25oC. Zn2 + (aq) + 4NH3 (aq) ⟺ Zn (NH3) 42 + (aq) , Kf = ? half reactionEo, V Zn (NH3) 42 + (aq) + 2e- ⟺ Zn (s) + 4NH3 (aq) -1.04 Zn2 + (aq) + 2e- ⟺ Zn (s) -0.76
- The cell potential for the electrochemical reaction shown below depends upon the Cl-and Cu2 + concentrations. Calculate the cell potential (in V) at 25oC if [Cu2 +] = 3.5 M and [Cl-] = 1.7 M. Note: The number of moles of electrons transported in this reaction is equal to 2.
Cu2 + (aq) + 2Cl- (aq) + 2Ag (s) ⇾ Cu (s) + 2AgCl (s) , Eo = 0.12 V