Some chemistry questions? did I answer them right?

[匿名]

2019-08-03 7:32 pm

1. What is the cell reaction for a voltaic cell composed of the following half-cells?
Co^2+ + 2e^- --> Co E^o = -0.28V
Na^+ + e^- --> Na E^o = -2.71V
a. Co2+ + Na --> Co + Na+
b. Co2+ + 2Na --> Co + 2Na+
c. Co2 + Na+ --> Co + Na --> my answer

2. what is the reducing gent in this reaction
MnO4^- + SO2 --> Mn^+2 + SO4^-2
a. SO4^-2
b. SO2 ---> my answer
c. Mn+2

3. How much H2SO4 is needed to neutralize 1 liter of a 0.50M solution of NaOH?
a. 0.25 mol
b. 0.50 mol ---> my answer
c. 1.0 mol

4. CI is oxidized and H is reduced in this reaction.
2CIO^- + H2 + 2e^- --> 2CI^- + 2OH^-
a. true
b. false ---> my answer

5. In which of the following compounds does the oxidation of nitrogen have a negative value?
a. NO
b. NO2 ---> my answer
c. NH4CI

thank you

回答 (1)

賣女孩的火柴

2019-08-03 9:09 pm

✔ 最佳答案

1.
Reduction half reaction: Co²⁺ + 2e⁻ → Co
Oxidation half reaction: 2Na → 2Na⁺ +2e⁻

Sum up the above two half reactions, and cancel 2e⁻ on the both sides.
Cell reaction: Co²⁺ + 2Na → Co + 2Na⁺

The answer: b. Co²⁺ + 2Na → Co + 2Na⁺

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2.
SO₂ is oxidized.
This is because the oxidation number of S increases from +4 (in SO₂) to +6 (in SO₄²⁻).
As the reducing agent in the reaction is oxidized, the reducing agent is SO₂.
(Never consider Mn²⁺ because it is a product. Only reactants can act as oxidizing agents or reducing agents.)

The answer: b. SO₂

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3.
H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O
Mole ratio H₂SO₄ : NaOH = 1 : 2
No. of moles of NaOH = (0.50 mol/L) × (1 L) = 0.50 mol
No. of moles of H₂SO₄ = (0.50 mol) × (1/2) = 0.25 mol

The answer: a. 0.25 mol

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4.
2CIO⁻ + H₂ + 2e⁻ → 2CI⁻ + 2OH⁻
CIO⁻ is reduced as the oxidation number of Cl decreases from +1 (in ClO⁻) to -1 (in Cl⁻).
H₂ is oxidized as the oxidation number of H increases from 0 (in H₂) to +1 (in OH⁻).

The answer: false

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5.
Oxidation number of N in NO = 0 - (-2) = +2
Oxidation number of N in NO₂ = 0 - 2(-2) = +4
Oxidation number of NH₄Cl = 0 - 4(+1) - (-1) = -3

The answer: c. NH₄Cl

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