Consider the following reaction:
3 C2H5OH + 2 K2Cr2O7 + 8 H2SO4 → 2 Cr2(SO4)3 + 3 CH3COOH + 2 K2SO4 + 11 H2O
Which statement below best describes what is happening as this reaction proceeds?
a. sulphuric acid is being reduced to sulphate ion
b. ethanol is being reduced to acetic acid
c. dichromate ion is being reduced to chromium ion
d. dichromate ion is being oxidized to chromium ion
e. sulphuric acid is being oxidized to sulphate ion
The correct answer is c. Check out the others.
a. sulphuric acid is being reduced to sulphate ion
b. ethanol is being reduced to acetic acid
c. dichromate ion is being reduced to chromium ion
d. dichromate ion is being oxidized to chromium ion
e. sulphuric acid is being oxidized to sulphate ion
a can't be true. SO4 of H2SO4 is still SO4. Neither oxidized nor reduced.
b can't be true. Ethanol is being oxidized to acetic acid.
c is correct.
d can't be right. dichromate (Cr is +6) is going to Cr(3+). Gain of electrons is reduction and not oxidation.
e can't be right. see a.
Be sure you understand each of these.
Well, let's take a closer look at the reaction. We have potassium dichromate, ethanol, and sulfuric acid reacting to form chromium(III) sulfate, acetic acid, potassium sulfate, and water.
The oxidation state of sulfur in sulfuric acid is +6, and in sulfate ion, it is +6 as well. So there is no change in the oxidation state of sulfur, which means it is neither being reduced nor oxidized.
The oxidation state of carbon in ethanol is -2, and in acetic acid, it is +2. It has been oxidized from -2 to +2, so we can rule out option b.
The oxidation state of chromium in dichromate ion is +6, and in chromium(III) sulfate, it is +3. It has been reduced from +6 to +3, so option c seems to be the correct answer.
So, the statement that best describes what is happening in this reaction is:
c. dichromate ion is being reduced to chromium ion.
c. dichromate ion is being reduced to chromium ion
In the given reaction, the dichromate ion (Cr2O7^2-) is being reduced to chromium ion (Cr^3+). This is indicated by the change in oxidation state of chromium from +6 in dichromate ion to +3 in chromium ion. Reduction involves the gaining of electrons, and in this reaction, the dichromate ion is gaining electrons to form chromium ion.
To determine the best statement that describes what is happening as this reaction proceeds, we need to identify which species are being oxidized and which species are being reduced.
Let's look at the reaction:
3 C2H5OH + 2 K2Cr2O7 + 8 H2SO4 → 2 Cr2(SO4)3 + 3 CH3COOH + 2 K2SO4 + 11 H2O
In this reaction, the species gaining oxygen, losing hydrogen, or losing electrons is being oxidized. And the species gaining hydrogen, losing oxygen, or gaining electrons is being reduced.
Now, let's examine each option:
a. sulphuric acid is being reduced to sulphate ion
Sulphuric acid (H2SO4) appears on both sides of the reaction. There is no change in its oxidation state, so this statement is not correct.
b. ethanol is being reduced to acetic acid
Ethanol (C2H5OH) is converted to acetic acid (CH3COOH) in the reaction. Ethanol loses two hydrogens and gains an oxygen, indicating that it is being oxidized, not reduced. Therefore, this statement is not correct.
c. dichromate ion is being reduced to chromium ion
Dichromate ion (Cr2O7^2-) is converted to chromium ion (Cr^3+) in the reaction. The dichromate ion decreases in oxidation state from +6 to +3, meaning it gains electrons and is reduced. Therefore, this statement is correct.
d. dichromate ion is being oxidized to chromium ion
This statement is the opposite of option c and is incorrect. The dichromate ion is being reduced, not oxidized.
e. sulphuric acid is being oxidized to sulphate ion
Similar to option a, sulphuric acid (H2SO4) appears on both sides of the reaction, and there is no change in its oxidation state. Therefore, this statement is not correct.
Therefore, the best statement that describes what is happening as this reaction proceeds is:
c. dichromate ion is being reduced to chromium ion