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The balanced equation for the oxidation of ethanol to ethanal using sodium dichromate in acidic conditions is as follows: 3C2H5OH + Na2Cr2O7 + 4H2SO4 → 3CH3CHO + Cr2(SO4)3 + Na2SO4 + 7H2O (i) Deduce the oxidation numbers of chromium in the sodium dichromate reagent and in the chromium sulfate product - Leaving Cert Chemistry - Question c - 2010
Question c
The balanced equation for the oxidation of ethanol to ethanal using sodium dichromate in acidic conditions is as follows: 3C2H5OH + Na2Cr2O7 + 4H2SO4 → 3CH3CHO + Cr... show full transcript
Worked Solution & Example Answer:The balanced equation for the oxidation of ethanol to ethanal using sodium dichromate in acidic conditions is as follows: 3C2H5OH + Na2Cr2O7 + 4H2SO4 → 3CH3CHO + Cr2(SO4)3 + Na2SO4 + 7H2O (i) Deduce the oxidation numbers of chromium in the sodium dichromate reagent and in the chromium sulfate product - Leaving Cert Chemistry - Question c - 2010
Step 1
Deduce the oxidation numbers of chromium in the sodium dichromate reagent and in the chromium sulfate product.
Answer
In the sodium dichromate ( Na2Cr2O7), each chromium (Cr) has an oxidation number of +6. This is calculated by considering the overall charge of the compound:
- Sodium (Na) has a +1 oxidation state, totaling +2 from two sodium atoms.
- The oxygen atoms (O) are in a -2 state, totaling -14 for seven oxygen atoms.
- To balance these, chromium must be +6, giving: 2Cr + 2 - 14 = 0, which resolves to 2Cr = 12, hence Cr = +6.
In the chromium sulfate (Cr2(SO4)3), the oxidation number of chromium is +3. The sulfate ion (SO4) has a -2 charge. Thus:
- In Cr2(SO4)3, the sulfate contributes -6 (from three sulfates).
- Hence, to balance: 2Cr + (-6) = 0, leading to 2Cr = +6 and therefore each Cr = +3.
Step 2
State the colour change observed as this reaction proceeds.
Answer
The colour change observed as this reaction proceeds is from orange to green. Initially, the solution containing sodium dichromate appears orange due to the Cr(VI) ions, and as the reaction occurs and chromium is reduced to Cr(III), the solution turns green.
Step 3
Describe a test you could carry out to confirm that the organic product is an aldehyde.
Answer
To confirm that the organic product is an aldehyde, you can perform a test using Fehling's solution or ammoniacal silver nitrate (Tollen's Reagent).
- Heat the solution with Fehling's solution. If an aldehyde is present, a brick-red precipitate will form due to the reduction of the copper(II) ions.
- Alternatively, using Tollen's reagent, if the substance is an aldehyde, a silver mirror will form on the test tube due to the reduction of silver ions.
Step 4
Give the name and structure of another organic compound that could be formed when ethanol is oxidised using acidified sodium dichromate.
Answer
Another organic compound that could be formed when ethanol is oxidized using acidified sodium dichromate is ethanoic acid (also known as acetic acid). The structural formula of ethanoic acid is:
O
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H--C--C--OH
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H H
This confirms the transformation of ethanol to a carboxylic acid upon oxidation.