Question 1-5 can be found in Expert Q and A, however i could not find any help a

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Question 1-5 can be found in Expert Q and A, however i could not find any help after that. thanks LNL7 Alcohol Content of Vodka by Dichromate Titration Assignment Introduction Questions: - Refer to the Background and Procedure information to this lab to answer these questions. 1. Why does excess dichromate ion have to be used in the first reaction with ethanol? Because ethanol is colorless; Cr3+ ion is green and Cr2O72- is orange, it is easier to obtain quantity of Cr2O72- instead of quantity of ethanol. 2. What is the oxidation number of chromium in the reactant and in the product in both reactions? Cr(VI) in Cr2O72- and Cr (III) in Cr3+ 3. What is the full name of the reagent used to consume the excess dichromate in the second reaction? Ammonium iron (II) sulfate hexahydrate 4. What is the full name of the redox indicator used to identify the endpoint in the titration? Sodium N, N-diphenyl-amine sulfonate 5. The Background explains that the technique of back-titration is used in this experiment. Explain why the titrations done in Parts 2 and 3 of Experiment 2 are back-titrations, and a general explanation of how you will determine the moles dichromate that reacted with the ethanol in the first reaction. In parts 2 and 3, the reacted dichromate is not calculated, the amount of dichromate left is calculated to determine how much dichromate reacted with the ethanol. Experiment 1: Preparing Solutions Show work and include units and the correct number of significant figures on all measurements and calculated results. 6. Calculate the molarity concentration of potassium dichromate, K2Cr2O7, in the first volumetric flask. This is also the concentration of dichromate ion. 7. Calculate the molarity concentration of Fe(NH4)2(SO4)2•6H2O in the second two volumetric flasks. This is also the concentration of Fe2+ ion. Experiment 2: Titrating the Vodka Sample

Explanation / Answer

6. Mass of K2Cr2O7 = 4.00 g

Molar mass of K2Cr2O7 = 294.185 g/mol

Moles of K2Cr2O7 = 0.0136

Total volume in the volumetric flask 1 = 100 mL = 0.10 L

Molarity of K2Cr2O7 = 0.0136 / 0.10

= 0.136 M

7. Mass of Fe(NH4)2(SO4)2•6H2O = 4.00 g

Molar mass of Fe(NH4)2(SO4)2•6H2O = 284.05 g/ mol

Moles of Fe(NH4)2(SO4)2•6H2O = 4.00 / 284.05

= 0.0140

Total volume in the volumetric flask 2 = 100 mL = 0.10 L

Molarity of Fe(NH4)2(SO4)2•6H2O = 0.0140 / 0.10

= 0.140 M

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