CHM110H5 Lecture Notes - Lecture 1: Redox, Burette, Bromate

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plumsardine237

14 Apr 2016

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Determination of the product of a redox reaction: In this experiment, the equation of a redox reaction has to be determined by the use of the experimental data. The reaction being used is between bromate ions and hydroxlammounium ions in an aqueous acid solution. Using stoichiometric methods, the number of moles of different products and reactants are to be determined in this equation. The ultimate goal is to identify the n containing product and write the above equation in balanced form. Volume used in each reaction: 10 ml or 0. 001 l. The solution changed from clear to pale yellow upon stirring. The temperature of the solution was from 23oc 25oc. The solution turned dark brown upon adding potassium iodide (ki). When na2s2o3 was added, the solution turned slight yellow with its temperature at. The adding of starch saw the solution turn dark bluish black while the temperature remained the same.

Related Questions

1. The following data were collected at 20 ^oC for the reaction of bromphenol blue, HBPB^2-, and hydroxide ions, OH^-, shown in the equation below

HBPB^2- + OH^- <---> BPB^3- + H₂O

a)What is the rate equation for the reaction?

Determination	[HBPB^2-]₀, M	[OH^-]_o, M	Rate, M/sec
1	7.22 x 10^-6	1.00	9.627 x10^-9
2	7.22 x 10^-6	0.25	2.490 x10^-9
3	3.63 x 10^-6	1.00	4.750 x10^-

The reaction was run three times with different initial concentrations of the reactants yielding the following rates:

b)Determine the reaction order with respect to HBPB^2-

c)Determine the reaction order with respect to OH^-

d)Calculate the rate constant for this reaction at 20 ^oC

e)What is the ârate lawâ for this reaction?

f)What other information do you need to calculate the activation energy for this reaction?

2. Why is it better to transfer one group of solutions into one flask and a second group into a second flask and then mix them, instead of pipetting the solutions sequentially into the same flask?

3. What will be the concentration of [I^-] in the reaction flask after mixing (See Run #6): 1.0 ml starch + 2.0 mL 1.2 x10^-2 M Na₂S₂O₃ + 4.0 mL 0.20 M KI + 4.0 mL 0.20 M KNO₃ + 4.0 mL 0.20 M (NH₄)₂S₂O₈ + 4.0 mL 0.20 M (NH₄)₂SO₄ ?

4. What will be the concentration of [S₂O₈^2-] in the same reaction mixture as above?

Using this information: I used 4.00 g potassium dichromate. The amount of Iron ll is 4.00 gram in 2nd flask. Used grey moose vodka 2.00 ml and filled flask with water. This was the 2% vodka solution. For the experiment I used 5.00ml of the vodka and added 35.00 ml of more water to make it 1/8 of 2% or 0.25% of the original. With this information and the answer's i have placed in the table please help with remainder of questions. Need to work to understand answers so I will get correct on upcoming test. Thanks.

Calculate the concentration of the dichromate ion in the first volumetric flask.

Calculate the concentration of the iron (II) ion in the second volumetric flask.

Experiment 2: Titrate the Vodka Sample

Lab Results

Record the following lab data in the table below. If you had to repeat one of the titrations, disregard the value that was different.

(a) volume of potassium dichromate solution added to the Erlenmeyer flask in mL	5.00ml
(b) coarse titration volume of iron (II) solution range in mL	14.10 -14.15 ml
(c) volume of iron (II) solution delivered from the burette in mL during the first fine titration	14.13ml
(d) volume of iron (II) solution delivered from the burette in mL during the second fine titration	14.11ml
(e) average volume of iron (II) solution used in the fine titrations	14.12ml
(f) the color of the analyte solution at the end point of the titration	purple
(g) the color of the analyte solution after adding the indicator	dark green

Data Analysis

Record and calculate the quantities in the table below using the data from your dichromate titrations. Use an average value for the volume of iron (II) solution used in the titration. If one of your values is very different, and you had to perform the titration three times, disregard the value that was very different when computing the average.

(a) volume of potassium dichromate solution added to the Erlenmeyer flask in mL 5.00ml
(b) moles of dichromate ion added to the Erlenmeyer flask
(c) average volume of iron (II) solution delivered from the burette in mL 14.12ml
(d) moles of iron (II) ions delivered from the burette
(e) moles of excess dichromate ions that reacted with the iron (II) ions (remember that the ratio in which they react is 1 dichromate : 6 iron (II))
(f) moles of dichromate that reacted with the ethanol in the vodka (Subtract excess dichromate ions that reacted with the iron (II) ions from the original moles of dichromate ion present.)
(g) moles of ethanol in the 5 mL diluted vodka sample according to the stoichiometric ratio of 2 dichromate ions to 3 ethanol molecules

The amount of alcohol in a drink is typically reported as percent alcohol by volume. Volume percent or volume/volume percent (% v/v) most often is used when preparing solutions of liquids. Volume percent is defined as:
% v/v = V_solute/V_solution Ã 100
Find the percent alcohol (ethanol) by volume for the vodka used in the lab by following the steps outlined in the table below.

(a) given the molar mass of ethanol of 46.07 g/mol, calculate the mass of alcohol (ethanol) in the tested sample solution
(b) given the density of ethanol of 0.7893g/ml, find the volume in mL of ethanol present in the diluted vodka solution
(c) record the volume of vodka used in the experiment in mL
(d) find the percent alcohol by volume (% v/v) in the diluted vodka solution
(e) the diluted vodka solution was prepared by diluting 2.00 mL vodka to 100.00 mL. Calculate the dilution factor used (N:1)
(f) multiply the percent alcohol by volume in the diluted vodka solution by the dilution factor to obtain the % v/v alcohol in the original vodka solution

Conclusions

The Grey Moose vodka tested in this lab reports a percent alcohol by volume of 40.0% on its label. How does your value compare to the reported one? If the values are different, give one possible experimental error that might have contributed to the difference.

Potassium permanganate is another strong oxidizing substance similar to potassium dichromate. An acidic solution of purple permanganate ions can get reduced to colorless Mn²⁺ ions in the presence of ethanol. Write down the redox reaction between permanganate and ethanol, and balance it using the half-reaction method.

Besides vodka, there are other colorless alcohol-containing beverages that can be titrated following the procedure in your lab. Given the average values for the percent alcohol by volume listed in the table below, which beverage do you expect to use the least amount of iron (II) standard solution during the titration? Assume all lab procedures stay the same.

	% alcohol by volume
White rum	37.0%
Vermouth	18.0%
White whine	12.0%

CHM110H5 Lecture Notes - Lecture 1: Redox, Burette, Bromate

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