1. a. In an extraction experiment, in which three compounds are extracted from a solid mixture. Why would the percent recoveries be less that 100%? Please explain.

b. How do you know if the recystaillization was effective (did purification result)? Talk about melting points

Determination of Iron in Vitamin Supplements by Spectrophotometric Analysis

A tablet containing iron, Fe (II) fumarate (Fe2+C4H2O4 2- ) and binder was dissolved in 0.1M HCl solution and the solution was filtered to remove any insoluble binder

Fe (II) in the above step was oxidized with hydrogen peroxide to Fe (III) as follows 2 Fe2+ + H2O2 + H+ → 2 Fe3+ + 2 H2O

The solution prepared in above step 3 was transferred to a 1000 mL volumetric flask. To this flask, 1M potassium thiocyanate (KSCN) was added and volume was brought to 1000 mL with water. Reaction of Fe (III) with KSCN formed a blue color solution.

Fe3+(aq) + SCN- (aq) Fe(SCN)2+(aq)

UV absorbance at 477 nm was measured for the solution prepared in step 3 and the absorbance value was recorded in the laboratory notebook

Steps 1 through 4 was repeated for additional 5 tablets (six tablets total). 6. Following are the UV absorbance values for the FeSCN complex prepared for each tablet.

Following are the UV absorbance values for the FeSCN complex prepared for each tablet.

Tablet Number               Absorbances

1 0.639

2                              0.683

3                              0.702

4                              0.732

5                              0.722

6                              0.767

A calibration curve was prepared from a ferric chloride (FeCl3) standards from 20 to 60 µg/mL concentration range that provided the following absorbance values.

Fe (µg/mL)      Absorbance @450nm

10                           0.434

20                           0.566

30                           0.625

40                          0.880

50                           1.002

The mass of iron in milligram in each tablet was recorded in the laboratory notebook. Calculate the mass of iron from the two tables for each tablet using the spectrophotometric method (Remember to correct for the dilution factor).

I made the Calibration Curve and got this equation.

y = 16.92x + 0.0064

How do I solve for the mass of iron using this equation?

Outline the mechanism of the conversion of α-ketoglutarate to succinyl-CoA catalyzed by α-ketoglutarate dehydrogenase complex.

Put these 5 steps in order:

1. decarboxylation

2. transacylation

3. dihydrolipoyl dehydrogenase activity

4. oxidation of 4-carbon group, reduction of lipoamide disulfide

5. enzymatical FADH2 reoxydation by NAD+

Aqueous solutions containing approximately 3 percent(w/w) H2O2 are sold in drug stores as a disinfectant. Determination of the actual concentration of H2O2 in a bottle of peroxide solution was done by diluting 1.00 mL to 100 mL with water, acidifying with dilute H2SO4 and titrating with a 0.01231 M KMnO4 solution. If 41.92 mL of the permangate solution was needed to reach the end point of the titration, what is the actual molar concentration of the H2O2 solution? Hint: Balance the reaction first: MnO4 - + H2O2 -> Mn2+ + O2 using half reactions

For main-group elements, are outer electron configurations similar or different within a group? Within a period? Explain.

A water is in equilibrium with CO2 in the atmosphere (partial pressure is 3.16 .10‾⁴atm) and with CaCO3(s). The pH is 8.1. Ignoring Ca complexes, what is the
solubility (S) of Ca?

Match the following aqueous solutions with the appropriate letter from the column on the right. 1. 0.14 m Al(NO3)3 A. Lowest freezing point 2. 0.17 m Cr(CH3COO)2 B. Second lowest freezing point 3. 0.18 m (NH4)2CO3 C. Third lowest freezing point 4. 0.48 m Sucrose(nonelectrolyte) D. Highest freezing point

Calculate the pH of a buffer solution that is obtained when 1.727 mL of 3.0 M HCl are added to a 48.273 mL of aqueous solution in which 0.727 g of Tris base has been dissolved. The allowed error is 0.02 pH units.

In Part B of the experiment you uses a weak base, sodium bicarbonate to completely convert a weak acid to a salt. Why was sodium bicarbonate able to completely convert the acid whereas many weak bases would have left some unreacted acid because of the equilibrium?

2. Balance the first redox reaction in acidic solution and the second redox reaction in basic solution.

S + NO3- → SO2 + NO

Cr2O72- + Fe2+ -----> Cr3+ + Fe3+

Determine the Vmax and the Km of the enzyme in the absence and presence of each inhibitor. Calculate the KI for each inhibitor. Are the inhibitors all the same? Which is the best inhibitor and why? What is the catalytic efficiency and turnover number of the enzyme knowing that during the experiments its concentration was 2 nM? What happens to the catalytic efficiency and turnover number of the enzyme in the presence of each of the inhibitor?

The following velocity data were obtained for an enzymatic reaction in the absence and presence of three different inhibitors (A, B, and C):

Initial velocity (v) Initial velocity (v) Initial velocity (v) Initial Velocity (v)

[S] Control (no inhibitor) (+A at 6μM) (+B at 30μM) (+C at 4mM)

(mM) (nM/min) (nM/min) (nM/min) (nM/min)

0.200 16.67 6.25 5.56 10.00

0.250 20.00 7.69 6.67 11.11

0.333 24.98 10.00 8.33 12.50

0.500 33.33 14.29 11.11 14.29

1.00 50.00 25.00 16.67 16.67

2.00 66.67 40.00 22.22 18.18

2.50 71.40 45.45 23.81 18.52

3.33 76.92 52.63 25.64 18.87

4.00 80.00 57.14 26.67 19.00

5.00 83.33 62.50 27.77 19.23

Given the data:

PbO(s), D_f H^q = -217.3 kJ mol^–1, S^q = +68.7 J mol^–1 K^–1
PbO₂(s), D_f H^q = -277.0 kJ mol^–1, S^q = +68.6 J mol^–1 K^–1
O₂(g), D_f H^q= 0.00 kJ mol^–1, S^q = +205 J mol^–1 K^–1

calculate the standard free energy change, D_rG^q, for the reaction:
PbO(s) + ½ O₂(g) ® PbO₂(s)

Select one:

a. +1.45 kJ mol^–1

b. –29.1 kJ mol^–1

c. –68.3 kJ mol^–1

d. –90.3 kJ m

1. draw a mechanism for the conversion of methoxybenzyl alcohol to methoxybenzaldehyde.

2.The ethyl acetate layer was extracted with 0.2M NaOH to remove traces of methoxybenzoic acid that result from additional oxidation of the aldehyde to the carboxylic acid. Explain how crystals of methoxybenzoic acid could be isolated from the NaOH solution.

3. Explain how TLC could be used to monitor the reduction of methoxybenzaldehyde to methoxybenzyl alcohol using NaBH4 as a reducing agent.

A student reacts 58g of salicylic acid with 10 mL of acetic anhydride producing 3.3g of acetyl salicylic acid. What is the percent yield of the reaction?