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Quantitative Analysis Calculations

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Please solve each of the following problems with all calculations shown.

1. A 25.00 mL portion of a solution known to contain NaBr was treated with excess AgNO3 to precipitate 0.02578 g of AgBr. Determine the concentration of NaBr in the original solution in molarity and ppm.

2. How many mL of a 3.45% solution of alcoholic dimethyl glyoxime would you need to provide a 50% excess with 1.8765 g of steel known to contain 2.917 wt% Ni. The density of the dimethyl glyoxime solution is 0.802 g/mL.

(etOH)
Ni+2 + 2 DMG ------------ > Bis(dimethylglyoximate)nicklel(II) + 2H+

FM for Ni+2 = 58.69 g /mol
FM for DMG = 116.12 g/mol (The question lists density at 0.802 g/mL, please use this figure)
FM for Bis(dimethylglyoximate)nicklel(II) = 288.91 g/mol

3. 25 multivitamin tablets containing iron with a total mass of 50.345 g were ground together and mixed thoroughly. 1.8320 g of this sample was then dissolved in 10.00 mL of 1.5 M HNO3 and heated to ensure the oxidation of all iron to the Fe+3 oxidation state. NH3 was added to cause the precipitation of FeOOH*xH2O (the red gelatinous substance you formed in lab). The precipitate was then ignited to produce 0.2167 g of Fe2O3. Determine the average mass of iron (II) sulfate heptahydrate (FeSO4*7H2O) the source of iron in many dietary supplements) in each multivitamin tablet.

4. Distinguish between the terms end point and equivalence point.

5. Explain the difference between a direct titration and a back titration.

6. Explain the properties that make a substance a primary standard.

7. A solution of HCl is standardized against primary standard Na2CO3 using bromocresol green as the indicator. A 0.2107 g sample of Na2CO3 required 37.98 mL of HCl solution to turn the solution from blue to green. The solution was boiled briefly and returned to a blue color. This solution then required 0.17 mL of HCl solution to turn greenish yellow. Determine the molarity of the HCl solution.

8. The HCl solution standardized in #7 is then used to titrate an unknown concentration of a NaOH solution with phenolphthalein as the indicator. A 25.00 mL quantity of the NaOH solution required 16.63 mL of HCl solution to turn the solution from a deep reddish pink to completely colorless. Determine the molarity of the NaOH solution.

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