February 11, 2016

Homework Help: chemistry

Posted by GM on Monday, July 5, 2010 at 7:40pm.

1.The equilibrium constant for the oxidation of elemental iron metal, Fe, by oxygen, O2 to form hematite, according to the reaction 2Fe + (3/2)O2 = Fe2O3 is known to have the value K=exp(+68.8) at 1000C. The equilibrium constant for the formation of CO2 from carbon and O2, C + O2 = CO2 at the same temperature is known to be K = exp(+48.90). Is it possible to prepare elemental iron in high yield from hermatite by using carbon (from coke) at 1000C? Justify your answer.

2.Glycolic acid is often used in “facial peels” and has a Ka of 1.5x10^-4. If a movie star is to have a solution of pH 2.1 applied to her face at night, what concentration of glycolic acid solution should be made up (assuming that it is a monoprotic acid, and that it dissolves freely in water)

3.The solubility product for silver (I) chloride is 1.6x10^-10 while that for sliver (I) iodide is 8.5x10^-17. Suppose 5g of AgCl is put in a liter of 0.1M sodium iodide solution. If a solid is eventually isolated, what is it, and how did it form?

4.The Kb of ammonia, NH3, is 1.8x10^-5. What is the pH of a 2.000 millimolar solution of ammonia , to 3 significant digits.

5.A weak monoprotic acid was calculated, using the usual formula for Ka, to give a pH of 7.4 at a certain concentration. The student who did the calculation was puzzled. What would you advice him/her to do?

6.Why is it that biochemists often remember the pKa of weak acids, rather than Ka?

7.If we suppose that Kw = 1.0x10^-14 at 25C, would it be larger or smaller at 100C? What is the value of K for the reaction 8H + 8OH = 8H2O at 25C? Would this value be smaller, or larger, at 100C?

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