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Question: 1 salts of carboxylic acids are frequently used as lubricants...

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Salts of carboxylic acids are frequently used as lubricants in metal-working operations. These lubricants have the undesirable effect of depositing stains on metal surfaces. Your company has assigned you the task of devising a cleaning method for removing this lubricant stain from metal surfaces. As a first step in the process design, your boss has suggested that you prepare a solubility diagram (a log [Metal] vs pH diagram). The lubricant is calcium laurate, i.e., the calcium salt of lauric acid C12H26COOH (or simply C12COOH or RCOOH).

Relevant thermodynamic data are provided below. Consider the pH 4-10 range only.

                                 Ca(RCOO)2(s) + 2H+ = Ca2+ + 2RCOOH(aq)        log K = -2.16
                                 RCOOH(aq) = RCOO- + H+                                          log K = -5.0

One of your colleagues has suggested that washing the metal surface with water of controlled pH will do the trick. Do you accept your friend's recommendation?


Consider a 10-4 molar Fe2+ solution at pH 2. Determine the corresponding pe when this solution is in equilibrium with:
    (a) Magnetite                         (b) Elemental iron
    Given: Fe = Fe2+ + 2e-                                            log K = 16.17
                 Fe3O4 + 8H+ + 2e- = 3Fe2+ + 4H2O            log K = 36.81


The three iron oxides of steel scale are hematite (Fe2O3), magnetite (Fe3O4), and wustite (FeO). Above 1,050 oF the most stable oxide is FeO.

    (a) Cooling below 1,050 oF causes the decomposition of wustite to magnetite and elemental iron. Write down a balanced chemical reaction for this process.

    (b) some of the magnetite reacts with atmospheric oxygen to give hematite. Write down the corresponding balanced chemical reaction.

     (c) If cooling is done too rapidly, not all the initial FeO undergoes transformation. Assuming that the various oxides exist as consecutive layers on the steel surface, provide a sketch that clearly shows the oxides representing (i) the inner layer, (ii) the middle layer, and (iii) the outer layer. Justify your selection with appropriate arguments.

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