Report Sheet: Reaction Stoichiometry: The Mole Ratio Concept Mass of Fe(NH)(SO2

Question

Report Sheet: Reaction Stoichiometry: The Mole Ratio Concept Mass of Fe(NH)(SO2 6H,O required Volume of 6.0 M HSO, added to standard iron (I) solution 0 2449 Volume Ratio Mole Ratio Mixture Absorbance at 430 nm CO(mol Fe'mol C0 0.0 mol 0.402 A00mL oml 40mL 4 0mL0.011 0 0u2 F 10.0m 0.0 mL 0.043 Attach your graph (plot of absorbance vs. Fe?/CrO mole ratio) to the report sheet with equations displayed 1. 2. At what mole ratio (mol Feay mol Cr02) do the linear segments intersect (read plot to 3. What is the Fe?/Cr,0,2 mole ratio rounded to the nearest whole number? 4. Use the mole ratio you found to balance the following equation.

Explanation / Answer

1) Plot the data as shown below.

Plot of absorbance vs mole ration of Fe2+/Cr2O72-

2) The mole ratio at which the two linear segments intersect is obtained by equating the two equations, i.e,

-0.0685x + 0.402 = -0.0045x + 0.0894

====> 0.402 – 0.0894 = -0.0045x + 0.0685x

====> 0.3126 = 0.064x

====> x = 0.3126/0.064 = 4.884

x gives the value of the mole ratio and the mole ratio of Fe2+/Cr2O72- must be 4.883:1 (ans).

3) The nearest whole number to the mole ratio is 5:1, i.e, the molar ratio of Fe2+ and Cr2O72- must be 5:1 (ans).

4) We must have the following reaction:

5 Fe2+ + Cr2O72- + H+ --------> 5 Fe3+ + 2 Cr3+ + H2O

Balance H+ and H2O by adding 14 and 7 repectively. Therefore, the balanced equation is

5 Fe2+ + Cr2O72- + 14 H+ --------> 5 Fe3+ + 2 Cr3+ + 7 H2O

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