Please answer all prelab and postlab questions directly into your lab notebook 1

Question

Please answer all prelab and postlab questions directly into your lab notebook 1. A student mixes 5.00 mL of 2.00 x 103 M Fe(NO)s with 5.00 mL 2.00 x 103 M KSCN. She finds that in the equilibrium mixture the concentration of FeSCN*2 is 1.40x 104 M a. What is the initial concentration in solution of the Fe+3 and SCN? b. What is the equilibrium constant for the reaction? C. 2. Why is it necessary to record the temperature even though you will not need it in your calculations? 3. If one of the cuvets was wet and not properly rinsed before you placed a sample for analysis in the Equilibrium samples (not the Standard Curve samples), how would that affect the equilibrium constant you would be reporting for that sample? Would it be too high, too low or unaffected? Explain.

Explanation / Answer

part C :

K+ and NO3- ions are spectator ions. those are left in the solution.

2)

temperature effects the equilibrium constant.

if temperature changes equilibrium constant also changes. so we have to record the temperature.

3)

if cuvet is not rinsed properly , it may contain dust particles. these dust particles may absorb some incident light.

from beer's law absorbance A = e b C

concentration increases , absorbance also increases. but here absorbance is more due to dust particles. so concentration is also more. but it is not actual concentration which effects the equilibrium constant. that will be too high.

Keq = [product] / [reactants]

if reactant concentration increases the reaction shift towards the product side. so product concentration increases.

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