Answer:
8.09x10⁻⁵M of Fe³⁺
Explanation:
Using Lambert-Beer law, the absorbance of a sample is proportional to its concentration.
In the problem, the Fe³⁺ is reacting with KSCN to produce Fe(SCN)₃ -The red complex-
The concentration of Fe³⁺ in the reference sample is:
4.80x10⁻⁴M Fe³⁺ × (5.0mL / 50.0mL) = 4.80x10⁻⁵M Fe³⁺
Because reference sample was diluted from 5.0mL to 50.0mL.
That means a solution of 4.80x10⁻⁵M Fe³⁺ gives an absorbance of 0.512
Now, as the sample of the lake gives an absorbance of 0.345, its concentration is:
0.345 × (4.80x10⁻⁵M Fe³⁺ / 0.512) = 3.23x10⁻⁵M.
As the solution was diluted from 20.0mL to 50.0mL, the concentration of Fe³⁺ in Jordan lake is:
3.23x10⁻⁵M Fe³⁺ × (50.0mL / 20.0mL) = 8.09x10⁻⁵M of Fe³⁺
The concentration of Fe³⁺ in Jordan Lake is = 8.09* 10⁻⁵ M
According to Lambert-Beer law ;The rate of absorbance of a sample is directly proportional to concentration of the sample
The reaction that produces a red complex
Fe³⁺ + KScN ----> Fe ( SCN )₃ ( red complex )
First step: Determine the Concentration of Fe³⁺ in reference sample
= 4.80x10⁻⁴ * ( 5.0 / 50.0 ) = 4.80 * 10⁻⁵M
reference sample was diluted from 5.0 mL to 50.0 mL
∴ Concentration of 4.80 * 10⁻⁵M has an absorbance = 0.512
Given that Lake sample absorbance = 0.345
Next step : Determine the concentration of the lake sample
Concentration of lake sample :
= absorbance of lake sample * ( conc of reference sample / absorbance )
= 0.345 * ( 4.80* 10⁻⁵ / 0.512 ) = 3.23* 10⁻⁵M.
Final step : Determine the concentration of Fe³⁺ in Jordan lake
= 3.23 * 10⁻⁵ * ( 50.0mL / 20.0mL) = 8.09* 10⁻⁵ M
Note : Solution was diluted from 20.0 mL to 50.0 mL
Hence we can conclude that The concentration of Fe³⁺ in Jordan Lake is = 8.09* 10⁻⁵ M .
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