Answer:
14,8mg of Copper
Explanation:
Lambert-Beer law says:
A = abC
Where A is absorbance (0,874-0,056 = 0,818), a is molar absorption coefficient (7,90x10³M⁻¹cm⁻¹), b is path length (1,0 cm) and C is molar concentration.
Solving for C:
C = 1,04x10⁻⁴M of (neocuproine)₂Cu+ = <em>1,04x10⁻⁴M Cu</em>
This concentration is the concentration of Copper measured using the absorbance.
The concentration of Copper in solution B is:
1,04x10⁻⁴M Copper× = <em>3,11x10⁻⁴M Copper</em>
Copper in solution A is:
3,11x10⁻⁴M Copper× = <em>9,32x10⁻⁴M Copper</em>
As the total volume of solution A is 250,0mL, moles of Copper in A are:
9,32x10⁻⁴M Cu × 0,2500L =<em> 2,33x10⁻⁴ moles of Copper</em>
In grams:
2,33x10⁻⁴ moles of Cu× = <em>0,0148 g of Copper ≡ </em>14<em>,8 mg of Copper </em>in an unknown
I hope it helps!