A 0.129 g sample of unknown mineral that contains copper is dissolved in 15 mL s

Question

A 0.129 g sample of unknown mineral that contains copper is dissolved in 15 mL solution of sulfuric acid. The absorbance of this sample was A = 0.115. Use the following calibration curve for (Cu2+) to determine the % copper in the unknown mineral. Use 6355 mol for the molar mass of Cu Round your answer to the nearest whole percent, le. 60.78% rounds to 61%) Cu2+ Standard Curve 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 y = 2.4606x + 0.02 72 R2-0.9997 0 0.05 01 0.15 00.250.3 Concentration (mol/L) Express your answer numerically to the nearest whole percent.

Explanation / Answer

y = 2.4606x+0.0272   where y = absorbance = 0.115 , we find x which is Conc

0.115 = 2.4606x + 0.0272

x =0.0357 mol/L

volume = 15 ml = 0.015 L

Moles of Cu2+ = M x V = 0.0357 x 0.015 = 0.000535

Mass of Cu2+ = moles x molar mass of Copper = 0.000535 x 63.546 = 0.034 g

sample mass = 0.129 g

% of copper in sample = ( 100 x 0.034) / ( 0.129) = 26.4 % rounded is 26 %

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