Question

A chemist needs to create a series of standard Cu- (aq) solutions for an absorbance experiment. For the first standard, he uses a pipet to transfer 20.00 mL of a 2.64 M Cup (aq) stock solution to a 500.0 mL volumetric flask, and he adds enough water to dilute to the mark. He then uses a second pipet to transfer 25.00 mL of the second solution to a 100.0 mL volumetric flask, and he adds enough water to dilute to the mark. Calculate the concentration of the Cu + (aq) solution in the 100.0 mL volumetric flask concentration:

Answer 1

Initlal mmoles of Cu²⁺ present in the solution = volume (mL) $\times$ molarity

= 20.00 $\times$ 2.64 = 52.8

volume of diluted solution = 500.0 mL

then,  molarity of Cu²⁺ in 500.0 mL solution

= (moles / volume)

= (52.8 /500.0 ) = 0.1056 M

again 25.00 mL 0.1056 is taken

so, mmoles in above solution

= 25.00 $\times$ 0.1056

= 2.64

volume of the final solution = 100.0 mL

therefore molar concentration of Cu²⁺ in 100.0 mL solution

= (moles /volume)

= (2.64/100.0)

= 0.0264 M