Question

A chemist needs to create a series of standard Cu2+(aq)Cu2+(aq) solutions for an absorbance experiment. For the first standard, he uses a pipet to transfer 5.005.00 mL of a 2.172.17 M Cu2+(aq)Cu2+(aq) stock solution to a 500.0500.0 mL volumetric flask, and he adds enough water to dilute to the mark. He then uses a second pipet to transfer 25.0025.00 mL of the second solution to a 100.0100.0 mL volumetric flask, and he adds enough water to dilute to the mark. Calculate the concentration of the Cu2+(aq)Cu2+(aq) solution in the 100.0100.0 mL volumetric flask.

Answer 1

5.43 × 10⁻³ M

Step-by-step explanation:

A chemist needs to create a series of standard Cu²⁺(aq) solutions for an absorbance experiment. For the first standard, he uses a pipet to transfer 5.00 mL of a 2.17 M Cu²⁺(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 Cu²⁺(aq) solution in the 100.0 mL volumetric flask.

Two successive dilutions are performed. In each one, we will use the dilution rule.

M₁ × V₁ = M₂ × V₂

where,

M: molarity

V: volume

1: initial solution (concentrated)

2: final solution (diluted)

First dilution

M₁ × V₁ = M₂ × V₂

2.17 M × 5.00 mL = M₂ × 500.0 mL

M₂ = 0.0217 M

This is the initial concentration for the second dilution.

Second dilution

M₁ × V₁ = M₂ × V₂

0.0217 M × 25.00 mL = M₂ × 100.0 mL

M₂ = 5.43 × 10⁻³ M

Answer 2

The concentration of the Cu²⁺ solution in the 10,0 mL volumetric flask is 5,425×10⁻³ M Cu²⁺

Step-by-step explanation:

The first dilution from a 2,17M Cu²⁺ solution gives:

2,17 M Cu²⁺ ×
`(5,00 mL)/(500,0 mL)` = 0,0217 M Cu²⁺solution

The second dilution gives as concentration:

0,0217 M Cu²⁺ ×
`(25,00 mL)/(100,0 mL)` = 5,425×10⁻³ M Cu²⁺ solution

I hope it helps!