Anonymous
Anonymous asked in Science & MathematicsChemistry · 1 month ago

Question 1: Titrations (15 points)

Copper metal is easily oxidized to Cu2+ by nitric acid according to the following equation: 3Cu(s) + 8HNO3(aq) → 3Cu(NO3)2(aq) + 2NO(g) + 4H2O(l)

A copper penny with a mass of 3.067 g is dissolved in 100.0 mL of 1.000 M nitric acid.

a. How many moles of copper are in the penny assuming it is pure copper? (5 points)

I think 0.048 mol Cu

b. When the reaction stops, the undissolved penny is removed. What is the mass of the undissolved penny? (6 points)

I have no idea

c. The solution prepared in step B is transferred quantitatively to a 250.00 mL volumetric and diluted to the line. What is the molarity of the Cu2+ ion in this solution? (4 points)

I have no idea

Relevance
• Ash
Lv 7
1 month ago

a.  moles of Cu = mass of Cu / molar mass of Cu

= (3.067 g)/(63.546 g/mol)

= 0.04826 mol

You are almost right. Note that the minimum sig fig in the division is 4. So our answer is in 4 sig fig, too

b. moles of HNO3 = 1.000 M x 100.0 mL

= (1.000 moles/1000 mL) x 100 mL

= 0.1000 moles

From balanced equation, moles of Cu reacting completely with HNO3 will be

= (3 moles Cu / 8 moles HNO3) x 0.1000 moles HNO3

= 0.03750 molesRemaining unreacted moles of Cu

= 0.04826 - 0.03750 = 0.01076 moles

mass of undissolved penny = balance moles of Cu x molar mass of Cu

= (0.01076 mol) x (63.546 g/mol)

= 0.6838 g

c. molarity of Cu⁺⁺ ion generated after the reaction...

= (0.03750 moles/100.0 mL)x 1000 mL

= 0.3750 M

C₁V₁ = C₂V₂

C₂ = C₁V₁/V₂

C₂ = (0.3750 M)(100.0 mL)/(250.0 mL)

C₂ = 0.1500 M  ← molarity of Cu⁺⁺ ion after the transfer to 250mL volumetric