Anonymous
Anonymous asked in Science & MathematicsChemistry · 1 month ago

URGENT CHEMISTRY HELP PLEASE?!!?

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

1 Answer

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  • Ash
    Lv 7
    1 month ago
    Favourite answer

    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 

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