Question

If a solution containing 17.91 g17.91 g of mercury(II) perchlorate is allowed to react completely with a solution containing 5.102 g5.102 g of sodium dichromate, how many grams of solid precipitate will be formed?

mass:

gg

How many grams of the reactant in excess will remain after the reaction?

mass:

gg

Assuming complete precipitation, how many moles of each ion remain in solution? If an ion is no longer in solution, enter a zero (0) for the number of moles.

Hg2+Hg2+:

molmol

ClO–4ClO4–:

molmol

Na+Na+:

molmol

Cr2O2−7Cr2O72−:

mol

Answer 1

mass of solid precipitate formed = 8.113 g

mass of reactant in excess = 10.13 g

Hg²⁺ = 0.02536 mol

ClO₄^2- = 0.08966 mol

Na⁺ = 0.03895 mol

Cr₂O₇^2- = 0 mol

Explanation

Balanced equation : Hg(ClO₄)₂ + Na₂Cr₂O₇ HgCr₂O₇ + 2 NaClO₄

Case 1 : Hg(ClO₄)₂ is the limiting reactant

mass Hg(ClO₄)₂ reacted = 17.91 g

moles Hg(ClO₄)₂ reacted = (mass Hg(ClO₄)₂ reacted) / (molar mass Hg(ClO₄)₂)

moles Hg(ClO₄)₂ reacted = (17.91 g) / (399.49 g/mol)

moles Hg(ClO₄)₂ reacted = 0.0448 mol

moles HgCr₂O₇ formed = (moles Hg(ClO₄)₂ reacted) * (1 mole HgCr₂O₇ / 1 mole Hg(ClO₄)₂)

moles HgCr₂O₇ formed = (0.0448 mol) * (1 / 1)

moles HgCr₂O₇ formed = 0.0448 mol

mass HgCr₂O₇ formed = (moles HgCr₂O₇ formed) * (molar mass HgCr₂O₇)

mass HgCr₂O₇ formed = (0.0448 mol) * (416.58 g/mol)

mass HgCr₂O₇ formed = 18.68 g

Case 2 :

Na₂Cr₂O₇ is the limiting reactant

mass Na₂Cr₂O₇ reacted = 5.102 g

moles Na₂Cr₂O₇ reacted = (mass Na₂Cr₂O₇ reacted) / (molar mass Na₂Cr₂O₇)

moles Na₂Cr₂O₇ reacted = (5.102 g) / (261.97 g/mol)

moles Na₂Cr₂O₇ reacted = 0.01947 mol

moles HgCr₂O₇ formed = (moles Na₂Cr₂O₇ reacted) * (1 mole HgCr₂O₇ / 1 mole Na₂Cr₂O₇)

moles HgCr₂O₇ formed = (0.01947 mol) * (1 / 1)

moles HgCr₂O₇ formed = 0.01947 mol

mass HgCr₂O₇ formed = (moles HgCr₂O₇ formed) * (molar mass HgCr₂O₇)

mass HgCr₂O₇ formed = (0.01947 mol) * (416.58 g/mol)

mass HgCr₂O₇ formed = 8.113 g

Since less mass of HgCr₂O₇ is formed in Case 2, therefore, Na₂Cr₂O₇ is the limiting reactant.

mass HgCr₂O₇ (precipitate) formed = 8.113 g