Problem: A 5.000 g mixture contains strontium nitrate and potassium bromide. Excess lead(II) nitrate solution, Pb(NO3)2(aq) is added to precipitate out 0.7822 grams of PbBr2(s). What is the percent by mass of potassium bromide in the mixture? What is the percent by mass of strontium nitrate in the mixture?

FREE Expert Solution

We're being asked to determine the mass percent of potassium bromide (KBr) and strontium nitrate (Sr(NO3)2) in the mixture.

We will first calculate the amount of KBr in the solution. KBr is an ionic compound and will break up in the solution:

KBr(aq) → Kα(aq) + Br-(aq)

All the Br- ions were precipitated using excess lead(II) nitrate solution, Pb(NO3)2(aq):

Pb(NO3)2(aq) → Pb2+(aq) + 2 NO3-(aq)

Pb2+ reacts with Br- to form the precipitate:

Pb2+(aq) + 2 Br-(aq) → PbBr2(s)

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Problem Details

A 5.000 g mixture contains strontium nitrate and potassium bromide. Excess lead(II) nitrate solution, Pb(NO3)2(aq) is added to precipitate out 0.7822 grams of PbBr2(s). What is the percent by mass of potassium bromide in the mixture? What is the percent by mass of strontium nitrate in the mixture?