An aqueous solution containing 5.72 g of lead(II) nitrate is added to an aqueous solution containing 5.85 g
of potassium chloride. The reaction goes to completion, but some was lost in the process of washing and drying the precipitate. The percent yield for the reaction is 81.9%
. How many grams of precipitate is recovered? How many grams of the excess reactant remain? Assume the reaction goes to completion.

3.93g are recovered

Explanation:

Pb(NO3)2 reacts with KCl as follows:

Pb(NO3)2 + 2KCl → 2KNO3 + PbCl2

To solve this question we need to find the moles of each reactant in order to find the limiting reactant:

Moles Pb(NO3)2 -Molar mass: 331.2 g/mol-

5.72g * (1mol/331.2g) = 0.01727 moles

Mole KCl -Molar mass: 74.5513g/mol-

5.85g * (1mol/74.5513g) = 0.07847 moles

For a complete reaction of 0.07847 moles of KCl are required:

0.07847 moles KCl * (1mol Pb(NO3)2 / 2mol KCl) = 0.03923 moles Pb(NO3)2

As there are just 0.01727 moles, Pb(NO3)2 is limiting reactant. Assuming 100% of yield:

Moles PbCl2 = Moles Pb(NO3)2

Mass PbCl2 -Molar mass: 278.1g/mol-

0.01727 moles * (278.1g / mol) = 4.80g

As percent yield is 81.9% = 0.819, the mass of PbCl2 recovered was:

4.80g * 0.819 = 3.93g are recovered

chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. these processes are called chemical reactions and, in general, are not reversible except by further chemical reactions. some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. understanding chemical changes is a major part of the science of chemistry.