Question

A precipitation reaction is caused by mixing 100. mL of 0.25 M K2Cr2O7 solution with 100. mL of 0.25 M Pb(NO3)2 solution. When the precipitate forms, it is filtered from the mixture.How many moles of solid product are formed?0.25 mol0.010 mol0.025 mol0.050 mol

Answer 1

Answer: 0.025 mol

Explanation:

To calculate the number of moles for given molarity, we use the equation:

$\text{Moles of solute}={\text{Molarity of the solution}}\times{\text{Volume of solution (in L)}}$     .....(1)

Molarity of $K_2Cr_2O_7$ solution = 0.25 M

Volume of $K_2Cr_2O_7$ solution = 100.0 mL = 0.1 L

Putting values in equation 1, we get:

$\text{Moles of} K_2Cr_2O_7={0.25}\times{0.1}=0.025moles$

Molarity of $Pb(NO_3)_2$ solution = 0.25 M

Volume of $Pb(NO_3)_2$ solution = 100.0 mL = 0.1 L

Putting values in equation 1, we get:

$\text{Moles of} Pb(NO_3)_2={0.25}\times{0.1}=0.025moles$

$K_2Cr_2O_7(aq)+Pb(NO_3)_2(aq)\rightarrow PbCr_2O_7(s)+2KNO_3(aq)$  

The solid precipitate formed here is lead dichromate.

According to stoichiometry :

1 mole of lead nitrate produce= 1 mole of lead dichromate

So, 0.025 moles of lead nitrate will produce =$\frac{1}{1}\times 0.025=0.025mol$ of lead dichromate

Hence, the amount of solid product (lead dichromate) formed is 0.025 moles.