<u>Answer:</u> The mass percent of potassium bromide in the mixture is 9.996%
<u>Explanation:</u>
- To calculate the number of moles, we use the equation:
.....(1)
<u>For lead (II) bromide:</u>
Given mass of lead (II) bromide = 0.7822 g
Molar mass of lead (II) bromide = 367 g/mol
Putting values in equation 1, we get:
![\text{Moles of lead (II) bromide}=\frac{0.7822g}{367g/mol}=0.0021mol](https://tex.z-dn.net/?f=%5Ctext%7BMoles%20of%20lead%20%28II%29%20bromide%7D%3D%5Cfrac%7B0.7822g%7D%7B367g%2Fmol%7D%3D0.0021mol)
- The chemical equation for the reaction of lead (II) nitrate and potassium bromide follows:
![2KBr+Pb(NO_3)_2\rightarrow PbBr_2+2KNO_3](https://tex.z-dn.net/?f=2KBr%2BPb%28NO_3%29_2%5Crightarrow%20PbBr_2%2B2KNO_3)
By Stoichiometry of the reaction:
1 mole of lead (II) bromide is produced from 2 moles of potassium bromide
So, 0.0021 moles of lead (II) bromide will be produced from =
of potassium bromide
- Now, calculating the mass of potassium bromide by using equation 1, we get:
Molar mass of KBr = 119 g/mol
Moles of KBr = 0.0042 moles
Putting values in equation 1, we get:
![0.0042mol=\frac{\text{Mass of KBr}}{119g/mol}\\\\\text{Mass of KBr}=0.4998g](https://tex.z-dn.net/?f=0.0042mol%3D%5Cfrac%7B%5Ctext%7BMass%20of%20KBr%7D%7D%7B119g%2Fmol%7D%5C%5C%5C%5C%5Ctext%7BMass%20of%20KBr%7D%3D0.4998g)
- To calculate the percentage composition of KBr in the mixture, we use the equation:
![\%\text{ composition of KBr}=\frac{\text{Mass of KBr}}{\text{Mass of mixture}}\times 100](https://tex.z-dn.net/?f=%5C%25%5Ctext%7B%20composition%20of%20KBr%7D%3D%5Cfrac%7B%5Ctext%7BMass%20of%20KBr%7D%7D%7B%5Ctext%7BMass%20of%20mixture%7D%7D%5Ctimes%20100)
Mass of mixture = 5.000 g
Mass of KBr = 0.4998 g
Putting values in above equation, we get:
![\%\text{ composition of KBr}=\frac{0.4998g}{5.000g}\times 100=9.996\%](https://tex.z-dn.net/?f=%5C%25%5Ctext%7B%20composition%20of%20KBr%7D%3D%5Cfrac%7B0.4998g%7D%7B5.000g%7D%5Ctimes%20100%3D9.996%5C%25)
Hence, the percent by mass of KBr in the mixture is 9.996 %