Question

Ancient Egyptians used a variety of lead compounds as white pigments in their cosmetics, including PbS, PbCO3, PbCl(OH), and Pb2Cl2CO3. Which of these compounds contains the highest percentage of lead (by mass)

Answer 1

Answer : The compound contains the highest percentage of lead (by mass) is, PbS.

Explanation :

To calculate the percentage of lead in sample, we use the equation:

$\%\text{ of lead}=\frac{\text{Mass of lead}}{\text{Mass of sample}}\times 100$

For $PbS$ :

Mass of $PbS$ = 239.3 g

Mass of Pb = 207.2 g

Putting values in above equation, we get:

$\%\text{ of lead}=\frac{\text{Mass of lead}}{\text{Mass of sample}}\times 100=\frac{207.2g}{239.3g}\times 100=86.58\%$

The percentage of lead in the $PbS$ is 86.58 %.

For $PbCO_3$ :

Mass of $PbCO_3$ = 267.2 g

Mass of Pb = 207.2 g

Putting values in above equation, we get:

$\%\text{ of lead}=\frac{\text{Mass of lead}}{\text{Mass of sample}}\times 100=\frac{207.2g}{267.2g}\times 100=77.55\%$

The percentage of lead in the $PbCO_3$ is 77.55 %.

For $PbCl(OH)$ :

Mass of $PbCl(OH)$ = 259.7 g

Mass of Pb = 207.2 g

Putting values in above equation, we get:

$\%\text{ of lead}=\frac{\text{Mass of lead}}{\text{Mass of sample}}\times 100=\frac{207.2g}{259.7g}\times 100=79.78\%$

The percentage of lead in the $PbCl(OH)$ is 79.78 %.

For $Pb_2Cl_2CO_3$ :

Mass of $Pb_2Cl_2CO3_$ = 545.3 g

Mass of Pb = 207.2 g

Putting values in above equation, we get:

$\%\text{ of lead}=\frac{\text{Mass of lead}}{\text{Mass of sample}}\times 100=\frac{207.2g}{545.3g}\times 100=37.99\%$

The percentage of lead in the $Pb_2Cl_2CO3_$ is 37.99 %.

Hence, from this we conclude that, the compound PbS contains the highest percentage of lead (by mass).