Lead(II) iodide is a bright yellow pigment historically used in art. It is produced by the precipitation reaction between lead(II) nitrate solution and potassium iodide solution:
Pb(NO3)2(aq)+2KI(aq)→PbI2(s)+2KNO3(aq) \text{Pb(NO}_3)_2\text{(aq)} + 2\text{KI(aq)} \rightarrow \text{PbI}_2\text{(s)} + 2\text{KNO}_3\text{(aq)} Pb(NO3)2(aq)+2KI(aq)→PbI2(s)+2KNO3(aq)A student investigated the law of conservation of mass using the following method:
The table below shows the student's results:
| Mass before mixing (g) | Mass after mixing (g) | |
|---|---|---|
| Beaker A and contents | 92.45 | 135.31 |
| Beaker B and contents | 78.12 | 35.26 |
Explain how the results demonstrate the law of conservation of mass. You must use data from the table in your answer.
Calculate the percentage atom economy for the production of lead(II) iodide (PbI2\text{PbI}_2PbI2) in this reaction. Give your answer to 3 significant figures.
Relative formula masses (MrM_{\text{r}}Mr): Pb(NO3)2=331\text{Pb(NO}_3)_2 = 331Pb(NO3)2=331, KI=166\text{KI} = 166KI=166, PbI2=461\text{PbI}_2 = 461PbI2=461, KNO3=101\text{KNO}_3 = 101KNO3=101