My class recently did a lab where we were each given a block of raw potash $($with impurities$)$ and were supposed to extract the pure KCl from it$.$ Impurities included soluble ones $($like NaCl$)$ and insoluble ones $($like clay$).$ We appraoched this lab by using the solubilities of KCl and other soluble impurities. We were first required to calculate the amount of water that would form a saturated solution with the KCl $($and NaCl$)$ at $70$ Celcius. After grinding the block and mixing $it$ with the water, $we$ were asked $to$ heat the solution $to90$ Celcius. When $it$ reached the desired temperature, $we$ performed a hot filtration and sperated the insoluble impurities from the soluble compounds $in$ the solution. Following that, $we$ carried out a few procedures $to$ extract the pure $KCl.$ However, $my$ question $is,$ why did $we$ initially calculate the volume $of$ the saturated solution $at70C$ and then heat the actual solution $(after$ having calculated its volume $at70C)to90C.Isit$ for ensuring that the $KCl$ remained disolved $in$ the solution the whole time and did not crystallize out? $Oris$ there more $toit?$ This $is$ one $of$ the questions $on$ the lab report $so$ I was just wondering about $it.$

We calculated our saturated solutions for $70C,$ however we heated $20C$ beyond this to $90C$ before

the hot filtration. Explain the purpose and importance of heat in this step of the process.