Question

the manufacture of many materials essential to engineering requires very high temperature processing. for example, to melt a metal a container is required that melts at a significantly higher temperature than the metal. containers that are used for high temperature applications such as these are called crucibles. common crucibles materials are ionic, or mainly ionic solids. examples are magnesium oxide (mg²⁺²o), calcium oxide (ca²⁺²o), and barium oxide (ba²⁺²o). arrange these four potential crucible materials in order of increasing melting point. (lowest melting) mgo < cao < bao (highest melting) (lowest melting) bao < cao < mgo (highest melting) (lowest melting) mgo < cao < bao (highest melting) (lowest melting) cao < bao < mgo (highest melting) dont test me yet, i am trying to gain an understanding before attempting to answer this question.

Explanation:

Step1: Recall ionic - solid melting point concept

The melting point of ionic solids depends on the lattice energy. Lattice energy is directly proportional to the product of ionic charges and inversely proportional to the distance between ions. In these oxides ($BaO$, $CaO$, $MgO$), the anions are all $O^{2 - }$, and the cations are $Ba^{2+}$, $Ca^{2+}$, $Mg^{2+}$. The ionic charges are the same. The key factor is the ionic radius.

Step2: Compare ionic radii of cations

The ionic radii follow the order $Mg^{2+} CaO>BaO$. Higher lattice energy means a higher melting point.

Answer:

$BaO < CaO < MgO$ (lowest melting - highest melting)