Question

How does molar mass affect solubility?

Answer 1

An increase in molar mass means an increase in size of the molecule and as the size of molecule increases, it becomes difficult for solvent molecules to hold on the solute particles.

Complete answer: In order to answer the question, we need to know about moles and molar mass. Now, matter is made up of atoms, and as matter has mass, then the atoms should have an individual mass. Molar mass of an element or compound is the mass which houses $6\times {{10}^{23}}$ particles. For, example, the hydrogen molecule has a molar mass of 2 grams. This means 2 grams of hydrogen contains $6\times {{10}^{23}}$atoms, and this number is also called the Avogadro’s number.
Number of moles of an element or a compound is the ratio of its given mass taken by the user, to its molar mass. More is the number of moles, more is the concentration of the substance. Now, let us come to the question.
We know that number of moles of a substance is given by the formula $number\,of\,mole=\dfrac{given\,mass}{molar\,mass}$, so, as the molar mass is constant, the only thing that can change the number of moles is the mass of the substance that is taken. Now, molar mass depends on the size of the constituent molecules. So, as the size of the atoms increases, it also means that the atoms are housing more neutrons, protons and electrons. So, an increase in size means an increase in molar mass. So, for a given amount of solvent, it is difficult to house more large sized particles. As a result, the solubility will decrease , increasing the molar mass.

Note: It is to be noted that solubility of a solute can be increased by a little amount if the solution is heated and solute is stirred continuously. Hydrogen, which has the lowest molar mass, is most soluble in oxygen, forming the ${{H}_{2}}O$ molecule. The reaction is an explosive one.