In a solution, solute is the portion that is mixed in smaller quantity, usually with a solvent to yield that solution. Determining the moles of solute requires an understanding of the concept of what a mole is. Depending on whether the solute is a compound or an element, one mole is equivalent to the respective molecular or atomic mass of the solute.
Determine the mass of the solute using a weighing machine. Write down the value on a piece of paper.
Determine the atomic or molecular mass of the solute. Refer to a periodic table to see the atomic masses of all the known elements. If the solute comprises a single element, then you must calculate the atomic mass of that element. If the solute comprises a mixture of elements, also called a compound, then you must calculate the molecular mass of the compound.
For instance, if the solute is sodium chloride, expressed in chemical equations as NaCl, then the molecular mass of this compound will be calculated as: atomic mass of sodium + atomic mass of chlorine.
The atomic mass of sodium is 23 grams and that of chlorine is 35 grams, so the molecular mass of NaCl is 58 grams.
Determine the moles of the solute. One mole is equivalent to the molecular mass of the solute, which is 58 grams. Divide the actual mass of the solute that was determined in Step 1 by the molecular mass of the solute to get the number of moles of the solute.
Assuming that the actual mass of the solute is 100 grams, the number of moles of the solute is: "(actual mass of the solute) / (molecular mass of the solute)" or "100/58", which is equal to 1.72 moles for this example.