# What is molality?

In chemistry, the concentration of a solution refers to the amount of solute dissolved in a solution. There are various ways to report concentrations depending on the units used. Some of the most common ones are molarity, molality, and percentages. Percent of a solute can be weight by volume (w/v) or weight by weight (w/w), which is simply the ratio of the mass of the solute to the total volume or weight of the solution.

Molarity and molality makes use of the ratio of the moles of solute to either the volume (in liter) of solution or the mass (in kilogram) of solvent, respectively. Molality is most often used in experiments that involve a significant change in temperature as molarity is sensitive to temperature due to expansion/compression that may result to significant changes in volume - and hence, apparent concentration.

In brief, molality is one way to express the concentration of a solution. It is the ratio of the number of moles of solute to the mass in kilograms of solution:

`m = (n_(solute))/(mass_(solvent))` .

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What is molarity?

The term molarity refers to the number of moles per liter of solution.

The mole is a standard unit of measurement in science used when we wish to know how many atoms and molecules are involved in a chemical reaction involving solutes dissolved in an aqueous or water-based solution. The advantage of measuring the number of chemicals in moles is that a mole is a standard number of molecules. A mole of one substance has the same number of molecules as a mole of a different substance.

When you hear someone mention they have a dozen of something, that value always means twelve of any object. A mole is a convenient unit of measurement that refers to a standard number of molecules in a solution. That number is Avogadro's number, which is 6.02 times 10 to the 23rd power. To calculate the number of molecules in a solution, we use atomic mass, which can easily be looked up in a periodic table.

For example, consider a molecule of sucrose sugar. This has the formula C12H22O11. We first must calculate the molecular mass of sucrose. This is done by adding up the masses of all the atoms in this molecule. We use a periodic table to find the atomic masses of each atom in the formula, and the subscript tells us the number of atoms of each element in sucrose.

So, 12 x 12 (for the carbon atoms), plus 22 x 1 (for the hydrogen atoms) plus 11 x 16 (for the oxygen atoms) = 342 daltons for the molecular mass of sucrose. It would be very difficult to weigh out small numbers of moleculesâ€”instead, we use moles.

We can also write this as 342 grams. To get a 1-liter solution of a mole of sucrose, then, we could simply measure out 342 grams of sucrose and slowly add water until the solution has a total volume of 1 liter. At that point, we have a 1-molar (1M) solution of sucrose.

The beauty of using moles is that it is a standard unit of measurement. It is a handy way for researchers to combine substances in fixed ratios of molecules in a lab.