How can I measure the concentration of salt in water?

1 Answer

Two common ways of measuring concentration are molarity and molality.

Molarity = moles salt/liters solution

Molality = moles salt/kg solution

Please note that a solution which is 1M (1 molar) will be slightly more concentrated than a solution which is #1m# (molal).

This is because 1Lof 1M solution contains 1 mole NaCl dissolved to make 1L of salt water solution. The 1L will be mostly water but a small volume is taken up by the salt. The the volume of the water will be slightly less than 1L.

In 1L of a #1M# solution, the 1 mol of NaCl is dissolved in 1 kg of water. Since water has a density of 1g/ml, the salt is dissolved in 1000g or 1000mL of water. So the salt here is dissolved in 1 L of water.

Here are two videos I've made which should be helpful.