Calculating concentration
When preparing a standard solution, usually a chemist will have calculated the mass of primary standard required (as you have done earlier in this module). However, it is common that the chemist is not careful to weigh exactly this amount. This is because for most purposes it does not matter whether the concentration is exactly, for example 0.1000 , provided that the concentration of the standard solution is known precisely.
The concentration of a solution indicates the quantity of solute (substance dissolved) in a particular volume of solution.
What is V for my standard solution?
What is n for my standard solution?
 volumetric flask
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Chemists often use amount in moles (n) and volume (V) of the solution in to give the concentration unit . This is expressed mathematically at the right.
is read moles per . Per means “divide by”; therefore saying the unit reminds you that concentration equals amount in moles divided by volume.
is read moles per . Per means “divide by”; therefore saying the unit reminds you that concentration equals amount in moles divided by volume.
What is V for my standard solution?
The volume equals the volume of the volumetric flask in .
The volume of these flasks is usually given in (like 250 ).
This volume in is multiplied by 10–3.
The volume of these flasks is usually given in (like 250 ).
This volume in is multiplied by 10–3.
What is n for my standard solution?
n is the amount in moles (This is a measure of the number of formula units of substance present in a given mass of the substance (6.02 × 1023 formula units in 1 mol). Chemists use amount in moles because the amounts in moles of two different substances that appear in a chemical equation are related.) of solute that you dissolved.
You have measured the mass (m) of the solute.
The amount in moles* of solute (n) can be calculated if this mass (m) is divided by the mass of one mole (M) of solute. This is expressed mathematically at the right.
You have measured the mass (m) of the solute.
The amount in moles* of solute (n) can be calculated if this mass (m) is divided by the mass of one mole (M) of solute. This is expressed mathematically at the right.