If you look at the label of a juice container, you will probably see the words "juice from concentrate" or "frozen concentrated orange juice". This is an example of how we can describe a solution in terms of how much solute and solvent are in that solution. A concentrated solution has a lot of solute as compared to solvent. A dilute solution has little solute as compared to solvent.
Dilute and concentrated can be relative terms. This can be illustrated by the three solutions below:
Solution A
500 g of sugar in100 mL of water
Solution B
100 g of sugar in100 mL of water
Solution C
1 g of sugar in100 mL of water
Solution A is concentrated since it has a large amount of solute as compared to solvent. Solution
C is dilute because it has a small amount of solute as compared to solvent. Solution B is dilute compared to solution A since it has less solute, but is concentrated compared to solution C because it has more solute than solution C.
The units most commonly used for concentration in chemistry is moles of solute in one Litre of solution, mol/L. This is also known as molar concentration, or molarity , M .
Concentration can be calculated according to the formula below:
Where M = Molarity
Mol = moles
L = volume in liters

Example 1.
Calculate the concentration of a sodium chloride solution if 0.200 moles is dissolved in 250.0 mL of solution.
Solution.
The units for concentration are moles per Litre. We are given moles of solute and 250 mL of solution. The volume of solution must be converted to Litres.
We can now substitute the given values into the equation:
0.200 moles of sodium chloride in 250. mL of solution has a concentration of 0.800 mol/L or
0.800 M.

Example 2.
What volume of a 1.25 mol/L solution contains 5.00 moles of solute?
Solution.
We are given a concentration of 1.25 mol/L and 5.00 moles of solute. To find volume, in
Litres, we rearrange our equation to solve for volume and substitute in the given values.
4.00 L of a 1.25 mol/L solution contains 5.00 moles of solute.
Example 3.
How many moles of solute are needed to make 400. mL of a 0.225 mol./L solution?
Solution.
We are given volume in mL and the concentration of the solution. We must first convert the volume of the solution to Litres.
Rearrange the equation to solve for moles and substitute.

When a chemist makes a solution from a solid solute, the chemist determines the mass of the solute needed to make a certain amount of solution. http://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/crm3s1_2.swf
Example 4.
What mass of sodium chloride is needed to make 0.250 L of a 0.100 mol/L solution?
Solution.
We are given: o o o
0.250 L of solution, that is volume.
0.100 mol/L of solution, that is concentration the solute is sodium chloride (NaCl)
We must find the mass of solute. Before we find mass, as in the previous module, we first must determine the moles of solute.
Step 1: Determine the number of moles of solute required.
To find the number of moles, rearrange the concentration equation to solve for moles.
Step 2: Determine the molar mass of NaCl and convert moles to mass.
You need about 1.46 g of sodium chloride to make 0.250 L of a 0.100 mol/L solution.

Example 5.
What is the molar concentration of a solution of copper (II) sulfate if 50.0 g is dissolved in 600. mL of solution?
Solution.
We are given: o o o the solute is copper (II) sulphate (CuSO
4
)
50.0 g of solute, that is mass
600. mL of solution, that is volume
We must find the concentration of the solution in mol/L.
Step 1: Given the mass of solute, convert to moles.
Since concentration is in moles per Litre and not grams per Litre, we must convert the given mass into moles.
To convert to moles, we must first write the formula and find the molar mass of copper (II) sulfate.

Step 2: Find the concentration of the solution.
The volume is given in mL, we must convert to L.