When a substance is dissolved in water it is called a solution. If more of the substance is dissolved the resulted solution is said to be concentrated. If a less amount of substance is dissolved it is said to be diluted. However these definitions are relative.
Concentration of the substance in a solution can be given in different units
e.g grams per liter, milligrams per liter . According to these units the concentration is the mass of the substance dissolved in a unit volume.
Most commonly used unit for concentration is however mol dm-3
(moles per cubic decimeter)
Which means how many moles of the substance is dissolved in a unit volume.
We can use this equation for calculations involve in concentration
C=n/V
Concentration= number of moles/ volume
When this equation is used the units are very important. If the concentration is given in mol dm-3
the volume also has to be given in dm-3
If the volume is given in cm-3
it can be divided by 1000 to find the value in dm-3
Question:
1. What is the concentration of a Sodium hydroxide solution if 8g of NaOH is dissolved in 500 ml of water?
To find the concentration using c=n/v we need
i. number of moles
n= m/ Mr
n= 8/ (23+16+1)
n= 0.2 mols
ii. volume
1 ml= 1 cm-3
Volume= 500/ 1000
Volume= 0.5 dm3
C=n/v
C= 0.2mols/ 0.5 dm3
C= 0.4 moldm-3
2. How many moles of HCl is there in 20 ml of a HCl solution with a concentration of 0.2 moldm-3?
C= n/v
0.2 moldm-3= n/ 0.02 dm-3
n= 0.004 mols
Q.1. Calculate the concentration of a NaOH solution if 0.16g of NaOH was dissolved in 250 ml of water.
Next about Percentage yield and Percentage purity
10:47 PM
calculating concentration
concentration
definition concentration
equation for concentration
question on concentration
