Parts Components Calculations
If you understand what a concentration expressed as a parts component means, you should be able to do the calculations you come across. Have a look at the example calculation to see how to use the meaning of the parts expression.
How many moles of Sodium Chloride (RMM 58.5) are there in 420 ml of solution if the concentration of Sodium Chloride is 1 part in 14? Answer to 4 significant figures.
- Find how many grams of Sodium Chloride there are in 420 ml of solution.
The concentration of Sodium Chloride is 1 part in 14
ie there is 1 g of Sodium Chloride in 14 ml of solution.
Thus 14 ml of solution contains 1 g of Sodium Chloride
Thus 420 ml of solution contains 420/14 x 1 g = 30 g of Sodium Chloride -
Find how many moles of Sodium Chloride there are in 420 ml of solution.
Moles of Sodium Chloride = Mass/RMM
Moles of Sodium Chloride = 30 / 58.5 moles = 0.51282 moles
Moles of Sodium Chloride = 0.5128 moles to 4 sig figs
Quick Check of Calculation
The quick check gives an approximate answer used to see if your answer is in the right size range. It should be done before the accurate calculation so that you can see if your calculation is going all right.
Concentration of NaCl is about 1 in 15.
Volume of Solution is about 450 ml.
RMM of NaCl is about 60.
Number of grams of NaCl is about 450/15 ie 30
Number of moles of NaCl is about 30 / 60 ie 0.5
So the answer needs to be somewhere near 0.5 moles.