Preparation of Ca 2+ Stock Solution Weigh out accurately the quantity of CaCO 3
ID: 529553 • Letter: P
Question
Preparation of Ca2+ Stock Solution
Weigh out accurately the quantity of CaCO3 required to make 100 mL of a 100 ppm Ca2+ solution and deliver it into a 50 mL beaker. Add ~20 mL of DI water to the beaker, and then add a minimum volume of 6 M HCl to dissolve the solid completely (add HCl drop by drop with glass rod stirring). Transfer all the solution to a 100 mL volumetric flask then rinse the beaker several times with small portion of water and add the rinsings to the volumetric flask. Dilute the solution to the mark with DI H2O.
Note: 100 ppm Ca2+ solution is not the same as 100 ppm CaCO3 solution.
Calcuate the concentration of Ca2+ stock solution (ppm) if I weighed out 0.0250 g of CaCO3?
Explanation / Answer
Solution:
Preparation of 100 ppm of Ca2+ solution from CaCO3 salt:
FW of salt = 100g.
At. wt. of Ca = 40g
1g Ca in relation to FW of salt = 100/40 = 2.5g
We know, 1 ppm = 1mg/L OR, 1000 ppm = 1g/L
Hence, 2.5g CaCO3 and dissolve in 1 liter volume = 1000 ppm Ca2+ standard solution.
In other words,
1000 mL volume of 1000 ppm Ca2+ standard solution requires = 2.5 g CaCO3
1 mL volume of 1 ppm Ca2+ standard solution requires = 2.5/1000x1000
100 mL volume of 100 ppm Ca2+ standard solution requires = 2.5x100x100/1000x1000
= 0.025 g CaCO3
Therefore,
0.025 g of CaCO3 in 100 mL gives a concentration of = 100 ppm