Question

Prepare 0.1N working standard solution in 250ml distilled water from stock standard solution 20% Na2CO3 in 50ml of distilled water, If you know that the A.wt of Na=32,O=16,C=12? what is the way I should follow to get the answer?!!!

a) Calculate the molarity
b) Convert percentage to moles
c) Dilute the solution
d) All of the above

Answer 1

To prepare a 0.1N working standard solution of Na2CO3, calculate the molarity of the stock solution, convert the percentage to moles, and correctly dilute the solution.

Step-by-step explanation:

To prepare a 0.1N working standard solution of Na2CO3 in 250 mL of distilled water from a 20% stock standard solution in 50 mL of distilled water, follow these steps:

1. Calculate the molarity of the stock solution.
2. Convert the 20% solution concentration to moles of Na2CO3.
3. Dilute the calculated amount of the stock solution to reach the desired 0.1N concentration in 250 mL of water.
   

The atomic weights of Na, C, and O are 32, 12, and 16 respectively, so the molecular weight of Na2CO3 is (2×32) + 12 + (3×16) = 106 g/mol. First, let's determine how many grams of Na2CO3 are in the 50 mL of stock solution: 20% of 50 mL is 10 g (since density of the solution is approximately considered as that of water for simplicity), which is (10 g / 106 g/mol) approx. 0.0943 mol of Na2CO3. To make this a 0.1N solution, we would need 0.1 mol of Na2CO3 per liter, and since we want to prepare 250 mL, we need 0.025 mol.

Finally, to dilute the stock solution, we can use the formula C1V1 = C2V2, where C1 is the concentration of the stock solution and V1 is the volume of stock solution needed. Plugging in the values, we can solve for V1 to find the volume of stock solution needed to add to 250 mL of water to make the 0.1N solution.

Therefore, the correct answer is (d) All of the above.