Calculation of Concentration of NO3- in Solution

To calculate the concentration of NO3- in the solution obtained by mixing 275 ml of 0.2 M KNO3, 325 ml of 0.4 M Mg(NO3)2, and 400 ml of H2O, we need to use the concept of additive volumes. The steps involved in the calculation are:

Step 1: Calculate the moles of KNO3 and Mg(NO3)2 in their respective solutions.

Moles of KNO3 = 0.2 M x 0.275 L = 0.055 mol
Moles of Mg(NO3)2 = 0.4 M x 0.325 L = 0.13 mol

Step 2: Calculate the total moles of NO3- in the mixture.

Total moles of NO3- = Moles of NO3- from KNO3 + Moles of NO3- from Mg(NO3)2
Total moles of NO3- = 0.055 mol + 2 x 0.13 mol (since Mg(NO3)2 has two NO3- ions)
Total moles of NO3- = 0.315 mol

Step 3: Calculate the total volume of the mixture.

Total volume of the mixture = 275 ml + 325 ml + 400 ml = 1000 ml or 1 L

Step 4: Calculate the concentration of NO3- in the mixture.

Concentration of NO3- = Total moles of NO3- / Total volume of the mixture
Concentration of NO3- = 0.315 mol / 1 L
Concentration of NO3- = 0.315 M

Explanation:

The concentration of NO3- in the mixture obtained by mixing 275 ml of 0.2 M KNO3, 325 ml of 0.4 M Mg(NO3)2, and 400 ml of H2O is 0.315 M. This is because the volumes of the solutions are additive, and the total moles of NO3- in the mixture can be calculated by adding the moles of NO3- from each component solution. Finally, the concentration of NO3- in the mixture is obtained by dividing the total moles of NO3- by the total volume of the mixture.