In a COD test, a sample consumes 1.20 mmol of K2Cr2O7 per litre. Take 1 mol of K2Cr2O7 as equivalent to 1.5 mol of O2 (O = 16). The COD of the sample is:

JEE Advanced levelSingle correct optionDifficulty 3 of 3ev151

In a COD test, a sample consumes $1.20 mmol$ of $K X_{2} Cr X_{2} O X_{7}$ per litre. Take 1 mol of $K X_{2} Cr X_{2} O X_{7}$ as equivalent to 1.5 mol of $O X_{2}$ (O = 16). The COD of the sample is:

Oxygen equivalent =

1.20 \times 1.5 = 1.80

mmol of

O X_{2}

per litre. Mass =

1.80 \times 32 = 57.6

mg/L. Using 1 mol of

O X_{2}

per mol of dichromate gives 38.4, and 3 mol gives 115.2.