The amount of organic carbon in a sample can be obtained by IR analysis of the carbon dioxide (CO2) released following complete combustion of the sample in oxygen. A reference sample of an organic compound is usually used to calibrate the instrument response.

In an analysis of the carbon content of a soil sample using this method, calibration of the instrument, after zeroing with a blank sample, was carried out by combusting a 0.1005 g sample of oxalic acid (COOH)2 which gave an instrument reading of 102540. Subsequent analysis of a 0.1115 g soil sample gave an instrument reading of 14515. Calculate the percentage of organic carbon in the soil sample.

I would do this.

%C in H2C2O4 is approx 27% but you should get a more accurate answer.
%C = (2*atomic mass C/molar mass)*1000.

1005g of 27% C gave a reading of 102540.
So the % C in the soil is 27% times two correction factors. One factor converts for the difference in IR reading, the other for the difference in sample size.
27% x (14515/102540) x (0.1005/0.1115)= ?
You must remember that this gives somewhat limited results; i.e., the soil sample carbon but decompose the same way oxalic acid does.

Can you go through this question in more detail?

To calculate the percentage of organic carbon in the soil sample, we can use the calibration data obtained from the combustion of the oxalic acid sample.

Step 1: Calculate the response factor
The response factor is the ratio of the instrument reading for the calibration sample to the known mass of the calibration sample.

Response Factor = Instrument reading / Mass of calibration sample

Given:
Instrument reading for oxalic acid = 102540
Mass of oxalic acid sample = 0.1005 g

Response Factor = 102540 / 0.1005 = 102130.67

Step 2: Calculate the amount of organic carbon in the soil sample
The amount of organic carbon in the soil sample can be calculated using the response factor and instrument reading of the soil sample.

Amount of organic carbon = (Instrument reading of soil sample / Response Factor) x Mass of soil sample

Given:
Instrument reading for soil sample = 14515
Mass of soil sample = 0.1115 g

Amount of organic carbon = (14515 / 102130.67) x 0.1115 = 0.0157 g

Step 3: Calculate the percentage of organic carbon in the soil sample
The percentage of organic carbon in the soil sample can be calculated by dividing the amount of organic carbon by the mass of the soil sample and multiplying by 100.

Percentage of organic carbon = (Amount of organic carbon / Mass of soil sample) x 100

Percentage of organic carbon = (0.0157 / 0.1115) x 100 = 14.08%

Therefore, the percentage of organic carbon in the soil sample is 14.08%.

To calculate the percentage of organic carbon in the soil sample, we need to use the calibration data and the instrument readings for the soil sample.

First, we need to calculate the response factor (RF) using the calibration data. The response factor relates the instrument reading to the actual amount of organic carbon in the sample. It is calculated using the following formula:

RF = (amount of organic carbon in the reference sample) / (instrument reading of the reference sample)

The reference sample used in this case is oxalic acid (COOH)2, and its weight is 0.1005 g, while the instrument reading is 102540.

RF = (0.1005 g) / (102540) = 9.8 x 10^-7 g/instrument reading

Next, we need to determine the amount of organic carbon in the soil sample. We can calculate this using the following formula:

amount of organic carbon in the soil sample = (instrument reading of the soil sample) x RF

For the soil sample, the instrument reading is 14515.

amount of organic carbon in the soil sample = (14515) x (9.8 x 10^-7 g/instrument reading) = 0.0142 g

Finally, we can calculate the percentage of organic carbon in the soil sample using the following formula:

percentage of organic carbon = (amount of organic carbon in the soil sample / weight of the soil sample) x 100

The weight of the soil sample is given as 0.1115 g.

percentage of organic carbon = (0.0142 g / 0.1115 g) x 100 = 12.75%

Therefore, the soil sample contains approximately 12.75% organic carbon.