A bomb calorimeter may be calibrated using a substance with a well-known heat of combustion. A commonly used calibrating agent is benzoic acid (C7H6O2) which has a heat of combustion of 3227 kJ for each mole of benzoic acid. 2.50 g of pure solid benzoic acid is placed in a calorimeter and completely reacted with oxygen. The temperature rise of the calorimeter is observed to be 8.90°C. Calculate the calibration factor of the calorimeter in kJ°C⁻¹.

SSCE VCE Chemistry Measuring Changes in Chemical Reactions: A bomb calorimeter may be calibr

A bomb calorimeter may be calibrated using a substance with a well-known heat of combustion - VCE - SSCE Chemistry - Question 3 - 2004 - Paper 1

Question 3

A bomb calorimeter may be calibrated using a substance with a well-known heat of combustion. A commonly used calibrating agent is benzoic acid (C7H6O2) which has a h... show full transcript

Worked Solution & Example Answer:A bomb calorimeter may be calibrated using a substance with a well-known heat of combustion - VCE - SSCE Chemistry - Question 3 - 2004 - Paper 1

Step 1

Calculate the amount of benzoic acid in moles

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Answer

The molar mass of benzoic acid (C7H6O2) is calculated as follows:

Carbon (C): 7 × 12.01 g/mol = 84.07 g/mol
Hydrogen (H): 6 × 1.008 g/mol = 6.048 g/mol
Oxygen (O): 2 × 16.00 g/mol = 32.00 g/mol

Thus, the total molar mass:

$RMM_{benzoic\,acid} = 84.07 + 6.048 + 32.00 = 122.12 \, g/mol$

Now, calculate the number of moles of benzoic acid:

$ext{moles of benzoic acid} = \frac{2.50 \, g}{122.12 \, g/mol} = 0.0205 \, moles$

Step 2

Calculate the energy released

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Answer

The energy released upon the complete combustion of the benzoic acid can be calculated using its heat of combustion:

$ext{energy} = 0.0205 \, moles \times 3227 \, kJ/mol = 66.1 \, kJ$

Step 3

Calculate the calibration factor

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Answer

Finally, the calibration factor for the calorimeter can be determined using the observed temperature rise:

$CF = \frac{66.1 \, kJ}{8.90 \, °C} = 7.43 \, kJ/°C$

This is the calibration factor of the calorimeter.

A bomb calorimeter may be calibrated using a substance with a well-known heat of combustion - VCE - SSCE Chemistry - Question 3 - 2004 - Paper 1

Worked Solution & Example Answer:A bomb calorimeter may be calibrated using a substance with a well-known heat of combustion - VCE - SSCE Chemistry - Question 3 - 2004 - Paper 1

Calculate the amount of benzoic acid in moles

Calculate the energy released

Calculate the calibration factor

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