Benzene has the empirical formula CH and an experimental molar mass of 78 g/mol. What is its molecular formula? Explain how you got your answer.
empirical mass = (12+1= 13)
molar mass = 78
78/13 = 6; therefore,
(CH)6 = C6H6/sub>
scratch that /sub>. It wasn't supposed to print.
empirical mass = (12+1= 13)
molar mass = 78
78/13 = 6; therefore,
(CH)6 = C6H6
so that's correct?
yes
To determine the molecular formula of benzene, we need to compare its empirical formula with its experimental molar mass. Let's break down the process step by step:
1. Find the empirical formula's molar mass:
- The empirical formula of benzene is CH, consisting of one carbon atom (C) and one hydrogen atom (H).
- The molar mass of carbon is approximately 12.01 g/mol, and the molar mass of hydrogen is approximately 1.01 g/mol.
- Multiply the molar mass of carbon (12.01 g/mol) by the number of carbon atoms (1) and the molar mass of hydrogen (1.01 g/mol) by the number of hydrogen atoms (1).
- The empirical formula's molar mass = 12.01 g/mol + 1.01 g/mol = 13.02 g/mol.
2. Compare the empirical formula's molar mass with the experimental molar mass:
- The experimental molar mass of benzene is given as 78 g/mol.
3. Calculate the ratio between the experimental molar mass and the empirical formula's molar mass:
- Divide the experimental molar mass (78 g/mol) by the empirical formula's molar mass (13.02 g/mol).
- This yields the ratio of 78 g/mol / 13.02 g/mol = 5.98.
4. Determine the molecular formula:
- The ratio obtained in step 3 represents the number of empirical formula units present in the molecular formula.
- Since we need to have whole numbers in the molecular formula, multiply the subscripts in the empirical formula by the ratio obtained in step 3.
- In this case, multiply the empirical formula CH by 5.98.
- This gives the molecular formula: (C x 5.98)H = C6H5.98.
However, molecular formulas are always expressed with whole numbers, so we need to round the ratio. Since 5.98 is close to 6, we can round it up to the nearest whole number:
- C6H5.98 would be rounded to approximately C6H6.
Therefore, the molecular formula of benzene is C6H6.