Write the empirical formula for: a. Hydrazine, N2H4 b. Octane, C8H18 c. Benzene, C6H6 d. Ammonia, NH3
The Correct Answer and Explanation is:
Here are the empirical formulas for the compounds you listed:
a. Hydrazine (N2H4):
The molecular formula for hydrazine is N2H4. To determine the empirical formula, you divide the subscripts by their greatest common divisor (GCD). In this case, both 2 and 4 have a GCD of 2. So, divide both subscripts by 2:
- N2H4 → N1H2, or simply NH2.
Empirical Formula for Hydrazine: NH2.
b. Octane (C8H18):
The molecular formula for octane is C8H18. Again, we need to divide the subscripts by the GCD. The GCD of 8 and 18 is 2. So, divide both subscripts by 2:
- C8H18 → C4H9.
Empirical Formula for Octane: C4H9.
c. Benzene (C6H6):
The molecular formula for benzene is C6H6. The GCD of 6 and 6 is 6, so divide both subscripts by 6:
- C6H6 → C1H1, or simply CH.
Empirical Formula for Benzene: CH.
d. Ammonia (NH3):
The molecular formula for ammonia is NH3. Since the subscripts for nitrogen (1) and hydrogen (3) have no common divisor other than 1, the empirical formula is the same as the molecular formula:
- NH3 → NH3.
Empirical Formula for Ammonia: NH3.
Explanation:
The empirical formula represents the simplest whole-number ratio of atoms of each element in a compound. To find the empirical formula, we first identify the molecular formula of the compound. Then, we determine the greatest common divisor (GCD) of the subscripts in the molecular formula. If the subscripts can be divided by a number greater than 1, we divide all the subscripts by that number to obtain the empirical formula. If the subscripts have no common divisor other than 1, the empirical formula is the same as the molecular formula.
In these examples:
- Hydrazine has an empirical formula of NH2 because 2 and 4 can be divided by 2.
- Octane has an empirical formula of C4H9 because 8 and 18 can be divided by 2.
- Benzene has an empirical formula of CH because both 6 and 6 can be divided by 6.
- Ammonia does not change because the ratio of N to H is already in its simplest form.
