Question

Please help solve these chemistry questions!!!

Practice with percent composition.
1. What is the percent composition of Fe if 111.7 g of Fe is recovered from a 159.7 g sample of Fe2O3?




2. What is the percent composition of O if 12 g of O is recovered from a 38 g sample of Cr2O3?




3. Calculate the percent composition of KCl.





4. Calculate the percent composition of N2O5.





Practice with empirical formulas
5. What is the empirical formula for a compound that contains 0.0260 mol C, 0.0325 mol H, and 0.0065 mol O.



Practice with Molecular Formulas
6. Determine the molecular formula for a compound that has an empirical formula of NO2 and a molar mass of 138.015 g/mol.





7. Nicotine is 74.1% C, 8.6% H, and 17.3% N by mass. It’s molar mass is about 160 g/mol.
a. What is it’s empirical formula?




b. What is it’s molecular formula?

Answer 1

To find the percent composition of Fe in Fe2O3, we need to calculate the molar mass of Fe and the molar mass of Fe2O3. The molar mass of Fe is 55.85 g/mol, and the molar mass of Fe2O3 is 159.7 g/mol.
To calculate the percent composition of Fe:
(55.85 g/mol / 159.7 g/mol) × 100% = 34.9%

Therefore, the percent composition of Fe in Fe2O3 is 34.9%.

Similarly, to find the percent composition of O in Cr2O3, we need to calculate the molar mass of O and the molar mass of Cr2O3. The molar mass of O is 16.00 g/mol, and the molar mass of Cr2O3 is 152 g/mol.
To calculate the percent composition of O:
(16.00 g/mol / 152 g/mol) × 100% = 10.5%

Therefore, the percent composition of O in Cr2O3 is 10.5%.

The formula for potassium chloride (KCl) consists of one potassium atom (K) and one chlorine atom (Cl). To calculate the percent composition of KCl, we need to calculate the molar mass of KCl.
The molar mass of KCl is:
39.10 g/mol (molar mass of K) + 35.45 g/mol (molar mass of Cl) = 74.55 g/mol

To calculate the percent composition of K:
(39.10 g/mol / 74.55 g/mol) × 100% = 52.4%

To calculate the percent composition of Cl:
(35.45 g/mol / 74.55 g/mol) × 100% = 47.6%

Therefore, the percent composition of KCl is 52.4% K and 47.6% Cl.

The formula for dinitrogen pentoxide (N2O5) consists of two nitrogen atoms (N) and five oxygen atoms (O). To calculate the percent composition of N2O5, we need to calculate the molar mass of N2O5.
The molar mass of N2O5 is:
2 × (14.01 g/mol) (molar mass of N) + 5 × (16.00 g/mol) (molar mass of O) = 108.01 g/mol

To calculate the percent composition of N:
(2 × 14.01 g/mol / 108.01 g/mol) × 100% = 25.9%

To calculate the percent composition of O:
(5 × 16.00 g/mol / 108.01 g/mol) × 100% = 74.1%

Therefore, the percent composition of N2O5 is 25.9% N and 74.1% O.

To determine the empirical formula for a compound with given mole ratios, we need to divide each mole value by the smallest mole value to obtain the simplest whole number ratio.
Given:
0.0260 mol C
0.0325 mol H
0.0065 mol O

Dividing each mole value by 0.0065 (the smallest mole value), we get:
C: 0.0260 mol / 0.0065 mol = 4
H: 0.0325 mol / 0.0065 mol = 5
O: 0.0065 mol / 0.0065 mol