[Naples]

1. A certain compound is composed of: 54.6% carbon, 9.0% hydrogen and 71.1% oxygen.  The molar mass of the compound is 90.0.  What are the empirical and molecular formulas of this compound?

C: 54.6g (1 mole / 12.01g) = 4.55 moles/4.44 moles = 1.02
H: 9.0g (1 mole / 1.01g) = 8.91 moles/4.44 moles = 2.01
O: 71.1g (1 mole / 16.00g) = 4.44 moles/4.44 moles = 1

So the formula would be CH₂O...is that supposed to be the molecular formula or the empirical formula?


2. What mass of oxygen is contained in a 3.50 L tank where the temp is 50.0^oC and the pressure is maintained at 4.5 atm?
I'm not really sure what formula I should be using to solve this.


3. What pressure will be exerted by each of the gases in the following mixture is the total pressure is 768.8 torr? .500g H₂, .245g O₂ and .335g N₂
I know that P_T = P₁ + P₂ + P₃...but I'm unsure of how to apply that to find the pressure of each gas.

[Yggdrasil]

1. A certain compound is composed of: 54.6% carbon, 9.0% hydrogen and 71.1% oxygen.  The molar mass of the compound is 90.0.  What are the empirical and molecular formulas of this compound?

C: 54.6g (1 mole / 12.01g) = 4.55 moles/4.44 moles = 1.02
H: 9.0g (1 mole / 1.01g) = 8.91 moles/4.44 moles = 2.01
O: 71.1g (1 mole / 16.00g) = 4.44 moles/4.44 moles = 1

So the formula would be CH₂O...is that supposed to be the molecular formula or the empirical formula?

This is the empirical formula.  To find the molecular formula, you need to know the elemental composition and the molecular weight.

2. What mass of oxygen is contained in a 3.50 L tank where the temp is 50.0^oC and the pressure is maintained at 4.5 atm?
I'm not really sure what formula I should be using to solve this.

First, use the ideal gas law to calculate the number of moles of oxygen.  You should then be able to calculate the mass of the oxygen when you know the number of moles.

3. What pressure will be exerted by each of the gases in the following mixture is the total pressure is 768.8 torr? .500g H₂, .245g O₂ and .335g N₂
I know that P_T = P₁ + P₂ + P₃...but I'm unsure of how to apply that to find the pressure of each gas.

The partial pressure of each component (P₁, etc.) are proportional to that component's mole fraction.  For example, P_H2 = P_T * (moles of H₂) / (total moles of gas).

[Fridushka]

here where the empirical formula is : CH₂O..its molar mass is equal to 30, and when the molecular is 90, all you have to do is to divide 90 by 30..!

[DrCMS]

1. A certain compound is composed of: 54.6% carbon, 9.0% hydrogen and 71.1% oxygen. 

Don't you think it's strange that you have 134.7% Carbon Hydrogen and Oxygen?

[Naples]

Yeah I realized that, but it's a summer assignment so I can't really ask my teacher until tomorrow, when I have my first day of school!!!