Empirical and Molecular Formula

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Empirical and Molecular formula

• Empirical formula: simplest whole number ratio of atoms to each other
• Molecular formula: actual number of atoms in the particle
• Not necessarily the same thing

Using Combustion Data to Determine Empirical Formula

• The initial mass of the sample is known
• The increase in the mass of the magnesium perchlorate gives you the mass of water produced
• The increase in the mass of the sodium hydroxide gives you the mass of carbon dioxide produced

yeah i don’t get it either

oh i got it

• When a compound containing carbon and hydrogen is subject to combustion with oxygen in a special combustion apparatus, all the carbon is converted to $C{O}_2$ and the hydrogen to $H_{2}O$
• The amount of carbon produced can be determined by measuring the amount of $C{O}_2$ produced.
  • This is trapped by the sodium hydroxide, and thus we can monitor the mass of CO2 produced by determining the increase in mass of the CO2 trap.
• Likewise, we can determine the amount of H produced by the amount of H2O trapped by the magnesium perchlorate.

Actual Method

1. Calculate number of moles of water
2. Determine number of moles of hydrogen atoms by multiplying moles of water by 2
3. Calculate numbers of moles of carbon dioxide
4. Determine moles of carbon atoms (moles of carbon atoms = moles of carbon dioxide)
5. Calculate mass of hydrogen and carbon, and subtract that from the mass of the product to get the mass of oxygen
6. Calculate moles of oxygen
7. Profit (find lowest whole number ratio)