# Chemistry test 3

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 Author: michaelirby98 ID: 270326 Filename: Chemistry test 3 Updated: 2014-04-14 16:43:24 Tags: chem Folders: chem test 3 Description: chem Show Answers:

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1. How to find the amount of moles of 10.0g of AL
(Grams of AL)(1mol/amu in grams) = Moles

10.0g)(1 mol/ 26.89g)= 0.37064
2. How to find amount of atoms in a specified amount 10.0g of AL
First convert 10.0g into mol = .37064 then find amount of atoms with avagadros number

(.37064mol AL)(6.022X1023/1 mole AL)

Keep number in scientific notation
3. Steps to get from grams of a substance to number of atoms
• Grams to mole,
• Moles to atoms (avogardos number)
4. Equation for precent composition
Percentage = Part/whole X 100
5. How to find percent composition of carbon  in C2H5OH
• Percent = Part/whole X 100
• First find the amu of the entire compd (46.068g/mol)
• Multiple C by number of

6. Empirical Formulas
The simplest whole number ratio of atoms in a molecule

H2O2 -> HO
7. How to calculate empirical formulas from percent compositions?

Do this for all compositions, then divide all #s by the lowest amount of moles.

Multiply numbers by 2 or 3 to get whole numbers
8. Molecular formula
A multiple of the emp formula

9. How would you find the molecular formula of 252g of C5H3 ?
• Find the mass of the 5C and 3H = 63.074 g/mol
• Then divide is with the mass you have.

then multiply emp1rical form by 4
10. How would you find molecular formula from percent compositions?

ex %49.47C, 5.191%H, 28.86%N, O, molec mass of 194g
• Make the %comp into grams.
• Divide that by elements amu

then you would divide that by the smallest amount of grams/mol
11. Determining amount of moles formed/ needed when reacting
• First you need to balance the equation.
• Then you use equivalence factors (4.30 moles of C3H8 and O= 4.30mol C3H= 5mol O2)

Then convert

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