1. Mass, Atoms, and Amu

2. Mass, Atoms, and Amu

3. Counting objects by mass
Avg. values for mass can be used to determine
-# of objects in a sample of obj.
-mass of a sample of a # of objects

4. Atomic mass units 1 amu = 1.66 x 10-24 g (which unit is bigger?)
Example:
pick an element, and write down the element’s avg. mass in amu per atom
How many amu’s will 1000 atoms of the element weigh?

5. Working with a model: chocolate
What’s the average atomic mass in amu per “atom” of chocolatium? Come up with a reasonable procedure and win a prize!

6. How many? In amu, what would the mass of 100 atoms of chocolatium be?
How many atoms are in 1.68 x 1024 amu of chocolatium?

7. Let’s try some with real elements
One together…
Calculate the mass in grams of a sample of S with 75 atoms
Try these with a partner
How many C atoms are in 300 amu of C?
How many Ca atoms are in 50 g of Ca?

8. Two more to be sure.
If you mass out g of Mg, how many Mg atoms are in this sample?
How many calcium atoms are in g of calcium?

9. The mole
Mole- abbreviated mol, the mole contains x 1023 units (no matter what substance)
IMP: a sample of an element with mass = avg atomic mass (in g) contains 1 mole of atoms

10. Molar Mass
Molar mass – mass in grams of 1 mol of a substance (unit is g/mol)
Per 1 mol of C2O3, there are:
___ mol C
___ mol O
Molar mass of cmpd = molar mass of each element x the number of moles of each element
C2O3

11. Calculating Molar Mass
Vitamin C: C6H8O6
Vanillin: C8H8O3
Nitrous Oxide: N2O
How many g are in 3 moles of each of the above compounds?

12. Try these in pairs How many N2 molecules in 5 mol N2?
How many mg of sodium in 3 mol of NaCl?
How many moles in g of H2O?
How many potatoes in a mole of potatoes?

13. How many? H2 molecules in a mole? Moles in a 5.01 g of sulfur?
Grams in 250 mol of nitrogen gas?
Moles in 5.68 mg of silicon?

14. Organizing- Let’s Make a List
For questions about atoms, mass, and moles

15. Percent Composition
In terms of compounds, the % composition of an elem. in a cmpd is the %, by mass of that elem. in the cmpd.
In math terms:
% comp = mass of element x 100%
total mass of cmpd

16. Same formula as % comp. of isotopes! Coolio.
Find the % composition of carbon and hydrogen in serotonin, C10H12N2O
Mass per mole of compound: ______
Mass of C per mol: _____
Mass of H per mol: _____

18. Try these two with a buddy.
Find the mass percent of nitrogen in N2O. What must the mass percent of O be?
Find the mass percent of each element in baking soda, NaHCO3

19. Cookie % Comp Lab Take two cookies of 3 of the 4 types.
Mass the two cookies on the balance, record mass.
Carefully remove the filling.
Mass the filling and cookies separately and record.
Calculate % filling and % cookie.
Questions: Possible errors? How does this relate to % composition by mass of compounds and to calc. of % abundance? If you loved the filling, which size cookie would you rather eat and why?