Mass, Atoms, and Amu

Mass, Atoms, and Amu

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

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?

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!

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?

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?

Two more to be sure. If you mass out 24.31 g of Mg, how many Mg atoms are in this sample? How many calcium atoms are in 40.08 g of calcium?

The mole Mole- abbreviated mol, the mole contains 6.022 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

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

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

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 19.00 g of H2O? How many potatoes in a mole of potatoes?

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?

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

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

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: _____

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

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?