Unit 2 Section C Conserving Matter

C.1 Keeping Track of Atoms Law of conservation of matter: In a chemical reaction, matter is neither created nor destroyed. Atoms are forever! Balanced chemical equation: the number of atoms of each element is the same on the reactant and product sides.

Anatomy of a chemical equation CH 4 + 2O 2 --> CO 2 + 2H 2 O Left side of the arrow = reactants Right Side of the arrow = products Subscripts = number of atoms in a given molecule Coefficients = number of the molecules present Formula unit = molecule for ionic compounds

2Cu + O 2 --> 2CuO

Count the atoms…balanced? 2 K + 2 H 2 O→2 KOH + H 2 3 CaBr 2 + 2H 3 PO 4 →6 HBr + Ca 3 (PO 4 ) 2

A Dozen What is a dozen? How many atoms are there in a dozen atoms? How many bottles are there in a dozen pop bottles? How many cars are there in a dozen cars? What is similar about all these examples? What’s different?

A New Unit: THE MOLE ? Photo from

The Chemist’s Mole A mole (abbreviated mol) is a counting unit to make calculations easier. 1 mol = 6.02 x “things” How many cars are there in 1 mole of cars?

6.02 x THIS NUMBER IS HUGE!!! Called Avogadro’s number Equal to the number of grains of sand on all the beaches in all the world! Equal to the number of glasses of water in the entire ocean! If one mole of marbles were spread over the surface of the Earth, our planet would be covered by a 50-mile-thick layer of marbles.

Which would you rather do? Count out 1 mole of carbon atoms? Mass (weigh) 1 mole of carbon atoms? Much easier to weigh something than to count something, however, it’s the atoms, not their mass, that do the reactions. The mole concept allows us to know the number of atoms in a given sample by only knowing the mass of the sample.

Molar Mass Molar Mass = mass of 1 mole of a substance. Add up the masses of all the atoms of a compound from the periodic table and you have the molar mass!

What is the molar mass of CO 2 ? Add up the masses from the periodic table. Mass of 1 C = Mass of 1 O = Mass of CO 2 = ( ) = 44.1 g/mol CO 2

Calculate the molar mass of the following compounds Ga Po CaCO 3 H 2 SO 4 (NH 4 ) 3 PO 4