GENERAL CHEMISTRY Chem BATAA EL GAFARY

Stoichiometry Chemical Arithmetic

The Mole: Is the amount of a substance that contains Avogadro’s No. of elementary units. 6.02x10 23 Avogadro’s Number NANA

If you had a mole of cats... They would create a sphere larger than Earth!

If you had a mole of H 2 O could you swim in it? NO! Water molecules are so small that a mole of H 2 O = 18ml

Gram Formula Mass Gram Molecular Mass Molar Mass mass in grams of 1 mole of a substance 1 mole of NaCl = 58g = 6.02 x particles of NaCl 1 mole of H 2 O = 18g = 6.02x10 23 molecules of H 2 0 of the in

Ex. What mole ratio of carbon to chlorine must be chosen to prepare the substance CCl 4 ? Ex.2: How many moles of carbon atoms are required to combine with 2.5 mol Cl to form the substance CCl 4 ?

a)In case of monoatomic elements: 1 mole = atomic mass(g) = 6.02x10 23 atoms Ex.: a)What is the mass in grams of 2 atoms, Ca ? b)How many moles are in 2 atoms of Ca ? c)How many atoms are in 120 g of Ca ? Ca = 40 Solution: a)40 g of Ca = 6.02x10 23 atoms X = 2 atoms x = 1.33X g of Ca

1 mol of Ca = 6.02x10 23 atoms y = 2 atoms y = 3.32 x mol of Ca 40 g of Ca = 6.02x10 23 atoms 120 g of Ca = Z Z = 1.81 x10 24 atoms of Ca

b) In case of compounds or diatomic or polyatomic elements: 1 mole = molecular weight (g) = 6.02x10 23 molecules Ex. How many atoms of oxygen are there in 75 g of H 2 SO 4 ? H = 1, S = 32, O = 16 SOLUTION: Molecular weight of H 2 SO 4 = 6.02x10 23 molecules 98 g of H 2 SO 4 = 6.02x10 23 molecules 75 g of H 2 SO 4 = x x = x10 23 molecules of H 2 SO 4 Each 1 molecule of H2SO4 contains 4 atoms of oxygen Each x10 23 molecules of H 2 SO 4 contains y atoms of oxygen y = 1.84 x10 24 atoms of oxygen

 Molecular Weight ( Molecular Mass or Molar Mass) If the substace is composed of molecules, the sum of the atomic masses is called molecular weight  Formula Weight ( Formula Mass ): the sum of the atomic weights represented by the formula of a substance is its formula weight.

Calculate the formula weight of iron sulphate Fe 2 (SO 4 ) 3. SOLUTION: 2 atomic weight Fe = 2 ( 55.9) = g 3 atomic weight S = 3 ( 32.1) = 96.3 g 12 atomic weight O = 12(16) = 192 g Formula weight of Fe 2 (SO 4 ) 3 = g

The relationship between mol and mass

Percentage Composition:

Chemical Formula: The definite composition of a particular compound is represented by its chemical formula. There are three types of chemical formula: