Stoichiometry SMK Negeri 13 Bandung

Stoichiometry Definition : Stoichiometry is the study of the quantitative relations between amounts of reactants and amounts of products in chemical reactions It allows us to calculate how much of one chemicals is needed to form another Teknologi dan Rekayasa

Unit of matter in chemistry = Unit in Stoichiometry Unit of matter in chemistry = mole One mole = 6.023X 1023 PARTICLES 6.023X 1023 IS AVOGADRO’S NUMBER Teknologi dan Rekayasa

ATOMIC MASS RELATIVE Mass of neutron = 1 amu Each atom has a specific mass determined by proton and neutron number Mass of neutron = 1 amu Atom with 6 neutron and 6 proton is 12 amu Mass of proton = 1 amu Nitrogen 14 = 14 amu 14 amu for nitrogen relative to carbon 12 Carbon-12 is the standard of atomic mass Teknologi dan Rekayasa

Molecular Mass Relative MOLECULE ARRANGED BY ATOMS MOLECULE’S MASS IS TOTAL AMOUNT OF ATOMIC MASS H2O consist of 2 H and 1 O Since Ar of H is 1 amu and Ar of O is 16 amu Mr of H2O is 18 amu One molecule of H2O is 18 amu One mole of H2O (6.023X 1023molecules) is 18 grams Teknologi dan Rekayasa

E.g. 1 mole Li = 6.94 g Li Molar mass The mass of one mole is called “molar mass” E.g. 1 mole Li = 6.94 g Li This is expressed as 6.94 g/mol Teknologi dan Rekayasa

Converting between grams and moles In order to convert from one to the other you must first calculate molar mass g = mol x g/mol mol = g ÷g/mol This can be represented in an “equation triangle ”g = mol X g/mol Teknologi dan Rekayasa

Converting grams to moles. Determine how many moles there are in 5.17 grams of Fe(C5H5)2. Given Goal units match 5.17 g Fe(C5H5)2 = moles Fe(C5H5)2 0.0278 Use the molar mass to convert grams to moles. Fe(C5H5)2 2 x 5 x 1.001 = 10.01 2 x 5 x 12.011 = 120.11 1 x 55.85 = 55.85

Ratios are found within a chemical equation. Stoichiometry (more working with ratios) Ratios are found within a chemical equation. 2HCl + Ba(OH)2  2H2O + BaCl2 1 1 coefficients give MOLAR RATIOS 2 moles of HCl react with 1 mole of Ba(OH)2 to form 2 moles of H2O and 1 mole of BaCl2

gram to gram conversions Aluminum is an active metal that when placed in hydrochloric acid produces hydrogen gas and aluminum chloride. How many grams of aluminum chloride can be produced when 3.45 grams of aluminum are reacted with an excess of hydrochloric acid? Al(s) + HCl(aq)  AlCl3(aq) + H2(g) 2 6 2 3 3.45 g ? grams Units match 3.45 g Al = g AlCl3 17.0 Let’s work the problem. We must always convert to moles. Now use the molar ratio. Now use the molar mass to convert to grams.

Molarity Molarity is a term used to express concentration. The units of molarity are moles per liter (It is abbreviated as a capital M) When working problems, it is a good idea to change M into its units.

Solutions A solution is prepared by dissolving 3.73 grams of AlCl3 in water to form 200.0 mL solution. A 10.0 mL portion of the solution is then used to prepare 100.0 mL of solution. Determine the molarity of the final solution. What type of problem(s) is this? Molarity followed by dilution.

Solutions 1st: 3.73 g = mol 0.140 L 200.0 x 10-3 L M1V1 = M2V2 2nd: A solution is prepared by dissolving 3.73 grams of AlCl3 in water to form 200.0 mL solution. A 10.0 mL portion of the solution is then used to prepare 100.0 mL of solution. Determine the molarity of the final solution. 1st: 3.73 g = mol L 0.140 200.0 x 10-3 L molar mass of AlCl3 dilution formula M1V1 = M2V2 2nd: (0.140 M)(10.0 mL) = (? M)(100.0 mL) final concentration 0.0140 M = M2

Converting grams to grams We cannot directly convert from grams of one compound to grams of another. we have to go through moles.• Many stoichiometry problems follow a pattern: grams(x) ↔moles(x) ↔moles(y) ↔grams(y)• Teknologi dan Rekayasa