Clicker questionsLaw of Multiple ProportionsSlide 3Slide 4Purity of SamplesSlide 6Slide 7Slide 8Slide 9Law of Conservation of MatterSlide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Clicker questions1. Sodium sulfate = Na2SO42. Aluminum phosphate = AlPO43. Calcium sulfide = CaS4. Iron (II) nitrate = Fe(NO3)25. Silver hydroxide = AgOH6. Fe2(SO3)3 = Iron (III) SulfiteLaw of Multiple Proportions•It is possible for two elements, A and B, to combine to form more than one compound.•The ratios of the masses of element B that combine with a given mass of element A in each compound can be expressed by small whole numbers.2Some other interpretations of chemical formulasWhat mass of phosphorus is contained in 45.3 grams of (NH4)3PO4?What mass of ammonium phosphate, (NH4)3PO4 (FW 148.97 g/mol), would contain 15.0 g of N15.0 g N / 14.0 g/mol = 1.07 mole N1.07 mole N x (1 formula unit (NH4)3PO4 / 3 N) = =.357 moles (NH4)3PO4 x 148.97 g/mol = = 53.2 g (NH4)3PO45Purity of Samples•The percent purity of a sample of a substance is always represented as% purity = mass of pure substancemass of sample´100%mass of sample includes impuritiesA bottle of sodium phosphate, Na3PO4, is 98.3% pure Na3PO4. What is the mass of Na3PO4 in 250.0 g of this sample of Na3PO4?98.3 g / 100 g x 250 g = 246 g Na3PO4250.0 – 246 g = 4 gChapter 3 Chemical Equations and Reaction StoichiometryChemical equations are used to describe chemical reactions and they show (1) the substances that reacts, called reactants; (2) the substances formed, called products; and (3) the relative amounts of the substances involved.The # in front of cpds are called coefficients and represent the # of molecules of each reactant or product needed to balance the equation.Methane reacts with oxygen to produce carbon dioxide and water.Write the chemical equation, then balance it.CH4 + 2O2  CO2 + 2H2OA balanced chemical equation must always include the same number of each kind of atom on both sides of the equation. (Law of Conservation of Matter provides the basis for “balancing” chemical equations – because matter is neither created nor destroyed during a chemical reaction)10Law of Conservation of Matter –There is no detectable change in quantity of matter in an ordinary chemical reaction.–Balanced chemical equations must always include the same number of each kind of atom on both sides of the equation.–This law was determined by Antoine Lavoisier.Iron (III) oxide reacts with carbon monoxide to yield pure elemental iron and carbon dioxideFe2O3 + 3CO  2Fe +3CO2NH3 burns in oxygen to form NO and waterClicker questionMagnesium metal is burned in air to produce magnesium oxide.Write the balanced chemical equation. Input just the numbers in order with no spaces in between (put a 1).When aluminum hydroxide is mixed with sulfuric acid, the products are aluminum sulfate and water. Write a balanced equation.Silver nitrate + hydrogen sulfide→silver sulfide + nitric acidSome helpful hints re balancing chemical equations.1. Look for elements that appear in only one place on each side of the equation, and balance those elements first.2. Pick a pair of cpds with a common element. Focus on the cpd with the largest subscript for the element in question to see I you can use that subscript as the coefficient for the other cpd3. If free, uncombined elements appear on either side, balance those last.Calculations based on chemical equationsH2 + O2 → H2O balanceI have 2.3 moles of H2, how many moles of water will I make (O2 is in excess).I want to produce 5.0 moles of H2O, how many moles of O2 do I have to start with?How many iron atoms can be produced by the reaction of 2.50 x 105 formula units of iron (III) oxide with excess carbon monoxide?232CO 3 + Fe 2 CO 3 + OFe 