Clicker questions 1 Sodium sulfate Na2SO4 2 Aluminum phosphate AlPO4 3 Calcium sulfide CaS 4 Iron II nitrate Fe NO3 2 5 Silver hydroxide AgOH 6 Fe2 SO3 3 Iron III Sulfite Law 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 2 Some other interpretations of chemical formulas What 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 N 15 0 g N 14 0 g mol 1 07 mole N 1 07 mole N x 1 formula unit NH4 3PO4 3 N 357 moles NH4 3PO4 x 148 97 g mol 53 2 g NH4 3PO4 Purity of Samples The percent purity of a sample of a substance is always represented as mass of pure substance purity 100 mass of sample mass of sample includes impurities 5 A 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 Na3PO4 250 0 246 g 4 g Chapter 3 Chemical Equations and Reaction Stoichiometry Chemical 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 2H2O A 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 Law 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 10 Iron III oxide reacts with carbon monoxide to yield pure elemental iron and carbon dioxide Fe2O3 3CO 2Fe 3CO2 NH3 burns in oxygen to form NO and water Clicker question Magnesium 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 acid Some 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 cpd 3 If free uncombined elements appear on either side balance those last Calculations based on chemical equations H2 O2 H2O balance I 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 Fe 2O3 3 CO 2 Fe 3 CO 2
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