VIEWS: 3 PAGES: 4 POSTED ON: 12/4/2011
Chemistry 20 – Gravimetric Stoichiometry NG Name: __________________________ Date: ______________ Read pages 286 – 290 of your textbook to complete the following notes guide. Review – types of reactions: reaction type general description formation element + element → compound 2 H2(g) + O2(g) → 2 H2O(g) decomposition compound → element + element 2 H2O(g) → 2 H2(g) + O2(g) (hydrocarbon) combustion substance + oxygen → __ CO2(g) + __ H2O(g) CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g) (methane, CH4(g), is a hydrocarbon because it consists of only hydrogen and carbon) single replacement compound + element → element + compound 2 HCl(aq) + Mg(s) → H2(g) + MgCl2(aq) double replacement compound + compound → compound + compound H2SO4(aq) + 2 NaOH(aq)→ Na2SO4(aq) + 2 HOH(l) What does the coefficient in front of a formula in a chemical equation tell you? e.g., N2(g) + 3 H2(g) → 2 NH3(g) it tells you PROPORTIONS! 1 part 3 parts 2 parts 1 molecule 3 molecules 2 molecules 1 mole 3 moles 2 moles (also called the mole ratio) 6.02 × 1023 particles 3 (6.02 × 1023 particles) 2 (6.02 × 1023 particles) What is a mole? see page 51 of Nelson textbook 1 mole of Na is 6.02 × 1023 Na atoms 1 mole of chlorine is 6.02 × 1023 chlorine molecules 1 mole = 6.02 × 1023 molecules Avogadro’s number is a constant, just like 1 dozen = 12, 1 mole = 6.02 × 1023 molecules So, for our example above, the mole ratio is 1: 3: 2. Stoichiometry is a method for predicting or analyzing the quantities of reactants and products involved in a chemical reaction. ○ it is simply using proportions to calculate the amounts of chemicals reacted and produced using chemical equations Gravimetric Stoichiometry is the method of predicting or analyzing the masses of reactants and/or products involved in a chemical reaction. ○ stoich dealing with mass and mole quantities ○ also called “mass to mass” stoich There are four basic steps involved in solving all gravimetric stoichiometry calculations: 1. balanced chemical reaction 2. mass → mole conversion 3. mole ratio 4. mole → mass conversion To convert between mass → moles or moles → mass, you must use the molar mass. ○ molar mass is found on your periodic table for each element and can be calculated for any compound if you can correctly provide the chemical formula g ○ molar mass is in units of grams per mole, or 1 mol 1 mol ○ this value can be inverted to when necessary to cancel out appropriate units g mass → moles or moles → mass 1 mol g g × × mol g 1 mol = mol =g ○ underneath the equation you can write the given information (mass of malachite), the required information (mass of copper(II) oxide) and any other values you will need (molar masses, in this case, which are the conversion factors) Convert the mass of malachite to moles of malachite (its chemical amount). m 1.00 g or n = = M 221.13g /mol nCu2(OH)2CuCO3(s) = 0.0045222267 mol = 0.0045222267 mol Convert moles of malachite to moles of copper(II) oxide using the mole ratio. 2 mol CuO(s) 0.0045222267 mol Cu 2 OH 2 CuCO3 s 1 mol Cu 2 (OH)2CuCO3 (s) = 0.0090444533 mol CuO(s) Convert the moles of copper(II) oxide into the mass of copper(II) oxide. 79.55 g nCu2(OH)2CuCO3(s) = 0.0090444533 mol CuO(s) = 0.719 g 1 mol or use m = nM = (0.0090444533 mol CuO(s) ) ( 79.55 g/ mol )= 0.719 g Alternatively, this entire question can be done all in one step, as follows: = 0.719 g CuO(s) Double check the significant digits in your answer. Go back to the original question to find the lowest number of significant digits. In this example, it was 3 digits, given a mass of 1.00 g in the question. Round your answer appropriately. Make sure to include units and the identity of the substance as part of your answer. There will be times when you will solve problems that do not necessarily involve all four steps of the stoichiometry process. But, the secret to stoichiometry is to practice, practice, practice! Show all your work for each and every question to get into good habits.
Pages to are hidden for
"5 - gravimetric stoich NG_2"Please download to view full document