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Uses of the Ideal Gas Equation: I. Solving for Molecular Mass of an unknown gas (Butane Lighter Lab) n = number of moles (units: mol) m = mass (units: grams) M = molecular mass (units: grams/mol) Note: M = m n therefore n = m M PV = nRT PV = mRT M Example: Solve for molecular mass (M) given m = 0.800 g, P = 106.7 kPa, T = 100°C, V = 0.372 L, R = 8.31 L∙kPa mol∙K II. Gas Stoichiometry A + B C + 1) V V 2) Mass V 3) V Mass 4) Mass Density 5) Density Volume 6) Limiting Reactants 7) Mass Molecular Mass 1 D Example 1: Volume to Volume Stoichiometry Gas Law Problem What volume of gas is produced from x liters substance? How many liters of hydrogen chloride gas will be produced from 2.00 L hydrogen gas? H2 (g) + Cl2(g) 2 HCl (g) 2.00 L ?? L Example 2: Mass to Volume Stoichiometry Gas Law Problem What volume of gas is produced from x grams substance? Steps: 1. Balance equation and compound formulas 2. Find moles 3. Find mole ratio 4. Convert moles gas volume of gas (1 mol = 22.4 L) How many liters of hydrogen gas will be produced from 6.54 g of zinc? 2 HCl (aq) + Zn (s) H2 (g) + ZnCl2 (aq) 6.54 g ?? L 2 Example 3: Volume to Mass Stoichiometry Gas Law Problem What mass of gas is produced from x liters substance? What mass of magnesium will react with excess sulfuric acid to produce 500 mL of hydrogen? Mg ?? g + H2SO4 H2 + 500 mL 3 MgSO4 III. Determining Gas Density Step 1: Start with PV = mRT and solve for the molecular mass (M). M Step 2: Density (D) is mass (m) per unit volume (V). Write in equation form: ________________ Step 3: You can introduce the density equation into the equation from step 1. Find m in M = mRT equation from step 1. Replace m with D. PV V Step 4: Solve for density (D). 4 Example 1: Calculate the density of sulfur dioxide at STP to 3 significant figures. (hint: from balloon worksheet) (Ans: 2.87 g/L) Example 2: What is the density of a sample of ammonia gas, NH3, if the pressure is 0.928 atm and the temperature is 63.0°C? (Ans: 0.527 g/L) 5