Warm-up (10/19) Lab 6 pre-lab out on desk! Come get an article to read at front QUIETLY – in your notes, write 2 questions you are curious about! Video: https://x.company/loon/

Stoich with gases Consider the following unbalanced equation: CH4 (g) + O2 (g)  CO2 (g) + H2O (g) If 2.0 L of methane are mixed with 4.5 L oxygen, how many liters of gaseous carbon dioxide are formed?

Stoich with gases – a little deeper A sample of methane gas having a volume of 2.80 L at 25ºC and 1.65 atm was mixed with a sample of oxygen gas having a volume of 35.0 L at 31ºC and 1.25 atm. The mixture was then ignited to form carbon dioxide and water. Calculate the volume of CO2 formed at a pressure of 2.50 atm and a temperature of 125ºC.

Answer to Warm up – part 1

Answer to Warm up – part 2

When the stopcocks are closed, the three flasks have the following volume and pressure values: He 1.00 L at 600. Torr, Ne 1.00 L at 553 Torr, and Ar 2.00 L at 323 Torr. Assuming the connecting tubes have negligible volume, what is the partial pressure of each gas and the total pressure after all the stopcocks are opened? Total volume = 4 L, so each sample is “diluted” from it’s original volume. P He = 600. Torr* (1/4) = 150. Torr. P Ne = 553 Torr * (1/4) = 138.25 Torr. BUT, remember that Argon’s container is only be “diluted” by half: P Ar = 323 * (2/4) = 161. 5 Torr. P total = Phe + Pne + P Ar = 150 Torr + 138.25 Torr + 161.5 Torr = 449.75 = 450. Torr

Gas applications: Molar Mass What is the formula (units) for molar mass? So, in any problem, if we know the grams and the number of moles, we can find an unknown molar mass!

Gas applications: Molar Mass A sample of gas has a volume of 445 mL and a mass of 1.500 g at a pressure of 95 kPa and a temperature of 28°C. What is its molar mass? Solve for moles, and then plug in molar mass = grams / moles = 89 g/mol

Lab 5 - Molar Volume of a Gas at STP (Avogadro’s work) At STP, any gas has a volume of: 22.4 L! Not really something you have to memorize (because PV=nRT gives you that) Why? What is the density of each gas? Gas molecules are so tiny and pressure doesn’t depend on mass (really) – the number of particles is what affects pressure! So, equal volumes at equal conditions of gases have the same number of moles! Super important!

Gas Density Demo We can’t do it, but they did on Jimmy Fallon! 0:56 start

Gas applications (5.4) A gas has a density of 1.65 g/L at 27°C and 92.0 kPa. What is its molar mass? First, assume 1 L of gas, and solve for moles of gas using PV=nRT. Then, Molar mass = g/mol = 44.7 g/mol

Lab #6: Unknown Volatile Liquid ID by Vapor Pressure

Lab #6: Vapor Pressure of a Volatile Liquid Application of PV = nRT Find the molar mass of the unknown and identify it based on the list of possibilities!

Lab #6 – do we understand what we need to do? Remember: ID sheet on Moodle (possible identities to choose from) – use it!

DEMOS! Can you explain? Shaving cream, egg

Extra Problems (if time) An unknown diatomic gas has a density of 3.164 g/L at STP. What is the identity of the gas? Calculate the volume of oxygen gas at STP required for complete combustion of 125 g of octane (C8H18). Cl2, 306 L

AP Challenge Problem WS Try them on your own! You can do it!

Homework Day 4 – all due F Lab 6 Calculations and Post-Lab questions IN YOUR LAB BOOK Data Table Calculations (Qs # 1-3 …separate EACH calculation) Post-Lab Questions (Qs #4-7: EXPLAIN WELL) Both WS 4 on Moodle – try them, the work through keys to prepare for…. Quiz 1: Monday! Use HW, labs, notes, and reading to help you study!