The Mole Concept cont’d – Not at STP Redraw the “Mole Map” developed yesterday for 1 mol (symbol for # of moles = n) # of Volume @ molecules STP The Mole (n) Molar Mass (M) Practice MC Q’s 1. What has more moles? A) 1.55x105 kg carbon tetrafluoride B) 1.08x1010 mg water C) 1.28x108g methanol 2. Which is lighter? A) 6.02x1024 formula units ZnCl2 B) 1.20x1029 molecules of N2O5 3. What volume of Ne gas will have the same # of molecules of 12.0 L of O2 gas if both are measured at the same temp & pressure? A) 24.0 L B) 12.0 L C) 6.0 L D) 22.4 L E) 44.8 L 4. How many molecules in 64.3 mg sample of tetraphosphorous decoxide, P4O10? A) 1.36x1023 B) 1.36x1020 C) 1.36x1026 5. The density of oxygen gas at STP is . . . a) 7.1x10-­‐4 g/mL b) 1.43x10-­‐3 g/mL c) 2.86x10-­‐3 g/mL d) 1.43 g/mL 6. Which sample has the greatest # of moles of oxygen? A) 2 mol H2O B) 0.5 mol C6H12O6 C) 0.15 mol Ca3(PO4)2 Gases NOT at STP – (The Ideal Gas Law) Text, pg. 472 * if the # of particles in a given volume of different types of gas are the same (at same temp & pressure) then the # of moles (n) of the gases are the same too. So, !
!
n α V, n = kV, !! =
!
!
!!
We also know, !
!!
!
!
V α , so, V α , 𝑉 =
!"
!
×𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡(R) R is the universal gas constant We can use 1 mol of gas at STP to calculate R, Look at p. 484 for Guidelines for Using the Ideal Gas Law and pg. 485 for converting R for different units. Sample Problem 1: What is the molar volume of a gas at standard ambient temperature and pressure (SATP)? The conditions for SATP are 298 K and 100 kPa. (pg. 485) Sample Problem 2: Dentists sometimes use laughing gas (dinitrogen oxide, N2O) to keep patients relaxed during dental procedures. A cylinder of N2O has a diameter of 23.0 cm and a height of 140 cm. The pressure is 108 kPa, and the temperature is 294 K. How many grams of laughing gas are in the cylinder? (p. 486)