UCSB CHEM 6AL Final Exam Questions With 100% Correct Answers.

Intermolecular forces and how they affect physical properties /purification techniques: dipole-dipole, electrostatic, hydrogen, ion, london, - Answer-*dipole-dipole*: polar covalent molecules such as aldehydes and ketones. positive and negative end. polar molecules must be close together for force to be significant. weaker than ion-dipole forces; increase with polarity of molecule. *electrostatic*: occur between charged species, cations and anions, and are responsible for very high MP and BP of ionic compounds and metals *hydrogen bonding*: hydrogen atom in a polar bond (NOF). considered a dipole-dipole interaction. quite polar. *ion-dipole*: interaction betwween a charged ion and apolar molecule. cations are attracted to negative end of dipole, and anions are attracted to positive end. *london dispersion*: dependent on surface area and polarizability of the surface of the molecule. only types of forces NON-polar covalent molecules can experience. result from the movement of electrons in the molecule, which generates temporary positive and negative regions in the molecule. melting point and melting point range - Answer-solid has ordered crystal lattice structure. heat makes this structure move enough to the point where it becomes a liquid. The melting point is how much energy it takes to make this lattice structre move. Impurities disrupt the crystal lattice, so impurities make a structure easier to melt. MP also broadens when a compound is impure. If there is water in the solid, it is impure. solid will stick to side of capillary if still wet. If you dont know the MP range, take a quick measurement to get a rough estimate, then take a second, more careful measurement. limiting reagents and percent yields - Answer-*limiting reagents*: the compound that runs out first. when limiting reagent runs out, reaction can no longer proceed and other compound is considered in excess. tell which is limiting reagent by converting grams or mg used to moles using molar mass. when you have moles, use the stoichimetric ratios to see which is the smaller amount of moles (mole of reagent under mole produced of product); this is your limiting reagent. could also compare mole ratios between reagents to see how much you would need of the other reagent to make reaction go to completion. use limiting reagent to see how much product we will get. *percent yield*: actual yield/theoretical yield X 100. If you expect 10 g but only get 8.4, your % yield is 84%. get theoretical yield by taking limiting reagent and seeing how much product can be made by LR. convert g to mol of LR, then convert mol of LR to mol of product; use molar ratio for this. then convert the mol of product by multiplying molar mass of product. distillation: ideal liquids/Raoults law - Answer-*ideal liquid*: a liquid that in incompressible (density is constant), irrotational (no turbulence, flow is smooth), and nonviscous (fulid has no internal friction). they do not exist in nature. it obeys Raoult's law for all compisitions.*Rauoults Law*: shown in picture. total pressure can be found by adding up partial pressure; partial pressure can be found with Raoult's law. to find mol fraction (Xa), divide mols of A over total moles of solution. Example: what is the partial pressure of EtOH (Po=45 kPa, MW= 46.07 g/mol) if 3.0 g of it is mixe with 3.0 g of unknown (MW= 32.04)? - Answer-18.5 a compound with high IMF will have a ____ BP than a compound with low IMF; Imagine a solution of water boiling in a round flask. the vapors above this liquid are ______ the liquid themselves. - Answer-higher; the same temp as T or F: higher vp means that a liquid is harder to turn into a vapor - Answer-F its easier!