C/P Flashcards
Hydrogen bonding
The formation of a hydrogen bond requires both a hydrogen bond donor: a molecule with a hydrogen bonded to a highly electronegative atom such as oxygen or nitrogen, and a hydrogen bond acceptor: an electronegative atom (such as O or N) with an available lone pair of electrons. Of the pairs listed, only glycine and methanol are able to act both as hydrogen bond donors and acceptors.
Compound with same geometry as methane
Methane (CH4) consists of a group IV element (C) involved in four identical bonds, with no lone electron pairs. It is therefore tetrahedral. SiCl4 likewise consists of a group IV element (Si) involved in four identical bonds. While the sulfur in H2S is also surrounded by four electron pairs which are directed at the corners of a tetrahedron, it is important to note that the geometry or shape of a molecule refers only to the positions of atoms, not electron pairs. H2S has a bent shape. In CO2, carbon is bonded to only two atoms, with no lone pairs, so the molecule is linear. Lastly, in XeF4, the xenon is surrounded by the four fluorine atoms with lone pairs above and below, giving a square planar appearance
Function of boiling chips
ebulliator was added to introduce small air bubbles into the system. This is the same function provided by a boiling chip at atmospheric pressure. The air bubbles break the surface tension of the liquid being heated and prevent superheating and bumping
How to improve separation of two compounds using distillation column
We presume that the separation of limonene and (+)-carvone can be improved by modifying either the apparatus shown in Figure 1 or the procedure (i.e., the separation as described in the passage did not achieve a totally satisfactory separation.) The separation of the two liquids takes place in the fractionating column as the two liquids vaporize and condense, with the lower-boiling liquid distilling first. If the fractionating column is shortened (Answer D), the liquids will vaporize and condense fewer times (i.e., there will be fewer theoretical plates) and the degree of separation will worsen. Cooling the condenser with ice water (Answer C) will have no effect on the degree of separation because condensation takes place after the separation has occurred. Creating a lower pressure inside the distilling apparatus (Answer B) will lower the boiling points of both liquids and narrow their difference in boiling point, making it necessary to also increase the length of the fractionating column in order to achieve the same degree of separation as obtained originally. Lengthening the fractionating column was not part of answer choice B. Heating the distillation flask (i.e., increasing the temperature) at a slower rate (Answer A) will allow both liquids more time in the fractionating column (increase the number of theoretical plates, allowing liquid and vapor to equilibrate); therefore, of the four options, this one is most likely to improve the degree of separation of the two compounds.
Increase in vapor pressure does what to the temperature?
Increase in VP increases the temperature of a liquid hence it boils faster i.e. the BP is lowered
Rf of a compound in chromatography
is the ratio of the distance travelled by the solvent over the distance travelled by the solute. It is between 0-1 since it must have moved but cannot be more than 1 since the solute travels longest
Bases
NaCl and Na2SO4 are salts and HCl is an acid. Only NaOH is a base and can catalyze the saponification of an ester
Alcohols generally require acid catalysis in order to undergo substitution by nucleophiles. The acid catalyst enhances the reaction by
the substitution reaction in question serves to replace the hydroxyl group and that hydroxide ion is one of the worst leaving groups in substitution reactions. Under acidic conditions, the hydroxyl group is protonated such that the leaving group is now water, a superior leaving group, rather than hydroxide ion.
Are tertiary amines good nucleophiles
The compound shown is aromatic and contains tertiary amino groups. Amines can act as bases or nucleophiles because of the lone pair of electrons on the nitrogen of the amino group
The shape of a molecule is determined by what?
The shape of a molecule depends on the number of valence electrons at the central atom since lone pairs of electrons exert stereochemical effects. Without the group numbers of the reactant atoms, it is impossible to determine the molecular shape of the product. If X = C, and Y = O, then the molecular geometry would be linear. If X = O and Y = H, however, the molecular geometry would be bent.
What would account for an extra FA chain upon triacylglycerol saponification? i.e. 4 instead of 3
If one of the R groups in the triacylglycerol contained a carbon–carbon double bond and if isomerization of the double bond occurred during the saponification reaction, four fatty acids would be obtained instead of three
What angle difference of a periodic wave and its reflection would destructive interference occur
The phase difference corresponding to a half of a wave is 180°. Half a wave difference in phase between two waves corresponds to destructive interference
Electric force on a charged particle thru an electric field
Electrical force depends on the particle’s charge and the strength of the electric field experienced by the particle, not on the particle’s speed
Pressure of a fluid
Pressure is given by (density) • g • (height). Here, mercury’s density is given as 14 times that of water but the column is only half as high, making the pressure of the mercury (14)(0.5) = 7 times more than that of the water
