LAB 1: Safety and Solubility Flashcards
(20 cards)
What can highly polar, h bonding solvents like water dissolve?
polar compounds and salts
Hexane is incapable of what?
H bonding, but it can dissolve large organic molecules (non-polar)
What is insoluble in water?
compounds that contain carbon and hydrogen but no heteroatoms or heteroatoms that are built into the structure such that the dipole cancels, and compounds containing non - H bonding atoms (organic halides)
Solubility is governed by?
Shape, size, nature of intermolecular forces. It also depends on how effectively the polar functional group can counteract the non-polar hydrocarbon character.
What is distinctive of compounds with large carbon skeletons?
Compounds with more than 5 carbons are typically more able to dissolve in non polar substances even with a functional group that is polar
What compounds contain polar functional groups?
alcohols, ketones, aldehydes, esters, amides
Hydrogen bonding occurs…?
Hydrogen atom must be covalently bonded to electronegative atom such as O, N, F, etc and must interact with a nearby molecule that has an O or N (high EN atom) with a lone pair of electrons. It’s a strong dipole-dipole attraction.
Homologous series
series of compounds with the same functional group and thus similar chemistry. The 5-carbon member is usually the upper limit to water solubility.
How can you overcome the 5-carbon barrier?
The 5-carbon barrier can be overcome if the functional group can be changed into a charged species (salt formation-> deprotonation). Functional group (acidic or basic) is converted to its corresponding salt by acid base reaction.
What is an acidic functional group?
R- OH or Ar- COOH
What is a basic functional group?
R - NH2
R2 - NH
Phenol
Benzene structure (6 carbons) with alcohol functional group. Largely non-polar.
Salt formation test (NaOH)
- If organic compound is insoluble in water but dissolves in NaOH (aq) it probably contains more than 5 carbons and an acidic functional group
- Phenols can also be made more water soluble this way because phenoxide ion (Ar-O -) is resonance stabled
Low pKa?
strong acid
High pKa?
weak acid
What can sodium bicarbonate (NaHCO3) be used for?
Used to distinguish between phenols and carboxylic acids. It is a strong enough base to deprotonate carboxylic acids. The reaction produces bubbles. Phenols are less acidic than carboxylic acids and do not react with NaHCO3 to form water-soluble salts. As a result, phenols are insoluble in 5% NaCHO3.
Salt formation test (HCl)
Water insoluble organic compound that dissolves in aqueous acid probably contains more than 5 carbons and a basic functional group.
In this experiment, a compound is soluble if…
if 0.01 g of the solute can dissolve in 1 ml of solvent at room temp
Properties of NaOH
Caustic metal base. Dissolves readily in water. Can also dissolve in methanol and ethanol. Insoluble in ether and other non-polar substances.
Properties of HCl
Polar bond due to electronegativity differences. Dissolves in polar substances like water readily.
