Lab 1 Flashcards
what factor are melting point, boiling point and solubility determined by
intermolecular forces
how are hydrocarbons bonded
weakly, by London/Vander Waal forces
what is the relationship between molecular size and molecular forces
as molecular size increases, molecular forces increase and you need more energy to pull the molecules apart
what is hexane
a common liquid solvent because it is strong yet flexible to form a fluid
dipole-dipole
- attraction increases when functional groups have atoms more electronegative then carbon
- pulls electrons and the bond becomes slightly negative, making the carbon slightly positive
relationship between polar bonds and dipole moments
there is a slight charge separation, which gives a dipole
ionic general melting point
usually solids with a high melting point (like table salt)
what are the functional groups that form ionic structures
- hydrogen on the -OH of carboxyl group in carboxylic acids reacts with a base to form salt (reversed by adding acid to lower pH)
- hydrogen on an -OH group attached to an aromatic ring is weakly acidic and reacts with strong base to form salt (reversed by adding acid)
- amines react with acid to form ionic amine salts
what type of thermometer is best for high temperatures
mercury-in-glass thermometers are highly accurate and ideal for high temps
characteristics of a digital thermometer
- low heat capacity
- fast response time
at what range of temps are non mercury thermometers best at
temps less then 150 degrees C
what can melting point tell you
- characterization
- future characterization
- purity
what is translational motion
when liquid turns to solid
how do you find the total attractive forces when you have pure compounds with identical molecules
it is the sum of all of the forces
definition of solubility
disrupting forces to get molecules to interact
trends in solubility based on size of hydrocarbon
bigger hydro=less soluble and vice versa
golden rule for predicting solubility
LIKE DISSOLVES LIKE
what type of bond and melting temp range do most organic molecules have
most are covalent and melt at temps below 300 degrees C
what type of bond and melting temp range do most inorganic molecules have
ionic bonds and a melting point at higher temps
what happens to ionic organic molecules and things with strong hydrogen bonds before they melt
they decompose
relationship between molecule size and melting point
large molecules melt at higher temperatures and vice versa
what type of isomers will have a higher melting point
symmetrical isomers will have higher melting points
what type of melting point do molecules have that can form hydrogen bonds
high
relationship between vpor pressure and melting point of pure compounds
the melting point of a pure compound is at the temp at which the vapor pressure of the solid and liquid are equal
what should the temp increase not be greater than per minute at the melting point
1 degree C per minute
be careful that the rate of heating is not too fast
how does hydrogen bonding work
- between organic molecules with -OH or -NH groups
- hydrogen is attracted to unshared pair of electrons in the o or the n
- turns into molecular velcro (can be pulled apart with sufficient energy)
when you are working with molecules of the same weight, how can you distinguish the boiling point
dipoles will have the second highest and hydrogen bonds will have the highest boiling point
relationship between hydroxyl group and boiling point when you have 2 structures of the same weight
1 hydroxyl group will be lower bp than 2
what is boiling point a function of
atmospheric pressure, because boiling point occurs when the vapor pressure is equalling the pressure exerted
what is superheating
when the temp is above the boiling point but it is not boiling
what does distillation allow us to find
the boiling point temperature range and also gives us an indication of purity
how does increased surface area affect the boiling point
it raises it, ex) branching makes less surface area than zig zag so it has a lower boiling point because it decreased the surface area between the attractive forces
