CHEM 1006

Percent Difference calculation

|actual - exp|/experimental x100

Percent difference calculation

|actual - worst outlier|/experimental x100

Purpose of Exp 1

Learning how to use equipment

Understand that you have to look at a solid to understand how to weight it

what to use as a solvent

Read a burette

eye level with the meniscus

what is easier to weigh

dry ingredients, wet ingredients leave resiude

what tool is better to use to weigh wet ingredients

graduated cylinder

why is a bottle top dispenser bad

air bubbles so you don’t get all the necessary liquid out.

Big lesson from Exp 1

not all solid may come out

to weight something weigh by difference

mass of a drop

0.05 ml

Why do we rinse a burette with NaOH

to prevent dilution, by removing residual water

Why standard deviation instead of avg

SD depends on how many times you do an experiment, and avg does not give you data quality.

what to use instead of SD

convert back into volume and calculate avg of worst outlier outlier.

volume difference

%diff/100 x avg volume

In a titration that is done well what precision do you expcet

0.15 ml

why do you loosen stopcock

so dried NaOH doesn’t get stuck

The solution in the burette is called the

titrant

Titrant is dispensed into the reaction flask until the reaction is complete (the analyte has reacted completely)

equivalence point

what is the purpose of a titration

to determine the unknown concentration of a substance (analyte) in a solution by reacting it with a solution of known concentration (titrant) until the reaction is complete, marked by an endpoint (like a color change

Read the burette to the nearest…

0.05 ml

How many titrations should you get out of one burette

2

if only a little amount of precipitate formed what does that tell you

the reaction was stochioemetrci and they never go to completion, not enough of reactant

why do you add water to the Buchner funnel

make sure the filter paper sticks

make sure vacuums working

double check filter paper by flipping it over

what is the point of heating the solution

speed up reaction

use catalyst to lower activation barrier

speed up reaction results that reaction went to completion

to dissolve starting materials

How does not putting watchglass on and water evaporates how does that affect calculation

it wont affect results

what trial would have the lowest yield

trial one because none of the reagents are in excess

contradiction between calculation and experiment and why

good lab techniques will result in NO. Poor lab techniques result in yet. Incorrect transfer of solids, poor filtration techniques or incorrect note taking.

weigh within

±/- 10 mg

what is the purpose of a centrifuge

apid spinning to separate substances by density,

parts needed for vacuum filtration

Buchner funnel, adapter, hose adapter, filter flask

why didn’t we get 100% yield

problem with filtration since some stuck to the filter paper since we put the black light on it

how well do filtrations work

some goes into solution and some stick to the filter paper

why do we dissolve in methanol and not water and what if we used water

because of solubility and if water was in there it would not mess it up

Good Observations

clear and colourless

solid, liquid, gas

shiny vs dull

no changes

everything

why does the mg ribbon have to be at the bottom of the tube to make copper

1. it floats because of bubbles

2. needs to be fully submerged

3. mix for 10s, reaction but eyes cannot see very rapid change

How to transport a centrifuge tube

1. in a beaker

2. with a cork on it

3. point it away from you

the difference between copper in the beginning and the end

start - shiny

end- dull and didn’t look like copper

what reactions take place in the copper cycle

acid - base, redox, precipitation and decomposition chemistry

what is an oxidizing liquid

a liquid that oxidizes other things ( oxidizing agent)

what is the purpose of PH indicators

to visually signal the acidity, neutrality, or basicity (alkalinity) of a solution by changing color

what is a stronger acid

inorganic acids

what is used as a cataylst the reaction of salicylic acid with acetic anhydride

sulfuric acid

why do we use a hot water bath

for safety (preventing fires with flammable substances like alcohol) and precision

why did we scrape the flask to recrystallize

added a nucleation site - a place for crystals to grow

other than aspirin what other product was made

acetic acid

why cant acetic anhydride come in contact with water

it decomposes in water and revert back to acetic acid

flammable vs combustible

flammable

Is ASA more soluble in ethanol or water

more soluble in ethanol since we dissolved it in ethanol before water

“Anhydride” means without water. What would happen if we had used a larger amount of 1M H2SO4 instead of 6 drops of conc. H2SO4?

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why do we use an ice bath

to kill the unreacted excess acetic anhydride

what happens to the yield if water is introduced to the acectic anyhdride

lower the yield

what is covalent bonding

electrons are being shared

ionic compunds have…

high melting point

high conduction

high solubility

Due to - electrostatic forces

covalent compounds have..

low melting point

low conduction

low solubility

weak intermolecular forces

How do covalent bonds behave

like springs, the energy required increase vibrations

common vibrational modes

bond stretches and bends

what bonds appear on IR spectroscopy

covalent

using correct geometry will lead to

same peaks as the literature

purpose of exp 7

computing various geometries for ions and fully covalent compounds we can pinpoint the geometries in these compounds

Exp 7 inorgnic or organic

inorgnic

for calculations exp7

single point calculations then molecular mechanics

which is more likely to have a lower frequency

stretching takes more energy becasue of higher frequncy

Bends were the same or differnet

bends were bang on and stretches were off(b/c of gas phase)

why was concetrated sulfuric acid used

speeds up reatcion

lowers activatuon energy

how can we get good yield

drive a reaction, heat it, catalyst, increase concentration, add excess

what angle is staggered

60

percent purity

mass of product/ mass of sample x100m

how to use a burette

rinse, clamp it, tighten the stopcock, use funnel, in sink over a beaker and don’t go past graduation.

how accurate should titrations be

3 drops

purpose of exp 8

determine the purity of acetylsalic acid through titration with naoh. one to one ratio

how to calculate rotational barrier

find most stable configuration, control it because you want the least stable

purpose of newman projections

depicting different molecular conformations obtained by rotating single bonds.

what formations are higher in energy

eclipsed formations are higher in energy due to close proximity between the three groups.

In exp 9 organic or inorganic

organic for sp³ carbons

what do you select when inputting rotational barriers

single point energy

what setting do you use when not rotating the molecule manully

equilibrium geometry

what do you select for ions and what do you select for neutral

ions- semi empiracla

neutral - molecular mechanics

what is the multiplicity for everything

singlet - no unpaired electrons

to get calculations

display then properties

once a yellow solution was obtained why was it important to move quick

so that it does not react with oxygen and get oxidized and stain the equipment.

leucoindgo was

oxidized

leucoindigo us

oxidized(left out in air)

Difference between leucoindigo and indigo

leucoindigo - adhered to fabric then oxidized to fabric

indigo - sat on top of paper towel and not water soluble

indigo was a

acid base reaction

leucoindigo reaction is

redox reaction

For every pair of jeans

10 g of indigo is required

exp 10 starting material and catalyst

o-nitrobenzaldehyde as a starting material and naoh

indigo to leucoindgo

reduced

leuconinigo to indigo

oxidized

what did we use to clean the glassware

the leucoindigo solution

steriosomes

same formula and atom connectivity but differ in three dimensional arrangement.

less than 85kj/mol

can convert to other conformations

above 85kj/mol

prevent molcules to convert to other conformations