chem241 final

Why should crystallization solvents be heated in a water bath rather than directly on the hot plate?

-The hot plate would get too hot and might boil away the solvent -The hot plate would get too hot and be a fire risk with the flammable organic solvent

What concentration of HCl or NaOH (1M or 6M) should be used in a seperatory funnel during an extraction and why?

1M instead of 6M so there is more water to dissolve water-soluble components.

What sort of condenser should you use for the elimination of alkyl bromides lab and why?

A water condenser instead of an air condenser because it is better at preventing your solvent and/or products from evaporating

What color is the tip of the sealed NMR tube that contains the standby reference solvent?

Blue

Why must deuterated solvents (such as D2O and CDCl3) be used to prepare NMR samples?

Deuterated solvents are "invisible" in an 1H NMR spectrum while non-deuterated solvents will obscure important peaks

If you have excess unreacted Mg at the end of the lab, how should you dispose of it?

Dissolve it in 6M HCl.

If you spill bromine on the bench, what actions should you take?

-Inform your TA of the spill -Quench the bromine with sodium bisulfite (a reducing agent)

What are hazards of dry ice?

-It can cause cryogenic burns -In sufficient quantity, it can displace oxygen and cause suffocation

What properties allow bromine to cause this health risk?

-It is a strong oxidizing agent -It is volatile and easily inhaled

What action(s) should you take to reduce the health risk of silica gel?

-Keep it wet with solvent so less powder gets into the air -Handle the silica gel in the fume hood -If some silica gel spills, wipe it up with a wet paper towel, not a dry paper towel -Wear personal protective equipment such as gloves and a lab coat to avoid getting silica gel on yourself

Why must the reaction temperature be carefully maintained at 50C instead of allowing the solution to reflux at 100C?

-Sodium hypochlorite is unstable at higher temps -At 100C, there's a higher risk of unwanted side reactions

Bromine must be removed from glassware before you rinse that glassware out with acetone. If acetone and bromine are mixed, they will produce bromoacetone. Why is bromoacetone very unpleasant?

It is a lachrymator because it reacts with water in your eyeball to produce HBr, making you cry and causing a lot of pain

Name the flammable organic solvents from the Distillation lab:

-Acetone -Methyl tert-butyl -ether -Toluene -Dimethyl carbonate -Cyclohexane

If some of the bromine/hydrobromic acid mixture spills on you, what actions should you take?

-Alert your TA -Remove your gloves and/or lab coat if any spilled -Wash any affected skin with plenty of water -If it got in your eyes, rinse them at the eye wash for 15 minutes

What are some of the hazards of dichloromethane (also known as methylene chloride)?

-Carcinogenic -Can cause chemical burns upon skin contact -Very volatile and easy to inhale

What are some of the hazards of sodium hypochlorite?

-Chemically reacts to form toxic chlorine gas -Corrosive if you spill it on your skin -Poisonous if ingested

What is true about mixing liquids in a separatory funnel?

-Everything should be done in your hood, -You should wear gloves, -your hood sash should be between your face and the separatory funnel, -don't aim the separatory funnel at anyone, -you should have a firm grip on the stopper and vent the funnel frequently by using the stopcock

What are the main hazard(s) of sodium methoxide in methanol and potassium tert-butoxide in tert-butanol?

-Flammable -Corrosive -Carcinogenic -Methanol is toxic

Why should your disposal of excess magnesium take place in a fume hood?

-The quench released hydrogen gas, which is flammable and explosive -The quench is highly exothermic and might cause the solvent to splash -HCl is corrosive

Why is it important to increase the amount of solvent used if a reaction or purification procedure is scaled up?

-To ensure that the larger amount of material remains soluble -To help protect the solution against large temperature changes from exothermic or endothermic processes -To increase the amount of material that is transferred from 1 layer to another during an extraction

Why must all parts of the oxidation and reduction reactions be carried out in the fume hood?

-To protect you against any unplanned explosions -To isolate any toxic gases produced -In case any reactions accidentally ignite

Which of the following should you do if the contents of your separatory funnel spill on yourself?

-alert your TA even if you have to shout -rinse the affected area with plenty of water -remove any affected clothing

When and why should you wear gloves when preparing NMR samples and acquiring NMR data?

Gloves should be worn while preparing the NMR sample because you are handling hazardous solvents -Gloves should not be warn while using the NMR spectrometer to avoid contaminating the computer keyboard

Often when quenching the reaction with water, a puff of corrosive smoke is seen. What is the origin of this smoke?

HCl being released from the reaction

What flammable gas is produced if sodium borohydride is mixed with water?

Hydrogen gas

How and when should you put the NMR machine into standby mode?

Insert the sealed-glass standard tube and click standby on the attached PC right after you email yourself your NMR file, even if other students are waiting

What is the main health risk of liquid bromine?

It is corrosive and causes chemical burns

When can diethyl ether and bunsen burnes be used together in lab?

NEVER No ether is allowed in lab until after everyone is finished with bunsen burners

Whenever you heat liquids, especially near their boiling point, you should always use a stir bar or boiling stones. Why is this?

Stirring prevents the liquid from bumping out of the flask.

What happens if you choose the wrong solvent while setting up your NMR experiment?

The NMR spectrometer will acquire data for the wrong chemical shift range and you will likely not have any usable data when you open Spinworks

What is the definition of "flash point"?

The lowest temperature at which a liquid can vaporize to form an ignitable mixture in the air

The Friedel Craft procedure states you should cool the reaction vial in an ice bath before adding ferrocene. Why is this necessary?

The reaction is exothermic and might spontaneously boil away the solvent

When assembling a simple or fractional distillation apparatus, where should clamps be placed?

The piece of glassware closest to the ground (the round bottom flask) should be clamped along with other glassware that's not directly above the round bottom flask such as the condenser.

Which of the following is correct about the order of adding solvent to your round bottom flask?

The solvent should be added to your flask before you begin heating to ensure that the solvent doesn't ignite on the hot thermowell surface.

What is the main hazard present when using the GC?

Thermal burns from the hot injector port and oven.

Silica gel is not flammable, nor is it chemically reactive. Why then is it considered hazardous, particularly with long term exposure?

When inhaled it damages the respiratory tract

If you are unsure of which layer of your separatory funnel is the organic vs aqueous layer, which of these is the safest way to figure it out?

add a few drops of water to each layer to see if the water mixes in (aqueous layer) or forms a separate layer (organic)

You are using sodium hypochlorite to oxidize borneol to camphor. What common household item is sodium hypochlorite found in?

bleach