December mocks - practical skills Flashcards
heating methods
bunsen burner heating mantle oil bath water bath sand bath
how do you run a reflux procedure
secure pear shaped flask with clamp stand
insert liebig condenser into flask and secure*
connect condenser to water supply so water flows in at bottom and out at top
add anti-bumping granules
add reagents
move apparatus over heat source
reflux for required amount of time
wait for glassware to cool before dissembling
*grease joint and/or secure with clip
how to you run a distillation procedure
secure pear shaped flask with clamp stand
insert stillhead into top of flask and secure*
attach condenser to side arm of stillhead and secure*
secure condenser with 2nd clamp stand
attach delivery tube to end of condenser and secure*
add reagents
move apparatus over heat source
attach thermometer holder and thermometer into top of stillhead
align bottom of thermometer with stillhead side arm
connect condenser to water source so water flows in at bottom and out at top
place clonical flask beneath delivery tube
distill for required amount of time
wait for glassware to cool before dissembling
*grease join and/or secure with clip
what are some practical considerations
greasing/securing the joints with a clip >makes a tight seal >prevents joints seizing during procedure anti-bumping granules >smoother boil >prevents overflowing >equipment remains more stable
how is a separating funnel used
identify layers by adding water to mixture - layer that gets bigger is aqeous
ensure tap is closed
pour mixture into funner and insert stopper
invert 10 times, removing the stopper every 2-3 invertions to let air escape
allow layers to settle
place a clonical flask under funnel, remove stopper and open tap until first layer has left the funnel
place another clonical flask under the separating funnel to collect the other layer
label flasks
how is redistillation used
sometimes organic liquids have relatively close boilong points
distillation apparatus is cleaned and dried and set up again so a second distillation can be carried out
the narrower the boiling range, the purer the product
what are the methods of preparation and purification of an organic liquid
separating funnel
drying with anhydrous salt
redistillation
what is quickfit apparatus
heat resistant glassware that fits easily and quickly together
conncetion greased or held in place with a clip
how are liquids dried with anydrous salts
common salts : CaCl2, MgSO4
add organic liquid to clonical flask
add drying agent to liquid and swirl with spatula to mix
place stopper on flask - prevent product evaporating
if solid is stuck together in a lump it still has water in it so add more drying agent until solid is dispersed in solution as a fine powder
decant the liquid from the solid into another flask
liquid is clear when dry
what are the techniques for purification of an organic solid
filtration under reduced pressure
recrystalllisation
measurement of melting points
how does filtration under reduced pressure take place
connect one end of pressure tubing to vacuum outlet or filter pump and other end to the end of rubber tubing on the Buchner flask
fit Buchner funnel to Buchner flask and secure with rubber bung
switch on vacuum pump or tap
check for good suction by placing your hand across the top of the funnel
place a piece of filter paper inside the Buchner funnel and wet with solvent
slowly pour reaction mixture into the centre of the filter paper
rinse out beaker with solvent so that all solid crystals collect in the Buchner funnel
rinse the crystals with more solvent and leave them under suction so that crystals dry
how does recrystallisation take place
pour solvent into clonical flask and move over heat source
tip the impure sample into a second clonical flask
slowly add the solvent to the impure sample until it dissolves into the solvent
once solid has dissolved allow solution to cool
crystals of desired product should form
when no more crystals form, filter the crystals under reduced pressure to obtain the dry crystalline solid
how do you determine the melting point of an organic solid
preparing sample:
ensure sample is completely dry and free-flowing
hold one end of capillary tube in hot flame of bunsen burner and rotate in flame until end of tube is sealed
fill capillary tube with crystals to about 3mm depth
measuring melting point:
electrically heated melting point apparatus;
place capillary tube containing sample into sample hole
place a 0-300 degrees thermometer into thermometer hole
start heating up the sample whilst observing it through the magnifying window
once the solid is completely melted, record the melting point
allow apparatus to cool
repeat with second sample
once melting point is approaches raise temperature more slowly whilst observing the sample
how do you prepare a standard solution
weigh solid
dissolve solid in beaker using less distilled water than will be need to fill the volumetric flask
transfer solution to volumetric flask
rinse last traces of solution into volumetric flask with distilled water
fill flask to the graduation line by adding distilled water dropwise until the bottom of the meniscus lines up with the graduation line
insert stopper
invert the volumetric flask several times to mix
how do you carry out an acid-base titration
add a measure volume of one solution to clonical flask
add other solution to burrette and record intial burrette reading
add a few drops of indicator to the solution in the clonical flask
run the solution in the burette into the solution in the clonical flask, swirling the clonical flask throughout to mix the two solutions until end point is reached
record the final burrette reading
this is the trial titre
repeat the tritration and run solution in burrette dropwise when nearing end point until end point is reached
carry out more titrations until two accurrate titres are concordant (within 0.10cm3)
