chemical analysis Flashcards
impure substance physical properties:
lower melting point, increased boiling point
what is a formulation:
mixtures prepared using a specific formula with diff components for a particular function
how to calculate Rf value:
dist trav by subst / dist trav by solvent
what is the resulting paper in chromatography?
chromatogram
explain how paper chromatography separates a mixture:
-during pc, molecules of each chem is sample move betw the stationary and mobile phase
-moph moves through the statiph over the course of the exp, and anything that’s dissolved will move with it
-dist a compound moves through statiph depends on how long it spends dissolved in the moph compared to on the statiph
-diff compounds interact diff in these compounds, they’ll move diff amounts through the statiph and be separated from e/o
test for oxygen:
glowing splint in tube of gas, if oxygen present splint will relight
test for chlorine:
expose substance to damp litmus paper that will turn blue to red to white if chlorine present
test for hydrogen:
expose lit flame into gas if hydrogen present squeaky pop that will happen from the H and O2 burning together to produce H2O
test for carbon dioxide:
bubble through limewater, if co2 present, limewater will turn cloudy because calcium carbonate forms, a solid
what are cations?
positively charged ions
describe the steps for a cation flame test:
-put platinum loop in dilute HCl and wash with distilled water then heat over a bunsen burner
-dip loop into test compound
-hold loop in hottest part (clear blue) flame
-see colour it turns
state the corresponding colours for the metals:
lithium- crimson
calcium- orange,red
potassium- lilac
sodium- yellow
copper- green
state a limitation for flame test:
if two metals mixed together, colour of flame will mix and you can’t tell which metal
corresponding colours for the metal hydroxide test and precipitate:
calcium: white
copper: blue
iron II: green
iron III: brown
magnesium: white
aluminium: white, but if excess NaOH then redissolves and forms colourless sol
what is a capillary tube
a thin glass used in paper chromatography
what is Rf value used for
to identify a chemical; the rf value can be looked up on a database with all rf values and can be compared
what is Rf value used for
to identify a chemical; the rf value can be looked up on a database with all rf values and can be compared
neumonic to remember flame test colors
LC,COR,PL,SY,CG
state difficulty of flame test regarding color con.
-hard to distinguish betw diff colors, esp if concentration of ion is low
advantages of instrumental methods
(flame emission spectroscopy)
-more rapid than flame test
-sensitive, will work even with only tiny sample of metal compound
-more accurate and likely to identify metal ion correctly than f.t.
test for aluminium ions
add sodium hydroxide (solution to water sample)
white precipitate (forms)
(precipitate which is) soluble in excess (NaOH)
test for sulfate ions
add barium chloride (solution) and (dilute) HCl (to water sample)
white precipitate (forms)
test for sulfate ions
-few drops of dilute HCl w/ few drops of Barium Chloride solution
-should form white precipitate of barium sulfate
Silver nitrate solution and dilute nitric acid are added to the solution.
A cream precipitate forms.
Which ion is shown to be present by the cream precipitate?
bromide (ion)
