chemical analysis

Question 1

impure substance physical properties:

Answer 1

lower melting point, increased boiling point

Question 2

what is a formulation:

Answer 2

mixtures prepared using a specific formula with diff components for a particular function

Question 3

how to calculate Rf value:

Answer 3

dist trav by subst / dist trav by solvent

Question 4

what is the resulting paper in chromatography?

Answer 4

chromatogram

Question 5

explain how paper chromatography separates a mixture:

Answer 5

-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

Question 6

test for oxygen:

Answer 6

glowing splint in tube of gas, if oxygen present splint will relight

Question 7

test for chlorine:

Answer 7

expose substance to damp litmus paper that will turn blue to red to white if chlorine present

Question 8

test for hydrogen:

Answer 8

expose lit flame into gas if hydrogen present squeaky pop that will happen from the H and O2 burning together to produce H2O

Question 9

test for carbon dioxide:

Answer 9

bubble through limewater, if co2 present, limewater will turn cloudy because calcium carbonate forms, a solid

Question 10

what are cations?

Answer 10

positively charged ions

Question 11

describe the steps for a cation flame test:

Answer 11

-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

Question 12

state the corresponding colours for the metals:

Answer 12

lithium- crimson
calcium- orange,red
potassium- lilac
sodium- yellow
copper- green

Question 13

state a limitation for flame test:

Answer 13

if two metals mixed together, colour of flame will mix and you can’t tell which metal

Question 14

corresponding colours for the metal hydroxide test and precipitate:

Answer 14

calcium: white
copper: blue
iron II: green
iron III: brown
magnesium: white
aluminium: white, but if excess NaOH then redissolves and forms colourless sol

Question 15

what is a capillary tube

Answer 15

a thin glass used in paper chromatography

Question 16

what is Rf value used for

Answer 16

to identify a chemical; the rf value can be looked up on a database with all rf values and can be compared

Question 16

what is Rf value used for

Answer 16

to identify a chemical; the rf value can be looked up on a database with all rf values and can be compared

Question 17

neumonic to remember flame test colors

Answer 17

LC,COR,PL,SY,CG

Question 18

state difficulty of flame test regarding color con.

Answer 18

-hard to distinguish betw diff colors, esp if concentration of ion is low

Question 19

advantages of instrumental methods
(flame emission spectroscopy)

Answer 19

-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.

Question 20

test for aluminium ions

Answer 20

add sodium hydroxide (solution to water sample)

white precipitate (forms)

(precipitate which is) soluble in excess (NaOH)

Question 21

test for sulfate ions

Answer 21

add barium chloride (solution) and (dilute) HCl (to water sample)

white precipitate (forms)

Question 22

test for sulfate ions

Answer 22

-few drops of dilute HCl w/ few drops of Barium Chloride solution
-should form white precipitate of barium sulfate

Question 23

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?

Answer 23

bromide (ion)

Question 24

Test for Halides with nitric acid and silver nitrate

Answer 24

-iodide; yellow precipitate of silver iodide
-bromide; cream precipitate of silver bromide
-chloride; white precipitate of silver chloride