Chemical analysis Flashcards
Test for chlorine
Damp, blue litmus paper (blue to white)
Test for oxygen
Glowing splint (splint will be relit)
Test for hydrogen
Squeeky pop (lit splint)
Test for carbon dioxide
Limewater (turns cloudy)
Test for carbonates
Add dilute HCl, then check for CO2 (using limewater)
Test for sulfates
Add dilute HCl, add barium chloride, white PPT formed
Test for halides
Add dilute nitric acid, add silver nitrate, different halides = different ppt
Chloride ions = white ppt
Bromide ions = cream ppt
Iodide ions = yellow ppt
What colour flame is a Lithium ion?
Crimson
What colour flame is a Sodium ion?
Yellow
What colour flame is a Potassium ion?
Lilac
What colour flame is a Calcium ion?
Orange - red
What colour flame is a Copper ion?
Green
What ppt does Calcium form?
White ppt (reacted with sodium hydroxide)
What ppt does iron II form?
Green ppt (reacted with sodium hydroxide)
What ppt does iron III form?
Brown ppt (reacted with sodium hydroxide)
What ppt does magnesium form?
White ppt (reacted with sodium hydroxide)
What ppt does copper form?
Blue ppt (reacted with sodium hydroxide)
Test for aluminium ions?
- Mix with sodium hydroxide
- White ppt will be formed
- Dissolves in excess to form colourless solution
How to differentiate between aluminium, magnesium and calcium ions?
- All form white ppt in sodium hydroxide
- Aluminium dissolves in excess to form colourless solution, magnesium and calcium remain undissolved
- Clacium has orange-red flame when burned
How to prepare a flame test
- Dip inoculating loop into dilute hydrochloric acid
- Hold loop over blue flame in bunsen burner until there is no colour change
- This has cleaned the wire loop to avoid contamination
Why must we clean the inoculating loop in flame tests?
- Test will only work with one type of ion present
- Two or more ions means the colour will mix, leading to an erroneous result
What is a pure substance?
- A substance that only contains one type of compound or element
Pure vs impure substances
- Pure substances melt and boil at specific temperatures
- Impure substances melt and boil over a range of temperatures
What is paper chromatorgraphy used for?
- Used to separate different inks in a dye
Steps of chromatorgaphy
- Draw the baseline at the bottom of the chromatography paper in pencil
- Place a dot(s) of the ink you want to separate on the baseline
- Fill a beaker with a solvent (water or ethanol) and place paper in it
- Make sure the baseline is above the solvent
- Place lid on top to prevent solvent from evaporating
- All soluble dyes in the ink will move up the paper at different rates and separate. Insoluble dyes will stay at the bottom
What is the mobile phase?
- The substance in which the molecules are able to move
- In chromatorgaphy this is the solvent
What is the stationary phase?
- The substance in which the molecules cannot move
- In chromatography this is the chromatography paper
What determines how far a substance travels up the chromatography paper?
- The more soluble the substance is in the solvent, the more time it will spend in the mobile phase and therefore will carried further up the paper
How to calculate Rf value and what does it help us do?
- Distance travelled by substance / distance travelled by solvent
- Allows scientists to compare the Rf value of the unkown substance with that of known substances under the same conditions (type of paper and solvent) to find out what substance it is
