Write a 6 Mark answer for a chromatography experiment
Draw pencil start line
Place spot of ink on start line (using glass capillary tube)
Name suitable solvent
Place suitable solvent in beaker.
Place paper in solvent so solvent is below start line
Use a lid
Allow dyes to travel at least ¾ up paper
Allow it to dry
Draw solvent line on wet edge
Count spots
Measure distance between 2 lines for:
Rf = Distance moved by solute/distance moved by solvent
Why do you draw the start line in chromatography in pencil
Pencil won’t dissolve in solvent and be carried up paper
Why is the solvent line below the start line
Otherwise ink would dissolve in solvent and not be carried up
In chromatography, what type of spots will pure chemicals produce
one spot in all solvents
What is the stationary phase in chromatography
Paper
What is the mobile phase in chromatography
Solvent
How far would chemicals strongly attracted to the stationary phase move
Very far
What is the test for hydrogen
Lighted splint makes ‘pop’ sound and goes out
What is the test for oxygen
Glowing splint relights
What is the test for CO2
Bubbles through limewater. Turns cloudy white
What is the test for chlorine
Damp blue litmus paper turns white (gets bleached)
What are pure substances
Made up of only one type of element or compound. Can’t physically simplify anymore. Specific fixed boiling and melting points. Is important in like medicine but could have unwanted side effects.
What are impure substances
mixture of 2 or more different elements or compounds. Change way something looks, works or tastes. Decrease melting point and increase boiling point
What is the melting point depression
Lowers melting point
What is a formulation
Mixture with many different chemicals that don’t react with each other, but when mixed together, have desired effect. ALWAYS fixed amounts.
What type of ions are flame tests used for
positive
What is the method for the flame test
Dip nichrome wire in concentrated HCl or heat it (sterilises/cleans it)
Dip nichrome wire in solution/powder and hold tip of wire in blue bunsen burner flame.
Observe colour change of flame
Clean with HCl for reuse
Flame test Colour: Lithium
Crimson
Flame test Colour: Sodium
Yellow-orange
Flame test Colour: Potassium
Lilac
Flame test Colour: Calcium
Brick red/orange-red
Flame test Colour: Copper
Green
Flame test Colour: Magnesium
No colour
What is the test for metal cations
Sodium hydroxide
Metal cation NaOH: Calcium and magnesium
White precipitate. Use flame test to differentiate
Metal cation NaOH: Copper
Blue precipitate
Metal cation NaOH: Iron (II)
Green
Metal cation NaOH: Iron (III)
Brown
Metal cation NaOH: Aluminium
Soluble and dissolves in excess sodium hydroxide
What is the method to determine Negative carbonate ions
Pour solution in tube
Pour limewater in another tube
Add HCl to solution
Only if bubbles seen, use teat pipette to transfer gas produced to limewater
Record results
Only a carbonate solution would get bubbles as adding dilute acid produces CO2.
Most carbonates don’t dissolve in water but group 1 carbonates do
CO2 turns limewater cloudy
What is the method for negative Halide ions
Pour solution in test tube
Add few drops of dilute nitric acid then silver nitrate solution
Nitric acid dissolves compound to remove carbonate ions
Negative Halide ions result: Iodide
Yellow precipitate
Negative Halide ions result: Bromide
Cream precipitate
Negative Halide ions result: Chloride
White precipitate
What is the method for negative sulfate ions
Pour solution in test tube
Add dilute HCl then barium chloride solution. HCl removes carbonate ions
Observe results
Negative Sulfate ions results
White precipitate = is insoluble salt barium sulfate. Shows sulfate ions present. Sodium sulfate and sodium chloride turn cloudy
What is Flame emission Spectroscopy
Method telling us metal ions are present in something from their characteristic line spectra and concentration of metal ions
How does FES work
Sample heated in flame
Energy excited electrons in metal ions. Jump into higher energy levels and releases light
In spectrometer, wavelength of light analysed by passing through spectroscope.
Each type of metal ion gives its own characteristic pattern of radiation called ‘line spectrum’
Measure intensity (absorbance) of light with specific wavelength to show concentration
What are the advantages of FES
Highly accurate. More sensitive that flame tests.
Can save lives
Quicker
Small samples recognised easily
Identify ion and concentration
What are the disadvantages of FES
Delicate = expensive
Complicated = Needs special training to use
Gives results only interpreted by comparison with data from known substances