12 - Experimental Techniques & Chemical analysis Flashcards
Def. Physical Property
Characteristic of a substance that can be measured or observed without changing the substance
What are the main physical properties?
- Melting point
- Boiling point
- Colour
- Solubility in water
- Solubility in another solvent
- Rf value
- Density
- Hardness
- Malleability
- Thermal and electrical conductivity
Describe simple distillation
A process used to separate the solvent from a solute in a solution.
In the process of simple distillation, a solution is heated and when the water has enough energy to evaporate to steam, the steam passes through a condenser.
The steam is cooled and condenses. The distillate drips through the delivery tube to the beaker.
Generally, the solvent is distilated from the solute, but this is not always the case.
Compare the characteristics of water and ethanol
Ethanol
- Flammable
- Boils at 78 degrees celcius
- Density ~0.8gcm-3
Water
- Not flammable
- Boils at 100 degrees celcius
- Density ~1.0gcm-3
What are the chemical tests for water?
- Recognition that water boils at 100 degrees celcius
- Blue Cobalt Chloride Paper (CoCl2) that turns pink in the presence of water
- White anhydrous Copper Sulfate (CuSO4) that turns blue in the presence of water
Describe Fractional distillation
A process used to separate mixtures of liquids with different boiling points.
It is similar to simple distillation, but has a fractionating column allow only one liquid to evaporate and continue through the apparatus.
Each liquid is called a ‘fraction’.
Def. Pure Substance
A pure substance particles of the same formula.
It can be an element or a compound.
A formula can be written for the substance
The impure substance is called a mixture
What determines where a substance will appear on a piece of chromatography paper?
The solubility of the substance.
The more soluble, the higher up the chromatography paper it will go.
What 2 pure substances are you required to know and why is their purity important?
1) Food Additives - To not prokoke allergies
2) Drugs in medecine - To not produce side effects
Describe how chromatography works
1) Draw a pencil line at the bottom a a peice of chromatography paper
2) Put a spot of the dye/substance you want to test on the line
3) Place the bottom of the paper in water or another solution e.g. salt solution
4) Let the solution dissolve the substance as it rises, and wash the substances up the piece of chromatography paper
Why do dyes move up the chromatography paper in the process of chromatography?
Because the solution soaks the dyes up, dissolves them and carries them up the paper.
What is the result from chromatography called?
A Chromatogram
What do you use to detect colourless substances in chromatography?
Using a locating agent
What does Rf Value stand for in chromatography?
Retention Factor Value
Def. Rf Value
The ratio of the distance travelled by a spot (solute) over the distance travelled by the solvent.
What is the formula for the Rf Value?
Rf = Distance travelled by solute/Distance travelled by Solvent
Why do different metals, when burnt, emit different coloured flames?
Because of the different electron shells. As the metal is heated, the electrons move arounsd and emit light.
What is the colour of Copper when burnt?
Blue-Green
What is the colour of Potassium when burnt?
Lilac
What is the colour of Barium when burnt?
Light green
What is the colour of Sodium when burnt?
Yellow
What is the colour of Calcium when burnt?
Orange-red
What is the colour of Lithium when burnt?
Red
What is the test for Oxygen?
Test with glowing splint, positive if flame relights
What is the test for Hydrogen?
Test with burning splint, positive if ‘pop’ sound is heard
What is the test for Ammonia?
Test with damp red litmus paper, Positive if turns blue
What is the test for Chlorine?
Test with damp blue litmus paper, Positive if turns red then bleaches to white
What is the test for Carbon Dioxide?
Pass gas through transparent limewater, positive if turns cloudy/milky
What is the test for Sulfur Dioxide?
Test with filter paper dipped in purple Potassium Manganate (KMnO4), positive if turns colourless
How do you identify if a substance is pure or impure?
If it has a fixed melting or boiling point, the substance is pure. If it melts and boils throughout a temperature range, it is impure.
How do the melting points of an impure substance differ from that of a pure substance
The melting point of an impure substance is lower that that of a pure substance.
The boiling point of an impure substance is higher that that of a pure substance.
What is the formula for percentage purity?
Purity (%) = Mass of pure product/Mass of impure sample x 100
What is the test for a carbonate ion (CO32-)?
Add dilute acid (nitric acid, hydrochloric acid), and you get fizzing/effervescence
What is the test for a chloride ion (Cl-)?
Acidify with dilute nitric acid, then add aqueous silver nitrate, and you get a white ppt (precipitate)
What is the test for a bromide ion (Br-)?
Acidify with dilute nitric acid, then add aqueous silver nitrate, and you get a cream ppt (precipitate)
What is the test for an iodine ion (I-)?
Acidify with dilute nitric acid, then add aqueous silver nitrate, and you get a yellow ppt (precipitate)
What is the test for a sulphate ion (SO42-)?
Acidify with dilute nitric acid, then add aqueous barium chloride or aqueous barium nitrate, to get a white precipitate
What is the test for a sulphite ion (SO32-)?
Add dilute hydrochloric acid, warm gently and test for sulphur dioxide with filter paper dipped in purple acidified aqueous potassium manganate (K₂MnO₄). Positive if turns colourless.
What is the test for a nitrate ion (NO3-)?
Add aqueous sodium hydroxide, then aluminium foil. Warm carefully and test with damp red litmus paper. Positive if turns blue.
What are the equations to show the process of testing for carbonates?
Carbonate + Acid –> Carbon Dioxide
e.g. Na2CO3 + 2HNO3 –> CO2 + 2NaNO3 + H2O
What are the equations to show the process of testing for a Halides?
Halide + Silver Nitrate –> Silver Halide + Nitrate
e.g. NaCl + AgNO3 –> AgCl + NaNO3
What are the equations to show the process of testing for Sulphates?
Sulphate + Barium Nitrate –> Barium Sulfate + Nitrate
e.g. ZnSO4 + Ba(NO3)2 –> BaSO4 + Zn(NO3)2
What is the effect of aqueous sodium hydroxide on aluminium cations (Al3+) ?
White ppt, soluble in excess, giving a colourless solution
What is the effect of aqueous sodium hydroxide on ammonium cations (NH4+) ?
Ammonia is produced on warming
What is the effect of aqueous sodium hydroxide on chromium (III) cations (Cr3+) ?
Green ppt, soluble in excess
What is the effect of aqueous sodium hydroxide on calcium cations (Ca2+) ?
White ppt, insoluble in excess
What is the effect of aqueous sodium hydroxide on copper (II) cations (Cu2+) ?
Light blue ppt, insoluble in excess
What is the effect of aqueous sodium hydroxide on iron (II) cations (Fe2+) ?
Green ppt, insoluble in excess
What is the effect of aqueous sodium hydroxide on iron (III) cations (Fe3+) ?
Red-brown ppt, insoluble in excess
What is the effect of aqueous sodium hydroxide on Zinc cations (Zn2+) ?
White ppt, soluble in excess, giving colourless solution
What is the effect of aqueous ammonia on aluminium cations (Al3+) ?
White ppt, insoluble in excess
What is the effect of aqueous ammonia on calcium cations (Ca2+) ?
no ppt/very slight white ppt
What is the effect of aqueous ammonia on chromium (III) cations (Cr3+) ?
Grey-green ppt, insoluble in excess
What is the effect of aqueous ammonia on copper (II) cations (Cu2+) ?
light blue ppt, soluble in excess, giving a dark blue solution
What is the effect of aqueous ammonia on iron (II) cations (Fe2+) ?
Green ppt, insoluble in excess
What is the effect of aqueous ammonia on iron (III) cations (Fe3+) ?
Red-brown ppt, insoluble in excess
What is the effect of aqueous ammonia on Zinc cations (Zn2+) ?
White ppt, soluble in excess, giving colourless solution
Def. Residue
A substance that remains after evaporation, distillation, filtration or any similar process
Def. Empirical formula
The simplest mole ratio of the elements in a compound.
How do you find the empirical formula?
1) Calculate the number of moles in each element using n = m/mr
2) Convert the number of moles to whole number ratios
In the tests for aqueous cations, what do precipitates form?
Hydroxides
