Chemical Analysis Flashcards
How do impurities affect the boiling point and melting point of a substance?
Boiling Point - increaces it
Melting Point - Decreaces it
For both, they widen the range of temperatures of which it will boil/melt
What is a formulation?
- A mixure of chemicals made to produce useful products.
- Each component plays a specific role in the formulation’s properties and must be in a precicely measured quantity
- examples include fuel, medicines, cleaning agents, fertilisers.
What is the mobile phase in chromatography?
What is the stationary phase in chromatography?
mobile phase - the solvent (e.g, water)
stationary phase - the solid or viscous liquid (e.g, the paper)
Recite the Rf value formula
distance travelled by substance / distance travelled by solvent
(MUST be under 1)
How does one test for hydrogen?
- place a LIT splint near the source that you wish to test
- in the presence of hydrogen, a squeaky pop will be heard
- this is because the hydrogen burns rapidly in the presence of oxygen, to produce H₂O
How does one test for oxygen?
- place a GLOWING splint near the source that you wish to test
- in the presence of oxygen, the splint will relight
How does one test for carbon dioxide?
- bubble limewater (calcium hydroxide) through the substance you wish to test
- in the presence of CO₂, the limewater will turn from colourless to cloudy
How does one test for chlorine?
- place (damp) litmus paper into the tube containing the substance you wish to test
- in the presence of chlorine, the litmus paper will go from red to white.
How do we test for the following metal ions?
Potassium (K⁺)
Copper (Cu²⁺)
Lithium (Li⁺)
Sodium (Na⁺)
Calcium (Ca²⁺)
- flame test
- when burned, these metal ions produce a characteristic colored flame:
Potassium (K⁺) - Lilac flame
Copper (Cu²⁺) - Green flame
Lithium (Li⁺) - Crimson flame
Sodium (Na⁺) - Yellow flame
Calcium (Ca²⁺) - Orangey-red flame
How does one undergo the flame test for metal ions?
(core practical)
- submerge the nichrome wire loop in dilute hydrochloric acid to steralise it
- place the nichrome wire loop into the sample that you wish to test
- hold the loop in a bunsen burner (on blue flame) and observe the change in the flame’s color
How are metal hydroxides formed?
metal ion + sodium hydroxide —> metal hydroxide
How can we differenciate between the following substances when reacted with sodium hydroxide?
- Copper (II)
- Iron (II)
- Iron (III)
- Calcium hydroxide
- Magnesium hydroxide
- Aluminium hydroxide
- Copper (II) forms a blue precipitate
- Iron (II) forms a green precipitate
- Iron (III) forms a brown precipitate
- Calcium ions form a white precipitate
- Magnesium ions form a white precipitate (must be burned to be distinguished between calcium hydroxide)
- Aluminium ions form a white precipitate, but in the presence of excess white precipitate, will dissolve into a colorless solution.
How does one test for a carbonate ion?
- add dilute acid to the sample, you will observe fizzing. water, carbon dioxide and a salt would be produced.
- bubble the gas through limewater. If it goes cloudy, it shows the presence of carbon dioxide, which means you have started with a carbonate ion.
What is a halide ion and how do you test for it?
A halogen with a negative charge (e.g, flourine, chlorine, bromine, iodine)
- add dilute nitric acid (this removes carbonate ions that could form a different pricipitate with the silver nitrate)
- add silver nitrate solution
- obeserve the precipitate colour
- flourine - no precipitate
- chlorine - white precipitate
- bromine - cream precipitate
- iodine - yellow precipitate
How do we test for sulfates?
- Add dilute hydrochloric acid (this removes carbonate ions that could disrupt the test by forming their own precipitate)
- add barium chloride solution. in the presence of sulfates, this forms a white precipitate.
What are the pros and cons of instrumental methods of chemical analysis?
pros
- more sensitive and accurate
- produces results quicker
- can analyse very small samples
cons
- need special training to use them
- instruments are usually expensive
- results only useful when compared to data from known substances
Why do some chemicals move further up the chromatography paper?
- Chemicals that have a stronger attraction to the stationary phase will not move very far.
- Chemicals that have a weaker attraction to the stationary phase will move further up the paper.
Why must the solvent start below the base line in chromatography?
If it starts above the base line it will disolve the solute into the solution where it cannot be seperated.
What is a chemical process?
What is a physical process?
Chemical processes form new elements by chemical reactions (e.g, respiration). Physical procsesses do not involve chemical reactions or the formation of a new element (e.g, change of matter).
What happens to the melting and boiling point of impure substances?
Impurities decrease the melting point (1)
Impurities increase the boiling point (1)
Why is orange juice an impure substance?
It contains more than one compound/element (1)
It is a mixture (1)
State the scientific name for rust
Hydrated iron (III) oxide.
Why is it better to use thermosoftening polymers to make plastic bottles?
Thermosoftening polymers melt. (1)
And therefore can be recycled. (1)
