C10- chemical analysis 🧪 Flashcards
What is a pure substances ?
- a pure substance, is a single element or compound not mixed with any other substance
How can a substance be tested, to determine if it is pure ?
- a substance’s melting and boiling point can be measured.
- this is because, a pure substance will melt at a specific fixed temperature
- and a pure substance, will have a specific boiling point
How can a substance be tested, to determine if it is impure ?
- like pure substances, a substance’s melting and boiling point can be measured.
- this is because, impure substances melt and boil over a range of temperatures
[Extra] Why is it important to test for pure and impure substances ?
- For substances used in preparing food and drugs, it is important that only permitted pure substances are being used.
- this is because, if a substance is impure, and laced with some other substances, these unapproved impurities might not be safe for human consumption- which could lead to undesirable effects on human health.
What is a formulation ?
- a formulation, is a complex mixture that has been designed as a useful product
- [and in a formulation, the quantity of each component is carefully measured, so that the product has the required properties]
Name some examples of a formulation ?
- fuels
- paints
- cleaning products
- medicines
- alloys
- fertilisers
- and, food
RECAP: What is paper chromatography ?
- paper chromatography, is a physical separation technique that separates substances based on their different solubilities
Describe a method you would do to carry out paper chromatography [5]
Hint: draw, pipette, place, solvent, dry
- draw a pencil line across chromatography paper (about 1 cm above the bottom)
- use a pipette, or capillary tube, to add small spots of each ink (A,B, C and D) to the line on the paper, as well as unknown ink (U) (equally spread across the paper)
- place the paper into a container with a suitable solvent (e.g. water) in the bottom - making sure the pencil line is above the water line
- and allow the solvent to move through the paper, but remove the chromatogram before it reaches the top
- then allow the chromatogram to dry, and measure the distance travelled by each spot and by the solvent
With chromatography, is there a limit to how many substances we can test?
- no, with chromatography this can be done with several colours; there has to be enough space on the paper.
What is the stationary phase in paper chromotography?
- In paper chromatography, the stationary stage is called the paper- because it doesn’t move.
What is the mobile phase in paper chromatography?
- In paper chromatography, the mobile phase is the solvent- since it does move.
In chromatography, what’s the difference between the stationary 🆚️ mobile phase?
- the stationary stage is called the paper- because it doesn’t move
- ; the mobile phase is the solvent- since it does move.
In paper chromatography, how do we know if a colour is a single substance?
- there will be only one spot
Why does paper chromatography work? [3]
- paper chromatography works, because each chemical in the mixture will be attracted to the stationary phase (the paper), to a different extent.
- and chemicals that are strongly attracted to the stationary phase (the paper) will not move very far.
- chemicals that are weakly attracted, will move further up the paper.
What will a pure chemcial produce, 🆚 chemicals in a mixture?
- a pure chemical produces singles spot in all solvents
- ; a chemical in a mixture may separate into different spots, based on the solvent.
