Flashcards in Chemical Analysis Deck (28):
What is the definition of a pure substance?
Contains only one type of particle (atom or molecule)
Not mixed with anything else
Will impurities in your sample decrease or increase the melting point?
Will lower the melting point and increase the melting range
Will impurities in your sample increase or decrease the boiling point?
Will increase the boiling point and may result in your sample boiling at a range of temperatures
What are some examples of pure substances?
What are some examples of impure substances?
Nail polish 💅🏻
What are formulations?
A mixture that has been designed as a useful product
Why are paints formulations?
They are composed of:
Pigment-gives the paint 🎨 colour
Solvent-thins pigment and binder so they spread well
Binder- helps paint attach itself
Additives- added to further change the physical ad chemical properties of te paint
Where are formulations really important to?
The pharmaceutical industry
Why are formulations useful to the pharmaceutical industry?
By altering the formulation of a pill, chemists can make sure it delivers the drug to the correct part of the body at the right concentration, that it’s consumable and has a long enough shelf life.
Where are formulations found in everyday life?
I’m cleaning products, fuels, cosmetics, fertilisers, metal alloys and even in food and drink.
What is the method for paper chromatography?
1)draw a line near the bottom of a sheet of filter paper using a pencil
2)add a spot of the ink to the line and place the sheet in a beaker of solvent e.g. water 💦
3)the solvent used depends on what’s being tested. Some compounds dissolve well in water, but sometimes other solvents, like ethanol are needed
4)make sure the ink isn’t touching the solvent- you don’t want to dissolve it
5)place a lid on top of the container to stop the solvent evaporating
6)the solvent seeps up the paper, carrying the ink with it
7)each dye in the ink will move up the paper at a different rate so the dyes will separate out. Each dye will form a spot in a different place-1 spot per dye in the ink
8)if any of the dyes in the ink are insoluble (won’t dissolve) in the solvent you’ve used, they’ll stay on the baseline
9)when the solvent has nearly reached the top of the paper, take the paper out of the beaker and leave it to dry
10)the end result is a pattern of spots called a chromatogram
Why do we use a pencil in paper chromatography to draw the line near the bottom of the filter paper rather than a pen?
Pencil marks are insoluble and won’t dissolve in the solvent.
What does chromatography separate?
The substances in a mixture
What can you use chromatography to identify?
What’s a mobile phase?
Where the molecules can move. This is always the liquid or gas (e.g. ethanol or water)
What is a stationary phase?
Where the molecules can’t move. This can be a solid or a really thick liquid (often filter paper)
How many spots will a pure substance form?
One spot in any solvent as there is only one substance in the sample
Which phase will a molecule with a higher solubility in the solvent and are less attracted to the paper spend more time in?
Mobile phase-and they’ll be carried further up the paper
Why do we put a watch glass on top of the beaker in paper chromatography?
To stop the solvent evaporating
What is the formula to find the Rf value for each chemical?
Rf= distance travelled by substance divided by distance travelled by solvent
What is the distance travelled by substance?
The distance from the baseline to the centre of the spot
How is chromatography carried out to see if a certain substance is present in the mixture?
To do this, you run a pure sample of that substance (a reference) alongside the unknown mixture. If the Rf values of the reference and one of the spots in the mixture match, the substance may be present
How is the Rf value dependent on the solvent?
If you change the solvent the Rf value for a substance will change.
How can you test both the mixture and the reference in a number of different solvents?
If the Rf value of the reference compound matches the Rf value of one of the spots in the mixture in all the solvents, then it’s likely the reference compound is present in the mixture. If the spots in the mixture and the spot in the reference only have the same Rf value in some of the solvents, then the reference compound isn’t present in the mixture.
What is the test for chlorine?
Chlorine bleached damp litmus paper, turning it white. (It may turn red for a moment first though-that’s because a solution of chlorine is acidic).
What is the test for oxygen?
If you put a glowing splint inside a test tube containing oxygen, the oxygen will relight the glowing splint.
What is the test for carbon dioxide?
Bubbling carbon dioxide through (or shaking carbon dioxide with) an aqueous solution of calcium hydroxide (known as limewater) causes the solution to turn cloudy.