Chemical Analysis

Question 1

What is the definition of a pure substance?

Answer 1

Contains only one type of particle (atom or molecule)

Not mixed with anything else

Question 2

Will impurities in your sample decrease or increase the melting point?

Answer 2

Will lower the melting point and increase the melting range

Question 3

Will impurities in your sample increase or decrease the boiling point?

Answer 3

Will increase the boiling point and may result in your sample boiling at a range of temperatures

Question 4

What are some examples of pure substances?

Answer 4

Ethanol 
Salt 
Copper 
Magnesium 
Oxygen 
Water

Question 5

What are some examples of impure substances?

Answer 5

Soap
Spoon 🥄 
Nail polish 💅🏻 
Toothpaste 
Copper sulphate 
Aspirin tablet

Question 6

What are formulations?

Answer 6

A mixture that has been designed as a useful product

Question 7

Why are paints formulations?

Answer 7

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

Question 8

Where are formulations really important to?

Answer 8

The pharmaceutical industry

Question 9

Why are formulations useful to the pharmaceutical industry?

Answer 9

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.

Question 10

Where are formulations found in everyday life?

Answer 10

I’m cleaning products, fuels, cosmetics, fertilisers, metal alloys and even in food and drink.

Question 11

What is the method for paper chromatography?

Answer 11

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

Question 12

Why do we use a pencil in paper chromatography to draw the line near the bottom of the filter paper rather than a pen?

Answer 12

Pencil marks are insoluble and won’t dissolve in the solvent.

Question 13

What does chromatography separate?

Answer 13

The substances in a mixture

Question 14

What can you use chromatography to identify?

Answer 14

The substances

Question 15

What’s a mobile phase?

Answer 15

Where the molecules can move. This is always the liquid or gas (e.g. ethanol or water)

Question 16

What is a stationary phase?

Answer 16

Where the molecules can’t move. This can be a solid or a really thick liquid (often filter paper)

Question 17

How many spots will a pure substance form?

Answer 17

One spot in any solvent as there is only one substance in the sample

Question 18

Which phase will a molecule with a higher solubility in the solvent and are less attracted to the paper spend more time in?

Answer 18

Mobile phase-and they’ll be carried further up the paper

Question 19

Why do we put a watch glass on top of the beaker in paper chromatography?

Answer 19

To stop the solvent evaporating

Question 20

What is the formula to find the Rf value for each chemical?

Answer 20

Rf= distance travelled by substance divided by distance travelled by solvent

Question 21

What is the distance travelled by substance?

Answer 21

The distance from the baseline to the centre of the spot

Question 22

How is chromatography carried out to see if a certain substance is present in the mixture?

Answer 22

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

Question 23

How is the Rf value dependent on the solvent?

Answer 23

If you change the solvent the Rf value for a substance will change.

Question 24

How can you test both the mixture and the reference in a number of different solvents?

Answer 24

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.

Question 25

What is the test for chlorine?

Answer 25

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).

Question 26

What is the test for oxygen?

Answer 26

If you put a glowing splint inside a test tube containing oxygen, the oxygen will relight the glowing splint.

Question 27

What is the test for carbon dioxide?

Answer 27

Bubbling carbon dioxide through (or shaking carbon dioxide with) an aqueous solution of calcium hydroxide (known as limewater) causes the solution to turn cloudy.

Question 28

What is the test for hydrogen?

Answer 28

If you hold a lit splint at the open end of a test tube containing hydrogen, you’ll get a “squeaky pop”. (The noise comes from the hydrogen burning quickly with the oxygen in the air to form H20).