purity, formulations, chromatography, instrumental analysis

Question 1

chemical definition of a pure substance

Answer 1

a single element or compound not mixed with any other substance

Question 2

everyday definition of a pure substance

Answer 2

a substance that has had nothing added to it and is in its natural state

Question 3

how to distinguish between pure and impure substances

Answer 3

pure substances boil and melt and specific temperatures, so any variation in the melting and boiling point means substance is impure.

impure = melt and boil over a range of temperatures

impure decrease melting points and increase boiling point

Question 4

what is a formulation (3 points)

Answer 4

a mixture designed as a useful product where each chemical involved has a particular purpose and is added in measured quantities (ensures right properties)

Question 5

7 examples of formulations

Answer 5

1. fuels
2. cleaning agents
3. paints
4. medicines
5. alloys
6. fertilisers
7. foods

Question 6

chromatography (for full method refer to topic 1): used for? (2)

Answer 6

separate mixtures and identify substances

Question 7

Rf value: what is it and how to calculate

Answer 7

distance moved by the compound (the centre of the spot to the original line) : distance moved by solvent

distance moved by substance / distance moved by solvent

Question 8

how to use chromatography to identify same compounds and a pure compounds

Answer 8

compound have different Rf values in different solvents

a pure compound will produce 1 single spot.

Question 9

how does chromatography separate mixtures

Answer 9

different compounds in the mixture has different solubility therefore they rise to different points- most soluble furthest-. create series of spots on chromatogram. attraction to the paper

Question 10

what are instrumental methods of analysis

Answer 10

ways to detect elements and compounds using machinery

Question 11

3 advantages of instrumental analysis

Answer 11

1. sensitive- detect tiny amounts of substance
2. fast
3. accurate

Question 12

3 types of instrumental analysis

Answer 12

1. flame emission spectroscopy
2. mass spectroscopy
3. infrared spectroscopy

Question 13

process of flame emission spectroscopy + how is concentration detected

Answer 13

1. sample placed in a flame
2. heat causes electrons to excite and move to higher energy levels
3. when they drop back into original energy levels, they release energy as light
4. light passes through a spectroscope which detects the wavelengths of light emitted

concentration = intensity of light

Question 14

how to use flame emission spectroscopy to identify ions in a compound

Answer 14

no 2 ions have the same spectroscope as their electron arrangements different

tell ions in a compound by seeing which ions’ spectroscope matches up, concentration of the ion = intensity