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Chemistry - Y10 + Y11 > Chemical Analysis - Y11 > Flashcards

Chemical Analysis - Y11 Flashcards

1
Q

What is a pure substance?

A

A single element or compound, not mixed with any other substance

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2
Q

What is key about a pure substance?

A

It will melt or boil at a specific temp

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3
Q

Where could you get the MP and BP of a substance?

A

From a data book

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4
Q

How can you test the purity of a substance?

A
  • By measuring its MP AND BP and comparing it with MP and BP of the pure substance (from data book)
  • The closer measured value is to actual MP or BP, the purer the sample is
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5
Q

What do impurities in your sample do?

A
  • Lower the MP
  • Increase the melting range of your substances
  • Increase the BP - may result sample boiling at a range of temps
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6
Q

What are formulations?

A

Mixture that has been designed as a useful
product

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7
Q

How are formulations made?

A

by mixing the components in carefully measured quantities to ensure
that the product has the required properties

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8
Q

What are paints formulations composed of?

A
  • Pigment -eg titanium oxide to give white pigment
  • Solvent- used to dissolve the other components + alter viscosity
  • Binder (resin) - forms a film that holds pigment in place after its been painted on
  • Additives - added to further change physical/chemical properties of the paint
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9
Q

What affects the chemicals used and their amounts so paint is right for the job?

A

Its purpose

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10
Q

What industry are formulations important in? How?

A
  • Pharmaceutical industry
  • By altering the formulation of a pill, chemists can make sure drug is delivered to a certain part of the body at the right conc, thats its consumable and has a long enough shelf life.
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11
Q

Where can formulations be found in everyday life?

A
  • Cosmetics
  • fuels
  • cleaing products
  • fertilisers
  • food/drink
  • metal alloys
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12
Q

How can you find a products formulation?

A

On the info on the packaging - info about its composition
eg ratio or percentage of each component tells you its formulation
also lets you choose a formulation with the right composition for your particular use

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13
Q

What is chromotography?

A
  • Used to separate mixtures
  • give info to help identify substances
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14
Q

What does chromotography involve?

A
  • Stationary phase - paper (doesnt move)
  • Mobile phase - solvent (moves)
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15
Q

What will a pure compound produce in chromotography?

A

a single spot in all solvents

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16
Q

What will a compounds in a mixture produce in chromotography?

A

seperate into diff spots depending on the solvent

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17
Q

Why do you draw starting line in chromotography in pencil?

A

If it was in pen, ink would move up the paper with the solvent

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18
Q

What state is the mobile phase always in?

A

Liquid or gas

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19
Q

What state is the stationary phase always in?

A

solid or really thick liquid

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20
Q

What chemicals in a chromotography will move further?

A

Chemicals that spend more time in the mobile phase than the stationary phase

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21
Q

What does the amount of time the molecules spend in each phase depend on?

A
  • How soluble they are in the solvent
  • How attracted they are to the paper
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22
Q

What molecules will move further up the paper?

A
  • They spend more time in the mobile phase
  • they have a higher solubility in the solvent
  • and which are less attracted to the paper
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23
Q

What is the result of a chromotography analysis called?

A

chromatogram

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24
Q

What is an Rբ value?

A
  • Ratio between the distance travelled by dissolved substaance and distance travelled by solvent
  • the further through the stationary phase a substance moves, the larger the Rբ value
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25
Rբ formula
distance travelled by substance / distance travelled by solvent
26
What to do if serveal diff substances have the same Rf value?
Repeat experiment using a diff solvent
27
Why would there not be an Rf value on the database?
Substance has never been analysed before, we would need to carry out further analysis to identify it
28
What is the Rf value dependent on?
* Solvent * if solvent is changed, value will change
29
What do Rf values value from? What do they mean?
* 0-1 * 0 - substance is not attracted to mobile phase * 1- substance isnt attracted to stationary phase
30
Chromotography Practical steps
1. Draw baseline in pencil, 1cm above bottom of chromotography paper 2. On the line, used a coloured marker on draw 1 dot on line, equal distance between dots, let it dry 3. Fill beaker and hand paper to a splint so it hangs and make sure it doesnt touch the paper 4. Cover beaker with lid so water doesnt evaporate 5. Let it sit so solvent can travel up, mark point where solvent reaches 6. Calculate Rf value | any solvent can be used not only water, lid for toxic fumes for some
31
Uses of methylated spirit?
* Fuel * Solvent * Antiseptic
32
How do you test for hydrogen
1. Insert burning splint 2. Pop sound = hydrogen
33
How do you test for oxygen
1. Insert glowing splint into test tube 2. Relights = oxygen
34
How do you test for carbon dioxide
1. Limewater (aqueous solution of calcium hydroxide) = pippete into test tube and bubble gas into limewater 2. limewater = cloudy = co2 present
35
How do you test for chlorine?
1. Damp litmus paper into mouth of test tube 2. Bleaches = chlorine
36
What do to before a flame test?
1. Place small amount of chemical onto wire mounted in a handle 2. Place end of it into blue bunsen burner flame 3. colour tells us metal ion present
37
What flame does lithium make?
crimson
38
What flame does sodium make?
yellow
39
What flame does potassium make?
lilac
40
What flame does calcium make?
orange-red
41
What flame does copper make?
green
42
Prob with flame tests
* Hard to distinguish colours especially when there is only a low conc of the metal compound * sometimes sample has a mixture of metal ions, can mask the colour of the flame
43
What do scientists do instead of using flame tests? What type of method is it?
Flame emission spectroscopy which is an instrumental method
44
What happens in flame emission spectroscopy?
1. Sample of metal ion in solution is placed into a flame 2. light given out is passed into a machin called spectroscope 3. spectroscope converts light into a line spectrum 4. position of lines are specific for a metal ion
45
What can flame emission spectroscopy also tell us and how?
The concentration of the metal ion by seeing how the lines become more intense at a high conc
46
Advntages of instrumental methods
* Rapid = more rapidly than flame tests * Sensitive - fes will work on a tiny sample of metal compound * accurate - more likely to identify metal ion correctly>flame test
47
If you add sodium hydroxide to WHAT IONS , they will produce a white precipitate
* Calcium * Magnesium * Aluminium
48
What happens if you add excess sodium hydroxide into solution of aluminium ions?
aluminium precipate dissolves
49
Sodium hydroxide + copper II ions =
blue precipitate of copper II hydroxide
50
Sodium hydroxide + iron II hydroxide =
green precipitate of iron II hydroxide
51
Sodium hydroxide + iron III ions
Brown precipitate of iron III hydroxide
52
Name the non metal ions
* carbonate * halides * sulfate
53
How do you test for the carbonate ion?
1. Add any dilute acid to sample 2. If present, acid will react and produce co2 = effervesence but it doesnt prove we have co2 3. bubble gas through lime-water, if it goes cloudy = co2 ion 4. Carbonate ion present
54
How do you test for halide ions
1. Add dilute nitric acid to sample 2. Add dilute silver nitrate solution 3. Halide ions produce a precipitate of silver halide, each halide makes diff colour precipitate
55
What colour precipitate do chloride ions make when testing for halide ions?
White of silver chloride
56
What colour precipitate do bromide ions make when testing for halide ions?
cream of silver bromide
57
What colour precipitate do iodide ions make when testing for halide ions?
yellow of silver iodide
58
How do you test for sulfate ions?
1. Add dilute HCL 2. Add barium chloride solution 3. If present = white prec
59
How do you test for metal ions (+)
Flame tests + sodium hydroxide solution
60
How do you test for non metal ions (-)
* sulfates * carbonate * halides
61
How would you test for chloride ions?
add silver nitrate and dilute nitric acid = white precipitate
62
Explain why positions of dye is different in a solution of ethanol and another of water
* position of dye depedns on solubility of solvent used * has diff solubilities in ethanol and water * therefore diff position
63
Why is the Rf value of a dye not affected by how far the solvent front is allowed to travel
ratio of the 2 distances remain the same
64
When is sodium hydroxide used for?
To identify specific metal ions by observing colour of precipitate
65
When is silver nitrate and dilute ntiric acid used for?
to test for presence of halide ions - form coloured precipitates
66
When is barium chloride solution and dilute hydrochloric acid used for?
to test presence of sulfate ions - produce white precipitate

Chemistry - Y10 + Y11 (11 decks)

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