C4 - predicting and identifying reactions and products Flashcards
1
Q
what are group 1 metals known as?
A
alkali metals
2
Q
what are some physical properties of group 1 metals?
A
- low melting/boiling points
- low density
- very soft
3
Q
what type of compounds do the alkali metals form?
A
ionic compounds
4
Q
what tests can you use to test for the presence of group 1 metal ions?
A
flame tests
5
Q
why are group 1 metals very reactive?
A
they readily lose their single outer electron
6
Q
why do the alkali metals get more reactive as you go down group 1?
A
the outer electron is further from the nucleus so it’s less strongly attracted to the nucleus and less energy is needed to remove it
7
Q
how do alkali metals react when put in water?
A
vigorously
8
Q
what does the reaction between alkali metals and water produce?
A
hydrogen gas and a hydroxide
9
Q
what are group 7 elements called?
A
halogens
10
Q
what type of molecules do halogens exist as?
A
diatomic
11
Q
what type of bond do the diatomic molecules that halogens exist as share?
A
a covalent bond
12
Q
what happens to the melting snd boiling points of the halogens as you go down group 7?
A
they increase
13
Q
what happens to reactivity as you go down group 7?
A
it decreases
14
Q
why do the halogens become less reactive as you go down the group?
A
it gets harder to attract the extra electron to fill the outer shell when it’s further away from the nucleus
15
Q
what do the halogens react with to form salts?
A
the alkali metals
16
Q
when the halogens react with the alkali metals to form salts, what are the names of these salts?
A
metal halides
17
Q
what type of reactions do the halogens undergo?
A
displacement reactions
18
Q
what does it mean to say that the halogens undergo displacement reactions?
A
a more reactive halogen can displace a less reactive one from a salt solution
19
Q
what can displacement reactions show?
A
reactivity trends
20
Q
how can you use displacement reactions to show the reactivity trend of the halogens?
A
- start by measuring out a small amount of a halide salt solution in a test tube
- add a few drops of a halogen solution to it and shake the tube gently
- if you see a colour change, then a reaction has happened; the halogen has displaced the halide ions from the salt
- if no reaction happens, there won’t be a colour change
- repeat the process using different combinations of halide salt and halogen
21
Q
what are group 0 elements called?
A
noble gases
22
Q
at room temperature, what are the noble gases like?
A
colourless gases
23
Q
what is a word that describes how nobles gases don’t react with much at all?
A
they are inert
24
Q
what are some trends within the noble gases?
A
boiling point, melting point and density all increase as you go down group 0
25
where are the transition metals on the periodic table?
in the middle
26
what are some properties of transition metals?
typical properties of metals: hard, strong, shiny, good conductors of heat and electricity, high melting points (apart from mercury), high densities
27
what are transition metals and their compounds good at being?
catalysts
28
how many ions od transition metals have?
the often have more than one ion
29
what colour are transition metals' compounds?
often very colourful
30
how reactive are transition metals?
often relatively unreactive
31
what does the way in which metals react with acids tell you?
about their reactivity
32
describe a classic experiment to do that shows that some metals are more reactive than others
1. place little pieces of various metals into dilute hydrochloric acid
2. the more reactive the metal is, the faster the reaction will go
3. very reactive metals will fizz vigorously whereas less reactive metals will bubble a bit and unreactive metals will not react with dilute acids at all
33
what test is used to show that hydrogen is forming?
the burning splint test; the louder the squeaky pop, the more hydrogen has been made in the time period and the more reactive the metal is
34
how is the speed of a reaction indicated by the rate at which bubbles of hydrogen are given of?
the faster the bubbles form, the faster the reaction and the more reactive the metal
35
what is the basic reaction between metal and water?
metal + water = metal hydroxide + hydrogen
36
what does the reactivity series show?
how reactive metals are
37
what do more reactive metals do to less reactive ones?
displace them
38
where should you carry out tests for gases and why?
in a fume cupboard to reduce the risk of anyone inhaling a toxic gas
39
what do you use to test for carbon dioxide?
limewater
40
how do you use limewater to test for carbon dioxide?
1. bubble the gas through limewater
2. if the gas is carbon dioxide, the limewater will turn cloudy
41
what do you use to test for hydrogen?
a lighted splint
42
how do you use a lighted splint to test for hydrogen?
1. hydrogen always makes a squeaky pop with a lighted splint
2. the noise comes from the hydrogen burning with the oxygen in the air to form water
43
what do you use to test for oxygen?
a glowing splint
44
how do you use a glowing splint to test for oxygen?
- you can test for oxygen by checking if the gas will relight a glowing splint
45
what do you use to test for chlorine?
damp blue litmus paper
46
how do you use damp blue litmus paper to test for chlorine?
1. hold a piece of damp blue litmus paper over the gas
2. if the gs is chlorine, it will bleach the litmus paper, turning it white
3. it may turn red for a moment first as a solution of chlorine is acidic
47
what do you use to test for halide ions?
silver nitrate solution
48
how do you use a silver nitrate solution to test for halide ions?
to test for chloride, bromide or iodide ions; add some dilute nitric acid followed by a few drops of silver nitrate solution
49
why is the nitric acid added first when testing for halide ions using silver nitrate solution?
to get rid of any carbonate ions as they produce a pale precipitate with silver nitrate too so could confuse results
50
why can't hydrochloric acid be used instead of nitric acid when testing for halide ions with silver nitrate solution?
because you'd be adding chloride ions
51
what colour precipitate does chloride give of silver chloride?
white
52
what colour precipitate does bromide give of silver bromide?
cream
53
what colour precipitate does iodide give of silver iodide?
yellow
54
what do you use to test for carbonates?
hydrochloric acid
55
how do you use hydrochloric acid to test for carbonates?
1. to test for carbonate ions in solution, first add some barium chloride solution
2. then you add some dilute hydrochloric acid
3. if there are carbonate ions present, the mixture will fizz as the carbonate will react with the acid to produce carbon dioxide gas
4. if you collect the gas and pass it through limewater, the limewater should turn cloudy
5. once all of the barium carbonate has reacted, you'll end up with a colourless solution containing Ba2+ ions
56
what do you use to test for sulfate ions?
barium chloride solution
57
how do you use barium chloride solution to test for sulfate ions?
1. the test for sulfate ions in solution is similar to the test for carbonate ions
2. first add some barium chloride solution; if there are sulfate ions in the solution, a white precipitate of barium sulfate will form
3. then you add some dilute hydrochloric acid to the test sample
4. barium sulfate will not react with dilute hydrochloric acid, so the white precipitate will not dissolve (that's how you know you have sulfate ions and not carbonate ions)
58
what are cations?
positive ions
59
what can you use to identify metal ions?
flame tests
60
how can flame tests be used to identify metal ions?
by putting your substance in a flame and seeing what colour the flame goes
61
how are flame tests carried out in the lab?
- fist clean a nichrome wire loop by dipping it into hydrochloric acid and then rinsing it out in deionised water
- then dip wire loop into sample of metal compound and put loop in clear blue part of bunsen flame (hottest bit)
- record what colour flame goes
62
what colour flame do lithium ions give in flame tests?
crimson red
63
what colour flame do sodium ions give in flame tests?
yellow
64
what colour flame do potassium ions give in flame tests?
lilac
65
what colour flame do calcium ions give in flame tests?
brick red
66
what colour flame do copper ions give in flame tests?
blue-green
67
why do flame tests only work if the mystery compound contains just one type of metal ion?
otherwise you'll get a confusing mixture of colours
68
besides flame tests, what else can be used as a test for metal ions?
sodium hydroxide
69
what do some metal ions for with sodium hydroxide?
a coloured precipitate
70
how does the test using sodium hydroxide for metal ions work?
1. many metal hydroxides are insoluble and precipitate out of solution when formed; some of these hydroxides have a characteristic colour
2. for this test, you add a few drops of sodium hydroxide solution to a solution of your mystery compound
3. if a hydroxide precipitate forms, you can use its colour to tell which metal ion was in the compound
71
what colour precipitate do calcium ions form with sodium hydroxide?
white
72
what colour precipitate do copper ions form with sodium hydroxide?
blue
73
what colour precipitate do iron (II) ions form with sodium hydroxide?
green
74
what colour precipitate do iron (III) ions form with sodium hydroxide?
brown
75
what colour precipitate do zinc ions form with sodium hydroxide?
white at first, then redissolves in excess NaOH to form a colourless solution
76
rather than a person doing chemical tests manually, what else can be used to analyse and identify elements/compounds?
instrumental methods
77
where is instrumental analysis used?
- science research labs
- medical labs
- police forensics work
- environmental analysis
- testing products in industry
78
what are some advantages to instrumental methods of analysis?
- they are very sensitive; can detect even the tiniest amounts of a substance
- they are very fast; can be automated
- they are very accurate; don't involve human error as manual analysis does
79
what are some examples of ways that chemists use machines to analyse samples and identify chemicals?
- infrared spectroscopy
- ultraviolet spectroscopy
- gas chromatography
- mass spectroscopy
80
describe infrared spectroscopy
- this technique produces a graph showing which frequencies of infrared radiation a molecule will absorb (or transmit)
- you can use the absorbance pattern on the graph to identify the molecule
81
describe ultraviolet spectroscopy
- similar to infrared spectroscopy but uses ultraviolet light
82
describe gas chromatography
- used to separate out chemicals in a mixture
- this technique produces a chromatogram with one peak for each chemical
- time that each chemical takes to pass through the machine (retention time) can be used to identify it
83
describe mass spectroscopy
- a technique that can be used to find the relative molecular mass of a mystery compound (or the relative atomic mass of a mystery element)
84
what can be used to identify unknown substances?
instrumental analysis
