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chemistry all note flashcards - 3rd And 4th > 4.6 - Chemical tests > Flashcards

4.6 - Chemical tests Flashcards

(80 cards)

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1
Q

what test is used to test for hydrogen

A

squeaky pop test

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2
Q

what is the method of the squeaky pop test

A
  1. collect a sample of gas in a tube
  2. attempt to ignite the gas using a lit splint
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3
Q

what is the positive result for hydrogen in the squeaky pop test

A

squeaky pop sound

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4
Q

what chemical reaction is taking place during the squeaky pop test

A

the combustion of H2 to form H2O
2H2(g) + O2(g) –> 2H2O(g)
the pop sound is caused by hot gas rushing out of the test tube

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5
Q

what test is used to test for oxygen

A

glowing splint test

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6
Q

what is the method of the glowing splint test

A
  1. collect a sample of gas in a test tube
  2. place a glowing splint into the tube
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7
Q

what is the positive result for oxygen in the glowing splint test

A

the splint relights

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8
Q

what is the chemical reaction taking place during the glowing splint test

A

the combustion of the wood in the splint
it relights because the pure O2 is more concentrated than the O2 in normal air. this means the wood in the splint combusts faster

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9
Q

what test is used to test for the presence of H2O

A

copper sulfate test

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10
Q

what is the method of the copper sulfate test

A
  1. add anhydrous copper sulfate (CuSO4)
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11
Q

what is the positive result for the presence of H2O

A

the anhydrous copper sulfate changes from white to blue

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12
Q

what is the test used to test the purity of H2O

A

measure its boiling point and compare it to 100 degrees C

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13
Q

what is the method of the boiling water test

A
  1. measure its boiling point
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14
Q

what is the positive result for the purity of H2O

A

the closer it is to 100 degrees C the more pure it is

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15
Q

what is the test used to test for carbon dioxide

A

limewater test

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16
Q

what is the method of the limewater test

A
  1. bubble a sample of gas through water
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17
Q

what is the positive result for carbon dioxide

A

a white precipitate forms - limewater turns cloudy

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18
Q

what is the chemical reaction taking place during the limewater test

A

limewater is saturated calcium hydroxide solution, Ca(OH)2
it forms a white precipitate of calcium carbonate (CaCO3) when it reacts with CO2
Ca(OH)2(aq) + CO2(g) –> CaCO3(s) + H2O(l)

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19
Q

what is the test used to test for chlorine

A

damp blue litmus test

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20
Q

what is the method of the damp blue litmus test

A
  1. place damp blue litmus paper in a sample of gas
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21
Q

what is the positive result for chlorine

A

the blue litmus turns white - it bleaches

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22
Q

what is the chemical reaction taking place during the damp blue litmus test

A

Cl2 is a good bleaching agent, so it easily removes colour from other substances
in this test it dissolves into the dampness (H2O) and removes the colour from the litmus

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23
Q

what is the test used to test ammonia

A

damp red litmus test

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24
Q

what is the method of the damp red litmus test

A
  1. place damp red litmus paper in a sample of gas
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25
what is the positive result for ammonia
the damp red litmus turns blue
26
what is the chemical reaction taking place during the damp red litmus test
this happens because the NH3 reacts with the dampness (H2O) to form OH- ions NH3(g) + H2O (l) --> NH4+(aq) + OH-(aq) the NH3 acts as a base by accepting H+ ions from the H2O the OH- ions are what's left after H2O has lost H+, and they are alkaline so the litmus turns blue
27
what are cations
positive ions, like Na+
28
what cations do I need to know
Li+/ Na+/ K+/ Ca 2+/ Cu 2+/Fe 2+/Fe 3+/ NH 4+
29
what do many metal cations cause a non-luminous (blue) Bunsen flame to do
change colour
30
what can we tell by looking at the colour of the bunsen flame after being in contact with a substance
we can tell which metal cation is in the substance
31
how do you conduct a flame test
1. dip a piece of nichrome/ platinum wire into hydrochloric acid these wires don't colour the flame, and the acid cleans the wire 2. dip the wire into a sample of solid or solution this causes some of the sample to stick onto the wire 3. place the tip of the wire into a non-luminous bunsen flame
32
what metal cation is involved if the flame colour is red
Li+
33
what metal cation is involved if the flame colour is yellow
Na+
34
what metal cation is involved if the flame colour is lilac
K+
35
what metal cation is involved if the flame colour is orange-red
Ca2+
36
what metal cation is involved if the flame colour is blue-green
Cu2+
37
what is sodium hydroxide used to test for
Cu2+/Fe2+/Fe3+
38
if one of Cu2+/Fe2+/Fe3+ is present when sodium hydroxide is added, what is formed
a metal hydroxide precipitate
39
how do you conduct a NaOH test
1. dissolve the sample in water 2. add a few drops of NaOH(aq)
40
what is the precipitate formula if its precipitate colour is blue
Cu(OH)2
41
what is the metal cation involved if its precipitate is blue
Cu2+
42
what colour precipitate does Cu2+ make
blue
43
what is the precipitate formula if its precipitate colour is green
Fe(OH)2
44
what is the metal cation involved if its precipitate is green
Fe2+
45
what colour precipitate does Fe2+ make
green
46
what is the precipitate formula if its precipitate colour is brown
Fe(OH)3
47
what is the metal cation involved if its precipitate is brown
Fe3+
48
what colour precipitate does Fe3+ make
brown
49
what are the two types of equations you can write for the reaction in a sodium hydroxide test
a fully balanced equation an ionic equation (just shows the formation of the precipitate)
50
what is an example of a fully balanced equation for the metal cation Cu2+
CuCl2(aq) + 2NaOH(aq) --> Cu(OH)2(s) + 2NaCl(aq) sample blue ppt containing Cu2+
51
what is an example of an ionic equation for the metal cation Cu2+
Cu2+(aq) m+ 2OH-(aq) --> Cu(OH)2(s)
52
what is used to test for ammonium ions
using sodium hydroxide
53
what is formed in an ammonia test
a gas
54
how is an ammonium test conducted
1. dissolve the sample in water 2. add some NaOH(aq) and warm it 3. test the gas evolved with damp red litmus paper
55
in the ammonium test if NH4+ ions are present in the sample what will happen
the litmus paper will turn blue
56
how does the ammonium test work
because the NH4+ from the sample and OH- ions from the ammonium react to produce NH3(g)
57
what is an equation for the reaction in the ammonium test
NH4+(aq) + OH-(aq) --> NH3(g) + H2O(l) sample test with containing damp NH4+ litmus paper
58
what are anions
negative ions like O2-
59
what anions do I need to know
Cl-/Br-/I-/CO3 2-/SO4 2-
60
what test is used to test for halide ions (Cl- Br- I-)
silver nitrate test
61
what are the halide ions
Cl-/Br-/I-
62
how is the silver nitrate test conducted
1. dissolve the sample in water 2. add nitric acid (HNO3) 3. add silver nitrate (AgNO3) solution
63
in the silver nitrate test if Cl-/Br-/I- ions are present what forms
a precipitate with the Ag+ ions from the AgNO3
64
what is the precipitate formula if its precipitate is white
AgCl
65
what halide ion is involved if the precipitate colour is white
Cl-
66
what colour precipitate does Cl- make
white
67
what is the precipitate formula if its precipitate is cream
AgBr
68
what halide ion is involved if the precipitate colour is cream
Br-
69
what colour precipitate does Br- make
cream
70
what is the precipitate formula if its precipitate colour is yellow
AgI
71
what halide ion is involved if the precipitate colour is yellow
I-
72
what colour precipitate does I- make
yellow
73
how is the carbonate test conducted
1. add hydrochloric acid (HCl), look for effervescence 2. if there is effervescence, bubble the gas through limewater
74
what happens in the carbonate test if CO3 2- ions were present in the sample
the gas evolved turns the limewater coudy
75
what would the reaction equation for the carbonate test look like (using calcium carbonate as the sample)
CaCO3(s) + 2HCl(aq) --> CaCl2(aq) + H2O(l) + CO2(g) sample test using limewater containing CO3 2-
76
why is it important to confirm the gas evolved is CO2 using limewater
acids also evolve a gas when they react with some other things. checking that the gas is CO2 prevents false positives
77
how is the sulfate test conducted
1. add hydrochloric acid (HCl), look for effervescence 2. if there's no effervescence, add barium chloride (BaCl2) solution
78
what happens in the sulfate test if SO4 2- ions are present
they will form a white precipitate with Ba2+ ions from the BaCl2
79
what does the equation for the formation of the white precipitate (BaSO4) look like
Ba2+(aq) + SO4 2-(aq) --> BaSO4(s)
80
why is it important to add the HCl in step 1 of the sulfate test
because carbonate ions also form a white precipitate with Ba2+ ions. by only continuing to step 2 if there's no effervescence, we can prevent a false positive

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