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chemistry > Chemical tests - TN > Flashcards

Chemical tests - TN Flashcards

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1
Q

test for hydrogen

A

burn it in oxygen
hear a squeaky pop

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2
Q

why is a squeaky pop heard when hydrogen is burnt in oxygen

A

all the hot gas rushing out of the test tube

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3
Q

test for oxygen and why

A

a glowing splint relighting - the oxygen in the tube is more concentrated than in normal air so the wood in the splint combusts faster

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4
Q

how to test for the presence of water

A

anhydrous copper sulfate turning white to blue

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5
Q

how to test the purity of water

A

measure its boiling point - 100*C

closer to 100*C = more pure

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6
Q

test for carbon dioxide and why

A

bubble it through limewater - limewater is a saturated calcium hydroxide solution. it forms a white precipitate of calcium carbonate when it reacts with CO2

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7
Q

test for chlorine

A

damp (the cl dissolves into the H2O) blue litmus turning blue to white - cl is a bleaching agent so it removes the colour.

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8
Q

test for ammonia and why

A

damp red litmus turning red to blue

NH3 reacting with the H2O to form OH- ions which are alkaline = blue colour

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9
Q

what is a cation

A

a positive ion

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10
Q

what kind of flame is needed on a Bunsen burner in order to carry out a flame test

A

a non-luminous (blue) flame

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11
Q

3 steps to conduct a flame test

A
  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
  3. place the tip of the wire into a non-luminous bunsen flame
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12
Q

flame test colour of lithium

A

red

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13
Q

flame test colour of sodium

A

yellow

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14
Q

flame test colour of potassium

A

lilac

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15
Q

flame test colour of calcium

A

orange-red

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16
Q

flame test colour of copper

A

blue-green

17
Q

how to test for copper without using a flame test

A

sodium hydroxide solution with a blue precipitate forming

18
Q

how to test for iron (II)

A

sodium hydroxide solution with a green precipitate forming

19
Q

how to test for iron (III)

A

sodium hydroxide solution with a brown precipitate forming

20
Q

how to conduct a sodium hydroxide test

A
  1. dissolve the sample in water
  2. add a few drops of NaOH
21
Q

how to test for ammonium (NH4)

A

sodium hydroxide solution - creates a gas that turns damp red litmus paper from red to blue

22
Q

chemical formula of ammonia

A

NH3

23
Q

chemical formula of ammonium

A

NH4

24
Q

what are the 3 steps for testing ammonium

A
  1. dissolve the sample in water
  2. add some NaOH and warm it
  3. test the gas evolved with damp red litmus paper (ammonia test)

it NH4 ions are present the paper will turn blue

25
Q

what is an anion

A

a negatively charged ion

26
Q

how to test for halides

A

silver nitrate test

27
Q

what are the 3 steps of the silver nitrate test

A
  1. dissolve the sample in water
  2. add nitric acid
  3. add silver nitrate solution

is cl, br, or i ions are present, a precipitate forms with the Ag ions from the AgNO

28
Q

during a silver nitrate test for halide ions: what colour does Chloride turn

A

white precipitate

29
Q

during a silver nitrate test for halide ions: what colour does bromide turn

A

cream precipitate

30
Q

during a silver nitrate test for halide ions: what colour does iodide turn

A

yellow precipitate

31
Q

why do you add nitric acid first when performing a silver nitrate test

A

because the Ag ions that we need to react with the halides, also react and forms precipitates with other anions such as OH- and CO3. the HNO3 reacts with those anions preventing false positives

32
Q

how to test for carbonates

A
  1. add hydrochloric acid, look for effervescence
  2. if there is effervescence, bubble the gas through limewater

if a carbonate is present, the limewater will turn cloudy

33
Q

why do we bubble the gas created (during a test for carbonates) through limewater

A

to test if the gas is actually CO2 because acids also evolve a gas when they react with some other things. this prevents false positives

34
Q

test for sulfates

A
  1. add hydrochloric acid, look for effervescence
  2. if there is no effervescence, add barium chloride solution

is SO4 ions are present they will form a WHITE PRECIPITATE wiht the Ba ions from the BaCl

35
Q

during a test for sulfates, why do we first add hydrochloric acid

A

because carbonates also form a white precipitate with Ba ions. by only continuing to step 2 if there is no effervescence (the test for carbonates), we can prevent a false positive

chemistry (30 decks)

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