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Chemistry > Chemical Tests > Flashcards

Chemical Tests Flashcards

1
Q

What is qualitative analysis

A

Qualitative analysis is the process of performing chemical tests on unknown compounds to determine their identity. These include tests for cations and anions

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2
Q

Describe the process of a flame test

A

Dip the tip of a platinum wire into concentrated hydrochloric acid and then in the flame of a bunsen burner in order to clean it and ensure that it doesn’t color the flame from previous tests. Once clean, the wire is dipped again in acid and used to pick up a few crystals of the compound to be tested. When the wire is held at the end of a blue, non-luminous flame, a new color in the flame will appear

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3
Q

What color does the lithium cation (Li+) produce

A

Red

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4
Q

What color does the sodium cation (Na+) produce

A

Orange

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5
Q

What color does the potassium cation (K+) produce

A

Lilac

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6
Q

What color does the calcium cation (Ca2+) produce

A

Orange red

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7
Q

What color does the copper cation (Cu2+) produce

A

Green

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8
Q

Why should the platinum wire be cleaned first before using it for the flame test

A

To avoid contamination and ensure that the wire won’t color the flame from previous tests

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9
Q

Why is a non-luminous flame used

A

A non-luminous flame is used to clearly see the color of the cation. The yellow color of the luminous flame would mask the color and visibility of the flame color of the test sample

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10
Q

What are the two possible tests for cations and which cations are they for

A

Flame test: Lithium, Sodium, Potassium, Calcium, Copper(II)

Adding sodium hydroxide solution: Copper(II), Iron(II), Iron(III)

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11
Q

Describe the process of adding sodium hydroxide to identify a cation

A

Add aqueous sodium hydroxide solution dropwise and then in excess to an aqueous solution containing a metal cation. This will produce a metal hydroxide. Since most metal hydroxides are insoluble, the color of the insoluble precipitate can be used to identify the cation

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12
Q

What color is the precipitate produced when adding sodium hydroxide to copper(II) cations

A

Blue

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13
Q

What color is the precipitate produced when adding sodium hydroxide to copper(II) cations

A

Blue

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14
Q

What color is the precipitate produced when adding sodium hydroxide to iron(II) cations

A

Green

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15
Q

What color is the precipitate produced when adding sodium hydroxide to iron(III) cations

A

Yellow/orange

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16
Q

Why can’t potassium ions be identified by adding sodium hydroxide

A

Potassium’s hydroxide is soluble

17
Q

What is the test for ammonium cation

A

Add Sodium hydroxide and heat the mixture. Ammonia gas will form, which is colorless. However it can turn moist red litmus paper blue

18
Q

What are the tests for anions and which anions are they for

A

Add solutions of nitric acid and silver nitrate: chloride ions, bromide ion, iodide ions (halides)

Add solutions of nitric acid or hydrochloric acid: Carbonate ions

Add solutions of hydrochloric acid and barium chloride: Sulfate ions

19
Q

Describe the test for halides

A

Add dilute nitric acid in order to remove the carbonate ions present. Then add an aqueous solution of silver nitrate (AgNo3) and observe the precipitate form

20
Q

Why is nitric acid added in the test for halides

A

The acid is added to remove carbonate ions. If carbonate ions were present, they would react with silver ions and form a white silver carbonate precipitate that would interfere with the results. Adding the acid dissolves the precipitate with effervescence

21
Q

Why is Hydrochloric acid not used for the test instead of nitric acid

A

Hydrochloric acid also had chloride ions, and thus you cannot confirm that the formation of the white precipitate is because of their presence in the compound and not in the acid

22
Q

What color is the precipitate produced when adding silver nitrate to chloride anions

A

White

23
Q

What color is the precipitate produced when adding silver nitrate to bromide anions

A

Cream

24
Q

What color is the precipitate produced when adding silver nitrate to iodide anions

A

Yellow

25
Q

Describe the test for sulfate

A

Add aqueous barium chloride and dilute hydrochloric acid in the solution. A white precipitate should form

26
Q

What color is the precipitate produced when adding barium chloride to sulfate anions

A

White

27
Q

Describe the test for carbonate

A

Add aqueous nitric acid. Vigorous effervescnece is produced and a colorless gas. If the gas turn limewater cloudy, then the anion is carbonate

28
Q

What is the test for ammonia

A

Hold damp red litmus paper to the mouth of a tube. The red litmus paper will turn blue

29
Q

What is the test for carbon dioxide

A

Carbon dioxide is bubbled through limewater. The limewater should turn cloudy

30
Q

What is the test for hydrogen

A

Hold a lighted splint near the mouth of a tube. A pop sound should be heard

31
Q

What is the test for oxygen

A

Hold a glowing splint near the mouth of a tube. Oxygen should relight it

32
Q

What is the test for chlorine

A

Hold damp litmus paper near the mouth of a tube. It should bleach the paper

Chemistry (5 decks)

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