Tests for metal ions

Question 1

flame test steps

Answer 1

1) heat a nichrome wire
2) dip it into a beaker with a small amount of hydrochloric acid (to clean it)
3) pick up a substance on the loop and burn it in the blue flame to observe the colour

Question 2

What type of metal ions do flame tests test for?

Answer 2

positive ions

Question 3

results of flame tests for:

Li+
Na+
K+
Ca[2+]
CU[2+]

Answer 3

Li+: red

Na+: yellow

K+: lilac

Ca[2+]: orange-red

CU[2+]: blue-green

Question 4

precipitate

Answer 4

insoluble solid formed from two reacting liquids

will make the solution turn cloudy

Question 5

sodium hydroxide test/hydroxide precipitates steps

Answer 5

1) place some of the sample solution in a test tube
2) add a few drops of dilute sodium hydroxide solution
3) observe the colour

Question 6

results of NaOH tests for:

Fe[2+]
Fe[3+]
Cu[2+]
Ca[2+]
Al[3-]

Answer 6

Fe[2+]: green

Fe[3+]: brown

Cu[2+]: blue

Ca[2+]: white

Al[3-]: white

Question 7

How do you tell the difference between calcium and aluminium when the NaOH test gives the same colour?

Answer 7

add more NaOH solution
the precipitate in the Al solution dissolves, leaving it colourless
the Ca solution doesn’t change

(or you could use this if you has access to other tests:)
calcium turns red in the flame tests
aluminium has no colour in the flame test

Question 8

Complete the equation:

FeSO[4] + 2NaOH -> ? + Na[2]SO[4]
aq) (aq) (s) (aq

Answer 8

FeSO[4] + 2NaOH -> Fe(OH)[2] + Na[2]SO[4]

aq) (aq) (s) (aq

Question 9

Why does the positive ion bond with the hydroxide?

Answer 9

the hydroxide has a negative charge, so the positive ion is attracted to it

Question 10

Complete the equation:

copper sulfate + sodium hydroxide -> ? + ?

Answer 10

copper sulfate + sodium hydroxide -> copper hydroxide + sodium sulfate

Question 11

Complete the symbol equation for this word equation:

iron (II) sulfate + sodium hydroxide -> iron (II) hydroxide + sodium sulfate

Answer 11

Fe2[3] + 2NaOH -> Fe2[2] + Na2[3]

aq) (aq) (s) (aq

Question 12

What type of elements form coloured precipitates in the NaOH test?

Answer 12

transition metals

calcium and aluminium are not transition metals

Question 13

Describe how to distinguish between the hydroxide precipitate formed by aluminum ions and that formed by calcium ions. [2]

Answer 13

add excess sodium hydroxide solution

the aluminium hydroxide precipitate dissolves (forming a colourless solution) but the calcium hydroxide precipitate does not

Question 14

Describe a laboratory test to distinguish between iron(II) chloride solution and iron(III) chloride solution. [3]

Answer 14

add sodium hydroxide solution

iron(II) chloride forms a green precipitate, but iron(III) chloride forms a brown precipitate

Question 15

Suggest a reason that explains why it is difficult to identify a mixture of ions in a flame test. [1]

Answer 15

the different colours interfere with each other

Question 16

Describe two different ways in which copper ions, Cu[2+], may be detected. [2]

Answer 16

the flame test gives a blue-green flame

addition of sodium hydroxide solution gives a blue precipitate