Topic 7-Testing For Ions

Question 1

What is a salt

Answer 1

A salt is a substance that consists of two ions, a positive ion- cation and a negative ion- anion

Question 2

Method of the flame tests for the presence of cation

Answer 2

~ assemble the apparatus and light the Bunsen Burner. Adjust the regulating collar to open the hole on the Bunsen burner and ensure a hot Bunsen flame
~ clean the flame test rod by dipping into concentrated hydrochloric acid
~ hold the flame test rod in the hot Bunsen flame. Repeat until the wire does not produce any colour in the flame.
~ dip the clean flame test rod into the concentrated hydrochloride acid again and dip into a small amount of the unknown solution.
~ place the rod in the Bunsen flame
~ observe the colour of the flame and identify the cation present
~repeat to identify the unknown solution

Question 3

Flame test for Na+ colour

Answer 3

Yellow

Question 4

Flame test for K+ colour

Answer 4

Lilac

Question 5

Flame test for Ba+ colour

Answer 5

Apple green

Question 6

Flame test for Ca+ colour

Answer 6

Brick red

Question 7

Flame test for Cu+ colour

Answer 7

Blue/ green

Question 8

What is a precipitate

Answer 8

A precipitate is an insoluble substance which is sometimes formed when two aqueous solutions are mixed

Question 9

Identifying cations by using …..

Answer 9

NaOH-

Question 10

Method of testing for cations using NaOH-

Answer 10

1) . Dissolve one spatula of the salt in a little H20
2) . Place 10cm3 of the solution in a test tube
3) . Add NaOH- solution drop by drop
4) . Observe the colour of the precipitate if one it produced
5) . For any white precipitate that is produced, continue to add NaOH- solution, drop by drop
6) . Observe what happens to the precipitate

Question 11

What is the colour of the precipitate when MgCl is tested for identifying cations using NaOH- and does it dissolve in excess?And work out the ionic equation

Answer 11

White
No
Mg2+(aq) + 2OH-(aq) —> Mg(OH)2(s)

Question 12

What is the colour of the precipitate when AlCl is tested for identifying cations using NaOH- and does it dissolve in excess?
And work out the ionic equation

Answer 12

White
Yes
Al3+(aq) + 3OH-(aq) —> Al(OH)3(s)

Question 13

What is the colour of the precipitate when Zn(ll)Cl is tested for identifying cations using NaOH- and does it dissolve in excess?
And work out the ionic equation

Answer 13

White
Yes
Zn2+(aq) + 2OH-(aq) —> Zn(OH)2(s)

Question 14

What is the colour of the precipitate when Cu(ll)Cl is tested for identifying cations using NaOH- and does it dissolve in excess?
And work out the ionic equation

Answer 14

Blue
No
Cu2+(aq) + 2OH-(aq) —> Cu(OH)2(s)

Question 15

What is the colour of the precipitate when Fe(ll)Cl is tested for identifying cations using NaOH- and does it dissolve in excess?
And work out the ionic equation

Answer 15

Green
No
Fe2+(aq) + 2OH-(aq) —> Fe(OH)2(s)

Question 16

What is the colour of the precipitate when Fe(lll)Cl is tested for identifying cations using NaOH- and does it dissolve in excess?
And work out the ionic equation

Answer 16

Red- brown
No
Fe3+(aq) + 3OH-(aq) —> Fe(OH)3(s)

Question 17

While testing for halide ions (group VII) we have to use …

Answer 17

Nitric acid —> HNO3

AgNO3

Question 18

What is the method for testing for halide ions

Answer 18

1) . Dissolve a spatula of the solid in 20cm3 water
2) . Place 5cm3 of the solution in a test tube
3) . Add four drop of HNO3
4) . Add AgNO3 drop by drop
5) . Observe the colour of the precipitate of one is produced

Question 19

While testing for halide ions and using AgNO3 in the test for NaCl what is the…

~ Halide ion present
~ Colour of the precipitate
~ ionic equation

Answer 19

Cl-
White
Ag+(aq) + Cl-(aq) —> AgCl(s)

Question 20

While testing for halide ions and using AgNO3 in the test for KBr what is the…

~ Halide ion present
~ Colour of the precipitate
~ ionic equation

Answer 20

Br-
Cream
Ag+(aq) + Br-(aq) —> AgBr(s)

Question 21

While testing for halide ions and using AgNO3 in the test for NaI what is the…

~ Halide ion present
~ Colour of the precipitate
~ ionic equation

Answer 21

I-
Yellow
Ag+(aq) + I-(aq) —> AgI(s)

Question 22

If sulphate ions are present a _______ _________ of BaSo4(s) will form when the sample is reacted with ……..

Answer 22

White precipitate

BaCl solution

Question 23

While testing for sultan ions we have to use…

Answer 23

BaCl

Question 24

What is the method used if you are testing for sulfate ions

Answer 24

~ dissolve a spatula of the salt in 20cm3 of deionised H20
~ place about 10cm3 of the solution into a test tube
~ add BaCl solution drop by drop
~ observe the colour of the precipitate if one is produced

Question 25

When testing for sulfate ions using BaCl we test on AlSO4. Is there a sulfate ion present, what is the colour of the precipitate and what is the ionic equation

Answer 25

Yes White Ba2+(aq) + SO4,2-(aq)—> BaSO4(s)

Question 26

When testing for sulfate ions using BaCl we test on MgCl. Is there a sulfate ion present, what is the colour of the precipitate and what is the ionic equation

Answer 26

No None No precipitate

Question 27

When testing for sulfate ions using BaCl we test on NaSO4. Is there a sulfate ion present, what is the colour of the precipitate and what is the ionic equation

Answer 27

Yes White Ba2+(aq) + SO4,2-(aq)—> BaSO4(s)

Question 28

Testing for carbonate CO3,2- ions we use

Answer 28

Limewater | Hydrochloride acid

Question 29

Acid + metal—>

Answer 29

Salt + H2O + CO2

Question 30

The method we use to test for carbonate

Answer 30

~ place the solid into a side arm test tube which has a downward delivery tube attached ~ fill a test tube with limewater and place the downward delivery tube in the test tube ~ add 5cm3 of HCl to the side arm test tube and quickly put the bung on ~ if the limewater becomes cloudy/ milky the gas evolved is CO2 and the salt is carbonate

Question 31

Testing for carbonate by using magnesium carbonate, what reactions will take place?

Answer 31

- bubbles of gas - solid disappears - limewater turns cloudy

Question 32

Testing for carbonate by using magnesium carbonate, what reactions will take place?

Answer 32

- bubbles of gas - solid disappears - limewater turns cloudy