Unit1Topic9 - Tests For Ions

Question 1

Definition of a salt

Answer 1

A salt is a compound that consists of at least two ions, a positive ion (the cation) and a negative ion (the anion) e.g. NaCl and CuSO4

Question 2

Describe the process of a flame test

Answer 2

(1) adjust regulating collar, light the Bunsen and ensure a hot Bunsen flame
(2) dip the nichrome wire into concentrated hydrochloric acid to clean it
(3) dip nichrome wire into a solution and hold it in a roaring Bunsen flame
(4) observe the colour of the flame and identify which cation is present
(5) repeat to identify the unknown solution

Question 3

Colour of flame: sodium Na+

Answer 3

Yellow

Question 4

Colour of flame: potassium K+

Answer 4

Lilac

Question 5

Colour of flame: calcium Ca+

Answer 5

Brick red

Question 6

Colour of flame: barium Ba2+

Answer 6

Apple green

Question 7

Colour of flame: copper Cu2+

Answer 7

Green/blue

Question 8

What are flame tests used for?

Answer 8

To indicate the presence of various metal ions as the flame will turn a characteristic colour

Question 9

Definition of a precipitate

Answer 9

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

Question 10

Sodium hydroxide solution will form ………, coloured ……… ……… precipitates when added to different salt solutions.

Answer 10

Gelatinous

Metal hydroxide

Question 11

Salt: magnesium chloride Mg2+
Colour of precipitate: ……
Redissolve is excess NaOH: …

Answer 11

White

No

Question 12

Salt: aluminium chloride Al3+
Colour of precipitate: ……
Redissolve is excess NaOH: …

Answer 12

White

Yes

Question 13

Salt: zinc (ii) chloride Zn2+
Colour of precipitate: ……
Redissolve is excess NaOH: …

Answer 13

White

Yes

Question 14

Salt: copper (ii) chloride Cu2+
Colour of precipitate: ……
Redissolve is excess NaOH: …

Answer 14

Blue

No

Question 15

Salt: iron (ii) chloride Fe2+
Colour of precipitate: ……
Redissolve is excess NaOH: …

Answer 15

Green

No

Question 16

Salt: iron (iii) chloride Fe3+
Colour of precipitate: ……
Redissolve is excess NaOH: …

Answer 16

Red-brown

No

Question 17

Ionic equation for the formation of the precipitate formed when magnesium chloride reacts with sodium hydroxide solution.

Answer 17

Mg2+ (aq) + 2OH- (aq) -> Mg(OH)2 (s)

Question 18

Ionic equation for the formation of the precipitate formed when aluminium chloride reacts with sodium hydroxide solution.

Answer 18

Al3+ (aq) + 3OH- (aq) -> Al(OH)3 (s)

Question 19

Ionic equation for the formation of the precipitate formed when zinc (ii) chloride reacts with sodium hydroxide solution.

Answer 19

Zn2+ (aq) + 2OH- (aq) -> Zn(OH)2 (s)

Question 20

Ionic equation for the formation of the precipitate formed when copper (ii) chloride reacts with sodium hydroxide solution.

Answer 20

Cu2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s)

Question 21

Ionic equation for the formation of the precipitate formed when iron (ii) chloride reacts with sodium hydroxide solution.

Answer 21

Fe2+ (aq) + 2OH- (aq) -> Fe(OH)2 (s)

Question 22

Ionic equation for the formation of the precipitate formed when iron (iii) chloride reacts with sodium hydroxide solution.

Answer 22

Fe3+ (aq) + 3OH- (aq) -> Fe(OH)3 (s)

Question 23

We can use ……… ……… ……… to detect the presence of the halide ions.

Answer 23

Silver nitrate solution

Question 24

Solution: sodium chloride
Halide ion present: …
Colour of precipitate: …
Ionic equation of silver halide formation: …

Answer 24

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

Question 25

Solution: potassium bromide Halide ion present: … Colour of precipitate: … Ionic equation of silver halide formation: …

Answer 25

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

Question 26

Solution: sodium iodide Halide ion present: … Colour of precipitate: … Ionic equation of silver halide formation: …

Answer 26

I- Yellow Ag+ (aq) + I- (aq)->AgI (s)

Question 27

Describe the test for halide ions

Answer 27

When silver nitrate solution reacts with salt solutions containing a halide ion, a characteristic coloured precipitate of the silver halide is produced

Question 28

Describe the test for sulfate ions

Answer 28

If sulfate ions are present a white precipitate of barium sulfate will form when the sample is reacted with barium chloride solution. This is bc barium sulfate is insoluble in water.

Question 29

Give the ionic equation when testing for sulfate ions

Answer 29

Ba2+ (aq) + SO42- (aq) -> BaSO4 (s)

Question 30

Equation for testing for carbonate ions

Answer 30

acid + metal carbonate -> salt + water + carbon dioxide

Question 31

The presence of carbon dioxide gas is tested by…

Answer 31

Bubbling it through limewater. If carbon dioxide is present the limewater will turn cloudy.

Question 32

Observations when testing for carbonate ions

Answer 32

Bubbles of gas Solid disappears Limewater turns cloudy