Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Chemical forensics
The positive (often metal) ions in salts are called cations and the negative non metal ions
in salts are called anions
...


Light a bunsen burner and open it on a roaring flame
...


Dip the end of a nichrome wire into hydrochloric acid to clean it
...


Dip the cleaned nichrome wire into the salt you are testing
...
Put it just above the inner blue cone of the flame an record the colour of the flame
...
Nichrome is used as the flame test wire because it
has a high melting point as inert
...
The colour of the precipitate can be used to identify
cations
...
Add a small amount of the solid to the test tube and add distilled water to dissolve the
solid and make a solution
...
Then add sodium hydroxide and watch the precipitate form
...
Add a small amount of the solid to the test tube and add distilled water to dissolve the
solid and make a solution
...
Add the sodium hydroxide and warm the mixture and test any gas produced with red
litmus paper made slightly wet with water
...

Symbol equation
CuSO₄ (aq) + 2NaOH (aq) ——-> Cu(OH)₂ (s) + Na₂SO₄ (aq)
Ionic equation
Cu2+ (aq) + 2OH⁻(aq) ——-> Cu(OH)₂ (s)
Reaction 2 - Iron (II) Chloride with sodium hydroxide
Symbol equation
FeCl₂ (aq) + 2NaOH (aq) ——-> Fe(OH)₂ (s) + 2NaCl (aq)
Ionic equation
Fe²⁺ (aq) + 2OH⁻ (aq) ——-> Fe(OH)₂ (s)
Reaction 3 - Iron (III) Chloride with sodium hydroxide
Symbol equation
FeCl₃ (aq) + 3NaOH (aq) ——-> Fe(OH)₃ (s) + 3NaCl (aq)
Ionic equation
Fe³⁺ (aq) + 3OH⁻ (aq) ——-> Fe(OH)₃ (s)
Reaction 4 - Ammonium Chloride with sodium hydroxide
Symbol equation
NH₄Cl (aq) + NaOH (aq) ——-> NH₃ (g) + NaCl (aq) + H₂O (l)
Ionic equation
NH₄⁺ (aq) + OH⁻ (aq) ——-> NH₃ (g) + H₂O (l)
Identifying anions in salts
Identifying halide ions using silver nitrate solution
We use silver nitrate solution (AgNO₃ (aq)) which has to be acidified with nitric acid
(HNO₃)

30

Name of anion

Formula of anion

Result

Chloride ion

Cl⁻

White precipitate

Bromide ion

Br⁻

Cream precipitate

Iodide ion

I⁻

Yellow precipitate

Word equation

Balanced equation

Ionic equation

Potassium chloride

Potassium chloride +
silver nitrate —-> Silver
chloride + Potassium
nitrate

KCl (aq) + AgNO₃ (aq)
Cl⁻ (aq) + Ag⁺ (aq) —->
—-> AgCl (s) + KNo₃ (aq) AgCl (s)

Potassium Bromide

Potassium bromide +
silver nitrate —-> Silver
bromide + Potassium
nitrate

KBr (aq) + AgNO₃ (aq)
—-> AgBr (s) + KNo₃
(aq)

Potassium Iodide

Potassium iodide + silver KI (aq) + AgNO₃ (aq) —nitrate —-> Silver iodide > AgI (s) + KNo₃ (aq)
+ Potassium nitrate

Br⁻ (aq) + Ag⁺ (aq) —->
AgBr (s)

I⁻ (aq) + Ag⁺ (aq) —-> AgI
(s)

Identifying sulfate ions (SO₄²⁻)
You can identify sulfate ions with barium chloride
...
Add distilled water to the solid to make a solution
...
Add a few drops of barium chloride solution (BaCl₂) as well as a few drops of diluted
hydrochloric acid
...

1
...

2
...

Name of anion

Formula of anion

Result

Carbonate ion

CO₃²⁻

The lime water turns cloudy

31

Identifying gases
Name

Formula

Test

Result

Hydrogen

H₂

Test with a lit splint

Burns with a squeaky
pop

Oxygen

O₂

Test with a glowing splint

Glowing splint reignites

Carbon dioxide

CO₂

Bubble gas through
limewater (calcium
hydroxide solution)

Lime water turns cloudy
(white precipitate
formed)

Chlorine

Cl₂

Test with damp blue
litmus paper

Litmus paper is bleached
(it looses it colour)
(chlorine gas is green)

Ammonia

NH₃

Test with damp red
litmus paper

Damp red litmus paper
turns blue (ammonia is
an alkaline gas)

32



---