AS Chemistry T4 - Inorganic Chemistry

What is the metal Ion Test?

Flame Test

How to conduct a flame test?

1. Mix a small volume of the unknown compound with a few drop of dilute HCl

2. Heat Nichrome wire / Platinum wire with Bunsen burner to sterilize it

3. Dip the wire the sample of the compound / acid mixture over a roaring flame

4. Observe the color of the flame

Results of the Flame Test

G1 Metals

• Lithium - Red

• Sodium - Orange / Yellow

• Potassium - Lilac

• Rubidium - Red

• Caesium - Blue

G2 - Metals

• Calcium - Brick Red

• Strontium - Crimson Red

• Barium - Apple Green

How to carry out a Sulphate Ion Test?

1. Add a few drops of dilute HCl to the unknown compound solution

2. Then add a few drop of BaCl solution

3. Note what you observe

Sulphate Ion Test Result

White precipitate of barium sulfate formed means that the sulfate ions are present.

How to Test for Halides?

1. Add nitric acid to a test tube with unknown compound (Removes ions that may interfere with reaction)

2. Then add silver nitrate solution (AgNO_3(aq))

Reaction:

Ag⁺_(aq) + H^-_(aq) —> AgH_(s)

Result of a Halide Test

Precipitate of Silver Halide Color depends on the Halide

1. Fluoride Fl^-

   no precipitate, (AgF) is soluble

2. Chloride Cl^-

   white precipitate

   > dissolved in dilute ammonia - colorless solution

3. Bromide Br^-

   cream precipitate

   dissolved in dilute ammonia - ppt unchanged

   dissolved in concentrated ammonia - forms colorless solution

4. Iodide I^-

   yellow precipitate

   Insoluble

Trend in solubility: G7 - Halogens

Solubility decreases down the group

How to test for Carbonate Ions?

(CO₃^2-) and (HCO₃^-)

1. Add dilute HCl to the unknown compound

2. Bubble the solution through lime water

3. Observe the change in limewater

Result for Carbonate Ions

Lime water turns from colorless to cloudy

How to test for Ammonium Ions

1. Ammonium gas is alkaline

2. Add sodium hydroxide to the solution

3. Gently heat the mixture and hold damp litmus paper above it

Why does litmus paper in ammonium test have to be damp?

Litmus paper must be damp so that the ammonium gas can dissolve and make the color change

Why in the Halide test do we use nitric acid to remove impurities instead of Hydrochloric Acid (HCl)

Hydrochloric acid contains Chloride ions so it would give a positive result in the Halide test.

How to test for Hydroxide Ions? (OH^-)

1. Dip litmus paper into the solution

Results for Hydroxide Test?

If Hydroxide Ions are present red litmus paper turns blue

indicating a basic alkaline solution

Reactivity of Group 2 Metals..

Increases down the group

Reason for Trend in Reactivity (Group 2) as you go down the group?

As you go down the Group 2

• Increased shielding - shield valance electrons from attraction of the nucleus

• Increased atomic radius - valance electrons are further → reduces electrostatic attraction between valance electrons & nucleus

→ Easier to lose 2 valance electrons to form 2+ ions

Trend in Ionisation Energy Down Group 2

Ionisation Energy Decreases

Explanation for Trend in Ionisation Energy Down Group 2

• Increased shielding - shields attraction of nucleus

• Increases Atomic Radius - Valance electron experience less of an electrostatic attraction from nucleus

  Making it easier to lose 2 Valance electrons

  → Ionisation energy decreases bc less energy is required to remove valance electrons as you go down Group 2

Group 2 Metal + Water

G2 Metal + Water → Hydroxide + Hydrogen

• Metal hydroxides are alkaline solutions

Types of Inorganic Reaction: Reaction of acids

dilute Hydrochloric Acid - Strong Acid

Sodium Hydroxide - Strong base

• Acids do not simply mix with water, when they dissolve in it

• They react with water to form aqueous hydrogen Ions

e.g. HCl_(aq) —> H^+_(aq) + Cl^- _(aq)

• All dilute acids produce H⁺_(aq) - all dilute acids react similarly

Acid + Metal

Acid + Metal —> Hydrogen Gas + Ionic Metal compounds (Salts)

Types of Inorganic Reaction: Acid + Metal Oxide

Alkalis - dissolve in water to form aqueous solutions

Neutralization Reaction (Acids)

Acid + Metal Hydroxide / Metal Oxide → Salt + Water

Why do Acids & Alkalis Neutralise eachother?

Hydrogen ions react with the Hydroxide ions to form water

H⁺_(aq) + OH^-_(aq) → H₂O_(l)

Solubility of Acids: Which acid is Soluble & Which is Insoluble in water

Soluble in water…

• All common acids

Insoluble in water…

XXX

Solubility of Salts: Which salt is Soluble & Which is Insoluble in water

Soluble in water…

• All nitrates

• All chlorides…

• All sulfates…

  → Calcium & Silver sulfate are slightly soluble

• All sodium, potassium & ammonium salts

Insoluble in water…

• silver chloride & Lead Chloride

• Barium sulfate & Lead Sulfate

G2: Reaction with Oxygen (General)

2M_(s) + O_{2 (g)} —> 2MO_(s)

Magnesium + Oxygen

2Mg_(s) + O_{2 (g)} —> 2MgO_(s)

• Mg burns with a bright white flame

Calcium + Oxygen

2Ca_(s) + O_{2 (g)} —> 2CaO_(s)

• Ca burns with a red flame

Strontium + Oxygen

2Sr_(s) + O_{2 (g)} —> 2SrO_(s)

• Sr burns with red flame

OR Sr_(s) + O_{2 (g)} —> SrO_2(s)

• forms SrO₂ peroxide

Barium + Oxygen

2Ba_(s) + O_{2 (g)} —> 2BaO_(s)

• Ba burns with apple green flame

OR Ba_(s) + O_{2 (g)} —> BaO_2(s)

• Ba forms BaO₂ peroxide

G2 Metals Reaction with Water (General) Equation

M_(s) + 2H₂O_(l) → M(OH)_(s) + H_2(g)

Beryllium + Water

Be doesn’t react with water

No reaction

Magnesium + Water

Magnesium doesn’t react with water

Magnesium reacts vigorously with steam

Mg_(s) + H₂O_(l) → MgO_(s) + H₂

_{Magnesium + water → magnesium oxide + hydrogen gas}

Calcium + Water

Ca_(s) + 2H₂O_(l) → Ca(OH)_(s) + H_2(g)

• Reacts moderately with cold water

• Forms strontium hydroxide + Hydrogen gas

Strontium + Water

Sr_(s) + 2H₂O_(l) → Sr(OH)_(s) + H_2(g)

• Reacts rapidly with cold water

• Forms strontium hydroxide + Hydrogen gas