Water: States and Properties

• Water is a colorless and transparent chemical substance and the main constituent of streams, oceans, and lakes.
• Water comprises 71% of the earth's surface, playing a vital role in sustaining life.
• The chemical formula of water is H2O, consisting of two hydrogen atoms and one oxygen atom held together by covalent bonds.

States of Water

• H2O in solid state is known as ice, water freezes at 0 °C.
• The gaseous state of water is known as water vapor, water reaches its boiling point at 100 °C converted into water vapor.

Physical Properties of Water

• Water is a colorless, odorless, and tasteless liquid.
• Water has higher thermal conductivity, specific heat, and surface tension compared to other liquids; its heat capacity is 4.1868 x 103 J kg-1 K-1.
• Water has low electrical conductivity which can be improved by adding ionic substances like salt.
• Water has its largest density at 4 °C (1 g/cm³), while the density of ice is smaller than liquid water.
• Water is a universal solvent, readily dissolving substances like acids, salts, sugar, and gases.

Chemical Properties of Water

• Water is stable at room temperature but still able to react.
• Reactive metals like Li, Na, K, Ca, Sr, and Ba react with cold water to produce H2 gas.
• Clean Mg reacts extremely slowly with cold water.
• A thin layer of insoluble Mg(OH)2 can form, preventing further reaction of Mg in cold water.

Reaction with Metals

• Reactive metals like Mg, Al, Zn, and Fe react with hot water and hot steam.
• Mg and Al react with hot water (80-90°C) to form hydroxides and H2.
• Mg, Al, Zn, and Fe react with hot steam to form oxides and H2.
• Less/non-reactive metals: Sn, Pb, Cu, Hg, Ag, Pt, and Au do not react with hot water or hot steam.

Reaction with Non-Metals

• Reactive non-metals like halogens (F2, Cl2, Br2, I2) react with water to produce acids.
• Non-reactive non-metals like C react with hot steam to produce syngas.
• C + H2O → CO + H2 produces syngas/water gas.

Reaction with Oxides

• Basic oxides like Na₂O and CaO react with water to form alkaline solutions.
• Acidic oxides like CO2, SO2, SO3, P4O10, Cl2O, and Cl2O7 react with water to give acidic solutions.

Reaction with Metal Carbides

• Metal carbides react with water to give metal hydroxide and hydrocarbon.
• Example: Be2C + 4H2O → 2Be(OH)2 + CH4.

Reaction with Metal Hydrides

• Metal hydrides react with water to give alkaline solution and H2 gas.
• Example: LiH + H2O → LiOH + H2.

React with Salts

• React with little amount of water to give hydrated salts.
• Aluminium hydrolyses with water in an exothermic reaction, example: AlCl3 + 3H2O → Al(OH)3 + 3HCl.

Importance and Uses of Water

• Agriculture depends on it for irrigation.
• The human body contains 50% to 78% water, 7 liters daily are needed to avoid dehydration.
• Water aids digestion, maintains body pH, and supports antibody movement.
• It regulates body temperature by providing a cooling effect.
• Water removes toxins through perspiration and urination.
• It's used to make emulsions and solutions and functions as a common solvent, a catalyst in certain conditions, and is important for living organisms.

Water Detection

• Anhydrous cobalt(II) chloride (CoCl2) turns from blue to red in the presence of water.
• Anhydrous copper(II) sulfate (CuSO4) changes from white to blue.

Hydrogen Gas

Introduction

• Hydrogen is a non-metal with the symbol H, its molecular formula is H2.
• It's a convenient, clean-burning fuel and can be produced from coal and water, critical in polyurethane plastics.
• Hydrogen itself is non-toxic and not carcinogenic.

States and Properties of Hydrogen

• Physical state (1 atm): white solid → colorless liquid → colorless gas.
• Colorless, odorless, tasteless and non-toxic at room temperature.
• The lightest gas is sparingly soluble in water.

Chemical Properties

• Not very reactive under standard conditions, but forms compounds with most elements.
• H2 is exploded with O2 to give water and a large amount of energy. 2H2(g) + O2(g) → 2H2O(g) + Heat energy

Reaction with Non-Metals

• Under specific conditions, H2 can react with halogens such as chlorine to give hydrogen chloride (HCl).
• Sulfur reacts with H2 giving hydrogen sulfide (H2S) at high temperatures.
• Nitrogen reacts with H2 to give ammonia (NH3) under high temperature and pressure (Haber process).
• Phosphorus reacts to give phosphorus trihydride under high temperature and pressure.

Reaction with Metals

• Reactive metals such as Li, Na, Ca, K, react at high temperature to give metal hydride.
• Metal hydrides formed conduct electricity in molten state.
• Metal hydrides react with water to give alkaline solution and H2.

Reducing Properties of Hydrogen

Hydrogen as a Reducing Agent

• It tends to react with some metal oxides at high temperature to reduce the metal oxides back to its metal elements
• H2 can also be used as a reducing agent to reduce copper(II) oxide, CuO, to Cu.

Uses of HydrogenGas

• Hydrogen is used to produce NH3 (NH₄)₂SO₄, urea, and NH₄NO₃.
• Hydrogen reacts with chlorine to give hydrochloric acid.
• Reacted with oxygen to get oxyhydrogen flame which is used to cut or weld metals.
• Used in metal extraction, as fuel in rockets, and a hydrogenating agent for polyunsaturated fats.

Hydrogen Gas Preparation (Laboratory)

• Can react with Reactive metals can react with dilute strong acid.
• Zinc and aluminum reacts with strong base to give hydrogen gas.
• Any metal elements that are more reactive than H can react with acid to give H2.

Preparation(Industry)

• Steam reforming of natural gas at high temperature to give additional H2.
• The CO produce can react with hot water vapor to give additional H2.

Hydrogen Detection

• Hydrogen gas gives a "pop" sound when tested with a light wooden splinter.

Group 1A Elements

Introduction to Group IA (Alkali Metals)

• The group IA metals, also known as alkali metals, form alkaline solutions when they react with water.
• These metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr), located in the first column of the periodic table.
• Alkali metals share similar chemical properties due to having one electron in their outermost shell.

Properties

Physical Properties

• Alkali metals are soft solids at room temperature and can be easily cut with a knife.
• They have low densities, allowing them to float on water.
• They exhibit low melting and boiling points, which decrease as you go down the group.
• Melting points of metals decrease down the group.

Chemical Properties

• Group IA elements are strong reducing agents with low ionization energy, low electronegativity, and negative electrode potentials.
• The reducing power and reactivity of elements increases down the group.
• It becomes easier to lose the outer electrons due to increasing atomic size.

Reaction with Air

• When Na and K contact with the O2 in the air at room temperature, they tend to form oxides.
• When Na is ignited in the air, it tends to give peroxide and oxide.
• When K is ignited in the air, it tends to give peroxide.

Reaction with Halogen

• Sodium and potassium react violently to form metal halides.

Reaction with Water

• Na and K Reacted with cold water to give alkaline solutions and H2.

Group IIA Elements (Alkaline Earth Metals)

Introduction

• Group IIA elements (alkaline earth metals) elements have s-block and a valence shell configuration of ns².
• They show only one oxidation state of +2 in their compounds.
• Group IIA compounds form basic oxides and hydroxides due to their metallic character.

Reactions

• IIA elements easily lose electrons to form stable ions with a noble gas configuration resulting compounds are ionic,

Trends

• Atomic and Ionic Radius increases down the group.
• Ionization Energy decreases down the group.
• Electronegativity decreases down the group.
• Melting and Boiling Points decreases down the group.
• Hardness decreases as metallic bonding becomes weaker.

Chemical Properties

• IIA elements are strong reducing agents with low ionization and electronegativity.

• Reducing power and reactivity increase down the group as its easier to loose outer electrons and atomic size increases.

• Reaction with Air: Mg and Ca reacts with oxygen and nitrogen in the air to form oxides and nitrides.

• Reaction with Halogen: Mg and Ca reacts with halogen, metal halides are formed.

• Reaction with Water: Mg and Ca reacts with water to give alkaline solutions and H₂.

• Reaction with Acid: Mg and Ca reacts with acid to give salts and H₂.

Reaction with Metal Carbides

• Metal carbides react with water to give metal hydroxide and hydrocarbon.
• Example: Be2C + 4H2O → 2Be(OH)2 + CH4.

Reaction with Carbon Dioxides

• Mg and Ca can react with some oxides (lower position in reactivity series) through redox reaction.

Chemical Testing Methods for Group 1 and Group 2 Elements

Flame Test

• Used to identify metal ions, salts, and characteristic colours are observed during the experiment.

Cation Analysis of Mg2+ and Ca2+

• By using sodium hydroxide and ammonia solution.
• Aqueous solutions of Mg2⁺ and Ca²⁺ react with sodium hydroxide and ammonia solution.

Industrial Extraction of Metals

Sodium and Potassium

• Extraction of alkali metals in industry.
• Economically, one of the most important alkali metals, is manufactured by Down's process in which NaCl is electrolysed.

Some Important Metal Compounds

Sodium Compounds

• Extraction of sodium.
• Sodium is manufactured by down's process.
• Describe different chlorine salts, production, uses and chemical properties.

Calcium Compounds

• Extraction of calcium.
• Calcium is extracted by electrolysis.
• Describe different calcium salts, production, uses and chemical properties.