Indicators and pH Scale

Indicators and pH Scale

• Litmus, phenolphthalein, and methyl orange are indicators used to identify acidity or alkalinity.
• Litmus turns red in acids and blue in alkalis.
• Phenolphthalein is colourless in acids and pink in alkalis,
• Methyl orange is red in acidic solutions and yellow in alkaline solutions.
• The pH scale ranges from 0 to 14.
• pH 0-6 is acidic, with 0 being strongly acidic.
• pH 7 is neutral.
• pH 8-14 is alkaline, with 14 being strongly alkaline.
• Universal indicator shows a range of colors, from red (strong acid) to purple (strong alkali). This helps estimate the pH of a solution.

Acids and Alkalis

• Acids release hydrogen ions (H⁺) in water.
• Alkalis release hydroxide ions (OH⁻) in water.
• Alkalis neutralize acids, forming water and salts.

Titrations

• Titration determines the concentration of an unknown acid or alkali.
• A known concentration of alkali is added to an acid until neutralization occurs.
• Steps include measuring acid volume, adding indicator drops, filling a burette with alkali, slowly adding alkali until color change, then recording alkali volume.
• Calculations from volume and concentrations allow determination of the unknown concentration..

Solubility Rules

• Soluble compounds include most nitrates, sodium, potassium, and ammonium compounds. Most chlorides are soluble except silver and lead chlorides. Most sulfates are soluble except barium, calcium, and lead sulfates.
• Insoluble compounds include most carbonates (except those of sodium, potassium, and ammonium) and most hydroxides (except those of sodium, potassium, and calcium).

Acids and Bases (Proton Transfer)

• Acids are proton donors (release H⁺ ions in solution).
• Bases are proton acceptors.
• Alkalis are soluble bases releasing OH⁻ ions.

Reactions of Acids

• Acids and metals react to produce hydrogen gas and salts. (Example: Zn + 2HCl → ZnCl₂ + H₂)
• Acids and bases(e.g., alkaline hydroxides, oxides, ammonia) react to form salts and water.(Example: HCl + NaOH → NaCl + H₂O)
• Acids and metal carbonates react to form salts, water, and carbon dioxide. (Example: 2HCl + CaCO₃ → CaCl₂ + H₂O + CO₂)

Preparation of Salts (Methods)

• Insoluble salts can be prepared by mixing two solutions of soluble salts that form an insoluble product. This is then filtered and dried. (Example: BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl)
• Soluble salts can be prepared by neutralizing an acid with an alkali, evaporating the produced solution.
• A third method is using an insoluble base reacted with the acid, filtering, then evaporating the solution. -A fourth method involves using excess metal oxide to a suitable acid. This reacts to produce a salt and water. The solution is filtered to remove excess metal oxide, then evaporated to obtain crystals of the salt. (Example of preparation of copper sulfate). Examples and methods are provided for different salts (e.g., copper(II) sulfate, lead(II) sulfate.

How to Write Ionic Equations

• Write the full equation for the reaction.
• Identify the soluble ions in the reactants and products.
• Remove spectator ions (ions that don't change in the reaction), then write the net ionic equation.