Non-Metal Oxides and Chemical Reactions

Non-Metal Oxides

• Formed when non-metals react with oxygen
• Not all non-metal oxides are dioxides (e.g., phosphorus pentoxide and water)

Important Points

• Systematic names follow IUPAC rules for consistency and clarity
• Chemical equations must be balanced to reflect the conservation of mass

Practice

• Word equation for the reaction between nitrogen and oxygen to form nitrogen dioxide:
  • Nitrogen + oxygen → nitrogen dioxide
• Chemical equation for the reaction of nitrogen and oxygen:
  • N₂ + 2O₂ → 2NO₂

pH Value

Key Concepts

• Acids and bases: characteristics and classifications
• pH value: measurement of acidity or basicity
• Indicators: substances that show whether a solution is acidic or basic

Characteristics of Acids and Bases

• Acids:
  • Taste sour
  • Feel rough between fingers
  • Can be corrosive
  • Can make bases lose their basic character
  • Turn blue litmus red
• Bases:
  • Taste bitter
  • Feel slippery between fingers
  • Can be corrosive
  • Can make acids lose their acidic character
  • Turn red litmus blue

Examples of Acids, Bases, and Neutral Substances

• Acids: orange juice, vinegar, lemon juice, citric acid, gastric acid (stomach acid)
• Bases: bicarbonate of soda, soaps, bleach, ammonia solution
• Neutral substances: water, table salt solution, cooking oil

Indicators

• Substances that show whether a solution is acidic or basic
• Examples: litmus, phenolphthalein, and methyl orange

Measuring Acidity and Basicity

• pH scale: measures the acidity of a substance, ranging from 1 to 14
• pH values:
  • Acidic: below 7
  • Basic: above 7
  • Neutral: equal to 7
• pH origin: term "pH" was first described by Danish biochemist Søren Peter Lauritz Sørensen in 1909
• pH in everyday life:
  • Shampoo: pH balanced
  • Skin soap: neutral pH
  • Swimming pool water: controlled pH

pH Example

• Lemon juice: more sour than orange juice, lower pH
• Swimming pool water: controlled pH for safe use

Diagram of pH Scale

• Acids: pH 1 to pH 6.9
• Neutral: pH 7
• Bases: pH 7.1 to pH 14

Understanding pH

• Stronger acids: closer to pH 1
• Stronger bases: closer to pH 14
• Measuring pH: using indicators

Neutralisation and pH

• pH scale: measures how acidic or basic a substance is
• Acids: pH < 7 (stronger acids have lower pH)
• Bases: pH > 7 (stronger bases have higher pH)
• Neutral: pH = 7
• Neutralisation reaction: acid + base → salt + water

Universal Indicator

• Used to measure pH of a solution by changing colors corresponding to pH scale

Experiment: Mixing Vinegar and Baking Soda

• Materials: vinegar, baking soda, universal indicator paper
• Procedure: mix each solution with universal indicator paper and observe color change
• Observation:
  • Vinegar (acid): low pH, turns indicator red/orange
  • Baking soda (base): high pH, turns indicator blue/green

Neutralisation Reaction

• Acid + base → salt + water
• Example 1: HCl + NaOH → NaCl + H₂O
• Example 2: 2HCl + MgO → MgCl₂ + H₂O
• General equation: acid + base → salt + water

Laboratory Acids and Safety

• Common laboratory acids: hydrochloric acid (HCl), nitric acid (HNO₃), sulfuric acid (H₂SO₄)
• Safety: handle with care, corrosive and hazardous

Non-Metal Oxides Forming Acids

• Non-metal oxides dissolve in water to form acids
• Examples:
  • CO₂ + H₂O → H₂CO₃ (carbonic acid)
  • SO₂ + H₂O → H₂SO₃ (sulfurous acid)
• Acid rain: formed when non-metal oxides (e.g., CO₂, SO₂) dissolve in rainwater, causing acidic solutions

Metal Oxides, Hydroxides, and Carbonates Forming Bases

• Metal oxides: form basic solutions
• Metal hydroxides: form basic solutions
• Metal carbonates: form basic solutions
• pH of metal compounds in water: typically basic solutions with pH > 7

Reaction of an Acid with a Metal Oxide

• General equation: acid + metal oxide → salt + water
• Example: reaction of magnesium oxide with hydrochloric acid
  • HCl + MgO → MgCl₂ + H₂O
• Steps to write reaction equations:
  1. Identify reactants (acid and metal oxide)
  2. Combine reactants to predict products (salt and water)
  3. Balance chemical equation to ensure equal atoms on both sides

Reaction of an Acid with a Metal Hydroxide

• General equation: acid + metal hydroxide → salt + water
• Example: reaction of sodium hydroxide with hydrochloric acid
  • HCl + NaOH → NaCl + H₂O
• Steps to write reaction equations:
  1. Identify reactants (acid and metal hydroxide)
  2. Combine reactants to predict products (salt and water)
  3. Balance chemical equation to ensure equal atoms on both sides

Reaction of an Acid with a Metal Carbonate

• General equation: acid + metal carbonate → salt + water + carbon dioxide
• Example: reaction of calcium carbonate with hydrochloric acid
  • HCl + CaCO₃ → CaCl₂ + H₂O + CO₂
• Applications of calcium carbonate:
  • Geological formations (limestone, chalk, marble)
  • Biological sources (shells, snails, pearls, oysters, bird eggshells)
  • Dietary sources (dark green leafy vegetables, calcium supplements)
  • Industrial applications (construction, adhesives, paints, ceramics, swimming pools)
  • Agricultural use (liming, neutralizing acidic soil)

Reaction of an Acid with a Metal

• General equation: acid + metal → salt + hydrogen gas
• Example: reaction of hydrochloric acid with magnesium
  • HCl + Mg → MgCl₂ + H₂
• Steps to write reaction equations:
  1. Identify reactants (acid and metal)
  2. Combine reactants to predict products (salt and hydrogen gas)
  3. Balance chemical equation to ensure equal atoms on both sides