chemistry; chemical reactions

explanation and representation of chemical reactions

How to Know if Something is Acidic or Basic (pH Scale)

• The pH scale is like a ruler that tells if something is acidic, neutral, or basic (alkaline).

• It goes from 0 to 14:

  • Acidic: pH<7(More H+ ions)

  • Neutral: pH=7

  • Basic: pH>7(More H− ions)

  How to Test if Something is Acidic, Neutral, or Basic

  • indicators, are things that change color when they touch acids or bases.

    • Litmus paper: Turns red in acid, blue in base.

    • Universal indicator: Changes into many different colors depending on pH.

  • pH meters are little machines that measure pH exactly by giving a number.

common acids and bases

💧 Acids (Taste sour, react with metals)

• HCl (Hydrochloric acid) – In your stomach (helps digest food).

• H₂SO₄ (Sulfuric acid) – Inside car batteries.

• HNO₃ (Nitric acid) – Used to make fertilizer for plants.

• H₃PO₄ (Phosphoric acid) – In some sodas (like cola).

🧼 Bases (Feel slippery, taste bitter)

• NaOH (Sodium hydroxide) – In soap.

• KOH (Potassium hydroxide) – In batteries.

• Ca(OH)₂ (Calcium hydroxide) – Used in cement (for buildings).

• Mg(OH)₂ (Magnesium hydroxide) – In antacids (medicine for heartburn).

Acidic, basic (alkaline) or neutral aqueous solutions

What Happens When You Mix Acids and Bases?

• If you mix an acid and a base, they cancel each other out. This is called neutralization.

• Why is this useful?

  • Swimming pools – If the water is too acidic, people add a base to balance it.

  • Aquariums – Some fish need water at the right pH to live.

Acid-base chemical reactions

Acid-Base Reactions (How They Work in Chemistry)

• Acid-base reactions are fundamental chemical reactions that involve the transfer of protons (H+) between substances.

• When an acid and a base mix, they make salt and water.

• General Reaction

  Acid+Base→Salt+Water

• Example:
  HCl + NaOH → NaCl + H₂O
  (Hydrochloric acid + Sodium hydroxide → Table salt + Water)

Highly and slightly soluble salts

Why Some Salts Dissolve in Water and Some Don’t

• Some salts dissolve completely, like table salt (NaCl) in water.

• Some do not dissolve well, like chalk (CaCO₃), which just sits at the bottom.

• A salt dissolves in water when the hydration energy is greater than or comparable to the lattice energy.

Chemical reactions of precipitation

What is a Precipitation Reaction?

• A precipitation reaction is a reaction where two solutions mix, and an insoluble salt (precipitate) forms.

How Stalactites and Stalagmites Form in Caves

• Water drips from the top of a cave, leaving behind tiny rock particles.

• Over hundreds of years, these tiny bits build up and form:

  • Stalactites → Hang from the ceiling.

  • Stalagmites → Grow from the floor.

  • Stalactites – They “hold tight” to the ceiling.

  • Stalagmites – They “might” reach the top!

Whats hard water?

• Hard water is water that contains a high amount of dissolved minerals, mainly calcium (Ca2) and magnesium (Mg2) ions.

• It is called hard because it makes it harder for soap to lather (foam) properly.

• It can also cause scale buildup in pipes, kettles, and boilers.

How Do We Fix Hard Water?

• Hard water damages washing machines and kettles.

• Ways to fix it:

  • Boil water (removes some hardness).

  • Add special chemicals (like washing soda).

  • Use a water softener (a machine that removes bad minerals).