ACID BASE AND SALTS

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GOVT GIRLS HIGH SCHOOL

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What is an ACID?

• pH less than 7
• Neutralizes bases
• Forms H ⁺ ions in solution
• Corrosive-reacts with most metals to form hydrogen gas
• Good conductors of electricity

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Acids Generate Ions

HNO₃ + H₂O 🡪 H₃O⁺ + NO₃

Weak vs. Strong Acids

• Weak Acids do not ionize completely: Acetic, Boric, Nitrous, Phosphoric, Sulfurous
• Strong Acids ionize completely: Hydrochloric, Nitric; Sulfuric, Hydriodic

Common Acids

• HCl- hydrochloric- stomach acid
• H₂SO₄- sulfuric acid - car batteries
• HNO₃ – nitric acid - explosives
• HC₂H₃O₂- acetic acid - vinegar
• H₂CO₃-carbonic acid – sodas
• H₃PO₄- phosphoric acid -flavorings

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What is a BASE?�

• pH greater than 7
• Feels slippery
• Dissolves fats and oils
• Usually forms OH^- ions in solution
• Neutralizes acids

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Weak vs. Strong Bases

• Weak Bases: ammonia; potassium carbonate, sodium carbonate
• Strong Bases: sodium hydroxide; sodium phosphate; barium hydroxide; calcium hydroxide

Common Bases

• NaOH- sodium hydroxide (LYE) soaps, drain cleaner
• Mg (OH)₂ - magnesium hydroxide-antacids
• Al(OH)₃-aluminum hydroxide-antacids, deodorants
• NH₄OH-ammonium hydroxide- “ammonia”

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Types of Acids and Bases

• In the 1800’s chemical concepts were based on the reactions of aqueous solutions.
• Svante Arrhenius developed a concept of acids and bases relevant to reactions in H₂O.

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• Arrhenius acid – produces hydrogen ions in water.
• Arrhenius base – produce hydroxide ions in water.

A broader ,more modern concept of acids and bases was developed later.

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Bronsted-Lowry acid- donates a hydrogen ion in a reaction.

Bronsted – Lowry base – accepts a hydrogen in a reaction.

• Conjugate acid- compound formed when an base gains a hydrogen ion.

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• Conjugate base – compound formed when an acid loses a hydrogen ion.

pH Scale

pH of Common Substances

Timberlake, Chemistry 7^th Edition, page 335

Reactions with indicators

pH paper

• pH paper changes color to indicate a specific pH value.

Buffers�

• A buffer is a solution that resists changes in pH when small amounts of acids and bases are added.

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Situations in which pH is controlled

• “Heartburn”
• Planting vegetables and flowers
• Fish Tanks and Ponds
• Blood
• Swimming pools

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Acids and Bases in Solution�

• HCl + H₂0 🡪 H₃O ⁺ + Cl^- (more hydronium ions, more acidic)
• NaOH in water 🡪 Na⁺ + OH^- (more hydroxide ions, more basic)
• NaOH + HCl 🡪 NaCl + HOH Acid + Base yields type of salt and water
• NH₃ + H₂0 🡪 NH₄⁺ + OH^- ammonia gas + water yields ammonium and hydroxide ions

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Acid Rain

Pollution in the air (sulfur dioxide, carbon dioxide, nitrogen dioxide) combines with water to form various acids.

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Rapid changes in pH can kill fish and other organisms in lakes and streams.

Soil pH is affected and can kill plants and create sinkholes

What is a SALT?

• A salt is a neutral substance produced from the reaction of an acid and a base.
• Composed of the negative ion of an acid and the positive ion of a base.
• One of the products of a Neutralization Reaction
• Examples: KCl, MgSO₄, Na₃PO₄

Neutralization Reaction

• A neutralization reaction is the reaction of an acid with a base to produce salt and water.
• Example

H₂SO4 + NaOH 🡪 NaHSO₄ + H₂O

Digestion and pH

• Digestion-process by which foods are broken down into simpler substances.
• Mechanical digestion-physical process in which food is torn apart (mouth)
• Chemical digestion- chemical reactions in which large molecules are broken down into smaller molecules. (stomach and small intestines)

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pH in the Digestive System

• Mouth-pH around 7. Saliva contains amylase, an enzyme which begins to break carbohydrates into sugars.
• Stomach- pH around 2. Proteins are broken down into amino acids by the enzyme pepsin.
• Small intestine-pH around 8. Most digestion ends. Small molecules move to bloodstream toward cells that use them

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mouth

esophagus

stomach

small intestine

large intestine

Digestive system