The Chemistry and Uses of Acids, Bases and Salts

Topics:

• Characteristic Properties of Acids and Bases
  • Acids
  • Properties of Acids
  • Bases
  • Properties of Bases
  • Neutralization reaction
  • Oxides
  • Indicators
  • PH and Universal Indicator
  • Acidity requires water
• Preparation of Salts
  • Salts
  • Color of salts
  • Preparation of Salts
  • Properties of Salts
• Properties and Uses of Ammonia
  • Properties of Nitrogen
  • Cycle of Nitrogen
  • Haber Process
  • Fertilizer
  • Eutrophication
• Sulfuric Acid
  • Sulphur
  • Contact Process
  • Uses of Sulphur

Characteristic Properties of Acids and Bases:

Acids:

Definition:

Acids are those substances that give H+ ions in aqueous solutions. e.g. HCl → H⁺ + Cl^– e.g. H₂SO₄ → 2H⁺ + SO^2-

Strong and Weak Acids:

Types of Acids:

Properties of Acids:

Physical properties of acids:

• Have a PH value less than 7
• Are corrosive in nature
• Soluble in water
• Turn blue litmus red
• Sour in taste

Chemical Properties of acids:

• When react with metals, they produce hydrogen gas and salts
  • 2HCl + 2Na → 2NaCl + H₂
  • H₂SO₄ + Mg → MgSO₄ + H₂
• When react with metal carbonates, they produce salt, water and carbon dioxide.
  • CaCO₃ + 2HCl → H₂O + CaCl₂ + CO₂
  • MgCO₃ + H₂SO₄ → H₂O + MgSO₄ + CO₂
• When react with metal oxides, they produce salt and water
  • 2HCl + CaO → CaCl₂ + H₂O
  • 2HNO₃ + CuO → Cu (NO₃) ₂ + H₂O
• When they react with metal hydroxides, they produce salt and water.
  • HCl + NaOH → NaCl + H₂O
  • 2HCl + Mg (OH) ₂ → MgCl₂ + 2H₂O
• When react with ammonia gas, form ammonium salts.
  • HCl + NH₃ → NH₄Cl
  • H₂SO₄ + NH₃ → (NH₄) ₂ SO₄

Bases:

Bases are those substances which donate OH^– ion in aqueous solution. e.g. NaOH → Na⁺ + OH^– e.g. Mg (OH)2 → Mg²⁺ + 2OH^–

Strong and Weak Bases:

Alkali:

A base that is soluble in water is known as an alkali.

Uses of Bases:

• Mg (OH)₂, also known as Milk of Magnesia, helps control acidity,
• Ca (OH)₂, Milk of Lime or Limewater, is painted on walls.

Properties of Bases:

Physical properties of Bases:

• Have a PH value more than 7
• Are slippery to touch
• Alkalis are soluble in water
• Turn red litmus blue
• bitter in taste
• can damage skin when concentrated

Chemical Properties of Bases:

• When react with acids, they produce salt and water
  • NaOH + HCl → NaCl + H₂O
  • H₂SO₄ + 2KOH → K₂SO₄ + 2 H₂O
• When metal hydroxides react with ammonium salts, they produce ammonia, salt and water.
  • NaOH + NH₄Cl → NH₃ + NaCl + H₂O
  • 2KOH + (NH₄) ₂ SO₄ → K₂SO₄ + 2NH₃ + 2 H₂O

Neutralization Reaction:

• The reaction between acids and bases to cancel the effect of each other.
• Reaction between the H⁺ ion and the OH^– ion to form water.

Oxides:

The binary compound of oxygen with any other element of the periodic table is known as Oxide.

Types of Oxides:

• Basic oxides- Oxides of metals:
  • When they dissolve in water, they form alkalis.
  • Mostly of metals from the group 1 and group 2 of periodic table (with the exception of Zinc Oxide, Aluminum Oxide and Lead oxide)
  • Na₂O, K₂O, MgO etc.
  • Na₂O + H₂O → 2NaOH
• Acidic oxides- Oxides of non-metals:
  • When they dissolve in water, they form acids,
  • Pb₂O₅, SO₂, NO₂, CO₂ etc.
  • SO₂ + H₂O → H₂SO₃ (sulfurous acid)
• Neutral Oxides:
  • Insoluble in water
  • PH 7
  • Neutral in nature
  • Turn Universal indicator green
  • CO, H₂O
• Amphoteric Oxides:
  • Insoluble in water
  • They behave like both acids and bases
  • Zinc Oxide (ZnO), Aluminum Oxide (Al₂O₃) and Lead oxide (PbO)

Indicators:

Indicators are dyes or mixture of dyes which indicate whether a substance is an acid or a base.

Types of Indicators:

(these indicators only tell the nature of the substance; they do not tell us about the strength of the acid or base)

PH and Universal Indicator:

PH:

The negative log of H⁺ ion concentration.

• 0-6 = acids,
• 7 neutral,
• 8-14 = bases.

Universal Indicator:

UI is a mixture of different dyes that not only identifies the nature of a substance as acidic or basic, but it also tells us their strength.

PH Scale for Universal Indicator:

Soil PH:

A low PH of soil can cause some plants to die. In order to maintain the PH of soil, we neutralize it using calcium hydroxide, Ca (OH)2. Calcium hydroxide reacts with the excess acid in the soil and neutralize it, balancing the PH.

Preparation of Salts:

Salt:

When hydrogen atom is replaced by a metal, salt is formed. E.g. 2HCl + 2Na → 2NaCl + H₂

Basicity:

The number of replaceable hydrogen atoms in an acid.

• Monobasic acid: HCl, HNO₃
• Dibasic acid: H₂SO₄, H₂CO₃
• Tribasic acid: H₃PO₄

Color of Salts:

Colors of some common salts are listed below:

Preparation of Salts:

Preparation of salt using acids have been discussed above. The two other methods are:

Preparation using precipitation:

When we have to prepare salts that are insoluble, we can use the precipitation method. Precipitate is the solid salt that settles at the bottom of the reaction vessel. We react two substances which can create a solid precipitate of our required salt.

Preparation using titration:

Titration method is the most common method and will also be discussed in the ATP part.

• We take an acid that has the non-metallic part of our salt. We pipette out 25 cm3 of the acid into a conical flask and add a few drops of phenolphthalein.
• We then add the hydroxide of the metallic part of our salt using a burette (or the other hand) and titer it until the color is midway between acid and base (light pink).
• We note the volume of alkali required to neutralize 25 cm³ of the acid.
• We repeat the process without the indicator and after neutralization, we leave the solution to evaporate and crystallize.
• The crystals are filtered out and dried between folds of filter paper.

Properties of Salts:

Some properties regarding solubility of salts are:

• nitrate, Group I and ammonium compounds are soluble in water
• chlorides, except lead and silver, are soluble in water
• sulfates, except lead, barium, and calcium, as soluble in water
• carbonates and hydroxides, except Group I and ammonium, are insoluble in water

Hydrated and Anhydrous Salts:

Salts that contain water of crystallization are called hydrated salts. Salts that do not contain water of crystallization are called anhydrous salts.

Properties and Uses of Ammonia:

Properties of Nitrogen:

• Nitrogen is a basic element of life. Ammonia is the best source of nitrogen.
• In our air, there is 78% nitrogen gas.
• Nitrogen is not very reactive as it has triple covalent bond between its atoms which does not break easily.

Cycle of Nitrogen:

• Nitrogen is constantly going through a complete cycle in our environment. It starts off as nitrogen and dissolves in rainwater.
• The rainwater enters soil and nitrogen becomes the part of our soil.
• The nitrifying bacteria, that create nitrate, turn nitrogen to nitrate which is taken up by plants.
• Animals eat plants and decompose nitrogen as ammonia.

Haber Process:

The process for creating ammonia in industries is called the Haber Process. The details of the process are as follows:

• 196 degree Celsius is nitrogen’s condensation point. We turn nitrogen to liquid nitrogen by liquifying air.
• We obtain hydrogen from fossil fuels or from methane gas (CH₄).
• Nitrogen and Hydrogen are reacted together to form ammonia under certain conditions.
• N₂ + 3H₂ ⇌NH₃
• The process is exothermic, hence decreasing the temperature would help produce more ammonia but to make the process fast, we slightly increase the temperature.
• To balance the increase in temperature for preventing the backward reaction to take place, we increase the pressure to 200-300 atm.
• Temperature is kept at around 450 degrees.
• We continuously remove ammonia to reduce the product moles and shift the equilibrium to create more ammonia.
• We then recycle the leftovers to make ammonia again.
• Since the reaction is slow, we also add catalyst (Iron, Magnesium oxide, Aluminum Oxide and Silicon dioxide).
• These are the optimum conditions for production of ammonia.

Fertilizers:

There are several macronutrients in fertilizers which are the major components in any fertilizer. These include:

• Nitrogen:
  • Early growth,
  • Leaves development
  • Green color
• Phosphorous:
  • Ripening of fruit
  • Immune system
• Potassium
  • Tomato, coffee and tobacco

Ammonia reacts with carbon dioxide and makes UREA which is a very important fertilizer. We have to make sure not to apply calcium hydroxide to soil where ammonium salt is present, or it will react with the salt causing the nitrogen to leave the soil as ammonia gas.

Eutrophication:

Eutrophication is when excess fertilizer (nitrate) gets dissolved in rainwater or flooded water and ends up in rivers and canals causing water pollution. This happens due to two reasons:

• Oxidizing and consuming dissolved oxygen,
• Formation of algae that stop oxygen and sunlight to reach marine life.

Sulfuric Acid:

Sulphur:

• Solid at room temperature,
• 114 melting point Yellowish,
• Further heating makes it turn red
• At 444 degrees, the boiling point, it burns in blue flame

Oxides:

Sulphur has two oxides: Sulphur dioxide and Sulphate (trioxide)

Contact Process:

• Molten sulfur and oxygen are reacted to form Sulphur dioxide.
• Sulphur dioxide is moved to dust remover, arsenic remover and electrostatic dust remover chambers (not in syllabus)
• Then sulfur dioxide is reacted with oxygen in the contact chamber to product Sulphur trioxide.
• The reaction is reversible.
  • 2SO₂ + O₂ ⇌ 2SO₃
• Exothermic reaction
• More pressure so more SO₃ is produced.
• Speed is increased by using catalyst: V₂O₅
• Pressure is kept at 2-3 atm.
• Temperature is kept at 450-500 degrees for reasons similar to Haber Process.
• SO₃ is then reacted with sulfuric acid to produce oleum
  • H₂SO₄ + SO₃ → H₂S₂O₇
• Oleum is highly concentrated sulfuric acid, so we add water to create the required concentration of sulfuric acid.
• The reason we don’t directly dissolve SO₃ in water is that it is highly soluble, and a very violent reaction happens which is difficult to control.

Uses of Sulphur:

• Sulfur dioxide:
  • Bleach
  • in the making of paper from wood pulp
  • as a food preservative (by killing bacteria)
• sulfuric acid:
  • battery
  • acid and in the manufacture of detergents
  • fertilizers

Lesson Tags

Acid | Bases | Salts | Detailed Notes For Preparation & Revision | O Level Chemistry 5070 and IGCSE Chemistry 0620

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