Grade 9

Grade 9


Acids, Bases and Salts


Understanding acids, bases, and salts is an essential part of chemistry, especially at the high school level. These compounds play a vital role in various chemical processes and everyday life applications. Let's learn in detail about the characteristics, reactions, and applications of acids, bases, and salts.

What are acids?

Acids are substances that taste sour and have a pH level less than 7. They are commonly found in foods and have properties that can be used in many chemical processes.

Properties of acids

  • Their taste is sour.
  • They turn blue litmus paper red.
  • They can conduct electricity in a solution.
  • They react with bases to form salt and water.
  • They release hydrogen ions (H+) in aqueous solution.

Here is a visual representation of an acid molecule:

H A

Examples of common acids

  • Hydrochloric acid (HCl) – found in stomach acid
  • Citric acid (C6H8O7) – found in citrus fruits such as lemons and oranges
  • Sulfuric acid (H2SO4) - used in car batteries
  • Acetic acid (CH3COOH) - found in vinegar

What are the bases?

Bases are compounds that, unlike acids, are bitter-tasting and slippery. They play an important role as cleaning agents and in other chemical reactions.

Properties of bases

  • Bitter in taste.
  • They turn red litmus paper blue.
  • They can conduct electricity in a solution.
  • Reacts with acids to form salt and water.
  • Release hydroxide ions (OH -) in aqueous solution.

Here is a representation of a base molecule:

Oh B

Examples of common bases

  • Sodium hydroxide (NaOH) - used in making soap
  • Calcium hydroxide (Ca(OH)2) - used in plaster
  • Ammonium hydroxide (NH4OH) - used as a cleaner
  • Potassium hydroxide (KOH) - used in batteries

Ph scale

The pH scale is a measurement of how acidic or alkaline a solution is, ranging from 0 to 14. It's important to understand where acids and bases fall on this scale.

Representation of pH scale:

0 7 14 Acidic Basic

Acids have a pH value less than 7. Neutral solutions such as pure water have a pH value of 7. Bases have a pH value greater than 7.

Salts

Salts are ionic compounds that are formed when acids react with bases. In these, a positive ion is formed from the base and a negative ion is formed from the acid.

Properties of salts

  • They may be soluble or insoluble in water.
  • Their melting point and boiling point are high.
  • They are usually neutral, that is, their pH value is close to 7.

Examples of normal salts

  • Sodium chloride (NaCl) - common table salt
  • Potassium nitrate (KNO3 ) - used in fertilizers
  • Calcium carbonate (CaCO3) - found in chalk and limestone
  • Magnesium sulfate (MgSO4 ) - used in bath salts

Formation of salts

When an acid reacts with a base, a neutralization reaction occurs, forming salt and water. Here the general reaction is shown as follows:

Acid + Base → Salt + Water

For example, when hydrochloric acid reacts with sodium hydroxide, sodium chloride and water are formed:

HCl + NaOH → NaCl + H2O

Applications and uses

Applications of acids

  • Food industry: Citric acid is used to preserve food and add a sour taste.
  • Cleaning agent: Acetic acid, found in vinegar, is used in cleaning products.
  • Industry: Sulphuric acid is used in the manufacture of fertilizers and in petroleum refining.

Applications of bases

  • Personal care: Bases such as sodium hydroxide are used in soap production.
  • Agriculture: Lime, which is calcium hydroxide, helps neutralize acidic soils.
  • Chemical industry: Ammonia solution is used as a cleaning agent in industries.

Applications of salts

  • Preservation: Sodium chloride is used to preserve foods by preventing the growth of bacteria.
  • Health care: Epsom salts (magnesium sulfate) are used to relieve muscle pain.
  • Construction: Calcium carbonate is an essential building material as it is found in cement and lime.

Conclusion

Acids, bases and salts are fundamental components of chemical reactions in both natural and industrial processes. By understanding their properties and reactions, we can effectively apply this knowledge to everyday applications, from food production to cleaning and industry.

These compounds highlight the complex nature of chemical interactions and their wide applications, and provide essential skills in many areas of study and work.


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