What are Acids and Bases?
Acids are chemical substances which are characterized by a sour taste in an aqueous medium. They have the tendency to turn blue litmus red. On the other hand, bases are chemical substances which are characterized by a bitter taste and are slippery to touch. Some bases are soluble in water, while others are not.
Water soluble bases are known as alkalis. They have the tendency to turn red litmus blue. Acids and bases react with a wide range of chemical compounds to form salts.
Table of Contents
Physical Properties of Acids and Bases
The physical properties of acids and bases are listed in the table below.
| Properties | Acids | Bases |
| Colour | Mineral acids are colourless liquids but sometimes sulphuric acid becomes yellow due to impurities. Some organic acids are white-coloured solids.
Examples: benzoic acid |
Bases are colourless except for the hydroxides of iron and copper. |
| Taste | Sour | Bitter |
| Touch | – | Slippery |
| Solubility | Soluble in water | Some bases are soluble in water. They are called alkalis. |
Physical Properties of Acid
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- The word “acid” comes from the Latin word ‘acere’ which means sour. This distinguishable property helps identify acids from other compounds such as salt and bases. Many acids can be hazardous if ingested and shouldn’t be tasted.
- Once the acid binds to the base, it becomes a neutral substance. Often this reaction can lead to water and salt. This is often seen when strong acids react with strong bases.
- Acids in an aqueous solution produce hydrogen ions which are responsible for the conductivity of the solution. The acid that conducts electricity strongly is a strong acid, and the acid that conducts electricity weakly is a weak acid.
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Chemical Properties of Acid and Bases
1. Reactions of Acids and Bases with Metals
When a metal reacts with an acid, it generally displaces hydrogen from the acids. This leads to the evolution of hydrogen gas. The metals combine with the remaining part of acids to form a salt. For example, the reaction of sulphuric acid with zinc.
Alkalis (bases that are soluble in water) react with metals to produce salt and hydrogen gas. For example, reaction of zinc with sodium hydroxide.
2. The Reaction of Metal Carbonates/Metal Bicarbonates with Acids
Metal carbonates/metal bicarbonates react with acids to produce salt, carbon dioxide and water. For example the reaction of sodium carbonate/sodium bicarbonate with hydrochloric acid.
3. The Reaction of Metal Oxide with Acids
Metal oxides react with acids to produce salt and water. For example reaction of copper oxide and dilute hydrochloric acid.
4. The Reaction of Non-metal Oxide with Bases
Non-metal oxides react with bases to produce salt and water. For example the reaction of carbon dioxide and lime water (calcium hydroxide)
5. The Reaction between Acids and Bases
Acids react with bases to produce salt and water. The reaction between acids and bases to give salts is known as neutralization reactions. For example the reaction of sodium hydroxide with hydrochloric acid.
Neutralization of Acid and Base
The reaction between an acid and a base invariably gives salt and water and is called neutralization. In a neutralization reaction, one H+ ion of acid is neutralized by one OH– ion of the base. When all the H+ ions in the acidic solution are neutralized by the same number of OH– ions of the basic solution, it is called complete neutralization. The relative amounts of acid and base required for complete neutralization depend upon the total number of H+ and OH– ions produced by the respective acid and base.
Comparative Study of Properties of Acids and Bases
A comparative study of properties of acids and bases is given below in table.
| Corrosive action on skin: All acids and some alkalies show corrosive action on skin as they form painful blisters when they come in contact with the skin. | H2SO4 absorbs water from skin tissues. HNO3 reacts with skin proteins to form a pulp like mass. NaOH and KOH are called caustic soda and caustic potash, respectively due to their causticizing action on the skin. |
| Reactions taking place between acids and bases: All acids react with alkalis (metal hydroxides) to form salt and water. The reaction of an acid with a base to form salt and water as the products is called neutralization. | 2KOH + H2SO4 → K2SO4 + 2H2O
Ca(OH)2 + 2HNO3 → Ca(NO3)2 + 2H2O |
Frequently Asked Questions – FAQs
What are the uses of acids?
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- Sulphuric acid is used in batteries.
- HCl is used for cleaning sanitary ware.
- Nitric acid is used to clean gold ornaments.
- Acetic acid is used as a preservative in pickles.
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Acids And Bases
Give two examples of acid.
Acids are liquids that give up the concentration to hydrogen ions. There are many common acid substances: lemon juice (citric acid), vinegar (acetic acid), stomach acid, and soda pop (carbonic acid). Acids are typically ionic with a positive hydrogen ion attached to a negative anion.
What are acids, base and salt? Give an example.
An acid is a substance which can donate hydrogen ions and a base is a substance which can donate hydroxide ions in an aqueous solution. Acid and base react to give an inorganic salt. Eg: HCl is an acid which can react with an alkali NaOH to produce NaCl as a salt and water.
How are the basic salts formed?
Basic salts are formed by the neutralization of a strong base and weak acid; for example, the reaction of sodium hydroxide (a strong base) with acetic acid (a weak acid) produces water and sodium acetate.
What are the properties of acids?
When dissolved in water, acids taste acidic, conduct electricity and react with metals to create hydrogen gas. Some indicator compounds can be used to detect acids, such as litmus. Acids turn blue litmus paper into red. Acid strength is measured on a pH scale.
What are examples of acids?
Acids are found in many substances: lemon juice (citric acid), vinegar (acetic acid), stomach acid, and soda pop (carbonic acid).
Is pure water basic or acidic?
H2O is an acid, as well as a base, therefore, water can act as an amphoteric substance. Since pH is defined as the negative log of the concentration of hydrogen ions, pure water has a pH of 7 or neutral. Pure water is neutral, as the number of positive hydrogen ions produced is equal to the negative number.
What is a pure acid?
Pure acids (without water) are composed of covalent small molecules. When water is added, the pure acid molecules dissociate in water to form ions, commonly referred to as “the ionized acid.” Pure acids are poor conductors of electricity. Due to the mobile ions present, acids diluted with water are considerably better conductors.
What are weak acids?
A weak acid is an acid which dissociates partially in an aqueous solution. The number of hydrogen ions produced by the dissociation of a weak acid will be lesser than that produced by a strong acid.
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