Definition Of Acids
An acid is a chemical substance whose aqueous solutions are characterized by a sour taste, the ability to turn blue litmus red, and the ability to react with bases and certain metals (like calcium) to form salts
More About Acids
- Aqueous solutions of acids have a pH of less than 7
- A lower pH means a higher acidity, and thus a higher concentration of hydrogen ions in the solution
- Chemicals or substances having the property of an acid are said to be acidic
- Common examples of acids include hydrochloric acid acetic acid (vinegar is a dilute solution of this liquid), sulfuric acid (used in car batteries), and tartaric acid (a solid used in baking)
- Acids can be solutions or pure substances, and can be derived from solids, liquids, or gases
- Acids are corrosive to skin, but there are some exceptions to this rule. Strong acids and concentrated acids are corrosive. Boric acid and carbonates are not corrosive
- The Arrhenius definition defines acids as substances which increase the concentration of hydrogen ions (H+), or more accurately, hydronium ions (H3O+), when dissolved in water
- According to Bronsted-Lowry definition an acid is a substance which can act as a proton donor
- A Lewis acid is a substance that can accept a pair of electrons to form a covalent bond
- Examples of Lewis acids includes all metal cations, and electron-deficient molecules such as boron trifluoride and aluminium trichloride
- Acids can be tested with litmus, a natural indicator
- Litmus is a purple dye, extracted from lichens, a plant
- When the litmus solution is neither acidic nor basic, its colour is purple
- There are two types of acids, mineral acids and organic acids
- An organic acid is an organic compound with acidic properties
- Among acids, there are strong and weak acids. According to Arrhenius definition, strong acids are those which ionize in water completely and furnish protons and increase hydronium ion concentrations
- Weak acids are those that ionize in water partially
1. Which one of the following substances is an acid?
A. Table salt
B. Soap solution
C. Lemon juice
D. Water
Answer: C. Lemon juice
2. Acids and alkalis can cause some dyes to change colour. These dyes are called:
A. bases
B. Mixtures
C. Solvents
D. Indicators
Answer: D. Indicators
3. Indigestion is caused by too much acid in the stomach. It can be cured by taking antacids. These work because:
A. They neutralize the acid
b. They taste good
C. They lower the pH value in stomach
D. They lower the pH value of blood
Answer: A. Antacids neutralize the acids in the stomach
