Acids, Bases and Salts
This chapter covers the chemical properties of acids and bases, how they react with metals, the pH scale, neutralization reactions, and the preparation and uses of important salts like washing soda and baking soda.
The pH scale measures the hydrogen ion concentration in a solution, ranging from 0 to 14. A pH below 7 is acidic, exactly 7 is neutral, and above 7 is basic (alkaline).
Q. Why does tooth decay start when the pH of the mouth is lower than 5.5?
Bacteria in the mouth produce acids by degrading sugar and food particles, lowering the pH below 5.5, which starts corroding tooth enamel (calcium hydroxyapatite).
Q. What is a neutralization reaction? Give one example.
A neutralization reaction occurs when an acid reacts with a base to form a salt and water, with evolution of heat: HCl + NaOH -> NaCl + H2O.
Baking soda (sodium hydrogen carbonate, NaHCO3) is a mild, non-corrosive base commonly used as an antacid to relieve stomach acidity.
Which gas is produced when zinc reacts with both hydrochloric acid and sodium hydroxide?
Correct answer: (A) Hydrogen gas
Zinc is called an _______ metal because it reacts with both acids and bases.
Amphoteric
An aqueous solution of an acid does not conduct electricity.
False — acids dissociate in water to produce hydrogen ions (H+), which act as charge carriers, so aqueous acid solutions do conduct electricity.