a) What is lime water?
b) How plaster of paris is formed?
c) What is the pH of our stomach
d) Name a strong base and a weak base.
e) Name a hydrated salt
f) What is a universal indicator? What is its advantage?
g) Give two important uses of washing soda and baking soda.
Answers
Answer:
a) Limewater is the common name for a saturated aqueous solution of calcium hydroxide. Calcium hydroxide, Ca(OH)₂, is sparsely soluble at room temperature in water. "Pure" limewater is clear and colorless, with a slight earthy smell and an astringent/bitter taste. It is basic in nature with a pH of 12.4.
b) Plaster of Paris is manufactured by heating gypsum at 423K or 150o C/300o F. On heating gypsum at 423 K, it loses water molecules and becomes calcium sulphate hemihydrate. This product is known as the plaster of Paris. However, when water is mixed with dry plaster of Paris, it re-structures into gypsum.
c) The normal volume of the stomach fluid is 20 to 100 mL and the pH is acidic (1.5 to 3.5).
d) 2A metal hydroxides / Copper hydroxide (Cu(OH)2)
e) The two common names of hydrated salts used in chemistry are iron sulphate heptahydrate and copper sulphate pentahydrate. Its colour is Green.
f) The advantage of the universal indicator is that it displays a variety of colors over the whole pH scale. This makes it possible to determine an approximate pH of a solution over a range from 1-14. whereas, A commonly used acid-base indicator is litmus.
g) Two important uses of washing soda are; It is used in the manufacture of soap and glass. It is used to remove the permanent hardness of water. Baking soda is chemically known as sodium bicarbonate or sodium hydrogen carbonate and it is also known as bicarbonate of soda which is represented as NaHCO3.