Which of the following materials fall in the category of a “pure substance”?
(a) Ice
(b) Milk
(c) Iron
(d) Hydrochloric acid
(e) Calcium oxide
(f) Mercury
(g) Brick
(h) Wood
(i) Air
In the context of chemistry, a pure substance is one that consists of a single type of element or compound. It has uniform composition and distinct chemical properties.
Let's evaluate each option:
(a) Ice: Ice is the solid form of water (H₂O). Since it is made up of only one substance (water molecules), it is a pure substance.
(b) Milk: Milk is a mixture of water, fats, proteins, and other components. It is not a pure substance.
(c) Iron: Iron (Fe) is a metal element and consists of only one type of atom, so it is a pure substance.
(d) Hydrochloric acid: Hydrochloric acid (HCl) is a compound made up of hydrogen and chlorine atoms in a fixed ratio, making it a pure substance.
(e) Calcium oxide: Calcium oxide (CaO) is a compound made up of calcium and oxygen atoms in a fixed ratio. Hence, it is a pure substance.
(f) Mercury: Mercury (Hg) is a chemical element and consists of only one type of atom, so it is a pure substance.
(g) Brick: A brick is a mixture of several materials like clay, minerals, etc., so it is not a pure substance.
(h) Wood: Wood is a natural material composed of a variety of substances (cellulose, lignin, water, etc.), making it a mixture, not a pure substance.
(i) Air: Air is a mixture of several gases (nitrogen, oxygen, carbon dioxide, etc.), so it is not a pure substance.
Ice
Iron
Hydrochloric acid
Calcium oxide
Mercury
These are the pure substances in the list.