Identify the pure substances and mixture from the following list : (a) solid common salt (b) milk (c) air (d) oxygen (e) fruit juice (f) brass (g) copper sulphate crystals (h) distilled water (i) sugar solution (j) honey (k) Ice cream (l) Iron sulphide
The Correct Answer and Explanation is:
Pure Substances:
- Solid common salt (NaCl) – This is a pure substance because it consists only of sodium chloride and doesn’t contain any other elements or compounds mixed with it.
- Oxygen (O2) – This is a pure substance because it is made up entirely of oxygen molecules (O2) and nothing else.
- Copper sulphate crystals (CuSO4) – Copper sulphate is a pure substance because it consists of only copper, sulfur, and oxygen in a fixed ratio, forming a specific compound.
- Distilled water (H2O) – Distilled water is a pure substance because it has been purified, containing only H2O molecules and no dissolved impurities or other substances.
- Iron sulphide (FeS) – Iron sulphide is a pure substance because it is a compound made of iron and sulfur in a fixed ratio, with no other materials mixed in.
Mixtures:
- Milk – Milk is a mixture because it consists of water, fats, proteins, lactose, vitamins, and minerals, all mixed together but not chemically bonded.
- Air – Air is a mixture because it contains a variety of gases like nitrogen, oxygen, carbon dioxide, argon, and trace gases in varying proportions.
- Fruit juice – Fruit juice is a mixture because it contains water, sugars, organic acids, and various compounds from the fruit, all mixed together.
- Brass – Brass is a mixture because it is an alloy made from copper and zinc, where the components retain their individual properties and are not chemically bonded.
- Sugar solution – A sugar solution is a mixture because sugar dissolves in water to form a solution, but the sugar and water can still be separated by evaporation.
- Honey – Honey is a mixture because it contains sugars, water, enzymes, amino acids, and other organic compounds, all mixed together.
- Ice cream – Ice cream is a mixture because it contains a variety of ingredients like water, milk, sugar, fat, and flavorings that are physically combined, not chemically bonded.
Explanation:
A pure substance is a material with a constant composition and distinct chemical properties. Elements and compounds are examples of pure substances. They consist of only one type of atom or molecule, and their properties do not change regardless of the amount or location.
A mixture, on the other hand, is a physical combination of two or more substances, where the individual components retain their properties. Mixtures can be heterogeneous (e.g., salad or soil) or homogeneous (e.g., air or sugar solution). Unlike pure substances, mixtures can usually be separated into their components through physical methods, such as filtration, evaporation, or distillation.
