Test: Is Matter Around Us Pure - 1 - UPSC

• A pure element or compound contains only one substance, with no other substances mixed in.
• Impure materials may be mixtures of elements, mixtures of compounds, or mixtures of elements and compounds.

Hydrogen sulfide is a flammable, colorless gas with a characteristic odour of rotten eggs. It is commonly known as hydrosulfuric acid, sewer gas, and stink damp. People can smell it at low levels.

Carbon dioxide is not a mixture since it contain fixed ratio of oxygen and carbon in 2:1, which is a property of compound not a mixture.

Cooking of food is a chemical change because after cooking, the raw ingredients or the vegetables cannot be regained again in the raw form.

Filtration is a method for separating an insoluble solid from a liquid. When a mixture of sand and water is filtered: the sand stays behind in the filter paper (it becomes the residue ) the water passes through the filter paper (it becomes the filtrate).

∴ KNO₃ has the highest solubility at 313 K.

Mercury is the only liquid metal and bromine is the only liquid non-metal. 

Mercury:

• Mercury is the only metal that is a liquid at normal temperatures and pressure. 
• Because of the behavior of the valence electrons, mercury has a low melting point, is an electrical and thermal conductor and doesn't form diatomic mercury molecules in the gas phase

Bromine:

• Bromine has 35 electrons and with7 electrons in its outer shell it has a valency of 1 so, is very reactive. 
• But, the electrons are very spread out from the atomic nucleus, hence it behaves like a liquid.
• It is non-metallic because it is a halogen gas that is liquid at STP.

Alloys are homogeneous mixtures of two or more elements. The elements could be two metals, or a metal and a non-metal.
Example: Brass is an example of a substitution alloy of copper and zinc.