Test: Is Matter Around Us Pure - 1

• 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.

True Solution is a homogeneous mixture of two or more substances in which substance dissolved (solute) in solvent has the particle size of less than 10-9 nm or 1 nm. Simple solution of salt in water is an example of true solution. Particles of true solution cannot be filtered through filter paper and are not visible to naked eye.

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.

Brass is an alloy made up of uniform composition of copper and zinc. It is a homogeneous mixture in which zinc and copper can be varied to create a range of brasses with varying properties.