A pure substance is obtained using different and complicate methods of chemistry: distillation, filtration, ion exchangers, crystallization, precipitation etc.
distillation
To obtain pure thorium metal it is necessary to separate thorium from other elements.
To separate rock salt into salt crystals and pure dry sand, first dissolve the rock salt in water, creating a saltwater solution. Next, filter the mixture to separate the sand, which will remain on the filter paper, from the saltwater solution. Finally, evaporate the water from the saltwater solution to obtain pure salt crystals, leaving behind the dry sand collected from the filtration process.
it is important to separate and purify substances so that: 1.we can get them in their pure form. 2.to remove undesirable particles from them.
It is no longer that same substance. A chemical changes the identity of the substance. Individual atoms cannot be broken down into smaller parts by normal physical or chemical change.
to pure them
distillation
by distillation
Sulphur is a pure element. Unless its mixed in with something else there is nothing to separate it from.
There are many substances.Some of them are ribosomes,enzymes,grana,starch granules,DNA etc
Impossible to find pure polonium; it is necessary to separate polonium from other radioisotopes.
A saline solution is a homogeneous mixture because its appearance and composition are uniform throughout the solution. A substance is salt. A saline solution is a combination of the two substances water and salt. However, in the salt-water solution, the salt is completely dissolved in the water.
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To obtain pure thorium metal it is necessary to separate thorium from other elements.
Filtering
A method is repeated processes of crystallization/recrystallization, for a supplementary refining.But it is a nonsense in your question: salt or pure salt are both sodium chloride, supposed to be pure.
Pure maple syrup doesn't contain salt.