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Common Misconceptions

3 min read

- Lack of clarity can be dangerous! Steer away from all these misconceptions!

All Solutions are Liquids

Is it a correct statement? No! Not at all!

If you think that solution is all about liquid, then let me clear here that a solution can be in the solid, liquid, or gaseous state. And, this depends on the physical state of the solvent. Solid solutions are those solutions in which the solvent is solid. The liquid solutions have liquid as a solvent, and the gaseous solutions contain gaseous solvent.

It is true that liquid solutions are the most significant types of solutions, but it does not mean we forget the other types of solutions.

Here, we have the examples of all the types of solutions-

All miscible liquids are completely miscible!

The term ''Miscible'' itself means when something can be mixed together. Miscible liquids are the two liquids that combine in any ratio to form a homogeneous solution.

Would you agree, if I say that all the miscible solutions are completely miscible? May be yes, may be no? Let me explain this to you!

Miscible liquids are generally categorised as:

Completely miscible liquids : When both the liquids are polar or both non-polar, they mix completely in all proportions to form a homogenous mixture.

Examples-Benzene and Hexane, Ethyl alcohol and Water

2. Partially miscible liquids: When two liquids are not exactly similar in nature, also not completely dissimilar, they dissolved in each other to a limited extent. They are said to be partially miscible..

Examples-Ether and Water, Phenol and Water, and Nitrobenzene and Hexane

To summarise, if I say two liquids are miscible, it's not necessary for them to be completely miscible. It may happen that they mix together only partially.

Molarity and Formality are always the same

Both molarity and formality are expressed as number of moles of solute per litre of solution. So, do we need two distinct terms? Let's find out.

Molarity generally demonstrates the concentration of a particular chemical species in a solution. On the other hand, formality tells us the total concentration of the substance without any emphasis on its chemical form.

Say, if I ask you for the molarity of a solution when 0.1 mol of

M g C l_{2}

is dissolved in 1 L of water, what would be your most likely answer?
Is it 0.1 M

M g C l_{2}

Before you come to that conclusion, think about what happens when an ionic compound dissolves in water. You probably know that it dissociates into its ions. So,

M g C l_{2}

gets dissociated into

M g^{2 +}

and

C l^{-}

ions when dissolved in water.

Molarity, as we said, expresses the concentration of a particular species in the solution - so, the solution will be 0.1M in

M g^{2 +}

and 0.2M in

C l^{-}

. And the molarity of

M g C l_{2}

will be zero, as there is no undissociated

M g C l_{2}

left.

However, as formality represents the total amount of

M g C l_{2}

, without any regards to its chemical form, it will still be 0.1 F.

So, if we are reading something like 0.1 M

M g C l_{2}

, we should know that it actually represents the concentration of the ions(

M g^{2 +}

C l^{-}

) in the solution.

However, there are some substances which do not undergo dissociation in water. For these substances, the value of formality and molarity will remain the same. For example, a solution of glucose which has a concentration of 0.1 M will be 0.1 F as well.

To conclude, it can be said that in case of ionic compounds, such as,

N a C l

M g_{2} C O_{3}

, the term formality is more appropriate than molarity.

I hope it is clear to you now!