Question

Why is 1 molar aqueous solution more concentrated than a 1 molal solution?

Answer 1

Hint: Molality refers to the concentration of the solute in a particular mass of solvent, but in case of molarity, the concentration of the solute is given in terms of the volume of the solution.

Complete answer:
A solution consists of a solute( the chemical present in small amounts) and a solvent(the chemical that is present in bulk). They are independent of states e.g solid, liquid, gas, e.t.c
The two ways by which concentration of the solute can be expressed are molality(m) and molarity(M).
Molality is expressed as the moles of solute that is contained in one kilogram of the solute. Mathematically,
$m=(\dfrac{given\,mass\,of\,solute}{molar\,mass\,of\,solute}\,)\times (\dfrac{1000}{mass\,of\,solvent\,in\,gram})$
 where m is molality
For Molarity(M), the moles of solvent are calculated which is present in 1 litre, or 1000ml of the solution. Mathematically, Molarity is
$M=(\dfrac{given\,mass\,of\,solute}{molar\,mass\,of\,solute})\times (\dfrac{1000}{volume\,of\,solution\,in\,ml})$
Since molality depends on mass of solvent, it is observed that the mass of solute, in this case, water, being the solvent has a mass less than 1000gm. Therefore, it means that 1 molar aqueous solution must contain 1 mole of solute in less than 1000 gram of solvent .Whereas 1 molal solution must have 1 mole of solute in 1000 grams of solvent. That is why the concentration will be more in 1 molar aqueous solution, than 1 molal.

Note:
Do not confuse molarity with molality. Molality depends on mass of solvent and molarity depends on volume of solution. Also, molarity changes on change of temperature, but molality doesn't. It is so because on increasing temperature, the volume of solution expands and affects the value of molarity.