Question

What is the concentration of sugar $[{C_{12}}{H_{22}}{O_{11}}]$ in $mol{L^{ - 1}}$ if it’s $20g$ are dissolved in enough water to make a final volume up to $2L?$

Answer 1

Here, in this we need to find out the concentration of sugar, so for that we will find out the molarity of sugar using its formula and putting all the given values into the formula, we will be able to find out the concentration of sugar.

Complete answer:
As we need to find out the molarity, so we will use to the formula:
$Molarity = \dfrac{m}{{M \times V}}$
Where $M$ is molar mass
$V$ is volume of solution taken in litres
$m$ is mass given in grams.
So, here in the question, we are given mass which is $20g$ and given volume of the solution which is $2L$. So, first we need to find out the molar mass of sugar $[{C_{12}}{H_{22}}{O_{11}}]$-
$[{C_{12}}{H_{22}}{O_{11}}] = 12 \cdot 12 + 22 \cdot 1 + 11 \cdot 16 = 342$
So, the molar mass of sugar comes out to be $342$.
Now, we will put these values in the formula in order to get the concentration of sugar-
$Molarity = \dfrac{{20}}{{342 \cdot 2}} = 0.029mol{L^{ - 1}}$
Therefore, the concentration of sugar when $20g$ is dissolved in water to make a final volume of $2L$ is $0.029mol{L^{ - 1}}$.

Note:
Here, we were supposed to find out the concentration of sugar for which we have used the formula of molarity but for this before putting the values in the formula we need to check the units first. Also, from the formula we can see that the molarity depends upon the volume taken which further varies with the change in the temperature, therefore, molarity is said to be temperature dependent whereas molality is temperature independent since it is said to be dependent only on the mass of the solvent taken.