Question

How many grams of $KN{O_{3}}$ should be used to prepare 2.00L of a 0.500M solution?

Answer 1

Molarity determines the number of moles of solute per liter of solution which is denoted by moles/Litre. These units are used for measuring the concentration of a solution.

Complete step by step answer:
- Molarity is used for the calculation of the volume of the solvent or the amount of solute.
- It is mathematically represented as

$$\begin{aligned} Molarity=\dfrac{moles\ of\ solute}{one\ litre\ of\ solution} \end{aligned}$$

- Now, to obtain the amount of $KN{O_{3}}$, we first have to find out the total number of moles. Since we have molarity and the volume of the solution, this can be carried out using the formula stated above.
- As we already know, molarity is measured in moles per liter, which states that 0.500M solution will contain 0.500 moles of $KN{O_{3}}$ for every 1L of solution.
- Since we have 0.500 moles for each litre of solution, and the total volume of 2.00L solution will consist of

$$\begin{aligned} 2\times 0.5\ moles=\ 1\ mole\ KNO_{3} \end{aligned}$$

Since the molar mass of potassium nitrate is 101 g/mol, 1 mole of this gives 101g of potassium nitrate.

Note: For calculating the molarity of a solution, the number of moles of solute should be divided by the total liters of the solution that is produced. If the amount of solute is given in grams, we must first calculate the number of moles of solute by using the molar mass of the solute and then calculate the molarity by using the number of moles and the total volume.