Question

To prepare a 2 M solution of potassium nitrate (KNO3), which quantities must be measured? The mass of the and the volume of the must be measured.

Answer 1

Answer:

Mass of salt and Volume of water

Explanation:

To prepare 2M solution of potassium nitrate. A certain mass of salt has to be weighed and dissolved in measured volume of water.

The 2M signifies the molarity (concentration) of the salt. It is given as;

Molarity =  moles / volume (liter) of solution.

Moles = Mass /  Molar mass

To get a molarity of 2 in a 1L water, our moles needs to be;

2 = moles / 1

moles = 2

substituting into the moles mass equation;

molar mass = 101.1032 g/mol

2 = mass / 101.1032

mass = 2 * 101.1032

mass = 202.2064g

This means 202.2064g of potassium ntrate needs to be dissolved in 1L of water to acheve a molarity of 2.

Answer 2

Answer:

The mass of the solute and the volume of the solution.

Explanation:

Hello,

In this case, given the formula of molarity:

$M=\frac{n_{solute}}{V_{solution}}$

In such a way, since the moles could not be directly measured, we must measure the mass of the solute and by using its molar mass, one could compute its moles. Moreover, since the solution is composed by the solvent (typically water) and the solute, we consequently must measure the volume of the solution needed for the preparation of such concentration-known solution. In such a way, we can actually prepare the required solution.

Best regards.