Basic Concepts of Preparing Solutions

The most common unit of solution concentration is molarity (M). The molarity of a solution is defined as the number of moles of solute per one liter of solution. Note that the unit of volume for molarity is liters, not milliliters or some other unit. Also note that one liter of solution contains both the solute and the solvent. Molarity, therefore, is a ratio between moles of solute and liters of solution. To prepare laboratory solutions, usually a given volume and molarity are required. To determine molarity, the formula weight or molar mass of the solute is needed. The following examples illustrate the calculations for preparing solutions.

If starting with a solid, use the following procedure:

• Determine the mass in grams of one mole of solute, the molar mass, MMs.

Molecular weight of FeSO4.7H2O = 278.03 g/mol

Molecular weight of FeSO4 = 151.901 g/mol

FeSO4.7H2O is simply the hydrated form of FeSO4.

• Decide volume of solution required, in liters, V.

• Decide molarity of solution required, M.

• Calculate grams of solute (gs) required using equation 1.

eq. 1. gs = MMs x M x V

• Example: Prepare 800 mL of 0.1 M FeSO4.7H2O (MM = 278.03 g/mol)

gFeSO4.7H2O = 278.03 g/mol x 0.1 mol/L x 0.8 L

gFeSO4.7H2O = 22.24 g FeSO4.7H2O

Dissolve 22.24 g of FeSO4.7H2O in about 400 mL of distilled water, then add more water until final volume is 800 mL.

Use this calculation for other concentrations of chemicals you want to prepare.

Guess you got frerrous one as FeSO4.7H2O you should dissolve it as required  taking the atomic proportion of 55.8 to 278 for Iron. Sokution is stable at subacidic pH with a drop of HCl 1% per l. Oxygen and high T induce oxidation https://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/Sigma/Product_Information_Sheet/f0131pis.pdf

Hi Guido,

As I am not in Chemistry field, I am not very familiar with the terms. Could you explain me further? Yes, the empirical formula is FeSO4.7H2O

I supposedly need to dilute 9.37 g Iron sulphate in 100 ml distilled water. I am wondering if I can literally use 9.37 g Iron sulphate-7-hydrate without water deduction? I only have the chemical in my lab. Is it alright to use both chemicals interchangeably?

Basic Concepts of Preparing Solutions

The most common unit of solution concentration is molarity (M). The molarity of a solution is defined as the number of moles of solute per one liter of solution. Note that the unit of volume for molarity is liters, not milliliters or some other unit. Also note that one liter of solution contains both the solute and the solvent. Molarity, therefore, is a ratio between moles of solute and liters of solution. To prepare laboratory solutions, usually a given volume and molarity are required. To determine molarity, the formula weight or molar mass of the solute is needed. The following examples illustrate the calculations for preparing solutions.

If starting with a solid, use the following procedure:

• Determine the mass in grams of one mole of solute, the molar mass, MMs.

Molecular weight of FeSO4.7H2O = 278.03 g/mol

Molecular weight of FeSO4 = 151.901 g/mol

FeSO4.7H2O is simply the hydrated form of FeSO4.

• Decide volume of solution required, in liters, V.

• Decide molarity of solution required, M.

• Calculate grams of solute (gs) required using equation 1.

eq. 1. gs = MMs x M x V

• Example: Prepare 800 mL of 0.1 M FeSO4.7H2O (MM = 278.03 g/mol)

gFeSO4.7H2O = 278.03 g/mol x 0.1 mol/L x 0.8 L

gFeSO4.7H2O = 22.24 g FeSO4.7H2O

Dissolve 22.24 g of FeSO4.7H2O in about 400 mL of distilled water, then add more water until final volume is 800 mL.

Use this calculation for other concentrations of chemicals you want to prepare.

Chukwuma Ndive Thanks for your suggestion.