Question

A solution of phosphoric acid, \(\mathrm{H}_{3} \mathrm{PO}_{4}\), is found to contain \(35.2 \mathrm{~g}\) of \(\mathrm{H}_{3} \mathrm{PO}_{4}\) per liter of solution. Calculate the molarity and normality of the solution.

Short answer

The molarity of the phosphoric acid solution (\(\mathrm{H}_{3}\mathrm{PO}_{4}\)) is 0.359 M, and the normality of the solution is 1.077 N.

Step-by-step solution

Finding the molar mass of H₃PO₄

First, we need to calculate the molar mass of phosphoric acid (\(\mathrm{H}_{3}\mathrm{PO}_{4}\)) using the atomic weights of its elements: - Hydrogen (H) has an atomic weight of 1 g/mol - Phosphorus (P) has an atomic weight of 31 g/mol - Oxygen (O) has an atomic weight of 16 g/mol The molar mass of \(\mathrm{H}_{3}\mathrm{PO}_{4}\) can be calculated as follows: \(3 \times 1 + 31 + 4 \times 16 = 98 \,\mathrm{g/mol}\)

Converting the mass of phosphoric acid to moles

We know that there are 35.2 g of phosphoric acid in a 1-liter solution. To convert this mass to moles, simply divide the mass by the molar mass: \(\frac{35.2\, \mathrm{g}}{98\, \mathrm{g/mol}} = 0.359\, \mathrm{mol}\)

Finding the molarity of the solution

Now, we can calculate the molarity of the solution by dividing the moles of phosphoric acid by the volume of the solution in liters: \(\frac{0.359\, \mathrm{mol}}{1\, \mathrm{L}} = 0.359\, \mathrm{M}\) So, the molarity of the phosphoric acid solution is 0.359 M.

Finding the number of acidic protons in H₃PO₄

Phosphoric acid (\(\mathrm{H}_{3}\mathrm{PO}_{4}\)) contains three acidic protons, as there are three hydrogen atoms available that can dissociate in solution.

Calculating the normality of the solution

Finally, we can calculate the normality of the solution by multiplying the molarity by the number of acidic protons in \(\mathrm{H}_{3}\mathrm{PO}_{4}\): \(0.359\, \mathrm{M} \times 3 = 1.077\, \mathrm{N}\) The normality of the phosphoric acid solution is 1.077 N.

Key concepts

Molarity

Molarity is an essential concept in solution chemistry that defines the concentration of a solute in a solution. It measures the number of moles of a solute dissolved in one liter of solution.

• Molarity is expressed using the symbol "M."
• To find molarity, divide the moles of solute by the volume of the solution in liters.

In the case of phosphoric acid (\(\mathrm{H}_{3}\mathrm{PO}_{4}\)), the molarity is calculated by first finding the number of moles in the given mass. Then, that value is divided by the volume of the solution. For example, 0.359 moles of \(\mathrm{H}_{3}\mathrm{PO}_{4}\) in 1 liter of solution gives a molarity of 0.359 M. This measure helps in determining how concentrated a solution is.

Normality

Normality is another concentration measure in solution chemistry, often used when dealing with acids and bases. It is closely related to molarity.

• Normality, denoted as "N," accounts for the equivalent concentration of a solute in solution.
• To find normality from molarity, multiply the molarity by the number of reacting units (or equivalents) in the solute.

Phosphoric acid (\(\mathrm{H}_{3}\mathrm{PO}_{4}\)), as a triprotic acid, means it can donate three protons. Therefore, multiply its molarity (0.359 M) by these three acidic protons to get a normality of 1.077 N. Normality is exceptionally useful for titration purposes and stoichiometry in reactions involving acids and bases.

Phosphoric Acid

Phosphoric acid, with the chemical formula \(\mathrm{H}_{3}\mathrm{PO}_{4}\), is a triprotic acid, meaning it contains three hydrogen atoms capable of being replaced in a reaction. This property allows it to participate in various chemical reactions, especially in neutralization processes.

• It has three dissociable hydrogen ions: beneficial in fertilizers and rust removers.
• Phosphoric acid is found in some soft drinks, food products, and cleaning agents.

Understanding its structure and reactivity is crucial when calculating concentrations like molarity and normality. These calculations support different chemistry applications, highlighting its importance in both industrial and laboratory settings.

Molar Mass

Molar mass is the sum of the atomic masses of all the atoms in a molecule, providing the mass of one mole of a given substance. It is crucial for converting between mass and moles in chemical calculations.

• The unit for molar mass is grams per mole (g/mol).
• To determine the molar mass of a compound, sum the atomic masses of all atoms in its formula.

For phosphoric acid \(\mathrm{H}_{3}\mathrm{PO}_{4}\), we calculate the molar mass as follows:\[3 \times 1 \, \text{(for Hydrogen)} + 31 \, \text{(for Phosphorus)} + 4 \times 16 \, \text{(for Oxygen)} = 98 \, \text{g/mol}\]Knowing the molar mass allows you to convert between the grams of the substance and the amount in moles, thus facilitating the determination of concentration like molarity.