Question

For each of the following solutions, the mass of solute taken is indicated, as well as the total volume of solution prepared. Calculate the normality of each solution. a. \(15.0 \mathrm{g}\) of \(\mathrm{HCl} ; 500 . \mathrm{mL}\) b. \(49.0 \mathrm{g}\) of \(\mathrm{H}_{2} \mathrm{SO}_{4} ;\) 250. \(\mathrm{mL}\) c. \(10.0 \mathrm{g}\) of \(\mathrm{H}_{3} \mathrm{PO}_{4} ; 100 . \mathrm{mL}\)

Short answer

The normalities of the given solutions are: a. 0.822 N for HCl b. 1.000 N for H2SO4 c. 0.340 N for H3PO4

Step-by-step solution

Find the molar mass of each solute

To find the molar mass of each solute, we sum up the atomic masses of the elements in each formula. The atomic masses are found on the periodic table and should be rounded to one decimal place. a. HCl: Molar mass = 1.0 g/mol (H) + 35.5 g/mol (Cl) = 36.5 g/mol b. H2SO4: Molar mass = 2*(1.0 g/mol) (H) + 32.1 g/mol (S) + 4*(16.0 g/mol) (O) = 98.1 g/mol c. H3PO4: Molar mass = 3*(1.0 g/mol) (H) + 31.0 g/mol (P) + 4*(16.0 g/mol) (O) = 98.0 g/mol

Determine the number of equivalents per mole for each solute

To determine the number of equivalents per mole, we need to look at the number of hydrogen ions that can be replaced or donated by the solute. a. HCl: 1 equivalent per mole of HCl b. H2SO4: 2 equivalents per mole of H2SO4 c. H3PO4: 3 equivalents per mole of H3PO4

Convert the masses of solute to gram equivalents

To convert the mass of solute to gram equivalents, divide the mass by the product of molar mass and the number of equivalents per mole. a. \( \frac{15.0 g}{(36.5 g/mol) \times 1} = 0.411\) gram equivalents of HCl b. \( \frac{49.0 g}{(98.1 g/mol) \times 2} = 0.250 \) gram equivalents of H2SO4 c. \( \frac{10.0 g}{(98.0 g/mol) \times 3} = 0.034 \) gram equivalents of H3PO4

Calculate the normality of each solution

To find the normality of each solution, divide the gram equivalents of solute by the liters of solution. a. Normality of HCl: \( \frac{0.411 \text{ gram equivalents}}{0.500 L} = 0.822 \ \text{N} \) b. Normality of H2SO4: \( \frac{0.250 \text{ gram equivalents}}{0.250 L} = 1.000 \ \text{N} \) c. Normality of H3PO4: \( \frac{0.034 \text{ gram equivalents}}{0.100 L} = 0.340 \ \text{N} \) So, the normalities of the given solutions are: a. 0.822 N for HCl b. 1.000 N for H2SO4 c. 0.340 N for H3PO4

Key concepts

Molar Mass Calculation

Molar mass is a critical concept when dealing with chemical solutions, as it allows us to convert between grams of a substance and moles, which is the standard unit of amount in chemistry. The molar mass of a compound is the sum of the atomic masses of all the atoms in its formula. You can find these atomic masses on the periodic table, typically expressed in grams per mole. Each element has a unique atomic mass, such as hydrogen with about 1.0 g/mol and oxygen with approximately 16.0 g/mol.

By adding the atomic masses of each element in the compound's formula, you calculate the molar mass. For example, for hydrochloric acid (HCl), its molar mass is calculated as the sum of the atomic mass of hydrogen (1.0 g/mol) and chlorine (35.5 g/mol), resulting in 36.5 g/mol.

Understanding molar mass is crucial for converting the given mass of a solute into moles, which is needed when calculating normality.

Chemical Equivalents

Chemical equivalents relate to the concept of equivalents in a chemical reaction, indicating how much of one substance reacts with a certain amount of another. Equivalents are often used to measure how many moles of a reacting species will donate or accept electrons, protons, or react in some other capacity.

For acids and bases, it boils down to understanding the number of hydrogen ions (H⁺) or hydroxide ions (OH⁻) involved in reactions. For example, hydrochloric acid (HCl) donates one hydrogen ion per molecule, which means it has one equivalent per mole. Sulfuric acid (H₂SO₄), however, can donate two hydrogen ions, making it have two equivalents per mole.

When converting between grams and equivalents, the mass of a compound is divided by the molar mass and then multiplied by the number of equivalents per mole. This conversion is necessary to determine the normality of a solution, as normality depends on the gram equivalents present in a given volume.

Solution Concentration

The concentration of a solution describes how much solute is dissolved in a unit volume of solution. Concentration can be expressed in various ways, and understanding these terms can help decipher the strength and reactivity of solutions in chemical processes.

Normality is a concentration unit that measures the gram equivalents of solute per liter of solution. It's particularly useful in acid-base chemistry and when dealing with reactions where equivalents matter more than just moles.

To calculate the normality of a solution, you first determine the gram equivalents of the solute, as described earlier. Then, you divide this quantity by the total volume of the solution in liters. For example, if you have 0.411 gram equivalents of HCl dissolved in 0.500 liters of solution, the normality is 0.822 N.

This quantitative measure is crucial for preparing solutions accurately in laboratory settings, ensuring that reactions proceed with the correct proportions of reactants.