Question

Acetylsalicylic acid is the active ingredient in aspirin. It took \(35.17 \mathrm{~mL}\) of \(0.5065 \mathrm{M}\) sodium hydroxide to react completely with \(3.210 \mathrm{~g}\) of acetylsalicylic acid. Acetylsalicylic acid has one acidic hydrogen. What is the molar mass of acetylsalicylic acid?

Short answer

The molar mass of acetylsalicylic acid is approximately \(180.34\mathrm{~g/mol}\).

Step-by-step solution

Find moles of sodium hydroxide

First, we need to find the moles of sodium hydroxide that were used in the reaction. To do this, we can use the formula: moles = volume × concentration The volume of sodium hydroxide used is \(35.17\mathrm{~mL}\) and its concentration is \(0.5065 \mathrm{M}\). Therefore, the moles of sodium hydroxide can be calculated as follows: moles = \(35.17\mathrm{~mL}\) × \(0.5065 \mathrm{M}\) moles = \(0.03517\mathrm{~L}\) × \(0.5065 \mathrm{M}\) = \(0.01780 \mathrm{mol}\)

Use stoichiometry to find moles of acetylsalicylic acid

Since acetylsalicylic acid has one acidic hydrogen, it reacts with sodium hydroxide in a 1:1 ratio. Therefore, the moles of acetylsalicylic acid reacted will be the same as the moles of sodium hydroxide used. moles of acetylsalicylic acid = moles of sodium hydroxide moles of acetylsalicylic acid = \(0.01780 \mathrm{mol}\)

Calculate the molar mass of acetylsalicylic acid

Now that we have the moles of acetylsalicylic acid reacted, we can calculate its molar mass using the formula: molar mass = mass / moles The mass of acetylsalicylic acid is given as \(3.210\mathrm{~g}\). Therefore, the molar mass of acetylsalicylic acid can be calculated as follows: molar mass = \(3.210\mathrm{~g}\) / \(0.01780\mathrm{~mol}\) = \(180.34\mathrm{~g/mol}\) So, the molar mass of acetylsalicylic acid is approximately \(180.34\mathrm{~g/mol}\).

Key concepts

Stoichiometry

Stoichiometry is the study of the quantitative relationships between the amounts of reactants and products in chemical reactions. It provides a way to calculate how much of each substance participates in a reaction. This concept is crucial for determining the amounts of substances required or produced in a given chemical process.

For example, in the reaction between acetylsalicylic acid and sodium hydroxide, stoichiometry helps us understand the relationship between the moles of each substance. Given that acetylsalicylic acid reacts in a 1:1 ratio with sodium hydroxide, the moles of acetylsalicylic acid are equal to the moles of sodium hydroxide used. Therefore, 0.01780 moles of sodium hydroxide are required to completely react with acetylsalicylic acid.

Key steps in stoichiometry problems include:

• Converting the volume of solutions to liters if initially given in milliliters.
• Calculating moles using concentration and volume.
• Interpreting balanced chemical equations to determine mole ratios.

Acetylsalicylic Acid

Acetylsalicylic acid, commonly known as aspirin, is a widely used drug with anti-inflammatory, analgesic, and antipyretic properties. It is an organic compound that contains one acidic hydrogen atom, making it capable of participating in acid-base reactions.

In chemical terms, acetylsalicylic acid has the molecular formula \(C_9H_8O_4\) and a characteristic structure that allows it to donate a hydrogen ion (proton). This ability to release a proton makes it reactive with bases such as sodium hydroxide, which can accept the proton.

The molar mass of acetylsalicylic acid is typically determined through experimental methods involving such reactions, where the key is the known 1:1 ratio with sodium hydroxide. As calculated, its molar mass is approximately 180.34 g/mol.

Understanding the structural and reactive properties of acetylsalicylic acid is crucial in various fields including pharmacology and analytical chemistry.

Sodium Hydroxide

Sodium hydroxide, known chemically as \(NaOH\), is a strong base used in various chemical applications, including acid-base titrations. It is highly soluble in water, producing hydroxide ions \((OH^-)\), which readily react with acids.

In the context of the reaction with acetylsalicylic acid, sodium hydroxide serves as the basic reactant that neutralizes the acidic proton of the acid. This neutralization reaction forms water and a salt, demonstrating the classic behavior of a strong base. The concentration of sodium hydroxide solution (molarity) and its volume are crucial for calculating the exact amount of moles available for the reaction.

The reaction can be simplified as:
\[ \text{Acetylsalicylic Acid} + \text{NaOH} \rightarrow \text{Salt} + \text{H}_2\text{O} \]
This illustrates the key role of sodium hydroxide in the stoichiometry of the reaction and in determining the molar mass of acetylsalicylic acid.

Acid-Base Reaction

An acid-base reaction is a type of chemical reaction that involves the exchange of protons between reactants. It results in the formation of water and a salt compound. These reactions are key to many biological and chemical processes.

During the reaction between acetylsalicylic acid and sodium hydroxide, acetylsalicylic acid (the acid) donates a proton to sodium hydroxide (the base). This exchange leads to the formation of water and a new compound, often referred to as a salt.

Acid-base reactions typically follow the general equation:
\[ \text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water} \]
Such a reaction helps to determine specific characteristics of the reactants, like the molar mass in a laboratory setting. Understanding the principles behind acid-base reactions is crucial for calculating the precise stoichiometry in chemical reactions, providing insight into the amounts of each substance involved.