Question

The equivalent weight of HM is sometimes defined as the molar mass per mol of carboxylic plus phenolic groups. For a particular sample of fulvic acid whose molar mass is 6036 daltons, there are \(4.2\) and \(2.2 \mathrm{mmol}\) of carboxylic and phenolic groups respectively per gram of the FA. What is the equivalent weight?

Short answer

The equivalent weight is approximately 943750 grams per mole.

Step-by-step solution

Calculate Total Groups per Gram

Add the millimoles of carboxylic and phenolic groups together to find the total number of millimoles of reactive groups per gram of fulvic acid. This is done by summing the carboxylic groups (\(4.2 \text{ mmol}\)) and the phenolic groups (\(2.2 \text{ mmol}\)), so you have \(4.2 + 2.2 = 6.4 \text{ mmol per gram}\).

Convert to Moles per Gram

Convert the total millimoles to moles by dividing by 1000 (since 1 mole = 1000 millimoles). This gives you \(\frac{6.4}{1000} = 0.0064 \text{ moles per gram}\).

Calculate Equivalent Weight

The equivalent weight is calculated by dividing the molar mass of the fulvic acid by the total moles of reactive groups per gram. So, equivalent weight \( = \frac{6036}{0.0064} \approx 943750 \text{ grams per mole}\).

Key concepts

Equivalent Weight

In chemistry education, the concept of equivalent weight is vital for understanding chemical reactions and stoichiometry. Equivalent weight refers to the amount of a substance that will react with or supply one mole of hydrogen ions (H⁺) in an acid-base reaction or one mole of electrons in a redox reaction.
To calculate it, you divide the molar mass by the number of equivalents in the substance.
For fulvic acid, the equivalent weight is derived from its molar mass and its active functional groups. These are the carboxylic and phenolic groups.
In the given exercise, you calculate the total equivalents by adding the moles of reactive groups and then find the equivalent weight by dividing the molar mass by these equivalents. Understanding this concept helps in exploiting the full chemical potential of compounds and is fundamental in titration calculations.

Fulvic Acid

Fulvic acid is an integral subject covered in chemistry education due to its complex structure and variety of functional groups. It is a component of humic substances, which are found in soil, compost, and other decomposed organic matter. These substances play a critical role in environmental chemistry.
Fulvic acid is rich in carboxylic and phenolic groups, contributing to its reactivity. These molecular groups facilitate important functions, such as chelating metal ions and influencing soil pH and fertility.
Understanding fulvic acid involves recognizing its effects on nutrient availability and plant growth. By learning about its characteristics, students can grasp its importance in ecological processes and in various industrial and agricultural applications.

Molar Mass

Molar mass is a fundamental concept in chemistry education that relates to the mass of a given chemical element or compound divided by the amount of substance in moles. It is expressed in units of grams per mole (g/mol).
Knowing the molar mass of a compound allows students to convert between mass and number of moles, which is important for chemical equations and reaction stoichiometry.
In the exercise, the molar mass of fulvic acid is used to determine its equivalent weight. This mass, expressed as 6036 daltons, provides a crucial piece of information for calculating how many grams of this acid would interact in a reaction, underscoring the importance of accurate molar mass determination in quantitative chemical analysis.