Question

Explain how the information in a chemical formula can be used to determine how much of a particular element is present in a given amount of a compound. Provide some examples of how this might be useful.

Short answer

To determine the amount of an element in a compound, identify the elements and their ratios from the chemical formula, calculate the molar mass of the compound, find the percentage by mass of the element, and then calculate the mass of the element in a given amount of the compound. This process is useful in stoichiometry, chemical synthesis, and quality control.

Step-by-step solution

Identifying the Elements

Examine the chemical formula to identify the different elements that make up the compound. Each element is represented by its chemical symbol, such as 'C' for carbon.

Determining Atomic Ratios

Determine the ratio of atoms of each element in the compound. The subscript number following an element's symbol tells you how many atoms of that element are present in one molecule of the compound. If there is no subscript, it means there is one atom of that element.

Calculating Molar Masses

Calculate the molar mass of the compound by adding the atomic masses of all the atoms in the compound's formula. The atomic mass of each element can be found in the periodic table.

Finding the Percentage by Mass

Find the percentage by mass of the particular element in the compound by dividing the total atomic mass of that element (found by multiplying the atomic mass by the number of atoms of the element) by the molar mass of the compound, and then multiply by 100%.

Determining Mass of the Element in a Given Amount

Calculate the mass of the element in a given amount of the compound by multiplying the percentage by mass with the total mass of the compound.

Applying to Practical Situations

Use the mass of an element in a compound to calculate required amounts for chemical reactions, to balance chemical equations, or to verify the purity of a substance.

Key concepts

Elemental Composition

Understanding the elemental composition of a compound is essential as it provides information about the types of atoms present and their proportions in the molecule. Each element in a chemical formula is represented by its unique chemical symbol, and the subscript numbers indicate the amount of each atom within a single molecule. If no subscript is present, one atom of that element is implied. Elemental composition is important for various applications such as determining nutritional content in food, estimating the resources contained within an ore, and even in forensics for material identification.

For example, water (H_2O) consists of two hydrogen atoms and one oxygen atom, which suggests that for every mole of water, there are two moles of hydrogen atoms and one mole of oxygen. Moreover, the knowledge of elemental composition is extremely useful for scientists in fields like pharmacology where drug formulation relies on precise amounts of each component.

Molar Mass Calculation

The concept of molar mass is a gateway to understanding the quantitative aspects of chemical compounds. Molar mass, expressed in grams per mole (g/mol), is calculated by adding the atomic masses of all the atoms in a compound's formula. This calculation enables chemists to convert between mass, moles, and the number of molecules. When using a periodic table, one must look up the atomic weights of each element and multiply them by the respective number of atoms indicated by the chemical formula.

Let's take carbon dioxide (CO_2) as an example. The molar mass is the sum of one carbon atom's atomic mass and two oxygen atoms' atomic masses. This principle allows for the accurate scaling up or down of reactions, crucial for industrial processes to produce the desired amounts of products.

Mass Percentage Calculation

Calculating the mass percentage of an element in a compound involves finding the proportion of the total mass that is attributable to that specific element. This calculation is done by dividing the atomic mass of the element(s) in question by the molar mass of the entire compound and then multiplying by 100 to obtain a percentage. Understanding mass percentage is critical for tasks like creating solutions with particular concentrations or assessing the purity of substances.

For instance, to determine the mass percentage of hydrogen in water (H_2O), you would sum the masses of the two hydrogen atoms, divide by the molar mass of water, and multiply by 100%. This technique is particularly useful in analytical chemistry where the composition of a sample can determine the course of an experiment or the quality control process of a product.

Stoichiometry

Stoichiometry is a key concept in chemistry that involves the calculation of the relative quantities of reactants and products in chemical reactions. Knowing the molar relationships—how many moles of each substance react or are produced—enables the prediction and measurement of the outcomes of chemical reactions. The stoichiometric coefficients in a balanced chemical equation provide the ratio of moles of reactants to products, ensuring that matter is conserved throughout the process.

For example, when methane (CH_4) combusts with oxygen to form carbon dioxide and water, stoichiometry tells us that one mole of methane reacts with two moles of oxygen. This foundation is essential in applications ranging from industrial synthesis to biochemistry, directly influencing economic efficiency and environmental impact by allowing precise adjustment of reaction conditions.