Question

A 1.912-g sample of calcium chloride is decomposed into its constituent elements and found to contain 0.690 g Ca and 1.222 g Cl. Calculate the mass percent composition of Ca and Cl in calcium chloride.

Short answer

Mass percent of Ca = (0.690 g / 1.912 g) * 100% = 36.09%; Mass percent of Cl = (1.222 g / 1.912 g) * 100% = 63.91%.

Step-by-step solution

Understanding the Problem

Review the data given. The total mass of calcium chloride is 1.912 g. It decomposes to yield 0.690 g of calcium (Ca) and 1.222 g of chlorine (Cl). We need to calculate the mass percent of each element in the compound.

Calculate Mass Percent of Calcium

To find the mass percent of calcium, divide the mass of calcium by the total mass of calcium chloride and multiply by 100%. The formula is: Mass percent of Ca = (mass of Ca / total mass of calcium chloride) * 100%.

Perform the Calculation for Calcium

Plug the values into the formula to calculate the mass percent of Ca: Mass percent of Ca = (0.690 g / 1.912 g) * 100%.

Calculate Mass Percent of Chlorine

Similarly, to find the mass percent of chlorine, divide the mass of chlorine by the total mass of calcium chloride and multiply by 100%. The formula is: Mass percent of Cl = (mass of Cl / total mass of calcium chloride) * 100%.

Perform the Calculation for Chlorine

Plug the values into the formula to calculate the mass percent of Cl: Mass percent of Cl = (1.222 g / 1.912 g) * 100%.

Calculate and Simplify the Percentages

Now, calculate and simplify the percentages for both Ca and Cl to find the final mass percentages.

Key concepts

Stoichiometry

Stoichiometry is a branch of chemistry that deals with the quantitative relationships between the reactants and products in a chemical reaction. In practice, it involves calculations that help us understand the ratios of elements and compounds as they react to form new substances.

For instance, in the provided exercise, stoichiometry is used to determine the mass percent composition of elements in calcium chloride. This involves dividing the mass of each element obtained from the chemical decomposition by the total mass of the compound, a stoichiometric calculation linking the masses to the proportions of each element within the compound. Understanding stoichiometry is crucial for predicting the outcomes of reactions and for scaling up from laboratory to industrial production processes.

Chemical Decomposition

Chemical decomposition is a process where a chemical compound is broken down (decomposed) into simpler compounds or its constituent elements. The decomposition can occur through various means such as heat, light, or chemical reaction.

In the exercise, calcium chloride undergoes decomposition, breaking down into calcium and chlorine. The mass of each element is then measured. Decomposition reactions are fundamental for understanding the composition of compounds and are often used in analytical techniques to measure the amounts of specific elements within a compound. The concept of decomposition is also applied in various scientific fields, such as the decomposition of organic matter in environmental science.

Empirical Formula

The empirical formula of a compound is the simplest whole-number ratio of atoms of each element present in the compound. It does not necessarily represent the actual numbers of atoms found in a molecule of the compound, but it gives the proportional number of atoms of each element.

Determining the empirical formula is a step often taken after finding the mass percent composition, as seen in the given exercise for calcium chloride. From the percentage composition, one can deduce the mole ratio of the elements, ultimately leading to the empirical formula. This is essential in chemistry because it allows chemists to understand the basic composition of a substance, which has practical applications in creating chemical reactions and manufacturing products.