Question

Suppose you have equal amounts of calcium, Ca, in two beakers. In one beaker, you react the calcium with oxygen, O. In the other beaker, you react the calcium with sulfur, S. h e reaction with oxygen forms the compound calcium oxide, CaO. a. What do you predict is the chemical formula of the compound formed from the reaction between calcium and sulfur? b. Which compound has more mass, the compound containing calcium and oxygen, or the compound containing calcium and sulfur? Explain your thinking.

Short answer

a. The chemical formula is CaS; b. CaS has more mass than CaO.

Step-by-step solution

Understanding Chemical Formulas

Calcium (Ca) typically forms ionic compounds by losing two electrons to achieve a stable configuration, resulting in a Ca\(^{2+}\) ion. Oxygen (O) typically gains two electrons to fill its outer shell, resulting in an O\(^{2-}\) ion. The result is a 1:1 compound, CaO. Sulfur (S) behaves similarly to oxygen and also forms an S\(^{2-}\) ion when it gains two electrons. Therefore, the compound formed with calcium will also be in a 1:1 ratio, resulting in the chemical formula CaS.

Evaluating Atomic Masses

We need the molar masses of the elements: Calcium (Ca) has a molar mass of 40.08 g/mol, Oxygen (O) is 16.00 g/mol, and Sulfur (S) is 32.07 g/mol. In the compound CaO, the molar mass is 40.08 + 16.00 = 56.08 g/mol. For CaS, it's 40.08 + 32.07 = 72.15 g/mol.

Comparing Compound Masses

Comparing the molar masses: CaO has a molar mass of 56.08 g/mol, while CaS has a molar mass of 72.15 g/mol. Therefore, for the same number of moles, CaS has more mass compared to CaO.

Key concepts

Ionic Compounds

Ionic compounds are formed when atoms transfer electrons, leading to the formation of charged particles called ions. These ions are then attracted to each other due to oppositely charged forces, resulting in a stable compound.
For instance, in the case of calcium reacting with either oxygen or sulfur, calcium loses two electrons to become a Ca\(^{2+}\) ion. Oxygen and sulfur each gain two electrons to become O\(^{2-}\) and S\(^{2-}\) ions, respectively.
This electron transfer is what gives ionic compounds their characteristic structure and stability. The ionic bond results in the formation of lattice structures, which contribute to their unique physical properties such as high melting and boiling points.

Molar Mass

The molar mass of a compound is crucial for understanding its substance quantities, as it equivalent to the mass of one mole of that compound in grams. It's calculated by adding the molar masses of all the atoms in the compound's chemical formula.
For calcium oxide (CaO), you'd sum the molar mass of calcium (40.08 g/mol) with oxygen (16.00 g/mol) to find a molar mass of 56.08 g/mol. Similarly for calcium sulfide (CaS), adding the molar mass of calcium (40.08 g/mol) to sulfur (32.07 g/mol) gives a molar mass of 72.15 g/mol.
Understanding molar masses allows you to compare different compounds and predict chemical behaviors, such as which compound would have more mass in a reaction.

Chemical Formulas

Chemical formulas are a simple representation of the elements in a compound and the ratios in which they combine. They are essential for understanding the composition of compounds.
For ionic compounds such as calcium oxide (CaO) and calcium sulfide (CaS), the formulas indicate a 1:1 ratio of positive to negative ions. Calcium always forms a Ca\(^{2+}\) ion, whereas oxygen and sulfur form O\(^{2-}\) and S\(^{2-}\) ions, respectively. This 1:1 ratio maintains the electrical neutrality of the compound.
Knowing how to interpret and construct chemical formulas is a key skill in chemistry that can help predict the products of various chemical reactions.

Calcium Compounds

Calcium compounds are an essential class of compounds in chemistry with significant practical applications. Calcium, a group 2 element, forms compounds by losing its two valence electrons, creating Ca\(^{2+}\) ions.
In reactions with nonmetals like oxygen or sulfur, calcium forms compounds such as calcium oxide (CaO) and calcium sulfide (CaS), respectively. These compounds have varied uses, from construction materials like lime (CaO) to potential uses in agricultural products.

• Calcium oxide (CaO) is often used in the manufacture of cement and in refining steel.
• Calcium sulfide (CaS) has applications in the production of decorative lighting and phosphorescent products.

Understanding the behavior and applications of calcium compounds is crucial for students and professionals in many chemical industries.