Question

Suppose you have equal amounts of calcium, \(\mathrm{Ca}\), in two beakers. In one beaker, you react the calcium with oxygen, \(\mathrm{O}\). In the other beaker, you react the calcium with sulfur, \(\mathrm{S}\). The reaction with oxygen forms the compound calcium oxide, \(\mathrm{CaO}\). 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 formula is \( CaS \). b. \( CaS \) has more mass than \( CaO \).

Step-by-step solution

Understanding the Reaction with Oxygen

Calcium reacts with oxygen to form calcium oxide. The chemical formula for calcium oxide is \( CaO \). In this compound, calcium (Ca) is combined with one oxygen (O) atom.

Predicting the Reaction with Sulfur

Calcium reacts with sulfur in a similar way to oxygen because both oxygen and sulfur belong to the same group (Group 16) in the periodic table and have similar chemical properties. Therefore, the compound formed will have one calcium atom and one sulfur atom. So, the chemical formula for the compound is \( CaS \).

Comparing Molar Masses

To determine which compound has more mass, we need to calculate the molar mass of each compound. The molar mass of \( CaO \) is calculated as: \( 40.08 \, \text{g/mol (Ca)} + 16.00 \, \text{g/mol (O)} = 56.08 \, \text{g/mol} \). The molar mass of \( CaS \) is: \( 40.08 \, \text{g/mol (Ca)} + 32.06 \, \text{g/mol (S)} = 72.14 \, \text{g/mol} \).

Conclusion on Mass Comparison

Since the molar mass of \( CaS \) (72.14 g/mol) is greater than the molar mass of \( CaO \) (56.08 g/mol), the compound containing calcium and sulfur (\( CaS \)) has more mass than the compound containing calcium and oxygen (\( CaO \)).

Key concepts

Understanding Molar Mass

When dealing with chemical reactions and compounds, molar mass is a crucial concept. Molar mass refers to the mass of one mole of a substance. It's expressed in grams per mole (g/mol). To find the molar mass of a compound, you simply add up the atomic masses of all the atoms present in the formula.

For example, let's consider the compounds from our exercise: calcium oxide (\( \mathrm{CaO} \)) and calcium sulfide (\( \mathrm{CaS} \)). In calcium oxide, the molar mass is found by adding the atomic mass of calcium (40.08 g/mol) to that of oxygen (16.00 g/mol), resulting in 56.08 g/mol.

On the other hand, calcium sulfide involves adding the atomic mass of calcium (40.08 g/mol) to that of sulfur (32.06 g/mol), which gives us a molar mass of 72.14 g/mol. This simple addition is how you determine which compound has more mass.

Understanding molar mass helps in predicting the amounts of reactants and products in a chemical reaction, ensuring that calculations align with conservation of mass principles.

The Role of the Periodic Table in Chemical Reactions

The periodic table is more than just a chart of elements. It's a powerful tool for predicting the behavior of elements during chemical reactions. Elements are organized by increasing atomic number, but also by chemical properties.

Elements in the same group (vertical columns) often share chemical properties because they have the same number of valence electrons, which are the electrons involved in forming bonds. For instance, oxygen and sulfur belong to Group 16, making them similar in behavior. This similarity is why calcium reacts with both oxygen and sulfur to form compounds with similar stoichiometry (\( \mathrm{CaO} \) and \( \mathrm{CaS} \)).

By understanding where an element is located on the periodic table, one can infer its reactivity, the types of ions it forms, and the nature of the compounds it will create. This makes the periodic table an essential guide in predicting the outcomes of chemical reactions.

Understanding Ionic Compounds

In chemistry, ionic compounds are composed of positive and negative ions that are held together by ionic bonds. These compounds typically form between metals and non-metals.

In our exercise, calcium, a metal, reacts with non-metals oxygen and sulfur to form the ionic compounds \( \mathrm{CaO} \) and \( \mathrm{CaS} \), respectively. Calcium donates its two valence electrons, forming a \( \mathrm{Ca}^{2+} \) cation. Oxygen and sulfur, being in the same group, each form anions (\( \mathrm{O}^{2-} \) and \( \mathrm{S}^{2-} \)) by gaining two electrons.

The attraction between the positive \( \mathrm{Ca}^{2+} \) ion and the negative anions (\( \mathrm{O}^{2-} \) or \( \mathrm{S}^{2-} \)) creates a stable ionic compound. Ionic compounds are generally solid at room temperature and have high melting and boiling points due to the strength of the ionic bonds.

Understanding the formation and properties of ionic compounds is fundamental in predicting the results of chemical reactions and the nature of new substances formed.