Question

How many hydrogen atoms are in each of the following: (a) \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH},\) (b) \(\mathrm{Ca}\left(\mathrm{CH}_{3} \mathrm{COO}\right)_{2},\) (c) \(\left(\mathrm{NH}_{4}\right)_{3} \mathrm{PO}_{4} ?\)

Short answer

In the given compounds: (a) \(C_{2}H_{5}OH\) has 6 hydrogen atoms. (b) \(Ca(CH_{3}COO)_{2}\) has 6 hydrogen atoms. (c) \((NH_{4})_{3}PO_{4}\) has 12 hydrogen atoms.

Step-by-step solution

Analyze molecular formulas

First, let's analyze each molecular formula and identify the parts that contain hydrogen atoms. (a) C2H5OH There is one part containing hydrogen atoms: H5 and OH. (b) Ca(CH3COO)2 In this compound, Ca does not contain hydrogen atoms. We need to analyze the part inside the parentheses: (CH3COO)2. We can see H3 inside. (c) (NH4)3PO4 In this compound, the part containing hydrogen atoms is inside the parentheses: NH4. There is no hydrogen atom in PO4.

Count hydrogen atoms in each part

Now that we have identified the parts containing hydrogen atoms in each formula, we can count them up to find the total number of hydrogen atoms. (a) C2H5OH H5 has 5 hydrogen atoms. OH has 1 hydrogen atom. 5 hydrogen atoms in H5 + 1 hydrogen atom in OH = 6 hydrogen atoms (b) Ca(CH3COO)2 The compound inside the parentheses, CH3COO, has 3 hydrogen atoms in CH3, and the subscript 2 indicates that there are two of these compounds. So, we have to multiply the hydrogen count by 2. 3 hydrogen atoms in CH3 x 2 = 6 hydrogen atoms (c) (NH4)3PO4 NH4 has 4 hydrogen atoms, and the subscript 3 represents that there are three NH4 in the compound. 4 hydrogen atoms in NH4 x 3 = 12 hydrogen atoms

Write down the answer

Now that we have calculated the total number of hydrogen atoms in each compound, let us write down the answer. (a) C2H5OH has 6 hydrogen atoms. (b) Ca(CH3COO)2 has 6 hydrogen atoms. (c) (NH4)3PO4 has 12 hydrogen atoms.

Key concepts

Molecular Composition

Understanding the molecular composition of chemical compounds is crucial for comprehending how atoms interact and bind to form different substances. The molecular formula of a compound provides detailed information about its composition. It specifies the types and numbers of atoms present in a molecule. For instance, the molecular formula \( \text{C}_2\text{H}_5\text{OH} \) for ethanol, tells us there are 2 carbon atoms, 6 hydrogen atoms, and 1 oxygen atom in each molecule of ethanol. This insight is foundational for predicting chemical behavior and properties.

• Molecular formulas indicate the exact number of each type of atom in one molecule of a compound.
• They are distinct from empirical formulas, which show the simplest ratio of elements present.
• Recognizing molecular composition helps in determining reactions, interactions, and physical characteristics of compounds.

Hydrogen Atom Counting

Counting hydrogen atoms in a molecule involves understanding the specific segments of the molecule that contribute hydrogen atoms. As seen in the examples provided, the hydrogen count is influenced by the molecular structure and subscripts in the chemical formula. When examining a compound like \( \text{Ca}\left(\text{CH}_3\text{COO}\right)_2 \), the subscript "2" tells us there are two sets of the \( \text{CH}_3\text{COO} \) group. Each \( \text{CH}_3\text{COO} \) group contains 3 hydrogen atoms. By multiplying this by the subscript, you conclude there are 6 hydrogen atoms in total.

• Subscripts after groups in parentheses dictate how many times the group is present.
• Always multiply the number of hydrogen atoms in any group by the subscript to get accurate totals.
• Take note of separate hydrogen-adding groups within formulas like \( \text{OH} \) in \( \text{C}_2\text{H}_5\text{OH} \), which contributes additional hydrogen atoms.

Chemical Compounds

Chemical compounds are substances formed by the combination of two or more different elements bonding together chemically. Each compound has unique properties and specific molecular formulas, which reflect its identity and composition. Consider \( \left(\text{NH}_4\right)_3\text{PO}_4 \). This compound consists of the ammonium ion \( \text{NH}_4^+ \), which links with the phosphate ion \( \text{PO}_4^{3-} \). Understanding such compositions involves grasping basic chemical bonding and stoichiometry principles.

• Compounds can be either ionic or covalent, based on the type of bonding between the atoms.
• The structure of compounds determines their reactivity and interaction with other substances.
• Formulas of compounds like \( \text{Ca}\left(\text{CH}_3\text{COO}\right)_2 \) provide a map of elemental arrangement that aids in predicting behavior under different conditions.