Question

Calculate the molar mass for each of the following substances. a. barium perchlorate b. magnesium sulfate c. lead(II) chloride d. copper(II) nitrate e. tin(IV) chloride f. phenol, \(\mathrm{C}_{6} \mathrm{H}_{6} \mathrm{O}\)

Short answer

The molar masses for the given substances are as follows: a. Barium perchlorate: \(336.23\ g/mol\) b. Magnesium sulfate: \(120.38\ g/mol\) c. Lead(II) chloride: \(278.1\ g/mol\) d. Copper(II) nitrate: \(187.57\ g/mol\) e. Tin(IV) chloride: \(260.51\ g/mol\) f. Phenol: \(94.12\ g/mol\)

Step-by-step solution

Identify elements and their moles in the compound

In barium perchlorate, we have barium (Ba), chlorine (Cl), and oxygen (O). The chemical formula of barium perchlorate is \(\mathrm{Ba(ClO4)2}\), which means we have: - 1 mole of barium - 2 moles of chlorine - 8 moles of oxygen

Calculate the molar mass

Using the periodic table, we can find the molar mass of each element and multiply by the number of moles. Then, add all the results together: Molar mass = (1 × 137.33) + (2 × 35.45) + (8 × 16.00) = 137.33 + 70.90 + 128.00 = 336.23 g/mol b. Magnesium sulfate

Identify elements and their moles in the compound

In magnesium sulfate, we have magnesium (Mg), sulfur (S), and oxygen (O). The chemical formula of magnesium sulfate is \(\mathrm{MgSO4}\). We have: - 1 mole of magnesium - 1 mole of sulfur - 4 moles of oxygen

Calculate the molar mass

Calculate the molar mass in the same way as before: Molar mass = (1 × 24.31) + (1 × 32.07) + (4 × 16.00) = 24.31 + 32.07 + 64.00 = 120.38 g/mol c. Lead(II) chloride

Identify elements and their moles in the compound

In lead(II) chloride, we have lead (Pb) and chlorine (Cl). The chemical formula of lead(II) chloride is \(\mathrm{PbCl2}\). We have: - 1 mole of lead - 2 moles of chlorine

Calculate the molar mass

Calculate the molar mass: Molar mass = (1 × 207.2) + (2 × 35.45) = 207.2 + 70.90 = 278.1 g/mol d. Copper(II) nitrate

Identify elements and their moles in the compound

In copper(II) nitrate, we have copper (Cu), nitrogen (N), and oxygen (O). The chemical formula of copper(II) nitrate is \(\mathrm{Cu(NO3)2}\). We have: - 1 mole of copper - 2 moles of nitrogen - 6 moles of oxygen

Calculate the molar mass

Calculate the molar mass: Molar mass = (1 × 63.55) + (2 × 14.01) + (6 × 16.00) = 63.55 + 28.02 + 96.00 = 187.57 g/mol e. Tin(IV) chloride

Identify elements and their moles in the compound

In tin(IV) chloride, we have tin (Sn) and chlorine (Cl). The chemical formula of tin(IV) chloride is \(\mathrm{SnCl4}\). We have: - 1 mole of tin - 4 moles of chlorine

Calculate the molar mass

Calculate the molar mass: Molar mass = (1 × 118.71) + (4 × 35.45) = 118.71 + 141.80 = 260.51 g/mol f. Phenol

Identify elements and their moles in the compound

In phenol, we have carbon (C), hydrogen (H), and oxygen (O). The chemical formula of phenol is \(\mathrm{C6H6O}\). We have: - 6 moles of carbon - 6 moles of hydrogen - 1 mole of oxygen

Calculate the molar mass

Calculate the molar mass: Molar mass = (6 × 12.01) + (6 × 1.01) + (1 × 16.00) = 72.06 + 6.06 + 16.00 = 94.12 g/mol

Key concepts

Understanding Chemical Compounds

Chemical compounds are substances composed of two or more different elements that are chemically bonded together. These bonds can occur through the sharing of electrons (covalent bonds), the transfer of electrons (ionic bonds), or other methods. The composition and structure of a chemical compound determine its properties and reactions.

Some key characteristics of chemical compounds include:

• Definite composition: The elements in a compound are always combined in a specific proportion by mass.
• Unique properties: Compounds have different properties from their constituent elements. For instance, water, made from hydrogen and oxygen, behaves differently from either element alone.
• Fixed ratios: The compound's formula indicates the fixed ratio of its elements. For example, in magnesium sulfate (\( \mathrm{MgSO_4} \)), magnesium, sulfur, and oxygen are combined in a 1:1:4 ratio.

Understanding chemical compounds is essential for predicting chemical behavior and how different substances will interact.

Decoding Molecular Formulas

A molecular formula gives the actual number of atoms of each element in a molecule of a compound. It provides essential information about the chemical makeup. However, it doesn't indicate the structure or how atoms are connected. Let's consider the chemical formula for phenol, \( \mathrm{C_6H_6O} \). This formula tells us:

• There are 6 carbon atoms.
• There are 6 hydrogen atoms.
• There is 1 oxygen atom.

The molecular formula differs from empirical formulas, which show the simplest whole-number ratio of atoms in a compound. For example, a compound with a molecular formula of \( \mathrm{H_2O_2} \) (hydrogen peroxide) has an empirical formula of \( \mathrm{HO} \).

When calculating molar mass, the molecular formula is crucial as it helps determine how many grams per mole each element contributes to the compound.

The Role of Stoichiometry in Chemistry

Stoichiometry is the field of chemistry that deals with the quantitative relationships of the reactants and products in a chemical reaction. It involves using balanced chemical equations to make these determinations. Stoichiometry helps chemists understand the proportions of elements in compounds, crucial for reactions to occur efficiently.

Key functions of stoichiometry include:

• Determining the amounts of substances consumed and produced in a reaction.
• Calculating reactant and product masses, using molar mass as derived from empirical or molecular formulas.
• Assisting in measuring the efficiency and yield of a reaction.

For example, knowing the exact stoichiometric relationships in the formation of lead(II) chloride (\( \mathrm{PbCl_2} \)) determines the precise amounts of lead and chloride needed, minimizing waste.

Utilizing the Periodic Table

The periodic table is an essential reference in chemistry, organizing elements based on properties and atomic structure. Each element's position on the table provides insights into its characteristics and interactions with other elements.

Features of the periodic table include:

• Groups and Periods: Columns (groups) share chemical properties, while rows (periods) indicate increasing electron shells.
• Atomic Number and Mass: Each element's atomic number is its number of protons, and its atomic mass is the average mass of the element's isotopes.
• Elemental Categories: Elements are classified into metals, nonmetals, and metalloids, which helps predict chemical behavior and bonding tendencies.

To calculate molar mass as done in the exercises, use the periodic table to find the atomic masses: add them according to the number of each atom present in the compound's molecular formula. This provides the mass in grams of one mole of the compound, essential for conversions in stoichiometry.