Question

Write the formula and calculate the molar mass for each of the following substances. a. carbon dioxide b. aluminum phosphate c. iron(III) carbonate d. lead(II) nitrate e. strontium chloride

Short answer

a. CO2, 44.01 g/mol b. AlPO4, 121.95 g/mol c. Fe2(CO3)3, 291.73 g/mol d. Pb(NO3)2, 331.22 g/mol e. SrCl2, 158.52 g/mol

Step-by-step solution

Write the formula for each substance

To write the formula for each substance, we must first identify the constituent elements, then write the formula by combining the elements in the correct stoichiometry (ratio of atoms/moles). a. Carbon dioxide (CO2): Carbon dioxide consists of 1 carbon atom (C) and 2 oxygen atoms (O2). b. Aluminum phosphate (AlPO4): Aluminum phosphate consists of 1 aluminum atom (Al), 1 phosphorus atom (P), and 4 oxygen atoms (O4). c. Iron(III) carbonate (Fe2(CO3)3): Iron(III) carbonate has 2 iron(III) atoms (Fe2), each connected to 1 carbonate ion (CO3). Since there are 3 carbonate ions, we write the formula as Fe2(CO3)3. d. Lead(II) nitrate (Pb(NO3)2): Lead(II) nitrate has one lead(II) atom (Pb) connected to 2 nitrate ions (NO3). We write the formula as Pb(NO3)2. e. Strontium chloride (SrCl2): Strontium chloride has 1 strontium atom (Sr) and 2 chlorine atoms (Cl2).

Calculate the molar mass for each substance

To calculate the molar mass, we simply add the molar mass of all the atoms in the chemical formula. Refer to a periodic table for the molar mass of each element. a. CO2: Molar mass = 1 × 12.01 (C) + 2 × 16.00 (O) = 12.01 + 32.00 = 44.01 g/mol b. AlPO4: Molar mass = 1 × 26.98 (Al) + 1 × 30.97 (P) + 4 × 16.00 (O) = 26.98 + 30.97 + 64.00 = 121.95 g/mol c. Fe2(CO3)3: Molar mass = 2 × 55.85 (Fe) + 3 × [1 × 12.01 (C) + 3 × 16.00 (O)] = 111.7 + 3 × (12.01 + 48.00) = 111.7 + 3 × 60.01 = 291.73 g/mol d. Pb(NO3)2: Molar mass = 1 × 207.2 (Pb) + 2 × [1 × 14.01 (N) + 3 × 16.00 (O)] = 207.2 + 2 × (14.01 + 48.00) = 207.2 + 2 × 62.01 = 331.22 g/mol e. SrCl2: Molar mass = 1 × 87.62 (Sr) + 2 × 35.45 (Cl) = 87.62 + 70.90 = 158.52 g/mol As a result, we have found the chemical formulas and molar masses for all provided substances: a. Carbon dioxide: CO2, 44.01 g/mol b. Aluminum phosphate: AlPO4, 121.95 g/mol c. Iron(III) carbonate: Fe2(CO3)3, 291.73 g/mol d. Lead(II) nitrate: Pb(NO3)2, 331.22 g/mol e. Strontium chloride: SrCl2, 158.52 g/mol

Key concepts

Chemical Formula

Understanding chemical formulas is essential when diving into chemistry, especially when calculating the molar mass of a substance. A chemical formula represents the types and numbers of atoms that make up a molecule. It's like a recipe that tells you exactly what and how much of each ingredient you need. For instance, in the compound carbon dioxide, denoted as CO₂, the 'C' stands for carbon, and the 'O₂' signifies that there are two oxygen atoms present for each carbon atom.

To write the correct chemical formula, you must understand the valency of each element—which tells us how many bonds an atom can form. Elements like aluminum in aluminum phosphate (AlPO₄) have a valency of three, usually forming three bonds. Knowing the correct stoichiometry or the ratio in which the elements combine is crucial in creating accurate chemical formulas.

Stoichiometry

Stoichiometry is at the heart of chemical equations and is a section of chemistry that involves the calculation of the reactants and products in a chemical reaction. It's essentially about the conservation of mass and the principle of balancing everything out. It tells us the proportions of reactants and products that are required or produced. For example, in iron(III) carbonate, Fe₂(CO₃)₃, the stoichiometry shows that there are two iron atoms for every three carbonate groups.

When we calculate the molar mass, we are applying stoichiometry. We add up the atomic masses of each element in the molecule, respecting their stoichiometric coefficients as shown in the formula. This counting lets us predict the mass of each substance involved in a reaction, which is essential for any laboratory work or industrial process where precise measurements are needed.

Periodic Table

The periodic table is not just a pivotal tool for chemists; it's the roadmap of chemistry. Each element in the periodic table has a unique molar mass, which is the mass of one mole of that element's atoms. When we look at the periodic table, we find essential details like atomic number, atomic mass, and valency, which help us in understanding the properties of elements. For instance, with lead(II) nitrate, Pb(NO₃)₂, we find the atomic mass of lead (Pb) to be 207.2, which we require to calculate its molar mass.

The periodic table also reveals patterns in element properties, often associated with their group or period. This systematic layout helps predict how elements might interact and what compounds they might form. With the right knowledge of how to use the periodic table, students can efficiently approach problems like finding the molar masses of strontium chloride or any other compound.