What is the formula and the formula mass in grams per mole (g / mol) of each species? c. magnesium hydroxide
The correct answer and explanation is:
Correct Answer:
- Chemical formula of magnesium hydroxide: Mg(OH)₂
- Formula mass (molar mass): 58.32 g/mol
300-Word Explanation:
Magnesium hydroxide is an inorganic compound commonly used as an antacid and laxative. Its chemical formula is Mg(OH)₂, meaning it consists of one magnesium (Mg) ion and two hydroxide (OH⁻) ions.
To calculate the formula mass (also known as molar mass), we add the atomic masses of all the atoms present in one formula unit of the compound. The atomic masses are based on values from the periodic table and are expressed in grams per mole (g/mol).
Step-by-step Calculation:
- Magnesium (Mg):
- Number of atoms: 1
- Atomic mass: 24.31 g/mol
- Total contribution: 1 × 24.31 = 24.31 g/mol
- Oxygen (O):
- Number of atoms: 2 (since OH appears twice)
- Atomic mass: 16.00 g/mol
- Total contribution: 2 × 16.00 = 32.00 g/mol
- Hydrogen (H):
- Number of atoms: 2 (since OH appears twice)
- Atomic mass: 1.01 g/mol
- Total contribution: 2 × 1.01 = 2.02 g/mol
Total Formula Mass:
24.31 (Mg)+32.00 (O)+2.02 (H)=58.33 g/mol24.31\ \text{(Mg)} + 32.00\ \text{(O)} + 2.02\ \text{(H)} = \boxed{58.33\ \text{g/mol}}
(Rounded slightly, this is typically cited as 58.32 g/mol in many textbooks.)
Summary:
- Formula: Mg(OH)₂
- Formula mass: 58.32 g/mol
This value tells us that one mole of magnesium hydroxide weighs 58.32 grams. It is essential for stoichiometric calculations in chemistry, such as determining how much of the compound is needed in a reaction.