Antacid neutralizes stomach acid by the following reaction:

Mg(OH)2 + 2HCl -----> MgCl2 + 2H2O
Calculate the amount of Mg(OH)2 (in grams) needed to neutralize 2.5 grams of HCl.

how many moles of HCL is 2.5 grams? The balanced equation states it will take half that number of moles of magnesium hydroxide

To calculate the amount of Mg(OH)2 needed to neutralize 2.5 grams of HCl, you need to use stoichiometry. Stoichiometry is a mathematical relationship between the balanced chemical equation and the quantities of the reactants and products involved.

Step 1: Determine the molar mass of HCl.
The molar mass of HCl is calculated by adding the atomic masses of hydrogen (H) and chlorine (Cl) together. The atomic mass of hydrogen is 1 gram/mol, and chlorine is 35.5 grams/mol. Therefore, the molar mass of HCl is 1 + 35.5 = 36.5 grams/mol.

Step 2: Convert grams of HCl to moles.
To convert grams to moles, divide the given mass of HCl (2.5 grams) by the molar mass of HCl calculated in Step 1.
2.5 grams HCl * (1 mol HCl / 36.5 grams HCl) ≈ 0.068 moles HCl

Step 3: Use the balanced chemical equation to determine the mole ratio.
From the balanced equation, you can see that the ratio of moles of HCl to moles of Mg(OH)2 is 2:1. This means that for every 2 moles of HCl, 1 mole of Mg(OH)2 is required.

Step 4: Convert moles of HCl to moles of Mg(OH)2.
Since the ratio of moles of HCl to moles of Mg(OH)2 is 2:1, the moles of Mg(OH)2 would also be 0.068 moles.

Step 5: Convert moles of Mg(OH)2 to grams.
To convert moles to grams, multiply the moles of Mg(OH)2 by the molar mass of Mg(OH)2. The molar mass of Mg(OH)2 can be calculated by adding the atomic masses of magnesium (Mg), oxygen (O), and hydrogen (H).
Molar mass of Mg(OH)2 = (24.3 grams/mol Mg) + (16.0 grams/mol O) + (1.0 grams/mol H) * 2 ≈ 58.3 grams/mol

0.068 moles Mg(OH)2 * (58.3 grams Mg(OH)2 / 1 mol Mg(OH)2) ≈ 4 grams Mg(OH)2

Therefore, approximately 4 grams of Mg(OH)2 would be needed to neutralize 2.5 grams of HCl.