4. How many grams of silver oxide are needed to react with 7.9 g of hydrochloric acid to produce silver chloride and water?

To solve this problem, we first need to write the balanced chemical equation for the reaction between silver oxide and hydrochloric acid. The balanced chemical equation is:
2Ag2O + 4HCl -> 4AgCl + 2H2O
From the balanced chemical equation, we can see that 2 moles of silver oxide react with 4 moles of hydrochloric acid to produce 4 moles of silver chloride and 2 moles of water.
Next, we can use this information to calculate the amount of silver oxide needed to react with 7.9 g of hydrochloric acid.
First, we calculate the number of moles of hydrochloric acid (HCl) using its molar mass:
Molar mass of HCl = 1.007 grams/mole (for H) + 35.453 grams/mole (for Cl) = 36.46 grams/mole
Number of moles of HCl = mass of HCl / molar mass of HCl
= 7.9 g / 36.46 g/mol
≈ 0.216 moles of HCl
From the balanced chemical equation, we know that 2 moles of Ag2O react with 4 moles of HCl. Therefore, we can use the mole ratio to calculate the number of moles of Ag2O needed:
Moles of Ag2O = (0.216 moles of HCl / 4 moles of HCl) * 2 moles of Ag2O
≈ 0.108 moles of Ag2O
Finally, we can convert the moles of Ag2O to grams:
Molar mass of Ag2O = 2*(107.87 g/mol) + 16.00 g/mol
= 231.74 g/mol
Mass of Ag2O = moles of Ag2O * molar mass of Ag2O
≈ 0.108 moles * 231.74 g/mol
≈ 25.04 grams
Therefore, approximately 25.04 grams of silver oxide are needed to react with 7.9 g of hydrochloric acid.