II. Pure magnesium metal is often found as ribbons and can easily burn in the presence of oxygen. When 3.86 g of magnesium ribbon burns with 155ml of oxygen at 1.0 atm and 275 K , a bright, white light and a white, powdery product is formed, magnesium oxide. How many grams of excess reactant remain?

Explanation:

Hello,

In this case, the undergoing chemical reaction is:

Next, we identify the limiting reactant by computing the moles of magnesium oxide yielded by 3.86 g of magnesium and 155 mL of oxygen at the given conditions via their 2:1:2 mole ratios and the ideal gas equation:

It means that the limiting reactant is the oxygen as it yields the smallest amount of magnesium oxide. Next, we compute the mass of magnesium consumed the oxygen only:

Thus, the mass in excess is:

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