Question

When magnesium burns in air, it combines with oxygen to form magnesium oxide according to the following equation. What mass in grams of magnesium oxide is produced from 2.00 mol of magnesium?
2Mg(s) + O2(g) -> 2MgO(s)
What is the given quantity? ______
What is the unknown quantity? ______
Write the two conversion factors needed to solve the problem.
________ _______
Calculate the molar mass of the unknown using the given quantity and the two conversion factors.
______

Answer 1

Answer: The given quantity is 2 moles of magnesium or 48 g of magnesium.

The unknown quantity is mass of MgO in grams.

Molar mass of MgO = 40 g

Explanation: $2Mg+O_2\rightarrow 2MgO$

As can be seen from the chemical equation, 2 moles of magnesium react with 1 mole of oxygen gas to give 2 moles of MgO.

According to mole concept, 1 mole of every substance weighs equal to its molar mass.

Thus $2\times 24= 48 g$ of magnesium produce=$2\times 40= 80 g$ of MgO.

Molar mass is the mass in grams of 1 mole of the substance.

Thus if 2 moles of MgO weigh= 80 g

1 mole of MgO will weigh=$\frac{80}{2}\times 1 =40g$

Thus molar mass of MgO is 40 g.