Magnesium combines with oxygen to form magnesium oxide. If 20.07 g of magnesium reacts completely with 6.70 g of oxygen, what is the percent by mass of oxygen in magnesium oxide?
Mg = 20.07
MgO = 20.07+6.70 = total
%Mg = (20.07/total)*100 = ?
75 or 74.9
To find the percent by mass of oxygen in magnesium oxide, we need to calculate the mass of oxygen in magnesium oxide and then divide it by the total mass of magnesium oxide and multiply by 100.
Step 1: Find the moles of magnesium and oxygen using their respective molar masses.
The molar mass of magnesium (Mg) is 24.31 g/mol.
The molar mass of oxygen (O) is 16.00 g/mol.
Moles of magnesium = mass of magnesium / molar mass of magnesium
Moles of magnesium = 20.07 g / 24.31 g/mol
Moles of magnesium = 0.825 mol (rounded to 3 decimal places)
Moles of oxygen = mass of oxygen / molar mass of oxygen
Moles of oxygen = 6.70 g / 16.00 g/mol
Moles of oxygen = 0.419 mol (rounded to 3 decimal places)
Step 2: Determine the mole ratio between magnesium and oxygen to find the limiting reactant.
The balanced chemical equation for the reaction is: 2 Mg + O2 -> 2 MgO
From the equation, we can see that 2 moles of magnesium react with 1 mole of oxygen to form 2 moles of magnesium oxide.
Based on the mole ratio, we can see that for every 2 moles of magnesium, we need 1 mole of oxygen to react completely. However, we only have 0.419 moles of oxygen available, which is less than the required amount.
Therefore, oxygen is the limiting reactant, and the reaction will consume all of the available 0.419 moles of oxygen.
Step 3: Calculate the mass of oxygen in magnesium oxide.
The molar mass of magnesium oxide (MgO) is 40.31 g/mol (24.31 g/mol for magnesium + 16.00 g/mol for oxygen).
Mass of oxygen in magnesium oxide = moles of oxygen in magnesium oxide * molar mass of oxygen
Mass of oxygen in magnesium oxide = 0.419 mol * 16.00 g/mol
Mass of oxygen in magnesium oxide = 6.704 g (rounded to 3 decimal places)
Step 4: Calculate the percent by mass of oxygen in magnesium oxide.
Percent by mass of oxygen in magnesium oxide = (mass of oxygen / mass of magnesium oxide) * 100
Percent by mass of oxygen in magnesium oxide = (6.704 g / (20.07 g + 6.704 g)) * 100
Percent by mass of oxygen in magnesium oxide = 24.97%
Therefore, the percent by mass of oxygen in magnesium oxide is approximately 24.97%.
To find the percent by mass of oxygen in magnesium oxide, we need to calculate the mass of oxygen in magnesium oxide and then divide it by the total mass of magnesium oxide.
First, we need to find the number of moles of magnesium and oxygen in the given amounts.
The molar mass of magnesium (Mg) is 24.31 g/mol, and the molar mass of oxygen (O) is 16.00 g/mol.
The number of moles of magnesium is calculated as follows:
moles of magnesium = mass of magnesium / molar mass of magnesium
moles of magnesium = 20.07 g / 24.31 g/mol
moles of magnesium = 0.8254 mol (rounded to four decimal places)
Similarly, the number of moles of oxygen is calculated as follows:
moles of oxygen = mass of oxygen / molar mass of oxygen
moles of oxygen = 6.70 g / 16.00 g/mol
moles of oxygen = 0.4188 mol (rounded to four decimal places)
According to the balanced chemical equation, the ratio of moles between magnesium and oxygen is 2:1. This means that for every 2 moles of magnesium, we have 1 mole of oxygen.
Since the ratio is 2:1, the number of moles of oxygen in magnesium oxide is half of the number of moles of magnesium:
moles of oxygen in magnesium oxide = 0.4188 mol / 2
moles of oxygen in magnesium oxide = 0.2094 mol (rounded to four decimal places)
Now, to find the mass of oxygen in magnesium oxide, we multiply the number of moles of oxygen in magnesium oxide by the molar mass of oxygen:
mass of oxygen in magnesium oxide = moles of oxygen in magnesium oxide * molar mass of oxygen
mass of oxygen in magnesium oxide = 0.2094 mol * 16.00 g/mol
mass of oxygen in magnesium oxide = 3.35 g (rounded to two decimal places)
Finally, to find the percent by mass of oxygen in magnesium oxide, we divide the mass of oxygen in magnesium oxide by the total mass of magnesium oxide and multiply by 100:
percent by mass of oxygen = (mass of oxygen / total mass of magnesium oxide) * 100
percent by mass of oxygen = (3.35 g / (20.07 g + 6.70 g)) * 100
percent by mass of oxygen = 3.35 g / 26.77 g * 100
percent by mass of oxygen = 12.50% (rounded to two decimal places)
Therefore, the percent by mass of oxygen in magnesium oxide is 12.50%.