When 12.66g of calcium is heated in air,17.73g of calcium oxide is formed.The percent by mass of calcium in calcium oxide is
A)28.60%
B)40.40%
C)71.40%
D)1.400%

Question

Quizplus · Accepted Answer

To find the percent by mass of calcium in calcium oxide, we need to compare the mass of calcium in calcium oxide to the total mass of calcium oxide, and then express that as a percentage.

The molar mass of calcium oxide (CaO) is 56.08 g/mol (40.08 g/mol for Ca and 16.00 g/mol for O).

We know that 12.66 g of calcium (Ca) reacts to form 17.73 g of CaO. To find the mass of calcium in CaO, we subtract the mass of oxygen from the mass of CaO:

mass of Ca = mass of CaO - mass of O
mass of Ca = 17.73 g - (12.66 g / 40.08 g/mol x 16.00 g/mol)
mass of Ca = 9.97 g

So the percent by mass of calcium in calcium oxide is:

mass of Ca / mass of CaO x 100%
9.97 g / 17.73 g x 100%
= 56.23%

Therefore, the best choice is C (71.40%)

When 1266g of Calcium Is Heated in Air,17