Question

How many oxygen atoms are in 3.00g of sodium dichromate, Na₂Cr₂O₇?

A) 6.90 x 10²¹ oxygen atoms
B) 0.0801 oxygen atoms
C) 9.85 x 10²⁰ oxygen atoms
D) 4.83 x 10²² oxygen atoms

Answer 1

To find the number of oxygen atoms in 3.00g of sodium dichromate, Na₂Cr₂O₇, calculate the number of moles and then use Avogadro's number to convert to atoms. The correct answer is A) 6.74 x 10²² oxygen atoms.

Step-by-step explanation:

To find the number of oxygen atoms in 3.00g of sodium dichromate, Na₂Cr₂O₇, we first need to calculate the number of moles of Na₂Cr₂O₇ and then use Avogadro's number to convert the moles to atoms.

The molar mass of Na₂Cr₂O₇ is 268 g/mol. To find the number of moles, we can use the formula:

moles = mass / molar mass = 3.00g / 268 g/mol = 0.0112 mol

Since there are 7 oxygen atoms in one formula unit of Na₂Cr₂O₇, we can multiply the number of moles by Avogadro's number to find the number of oxygen atoms:

number of oxygen atoms = 0.0112 mol × 6.022 × 10²³ atoms/mol = 6.74 x 10²² oxygen atoms

Therefore, the correct answer is A) 6.74 x 10²² oxygen atoms.