Potassium dichromate (K2Cr2O7) is used in tanning leather, decorating porcelain and water proofing fabrics. Calculate number of chromium atoms in 78.82 g of this compound.

3.22×10²³ Cr atoms are in 78.82g of K₂Cr₂O₇

Explanation:

Potassium dichromate → K₂Cr₂O₇

We determine the molar mass → 39.1 g/mol . 2 + 52 g/mol . 2 + 16g/mol . 7 = 294.2 g/mol

1 mol of K₂Cr₂O₇ has 2 moles of K, 2 moles of Cr and 7 moles of O.

1 mol = 294.2 g. Therefore, 294.2 g of compound have 2 moles of Cr

Let's make a rule of three:

294.2 g of K₂Cr₂O₇ have 2 moles of Cr

Then, 78.82 g of K₂Cr₂O₇ may have (78.82 . 2) / 294.2 = 0.536 moles

To calculate the number of atoms, you should know that:

1 mol contains NA atoms (6.02×10²³ particles)

Then 0.536 moles may contain (0.536 . NA) /1 = 3.22×10²³

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