How many moles of compound are there in 15.0g of potassium dichromate, K2Cr2O7?

The molar mass of substance is a property defined as its mass per unit quantity of substance, in other words, molar mass is the amount of mass that a substance contains in one mole.

The molar mass of a compound (also called Mass or Molecular Weight) is the sum of the molar mass of the elements that form it (whose value is found in the periodic table) multiplied by the number of times they appear in the compound.

Molar mass of K₂Cr₂O₇

In this case, you know the molar mass of the elements is:

K= 39.1 g/mole
Cr= 52 g/mole
O= 16 g/mole

So, the molar mass of the compound K₂Cr₂O₇ is calculated as:

K₂Cr₂O₇= 2× 39.1 g/mole + 2× 52 g/mole + 7× 16 g/mole

Solving:

K₂Cr₂O₇= 294.2 g/mole

Moles of K₂Cr₂O₇

Next, you can apply the following rule of three: If by definition of molar mass 294.2 grams are contained in 1 mole of the compound, 15 grams of the compound, in how many moles are they composed?

[tex]moles=\frac{15 gramsx1 mole}{294.2 grams}[/tex]

moles= 0.051

Finally, 15 grams are contained in 0.051 moles of the compound K₂Cr₂O₇.

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