Question

How many moles of potassium sulfide are there in 61.0g

A. 0.592 mol

B. 0.859 mol

C. 671 mol

D. 0.555 mol

Answer 1

Considering the definition of molar mass, the correct answer is option D. 0.555 moles are in 61 grams of potassium sulfide, K₂S.

Definition of molar mass

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 potassium sulfide

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

• K= 39 g/mole
• S= 32 g/mole

So, the molar mass of the compound K₂S is calculated as:

K₂S=2× 39 g/mole + 32 g/mole

Solving:

K₂S= 110 g/mole

Moles that contain 61 grams of K₂S

Now, you can apply the following rule of three: if 110 grams of the compound are contained in 1 mole, 61 grams are contained in how many moles?

$amount of moles=\frac{61 gramsx1 mole}{110 grams}$

amount of moles= 0.555 moles

Finally, the correct answer is option D. 0.555 moles are in 61 grams of potassium sulfide, K₂S.

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