Petunia needs 66.48 grams of potassium hydroxide (KOH) to run a reaction in class. How many moles of potassium hydroxide does she need? Please round your answer to two digits after the decimal point, and remember to include correct, complete units (including substance formula).

She needs 1.19 moles of potassium hydroxide.

Explanation:

Being the molar mass of the elements:

then the molar mass of potassium hydroxide is:

KOH= 39 g/mole + 16 g/mole + 1 g/mole= 56 g/mole

Being the mass of one mole of a substance, which can be an element or a compound, you can apply the following rule of three: if 56 g of KOH are present in 1 mole, 66.48 g of KOH in how many moles of the compound are they?

moles of KOH= 1.19

She needs 1.19 moles of potassium hydroxide.