Question

2.5 Kg of Ca(OH)2 represents how many moles of Ca(OH)2?Group of answer choices33.7 moles74.5 moles148.3 moles222 moles

Answer 1

Answer : Option A , 33.7 moles

We are given :

• Mass of Ca(OH)2 = 2.5 kg = 2.5kg *1000g/kg = ,2500 grams,.

Step 1:

Calculate Molecular Mass of Ca(OH)2 = 74.09268 mol/g, calculated as follows :

`\begin{gathered} \text{Mol mass Ca(OH2 ) = mol mass Ca + 2}\cdot mol\text{ mass O + 2 }\cdot\text{ mol mass H } \\ \text{=40.098 + 2}\cdot15.999\text{+ 2 }\cdot1.00784 \\ =74.093\text{ g/mol} \end{gathered}`

Recall that Molecular mass of a substance is obtained from the periodic table .

Step 2 : Use the formula : moles = mass /molecular mass , to calculate number of moles of Ca(OH)2:

`\begin{gathered} \text{Moles Ca(OH)}_2=\text{ }(massCa(OH)_2)/(lecularmassCa(OH)_2) \\ \text{ =}\frac{2500\text{ g }}{74.093g}\cdot\text{ mol } \\ \text{ =33.74 moles } \\ \text{ }\approx33.7\text{ moles } \end{gathered}`

This means that there is 33.7 moles in 2.5kg of Ca(OH)2