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Verified Answer :

MissPhiladelphia

For the answer to the question above, we have to use this formula
moles equal mass divided by the molar mass 

a) 4.50 g divided by the molar mass of water 
molar mass of water = 2x1.0 + 1x16.0 = 18 
4.50 g / 18.0 g per mole = 0.25 moles 

b) 471.6 g / Molar mass of Ba(OH)2 = moles 

c) 129.68 g / molar mass of Fe3(PO4)2 = moles 

atoms of P in Mg3(PO4)2 
2 atoms of P in each molecule of Mg3(PO4)2 
247 g / molar mass of Mg3(PO4)2 = moles 
moles of Mg3(PO4)2 x 6.022x10^23 = molecules of Mg3(PO4)2

I hope my answers gave you clarity on your question.

Explanation:

To calculate the number of moles, we use the equation:

\(\text{Number of moles}=\frac{\text{Given mass}}{\text{Molar mass}}\)    ......(1)

  • For 1: 4.50 g of water

Given mass of water = 4.50 g

Molar mass of water = 18 g/mol

Putting values in equation 1, we get:

\(\text{Moles of }H_2O=\frac{4.50g}{18g/mol}=0.25mol\)

Hence, the moles of given amount of water is 0.25 moles.

  • For 2: 471.6 g of barium hydroxide

Given mass of barium hydroxide = 471.6 g

Molar mass of barium hydroxide = 171.34 g/mol

Putting values in equation 1, we get:

\(\text{Moles of }Ba(OH)_2=\frac{471.6g}{171.34g/mol}=2.75mol\)

Hence, the moles of given amount of barium hydroxide is 2.75 moles.

  • For 3: 129.68 g of iron phosphate

Given mass of iron phosphate = 129.68 g

Molar mass of iron phosphate = 150.82 g/mol

Putting values in equation 1, we get:

\(\text{Moles of }Fe_3(PO_4)_2=\frac{129.68g}{150.82g/mol}=0.86mol\)

Hence, the moles of given amount of iron phosphate is 0.86 moles.