What mass of sodium phosphide would be needed to react fully with 5.4x1025 formula units of strontium oxide?

5974 g of Na₃P

Explanation:

We determine the reaction:

2Na₃P + 3SrO  →  3Na₂O + Sr₃P₂

2 moles of sodium phosphide react to 3 moles of strontium oxide to produce 3 moles of sodium oxide and 1 mol of strontium phosphide.

We know that 1 mol of anything contains 6.02×10²³ formula units, so:

5.4×10²⁵ formula units . 1 mol/6.02×10²³ formula units = 89.7 moles

This is the amount we have, initially for SrO.

Ratio is 3:2. 3 moles of SrO react to 2 Na₃P

Then 89.7 moles of SrO may react to (89.7 . 2) /3 = 59.8 moles of Na₃P

We convert the moles to mass (mass . molecular weight)

59.8 mol . 99.9 g /mol = 5974 g

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