Answer:
150 g (0.15 kg)
Explanation:
From the equation, 2 mol Ca₂(PO₄)₂ give us 1 mol P₄.
To calculate the weight, we need the molecular weights (Mw) of the elements:
Mw Ca= 40 g
Mw P= 31 g
Mw O= 16 g
2 mol Ca₂(PO₄)₂= 2 x (3 x (40g) + 2 x (31g) + 8 x (16 g))
2 mol Ca₂(PO₄)₂= 620 g
1 mol P₄= 4 x (31g) = 124 g
So, we can obtain 124 g of P₄ from 620 g Ca₂(PO₄)₂ (this is our recipe!)
Now, if the 75% of 1kg (=1000g) is Ca₂(PO₄)₂, we have:
1000 g x 75/100= 750 g Ca₂(PO₄)₂
Finally:
620 g Ca₂(PO₄)₂ ---------------------- 124 g P₄
750 g Ca₂(PO₄)₂ ------------------------X= (750 g x 124 g)/620 g= 150 g