1) a compound with a formula weight of 630, consists of 32.79% sodium , 13.02% A

Question

1) a compound with a formula weight of 630, consists of 32.79% sodium , 13.02% Al, and the rest flourine. what is the empirical and molecular formula

2) a compund weighing 5.325 g with a formula weight of 408 consists of 3.758 g carbon, 0.316 g hydrogen, and the rest oxygen, determine the empircal and molecular formula.

3) a compound with a formula weight of 62.1 consists of 9.7% hydrogen, 51.6% oxygen and the rest catbon, what is the empirical and molecular formula

4) how many calcim atoms are in 0.154 grams of calcium phosphate

Explanation / Answer

1.

Element    Mass    No.of moles       DIvision by small number      Nearest whole number

   Na        32.79    32.79/23 = 1.426   1.426 / 0.4822 = 2.96                    3

Al          13.02   13.02/27 = 0.4822   0.4822 / 0.4822 = 1                       1

F          54.19     54.19/19 = 2.852    2.852 / 0.4822 = 5.91                     6

So, the emperical formula = Na3AlF6

Emperical formula mass = 3(23)+27+6(19) =210

Formula weight = 630

Therefore,

n = formula weight / emperical formula weight

n = 630 / 210

n = 3

Therefore,

Molecular formula = [Na3AlF6]n = [Na3AlF6]3 = Na9Al3F18

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