Problem 6
Borax is a hydrated compound with the following composition:
1 2 . 0 4 % N a ; 1 1 . 5 2 % B ; 2 9 . 3 2 % O ; 4 7 . 1 2 % H X 2 O
From the given percentage composition, what is the empirical formula of borax?
Relative Atomic Masses : B = 10.8; Na = 23.0; O = 16; H = 1.0
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2 solutions
Got it correct with memory.... xD
Substituent N a B O H X 2 O % by mass 1 2 . 0 4 1 1 . 5 2 2 9 . 3 2 4 7 . 1 2 Molar mass 2 3 1 0 . 8 1 6 1 8 relative mole 0 . 5 2 3 4 7 8 2 6 1 1 . 0 6 6 6 6 6 6 6 7 1 . 8 3 2 5 2 . 6 1 7 7 7 7 7 7 8 ÷ by the lowest 1 2 . 0 3 7 6 5 2 2 7 3 . 5 0 0 6 2 2 9 2 4 5 . 0 0 0 7 3 8 2 8 × 2 2 4 7 1 0
The relative moles of the substituent are obtained from molar mass % by mass . Then they are divided by the lowest relative moles (which is that of N a , then × 2 to get whole numbers for the formula. Therefore, the formula is N a X 2 B X 4 O X 7 ˙ 1 0 H X 2 O .