Tentukan persen massa dan fraksi mol larutan NaOH dgn konsentrasi 4 molal

Asumsikan :
m NaOH = a gram
m air = b kg
Mr NaOH = Ar Na + Ar O + Ar H
= 23 + 16 + 1
= 40

Mr Air = 2 Ar H + Ar O
= 2(1) + 16
= 18

Kemolalan NaOH = 4 molal
n NaOH / m air = 4 molal
( a gram / 40 ) / b kg = 4 molal
1/40 a mol / b kg = 4 molal
a / 40 b = 4
a = 160 b

m total = m NaOH + m air
= 160 b + b
= 161 b

% NaOH = ( m NaOH / m total ) × 100%
% NaOH = ( 160 b / 161 b ) × 100%
% NaOH = 99,38%

Fraksi mol

n NaOH = m / Mr = a gram / 40 = 160.000 b gram / 40 = 4000 b mol

n air = m air / Mr air
= b kg / 18 = 1000 b gram / 18 = 55,556 b mol

n total = n NaOH + n air
= 4000 b mol + 55,556 b mol
= 4055,56 b mol

X NaOH = n NaOH / n total
= 4000 b mol / 4055,56 b mol
= 0,9863

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