Question

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Tentukan Kemolaran (molaritas) larutan berikut !
1. Larutan yg mengandung 12% massa CH3COOH, Massa Jenis larutan adalah 1,2 gr/mL
2. Larutan yg mengandung 10% massa NaOH, Massa jenis larutan adalah 1,1 kg/L

Answer 1

Nomor 1
Mr CH3COOH = 60
ρ = 1,2 gr / mL
% w/w CH3COOH = 12%

Asumsikan massa larutan = 100 gram
m CH3COOH = kadar × m larutan = 12% × 100 gr = 12 gram

n CH3COOH = m / Mr = 12 gram / 60 = 0,2 mol

V larutan = m / ρ = 100 gr / 1,2 gr/mL = 83,33 mL

[CH3COOH] = n × (1000 mL / V ) = 0,2 mol × 1000 mL / 83,33 mL = 2,4 M

Cara Cepat
[CH3COOH] = ρ × kadar × 10 / Mr CH3COOH
[CH3COOH] = 1,2 gr / mL × 12% × 10 / 60
[CH3COOH] = 2,4 M

Nomor 2
Mr NaOH = 40
ρ = 1,1 kg / L = 1100 gr / 10^6 mL = 0,0011 gr/mL
% w/w NaOH = 10%

Asumsikan massa larutan = 100 gram
m NaOH = kadar × m larutan = 10% × 100 gr = 10 gram

n NaOH = m / Mr = 10 gram / 40 = 0,25 mol

V larutan = m / ρ = 100 gr / 0,0011 gr/mL = 90909,091 mL = 90,9 L

[NaOH] = n / V = 0,2 mol / 90,9 L = 2,75 × 10^-3 M


Cara Cepat
[NaOH] = ρ × kadar × 10 / Mr NaOH
[NaOH] = 0,0011 gr/mL × 10% × 10 / 40
[NaOH] = 2,75 × 10^-3 M