Question

Sodium hydroxide (NaOH) is produced, stored and shipped as a 50 wt% solution in water. a) What is the mole fraction of NaOH in a 50 wt% NaOH solution? (4 marks) b) The user buys 50 wt% sodium hydroxide, and dilutes it with pure water to 10 wt% NaOH solution for his uses. i. Sketch this process. [3 marks] II. Show the overall mass balance for this process, indicating assumptions. [4 marks)

Answer 1

O Consider Hs2-Ms, = AUS In table provided of water tb Naon increases then molar enthalphy decreases Lgoes we can see as mole ratio more on -ve Side]. This decrease in enthalphy COmes out as heat as pez enegy is generatid in He'dilution provess Conscevathion law. Hence heat get hottes Mence the solution will

(Consider x gm of 50 wt% NalH dilution I gm of water foe of 10 t% WaDH as product Now mass halance as below Now Consider a = 100 kg (50 wt% WaOH soluthen) Naon Chure ) = 50 kg in d water li = 67 50 ký in e Now z = 100ty we know firal Solution is 10% Hence 10% = Naon wt X ID0 50 10 X100 100 +7 10x (100 +y) = 50X 100 1000t 107 5000 = 5000- 000 = 4000 4000 70 Now kg of water added = 400 kg. 400 50 kg of Aure Naon fed 17 kg ot water added /kg of pure Naon fed

Mole Now we Will Cala solution gm NaOH (Pure) = 50 gm Consider 100 water (Pure) = 50 Naon moles 50 Naon moteculat wright (23+16+1) 40 = 1:25 mrle Water moles 50 water moleule weight (2416) 50 18 = 2.778 moles of aaon meles of Naont wwater mole frachion of Naln 1-25 125+2.778 0.31 mole frachion if NaoH =031 6)-> water Dilution 50% NaoH (a) 10% NaOH