Question

Din 1,2 kg solutie de hidroxid de sodiu 10% si 1,8 kg de solutie de hidroxid de sodiu 40% rezulta o solutie de concentratie:
A. 14%
B. 22%
C. 28%
D. 32%
E. 36%

Answer 1

100 kg sol.....10kg NaOH
1,2 kg sol.......x=0.12kg

100kg sol.......40kg NaOH
1,8kg sol........y=0.72kg 

ms=1,2+1,8=3 kg
m=x+y=0,12+0,72=0,84 kg
 3 kg sol..........0,84kg NaOH
100 kg sol.........z=28% deci C

Answer 2

Cp1=md1/ms1*100==>md1=Cp1*ms1/100=10*1.2/100=0.12kg NaOH

Cp2=md2/ms2*100==>md2=0.72kg NaOH

mdf=md1+md2=0.12+0.72=0.84kg
msf=ms1+ms2=1.2+1.8=3kg

Cpf=mdf/msf*100=0.84/3*100=28%