2. a) mH₂O = 200g
msi = 150g sol.
C = 25%
C = md/ms×100 ⇒ md = C×ms/100 = 25×150/100 = 37,5g
msf = msi + mH₂O adaugata = 150+200 = 350g
Cf = mdi/msf×100 = 37,5/350×100 = 10,714%
b) md ad= 8g NaCl
msi = 80g
C=4%
Ci = mdi/msi×100 ⇒ mdi = Ci×msi/100 = 4×80/100 = 3,2g NaCl
mdf = mdi+md ad = 3,2+8 = 11,2g
msf = msi+md ad = 80+8 = 88g
Cf = mdf/msf×100 = 11,2/88×100 = 12,72%
c) md ad = 15g NaCl
m H₂O ad = 100g
msi = 225g NaCl
Ci=15%
Ci = mdi/msi×100 ⇒ mdi = Ci×msi/100 = 15×225/100 = 33,75g NaCl
mdf = mdi+md ad = 33,75+15 = 48,75
msf = msi+md ad + m H₂O ad = 225+15+100 = 340g sol. NaCl
Cf = mdf/msf×100 = 48,75/340×100 = 14,33%
6.md ad = ? g NaCl
msi = 200g
Ci = 10%
Cf = 25%
Ci = mdi/msi×100 ⇒ mdi = 10×200/100 = 20g NaCl
msi = mdi+mH₂O =⇒ mH₂O = msi-mdi = 200-20 = 180g
Cf×mH₂O = mdf(100-C)
25×180 = mdf(100-25)
4500 = 75mdf ⇒ mdf = 4500/75 = 60g NaCl
md NaCl ad = mdf-mdi = 60-20 = 40g