a) NaOH + HCl ---> NaCl + H2O
b) Có nNaOH = 20 : 40 = 0,5 (mol)
Theo PTHH, nHCl = nNaOH 
=> nHCl = 0,5 (mol)
=> mHCl = 0,5 . 36,5 = 18,25 (g)
c) có nNaCl = nNaOh = 0,5 (mol)
=> mNaCl = 0,5 . 58,5 = 29,25 (g)
có m ddNaCl = 20 + 180 =200 (g)
=> C

a)NaOH+HCl ---NaCL+H2O
    1          1           1         1
   0,5       0,5        0,5      0,5
b)nNaOH=20/40=0,5mol
nHCl=180/36,5=4,9mol
HCl dư,tính theo NaOH
mHCl=0,5.36,5=18,25g
c)mdds=mddNaOH+mddHCl=20+180=200g
C%NaCl=(18,25/200).100%=9,125%

mNaCl=0,5.58,5=29,25g
C%=(29,25/200).100%=14,625%