a) 1. Ca(OH)2+2 HF--->CaF2+2 H2O
Ca2+ +2OH- +2H+ +2F- --->Ca2+ +2F- +2H2O
2 OH- +2 H+ --->2 H2O
2. Ca+2 HF--->CaF2+H2
3. CaO+2 HF--->CaF2+H2O
b) 1. 2 NaOH+H2SO4--->Na2SO4+2 H2O
2 Na+ +2OH- +2H+ +SO4 2- --->2 Na+ +SO4 2- +2 H2O
2 OH- +2 H+ --->2 H2O
2. 2 Na+H2SO4--->Na2SO4+H2
3. Na2O+H2SO4--->Na2SO4+H2O