a. pH=2.07
b. pH=3
c. pH=8
pH=-log [H⁺]
a) 0.1 M HF Ka = 7.2 x 10⁻⁴
HF= weak acid
[tex]\tt [H^+]=\sqrt{Ka.M}\\\\(H^+]=\sqrt{7.2.10^{-4}\times 0.1}\\\\(H^+]=8.5\times 10^{-3}\\\\pH=3-log~8.5=2.07[/tex]
b) 1 x 10⁻³ M HNO₃
HNO₃ = strong acid
[tex]\tt pH=-log[1\times 10^{-3}]=3[/tex]
c) 1 x 10⁻⁸ M HCl
[tex]\tt pH=-log[1\times 10^{-8}]=8[/tex]