Question

An alkalie is titrated against an acid with methyl orange as indicator, which of the following is a correct combination
A. `{:("Base","Acid","End point"),("Strong","Strong","Pinkish red to yellow"):}`
B. `{:("Base","Acid","End point"),("Weak","Strong","Yellow to pinkish red"):}`
C. `{:("Base","Acid","End point"),("Strong","Strong","Pink to colourless"):}`
D. `{:("Base","Acid","End point"),("Weak","Strong","Colourless to pink"):}`

Answer 1

Correct Answer - B
`underset("weak base")(NH_(4)OH)+underset("Strong acid")(HCl) to NH_(4)Cl+H_(2)O`
At end point pH will be less than 7
as strong acid weak base salt have `pH=7-((pK_(b)+logc))/(2)`
`therefore`Methyl orange will change colour from yellow to pinkish red at the end point.