( ( Acid-base indicators ) ( ( are ( ( substances ( that ( change color ) ) ) ( as ( ( ( ( ( ( a function ) ( of pH ) ) , ) usually ) over ) ( ( a range ) ( of ( ( ( 1 to ) 2 ) ( pH units ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Acid-base) (NNS indicators)) (VP (VBP are) (VP (VBG substances) (NP (DT that) (NN change) (NN color)) (PP (IN as) (NP (NP (NP (DT a) (NN function)) (PP (IN of) (NP (NN pH)))) (, ,) (RB usually) (IN over) (NP (NP (DT a) (NN range)) (PP (IN of) (NP (QP (CD 1) (TO to) (CD 2)) (NN pH) (NNS units)))))))) (. .)))
Acid-base indicators are substances that change color as a function of pH, usually over a range of 1 to 2 pH units.
(ROOT (S (SBAR (IN If) (S (NP (DT a) (NN substance)) (VP (VBZ has) (NP (DT a) (NN ph) (NN value)) (NP (QP (JJR greater) (IN than) (CD 7)))))) (, ,) (NP (DT that)) (VP (VBZ indicates) (SBAR (IN that) (S (NP (PRP it)) (VP (VBZ is) (NP (NN base)))))) (. .)))
If a substance has a ph value greater than 7,that indicates that it is base.