Question

Critique the accuracy of each of these statements.

A) Indicators such as methyl red provide accurate and precise measurements of pH.

B) According to the Arrhenius definition of acids and bases, ammonia qualifies as a base.

C) The strength of an acid or base changes as its concentration changes.

Answer 1

A)

Methyl red indicates a pH below 5 when it is red and a pH above 5 when it is yellow. The predominantly red-colored methyl red caeca and ventriculus were therefore indicative of a pH below 5. On the other hand, a predominant yellow color was found in the colon, indicating a pH higher than 5. A yellow postcolon indicated a pH more basic than pH 6. This is in respect to the methyl red transition range (4.4–6.2) and the absence of yellow color below pH 6.2.

B)

Arrhenius theory says that acids are substances that dissociate in water to yield electrically charged atoms or molecules, called ions, one of which is a hydrogen ion (H ⁺), and that bases ionize in water to yield hydroxide ions (OH ⁻).

since ammonia doesn't have hydroxyl group...it can be classified as Arrhenius base...rather a aqueous solution of ammonia can be called as Arrhenius base...as it forms NH4OH..which can eventually release OH- ions .

C)

strength of acids and bases are measured as pH ...and we know that the pH = -log[conc.]

so as the concentration changes the pH hence the strength changes.