Question

Match the following pH values: 1, 2, 5, 6, 6.5, 8, 11, 11, and 13 with the following chemicals (of equal concentration): HBr, NaOH, NaF, NaCN, NH₄F, CH₃NH₃F, HF, HCN, and NH₃. Answer this question without performing calculation.

Short answer

Strong acids have a high concentration of H⁺ ions, thus low pH, while strong bases have low concertation of H⁺ ions, hence high pH.

Step-by-step solution

Acid, Bases, and Salts

HBr: Strong acid, hence pH should be close to 0

HF: Weak acid

HCN: Weak acid, weaker than HF

NH₄: (Salt of a weak acid and weak base, pH should be near 7)

CH₃NH₃F :(Salt of a weak acid and weak base,pH should be near 7)

NaF: (Salt of a weak acid and strong base, pH should be more than 7)

NaCN: (Salt of a weak acid and strong base, pH should be more than 7)

NH₃: Weak base

NaOH: Strong base (high pH, near 14)

Order of acidic character :

HBr >HF>HCN>NH₄F>CH₃NH₃F>NaF>NaCN>NH₃>NaOH

Assigning pH

As the acidic character increases, the pH decreases; hence a stronger acid has a low pH.

HBr: pH= 1

HF: pH=2

HCN: pH = 5

NH₄F: pH = 6

CH₃NH₃F: pH = 6.5

NaF: pH =8

NaCN: pH =11

NH₃: pH= 11

NaOH: pH = 13