Calculate the ph at 25 degree celsius of a 0.19m solution of potassium cyanide (kcn). note that hydrocyanic acid (hcn) is a weak acid with a pka of 9.21. round your answer to 1 decimal place.

11.3

Explanation:

KCN is a strong electrolyte that dissociates in water according to the following equation.

KCN(aq) → K⁺(aq) + CN⁻(aq)

The molar ratio of KCN to CN⁻ is 1:1. Then, [CN⁻] = 0.19 M.

CN⁻ is a base that reacts with water according to the following equation.

CN⁻(aq) + H₂O(l) = HCN(aq) + OH⁻(aq)

Given pKa of HCN, we can calculate pKb of CN⁻ using the following expression.

pKa + pKb = 14

pKb = 14 - pKa = 14 - 9.21 = 4.79

The basic dissociation constant (Kb) is:

pKb = -log Kb

Kb = antilog -pKb = 1.62 × 10⁻⁵

We can find the concentration of OH⁻ using the following expression.

[OH⁻] = √(Kb × Cb)

[OH⁻] = √(1.62 × 10⁻⁵ × 0.19) = 1.8 × 10⁻³ M

The pOH is:

pOH = -log [OH⁻]

pOH = -log 1.8 × 10⁻³ = 2.7

The pH is:

pH = 14 - pOH

pH = 14 - 2.7 = 11.3

answer: enthalpy

explanation:

for a exothermic reaction, the energy is released i.e. the energy of the products is lower than the energy of the reactants.

= enthaply

= energy of products

= energy of reactants

as , thus comes out to be negative. negative value of enthalpy shows that the reaction is exothermic.

a rain shadow is a dry region of land on the side that is protected against the prevailing winds of a mountain range. the prevailing winds are the winds that occur most of the time in a particular place of the earth

prevailing winds carry air toward the mountain range. as the air rises up over a mountain range, the air cools, water vapor condenses, and clouds form. on this side of the mountains, called the windward side, precipitation falls in the form of  rain  or snow. this dry air produces a  rain shadow.