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suter [353]
3 years ago
13

The ka for hcn is 4.9 ⋅ 10-10. What is the value of kb for cn-?

Chemistry
1 answer:
marusya05 [52]3 years ago
5 0

Answer:

kb = 2,0x10⁻⁵

Explanation:

The ka for HCN is:

HCN ⇄ H⁺ + CN⁻; ka = 4,9x10⁻¹⁰ <em>(1)</em>

The inverse reaction has an equilibrium constant of:

H⁺ + CN⁻ ⇄ HCN k = 1/4,9x10⁻¹⁰ = 2,0x10⁹ <em>(2)</em>

As the equilibrium of the water is:

H₂O ⇄ H⁺ + OH⁻; kw = 1x10⁻¹⁴ <em>(3)</em>

The sum of (2) + (3) gives:

H₂O + CN⁻ ⇄ HCN + OH⁻; kb = kw×k = 1x10⁻¹⁴×2,0x10⁹ =

2,0x10⁻⁶; <em>kb = 2,0x10⁻⁵</em>

<em />

<em>-In fact, the general formula to convert from ka to kb is:</em>

<em>kb = kw / ka-</em>

<em />

I hope it helps!

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