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4 years ago

What is the ph of a 0.20 M solution of NH4Cl? [Kb(NH3) = 1.8 x 10^-5]

Chemistry

2 answers:

Pavlova-9 [17]4 years ago

8 0

"NH4+ <----> NH3 + H+

The constant of this equilibrium is: K = Kw / Kb = 1 x 10^-14 / 1.8 x 10^-5 =5.56 x 10^-10

5.56 x 10^-10 = x^2 / 0.20-x

x = [H+] =1.1 x 10^-5 M

pH = 5.0"

ad-work [718]4 years ago

5 0

Answer:

5.0

Explanation:

NH₄Cl is a strong electrolyte that ionizes according to the following equation.

NH₄Cl(aq) → NH₄⁺(aq) + Cl⁻(aq)

NH₄⁺ is a weak acid according to the following equation.

NH₄⁺(aq) ⇄ NH₃(aq) + H⁺(aq)

Given Kb for NH₃, we can calculate the Ka for NH₄⁺.

Ka. Kb = Kw

Ka = Kw / Kb = 10⁻¹⁴/1.8 × 10⁻⁵ = 5.6 × 10⁻¹⁰

For a weak acid, we can find [H⁺] using the following expression.

[H⁺] = √(Ca × Ka) = √(0.20 × 5.6 × 10⁻¹⁰) = 1.1 × 10⁻⁵ M

where,

Ca: concentration of the acid

The pH is

pH = -log [H⁺] = -log 1.1 × 10⁻⁵ = 5.0

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3 years ago

Balance the following skeleton reaction and identify the oxidizing and reducing agents: Include the states of all reactants and

coldgirl [10]

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a. The oxidizing agent is: $BH_4^-$

b. The reducing agent is: $ClO_3^-$

Explanation :

Redox reaction or Oxidation-reduction reaction : It is defined as the reaction in which the oxidation and reduction reaction takes place simultaneously.

Oxidation reaction : It is defined as the reaction in which a substance looses its electrons. In this, oxidation state of an element increases. Or we can say that in oxidation, the loss of electrons takes place.

Reduction reaction : It is defined as the reaction in which a substance gains electrons. In this, oxidation state of an element decreases. Or we can say that in reduction, the gain of electrons takes place.

Reducing agent : It is defined as the agent which helps the other substance to reduce and itself gets oxidized. Thus, it will undergo oxidation reaction.

Oxidizing agent : It is defined as the agent which helps the other substance to oxidize and itself gets reduced. Thus, it will undergo reduction reaction.

The given chemical reaction is,

$BH_4^-(aq)+ClO_3^-(aq)\rightarrow H_2BO_3^-(aq)+Cl^-(aq)$

The oxidation-reduction half reaction will be :

Oxidation : $BH_4^-\rightarrow H_2BO_3^-$

Reduction : $ClO_3^-\rightarrow Cl^-$

Now balance oxygen atom on both side.

Oxidation : $BH_4^-\rightarrow H_2BO_3^-+3H_2O$

Reduction : $ClO_3^-+3H_2O\rightarrow Cl^-$

Now balance hydrogen atom on both side.

Oxidation : $BH_4^-+4OH^-\rightarrow H_2BO_3^-+3H_2O$

Reduction : $ClO_3^-+3H_2O\rightarrow Cl^-+6OH^-$

Now balance the charge.

Oxidation : $BH_4^-+4OH^-\rightarrow H_2BO_3^-+3H_2O+4e^-$

Reduction : $ClO_3^-+3H_2O+6e^-\rightarrow Cl^-+6OH^-$

In order to balance the electrons, we multiply the oxidation reaction by 6 and reduction reaction by 4 and then added both equation, we get the balanced redox reaction.

Oxidation : $6BH_4^-+24OH^-\rightarrow 6H_2BO_3^-+18H_2O+24e^-$

Reduction : $4ClO_3^-+12H_2O+24e^-\rightarrow 4Cl^-+24OH^-$

The balanced chemical equation in acidic medium will be,

$6BH_4^-+4ClO_3^-\rightarrow 6H_2BO_3^-+6H_2O+4Cl^-$

$3BH_4^-+2ClO_3^-\rightarrow 3H_2BO_3^-+3H_2O+2Cl^-$

In the redox reaction, $ClO_3^-$ act as oxidizing agent and $BH_4^-$ act as an reducing agent.

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