Chemistry, 25.10.2019 08:43 mrmendrala

Acertain weak base has a kb of 8.50 × 10-7. what concentration of this base will produce a ph of 10.38?

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We are given a pH of 10.38
*pH + pOH = 14

10.38 + pOH = 14
----> pOH = 3.62

pOH = -log [OH]
----> [OH] = 2.3988x10^-4

Set up an I.C.E table using the concentration of OH found (y) and x being the unknown:
[base] + H2O ------> [conjugate acid] + OH
I x 0 0
C -y +y +y
E x-y y y

Given Kb, we can set up the equilibrium equation:
K = $\frac{prdoucts}{reactants}$
K = $\frac{y ^{2} }{x-y}$

We can substitute y for the concentration of OH we found, and K for the Kb value:
$8.50* 10^{-7} = \frac{(2.3988* 10^{-4})^{2} }{x-2.3988*10^{-4} }$

Solve the equation algebraically to get x.
X = 6.8*10^-2

Hope that helps.
If you need more clarification just let me know

Answer from: Ideen

Concentration of weak base : 0.0679

Further explanation

pH is the degree of acidity of a solution that depends on the concentration of H ions. The greater the value the more acidic the solution and the smaller the pH.

pH = - log [H⁺]

So that the two quantities between pH and [H⁺] are inversely proportional because they are associated with negative values.

A solution whose value is different by n has a difference in the concentration of H ions of 10ⁿ.

According to Arrhenius, Base is a compound which in water releases OH-ions

Electrolytes (acids or bases) with a small degree of ionization are classified as weak electrolytes

OH concentration and molarity can be related to the formula

$\rm [OH^-] = \sqrt{Kb.M}$

Kb = base ionization constant

M = molarity

A certain weak base has a Kb of 8.50 × 10⁻⁷

pH = 10.38

pOH = 14 - 10.38

pOH = 3.62

$\rm [OH^-]=10^{-3.62}$

Then :

$\rm [10^{-3.62}^2] = \sqrt{8.5.10^{-7}.M}$

$\rm M=\dfrac{10^{-7.24}}{8.5.10^{-7}}\\\\M=1.18.10^{-1.24}\\\\M=\boxed{\bold{0.0679}}$

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Answer from: Quest

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.

Answer from: Quest

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Acertain weak base has a kb of 8.50 × 10-7. what concentration of this base will produce a ph of 10....

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