Chemistry, 23.11.2019 04:31 gnoelle98

Anew potential heart medicine, code-named x-281, is being tested by a pharmaceutical company, pharma-pill. as a research technician at pharma-pill, you are told that x-281 is a monoprotic weak acid, but because of security concerns, the actual chemical formula must remain top secret. the company is interested in the drug's ka value because only the dissociated form of the chemical is active in preventing cholesterol buildup in arteries.
to find the pka of x-281, you prepare a 0.089 m test solution of x-281 at 25.0 ∘c. the ph of the solution is determined to be 2.40.
a. what is the pka of x-281? express your answer numerically.
at 25∘c, for any conjugate acid-base pair
pka + pkb = 14.00
b. what is pkb of the conjugate base of x-281? (assume 25 ∘c.) express your answer numerically.

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Answer from: edog32

a. pka = 3,73.

b. pkb = 10,27.

Explanation:

a. Supposing the chemical formula of X-281 is HX, the dissociation in water is:

HX + H₂O ⇄ H₃O⁺ + X⁻

Where ka is defined as:

$ka = \frac{[H_3O^+][X^-]}{[HX]}$

In equilibrium, molar concentrations are:

[HX] = 0,089M - x

[H₃O⁺] = x

[X⁻] = x

pH is defined as -log[H₃O⁺]], thus, [H₃O⁺] is:

$[H_3O^+]} = 10^{-2,40}$

[H₃O⁺] = 0,004M

Thus:

[X⁻] = 0,004M

And:

[HX] = 0,089M - 0,004M = 0,085M

$ka = \frac{[0,004][0,004]}{[0,085]}$

ka = 1,88x10⁻⁴

And pka = 3,73

b. As pka + pkb = 14,00

pkb = 14,00 - 3,73

pkb = 10,27

I hope it helps!

Answer from: Quest

chemistry sucks a**

explanation:

Answer from: Quest

assuming that your periodic table has eighteen columns, you should highlight the four elements in the third column from the left of the table.

explanation

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the $3d$ have energy higher than those in the $4 s$ orbital while lower than those of the $4 p$ orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the $4s$ orbital is therefore filled right after $3p$ orbitals and before $3 d$ orbitals.

potassium has electron configuration $[\text{ar}] 4 s^{1}$ and calcium $[\text{ar}] 4 s^{2}$ . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration $[\text{ar}] 4 s^{2} \; 3d^{1}$ and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the $ns^{2} \; (n-1) p^{1}$ and should be highlighted as well.

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Anew potential heart medicine, code-named x-281, is being tested by a pharmaceutical company, pharma...