Answer:
pKa = 3.675
Explanation:
∴ <em>C</em> X-281 = 0.079 M
∴ pH = 2.40
let X-281 a weak acid ( HA ):
∴ HA ↔ H+ + A-
⇒ Ka = [H+] * [A-] / [HA]
mass balance:
⇒<em> C</em> HA = 0.079 M = [HA] + [A-]
⇒ [HA] = 0.079 - [A-]
charge balance:
⇒ [H+] = [A-] + [OH-]... [OH-] is negligible; it comes from to water
⇒ [H+] = [A-]
∴ pH = - log [H+] = 2.40
⇒ [H+] = 3.981 E-3 M
replacing in Ka:
⇒ Ka = [H+]² / ( 0.079 - [H+] )
⇒ Ka = ( 3.981 E-3 )² / ( 0.079 - 3.981 E-3 )
⇒ Ka = 2.113 E-4
⇒ pKa = - Log ( 2.113 E-4 )
⇒ pKa = 3.675
The quantity of substance remains after 850 years is 8.98g if the half life of radioactive radium is 1,599 years.
<h3>What is half life period? </h3>
The time taken by substance to reduce to its half of its initial concentration is called half life period.
We will use the half- life equation N(t)
N e^{(-0.693t) /t½}
Where,
N is the initial sample
t½ is the half life time period of the substance
t2 is the time in years.
N(t) is the reminder quantity after t years .
Given
N = 13g
t = 350 years
t½ = 1599 years
By substituting all the value, we get
N(t) = 13e^(0.693 × 50) / (1599)
= 13e^(- 0.368386)
= 13 × 0.691
= 8.98
Thus, we calculated that the quantity of substance remains after 850 years is 8.98g if the half life of radioactive radium is 1,599 years.
learn more about half life period:
brainly.com/question/20309144
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Answer:
1) Basic
2) Basic
3) Acidic
Explanation:
pH of a solution is a measure of the H3O+ ions in the solution and hence reflects its acidity.
![pH = -log[H3O+]](https://tex.z-dn.net/?f=pH%20%3D%20-log%5BH3O%2B%5D)
Solutions are classified as acidic, basic or neutral based on the pH range
-pH < 7, acidic
- pH = 7, neutral
- pH > 7, basic
1) [H3O+] = 2.5*10^-9M
![pH = -log[H3O+]=-log[2.5*10^{-9}]=8.60](https://tex.z-dn.net/?f=pH%20%3D%20-log%5BH3O%2B%5D%3D-log%5B2.5%2A10%5E%7B-9%7D%5D%3D8.60)
Since pH > 7, solution is basic
2)[OH-] = 1.6*10^-2M
![pOH = -log[OH-]=-log[1.6*10^{-2}]=1.80](https://tex.z-dn.net/?f=pOH%20%3D%20-log%5BOH-%5D%3D-log%5B1.6%2A10%5E%7B-2%7D%5D%3D1.80)
pH = 14 - pOH = 14 - 1.80 =12.2
Since pH > 7, solution is basic
3) [H3O+] = 7.9*10^-3M
![pH = -log[H3O+]=-log[7.9*10^{-3}]=2.10](https://tex.z-dn.net/?f=pH%20%3D%20-log%5BH3O%2B%5D%3D-log%5B7.9%2A10%5E%7B-3%7D%5D%3D2.10)
Since pH < 7, solution is acidic
The energy density is calculated by dividing the energy given by the mass of the material. From this item, the energy is 78 kcal and the mass is 50 grams. Performing the operation will give us an answer of 1.56 kcal/grams.
