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
Answer:
The molar mass of the unknown substance is 255g/mole
Explanation:
Freezing point depression is given by
ΔT = i · Kf · m
Where
m = molality of the solute
i = van't Hoff's factor = i for non electrolyte
Kf = 20.4 °C/m = cryoscopic constant
ΔT = Freezing point depression
Therefore ΔT = 6.6 - 5 = 1.6 °C
1.6 °C = 20.4 °C/m × 1 × m
Therefore m = 1.6/20.4 = 0.0784 m
number of moles in 2.50 g of cyclohexane = 0.0784 m or 0.0784 moles of the substance in 1000 grams of cyclohexane. That is
2.5 ×0.0784/1000 moles in 2.5 graams of cyclohexane that is
1.96 × 10⁻⁵ moles in 2.5 grams of cyclohexane
1.96 × 10⁻⁵ moles of the substance weighs 0.050 grams
Therefore 1 Mole weighs (0.05 g)/(1.96 × 10⁻⁵ moles) = 255g/mole
The Sun appears bigger and brighter because it is much closer to Earth.
Explanation:
Stars are the celestial objects, formed by collection of luminous body which is spherical in nature. Stars are formed by its own gravity.
Sun is also a star which is bigger in nature. Sun is present at the center of the solar system around which the planets revolve. sun is the main source of light and heat for all the planets revolving around it during day times.
There are also some stars which are bigger and brighter than sun but due to its presence in the solar system at the central position makes it closer to the earth. Therefore this is the main reason sun is bigger and brighter as it is much closer to Earth.
