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Monica [59]
2 years ago
8

A balloon contains 8.4 L of helium gas at STP. How many moles of helium are in the balloon?

Chemistry
1 answer:
ozzi2 years ago
3 0

Answer:

0.38\ \text{moles of He}

Explanation:

\rho = Density of helium at stp = 0.179 g/L

M = Molar mass of helium = 4 g/mol

V = Volume of helium = 8.4 L

Mass of helium

m=\rho V\\\Rightarrow m=0.179\times 8.4\\\Rightarrow m=1.5036\ \text{g}

Number of moles is given by

n=\dfrac{m}{M}\\\Rightarrow n=\dfrac{1.5036}{4}\\\Rightarrow n=0.3759\approx0.38\ \text{moles of He}

The number of moles of helium in the balloon is 0.38\ \text{moles}

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An unknown acid solution has PH 3.4. 66% of the acid is ionized. Whats the pka?
juin [17]

Answer:

pKa=3.58

Explanation:

Hello,

In this case, since the pH defines the concentration of hydrogen:

pH=-log([H^+])

[H^+]=10^{-pH}=10^{-3.4}=3.98x10^{-4}

And the percent ionization is:

\% \ ionization=\frac{[H^+]}{[HA]}*100\%

We compute the concentration of the acid, HA:

[HA]=\frac{[H^+]}{\% \ ionization}*100\%=\frac{3.98x10^{-4}}{66\%}  *100\%\\\\

[HA]=6.03x10^{-4}

Thus, the Ka is:

Ka=\frac{[H^+][A^-]}{[HA]}=\frac{3.98x10^{-4}*3.98x10^{-4}}{6.03x10^{-4}}\\  \\Ka=2.63x10^{-4}

So the pKa is:

pKa=-log(Ka)=-log(2.63x10^{-4})\\\\pKa=3.58

Regards.

5 0
2 years ago
plz answer fast Which is not a crystalline allotrope of carbon? Select one: a. soot b. diamond c. graphite
Norma-Jean [14]

Answer:

graphite

Explanation:

Graphite is opaque, a very good lubricant, a good conductor of electricity, and a thermal insulator. Allotropes of carbon are not limited to diamond and graphite, but also include buckyballs (fullerenes), amorphous carbon, glassy carbon, carbon nanofoam, nanotubes, and others.

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8 0
2 years ago
Need help on last 3 questions
Olin [163]

Answer:

Explanation:

1)

Given data:

Initial volume of balloon = 0.8 L

Initial temperature = 12°C ( 12+273= 285 K)

Final temperature = 300°C (300+273 = 573 K)

Final volume = ?

Solution:

V₁/T₁ = V₂/T₂

V₂ = V₁T₂/T₁  

V₂ = 0.8 L .573 K / 285 K

V₂ = 458.4 L / 285

V₂ = 1.61 L

2)

Initial pressure = 204 kpa

Initial temperature = 29°C ( 29 + 273 = 302 K)

Final temperature = ?

Final pressure = 300 kpa

Solution:

P₁/T₁ = P₂/T₂

T₂ = T₁P₂/P₁  

T₂ = 302 K . 300 kpa / 204 kpa

T₂ = 90600 K/ 204

T₂ = 444.12 K

3)

Given data:

Initial volume = 14 L

Initial pressure = 2.1 atm

Initial temperature = 100 K

Final temperature = 450 K

Final volume = ?

Final pressure = 1.2 atm

Formula:  

P₁V₁/T₁ = P₂V₂/T₂  

P₁ = Initial pressure

V₁ = Initial volume

T₁ = Initial temperature

P₂ = Final pressure

V₂ = Final volume

T₂ = Final temperature

Solution:

V₂ = P₁V₁ T₂/ T₁ P₂  

V₂ = 2.1 atm × 14 L × 450 K / 100 K × 1.2 atm  

V₂ = 13230 L / 120

V₂ = 110.25 L

5 0
3 years ago
Thermal energy changes states because
Artyom0805 [142]
.Thermal energy, an extensive property, depends on the number of particles in a substance as well as the amount of energy each particle has. If either the number of particles or the amount of energy in each particle changes, the thermal energy of the sample changes. With identi- cally sized samples, the warmer substance has the greater ther- mal energy. hope that helps.
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2 years ago
Alice added sodium chloride to water and stirred the water for several minutes. Alice is most likely trying to demonstrate that
SashulF [63]

Answer is: 2. can dissolve.

Ionic compounds separates into particles (ions) in water because of their ionic bond.

For example sodium chloride is ionic compound and strong electrolyte and dissociates in water on hydrated sodium cations and chlorine anions:

NaCl(aq) → Na⁺(aq) + Cl⁻(aq).

Ionic bond is the electrostatic attraction between oppositely charged ions (cations and anions).

6 0
3 years ago
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