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mash [69]
3 years ago
7

g A 500. mL solution contains 0.665 M NaC2H3O2 and 0.475 M HC2H3O2. What mass of HCl in grams needs to be added for the solution

to have a pH of 4.21? The Ka of acetic acid is 1.8 x 10-5.
Chemistry
1 answer:
77julia77 [94]3 years ago
8 0

Answer:

7.38g HCl

Explanation:

Using H-H equation for acetic buffer:

pH = pKa + log [NaC2H3O2] / [HC2H3O2]

<em>Where pKa is -log Ka = 4.74 and [] could be taken as moles of each compound.</em>

The initial moles of each specie is:

[NaC2H3O2]:

0.500L * (0.665mol/L) = 0.3325moles

[HC2H3O2]:

0.500L * (0.475mol/L) = 0.2375 moles

That means total moles are:

[NaC2H3O2] + [HC2H3O2] = 0.57 moles <em>(1)</em>

And solving H-H equation for a pH of 4.21:

4.21 = 4.74 + log [NaC2H3O2] / [HC2H3O2]

0.29512 = [NaC2H3O2] / [HC2H3O2] <em>(2)</em>

Replacing (1) in (2):

0.29512 = 0.57mol - [HC2H3O2] / [HC2H3O2]

0.29512 [HC2H3O2] = 0.57mol - [HC2H3O2]

1.29512 [HC2H3O2] = 0.57mol

[HC2H3O2] = 0.44 moles

The HCl reacts with NaC2H3O2 producing HC2H3O2, that means you need to add:

0.44 moles - 0.2375 moles =

0.2025 moles of HCl

Using molar mass of HCl (36.45g/mol), to convert these moles to grams:

0.2025 moles * (36.45g/mol) =

<h3>7.38g HCl</h3>

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A cylinder is filled with 10.0L of gas and a piston is put into it. The initial pressure of the gas is measured to be 209.kPa. T
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Answer : The final pressure of the gas will be, 26.8 kPa

Explanation :

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P\propto \frac{1}{V}

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P_1V_1=P_2V_2

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P_1 = initial pressure of the gas = 209 kPa

P_2 = final pressure of the gas = ?

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V_2 = final volume of the gas = 78.0 L

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3 0
3 years ago
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vodomira [7]

Answer:

Final volume 30.513 L.

Explanation:

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Final pressure = 1.5 atm

Solution:

P₁V₁/T₁ = P₂V₂/T₂

V₂ = P₁V₁ T₂/ T₁ P₂  

V₂ = 2.3 atm × 17 L × 350 K / 299 K × 1.5 atm

V₂  =  13685 atm .L.  K  / 448.5 K . atm

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