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Lana71 [14]
3 years ago
12

A 30.0-mL sample of 0.165 M propanoic acid is titrated with 0.300 M KOH.

Chemistry
1 answer:
Svetach [21]3 years ago
5 0

Answer:

1) pH = 4.51

2) pH = 4.87.

3) pH = 12.32

Explanation:

1) the Ka of propanoic acid is 1.34 X 10⁻⁵

Therefore pKa = 4.87

When we add 5 mL of 0.300 M NaOH the moles of base added is

moles = molarity X volume

moles = 0.300 X 5mL = 1.5 mmoles

moles of acid present = molarity X volume = 0.165 X 30.0 = 4.95 mmoles

on addition of 1.5 mmoles of base the moles of acid neutralized = 1.5mmole

This will result in formation of salt of the acid

the moles of salt formed = 1.5 mmoles

the moles of acid left = 4.95 - 1.5 = 3.45 mmol

this acid and its salt mixture results in formation of a buffer

the pH of buffer is calculated as:

pH = pKa + log [salt] / [acid]

pH = 4.87 + log [1.5/3.45] = 4.51

2) at half equivalence point the moles of acid becomes equal to moles of salt formed thus the pH of solution will become equal to the pKa of acid

pH = 4.87.

3) the moles of based added due to addition of 20.0 mL = molarity X volume

moles = 0.300 X 20 = 6mmol

This will completely neutralize the acid (4.95 mmol)

after neutralization the moles of base left = 6-4.95 = 1.05 mmol

Total volume of solution  = volume of acid + volume of base =30+20=50

concentration of hydroxide ion (due to excess base) = \frac{mmoles}{volume(mL)}

[OH⁻]=0.021

pOH = -log[OH⁻]=1.68

pH = 14-pOH = 12.32

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Answer:

The number of moles of benzaldehyde = 0.0253 moles

Explanation:

The molecular formula of benzaldehyde is C₇H₆O

Its molecular mass is calculated from the atomic masses of the constituent atoms.

C = 12.0 g: H = 1.0 g; O = 16.0 g

Molecular mass = ( 12 * 7) + (1 * 6) + (16 * 1) = 106.0 g/mol

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mass of benzaldehyde = 2.68; molar mass = 106.0 g/mol

Number of moles of benzaldehyde = 2.68 g/ 106 g/mol = 0.0253 moles

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8 0
3 years ago
A gas starts at a volume of 23 L and a pressure of 1.23 atm. What is the new pressure if you
Anna71 [15]

Answer:

<h2>1.89 atm</h2>

Explanation:

The new volume can be found by using the formula for Boyle's law which is

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Since we are finding the new volume

V_2 =  \frac{P_1V_1}{P_2}  \\

From the question we have

V_2 =  \frac{1.23 \times 23}{15}  =  \frac{28.29}{15}  \\  = 1.886

We have the final answer as

<h3>1.89 atm</h3>

Hope this helps you

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