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Chemistry
Posted 10 months ago
Please also explain how you calculate the initial moles, because I do not get the correct number.Calculate the pH\mathrm{pH} of the resulting solution at 25 degrees C\mathrm{C}, when 50,1ml50,1 \mathrm{ml} of 0,100 mol/0,100 \mathrm{~mol} / sodium hydroxide solution NaOH\mathrm{NaOH} has been added to 50,0ml50,0 \mathrm{ml} of;
a) 0,100 mol/I0,100 \mathrm{~mol} / \mathrm{I} hydrochloric acid HCl\mathrm{HCl} solution.
b) 0,100 mol/l0,100 \mathrm{~mol} / \mathrm{l} ethanoic acid CH3COOH\mathrm{CH} 3 \mathrm{COOH} solution. pKa\mathrm{pKa} of ethanoic acid =4,76=4,76.
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Answer from Sia
Posted 10 months ago
Solution
1
Calculate initial moles of NaOH: To find the initial moles of NaOH, use the concentration and volume of the NaOH solution. The formula is n=C×Vn = C \times V, where nn is the number of moles, CC is the concentration in mol/L, and VV is the volume in liters
2
Calculate initial moles of HCl: Similarly, calculate the initial moles of HCl using its concentration and volume
3
Reaction between NaOH and HCl: NaOH and HCl react in a 1:1 molar ratio to form water and sodium chloride. The reaction is NaOH+HClNaCl+H2O \mathrm{NaOH} + \mathrm{HCl} \rightarrow \mathrm{NaCl} + \mathrm{H_2O}
4
Determine the limiting reactant: Since both NaOH and HCl have the same molarity and nearly the same volume, they will completely neutralize each other
5
Calculate the pH: After neutralization, the pH of the resulting solution will be neutral, which is 7 at 25°C
Answer
The pH of the resulting solution after adding NaOH to HCl is 7.
Key Concept
Neutralization reaction between a strong acid and a strong base results in a neutral pH.
Explanation
Since NaOH and HCl react in a 1:1 ratio and their initial moles are equal, they completely neutralize each other, resulting in a neutral pH of 7.


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Solution
1
Calculate initial moles of NaOH: Use the concentration and volume of the NaOH solution to find the initial moles
2
Calculate initial moles of CH3COOH: Calculate the initial moles of ethanoic acid using its concentration and volume
3
Reaction between NaOH and CH3COOH: NaOH and CH3COOH react in a 1:1 molar ratio. The reaction is NaOH+CH3COOHCH3COONa+H2O \mathrm{NaOH} + \mathrm{CH_3COOH} \rightarrow \mathrm{CH_3COONa} + \mathrm{H_2O}
4
Determine the limiting reactant: Since both NaOH and CH3COOH have the same molarity and nearly the same volume, they will completely neutralize each other
5
Calculate the pH of the buffer solution: After neutralization, the solution will contain the salt CH3COONa, which hydrolyzes to form CH3COO- and Na+. The CH3COO- will react with water to form CH3COOH and OH-. Use the Henderson-Hasselbalch equation to calculate the pH: pH=pKa+log([CH3COO][CH3COOH]) \mathrm{pH} = \mathrm{pKa} + \log \left( \frac{[\mathrm{CH_3COO^-}]}{[\mathrm{CH_3COOH}]} \right) . Since the moles of CH3COOH and CH3COO- are equal, the ratio is 1, and the log of 1 is 0
Answer
The pH of the resulting solution after adding NaOH to CH3COOH is 4.76.
Key Concept
The pH of a buffer solution can be calculated using the Henderson-Hasselbalch equation.
Explanation
After neutralization, the solution acts as a buffer with equal concentrations of CH3COOH and CH3COO-, resulting in a pH equal to the pKa of ethanoic acid.

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