Give an example of a basic buffer solution.
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Ammonia (NH₃) and ammonium chloride (NH₄⁺Cl⁻).
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Give an example of a basic buffer solution.
Ammonia (NH₃) and ammonium chloride (NH₄⁺Cl⁻).
What is the formula to calculate the new concentration of excess acid after neutralization?
[HA] = (initial moles HA - moles OH-) / total volume (dm³).
How does an acidic buffer work when small amounts of acid are added?
The equilibrium shifts to the left, removing nearly all the H⁺ ions added.
What components make up an acidic buffer solution?
A weak acid and a salt of that weak acid.
What is a buffer solution?
A solution where the pH does not change significantly when small amounts of acid or alkali are added.
What is the pH of a 0.1 mol dm⁻³ NaOH solution?
13.00.
Give an example of an acidic buffer solution.
Ethanoic acid (CH₃CO₂H) and sodium ethanoate (CH₃CO₂⁻Na⁺).
What is the dissociation equation for NaOH?
NaOH → Na⁺ + OH⁻.
What is the relationship between Ka, [H+], [A-], and [HA]?
Ka = [H+][A-] / [HA].
What is the relationship between [H+], [CH₃CO₂H], and [CH₃CO₂-] in a buffer solution?
[H+] = K_a x [CH₃CO₂H] / [CH₃CO₂-].
What are the four main types of titration curves?
What is the color change for phenolphthalein?
Colorless in acid to pink in alkali.
What must be true for an indicator to work effectively in a titration?
The pH range of the indicator must lie on the steep part of the titration curve.
What is the Bronsted-Lowry definition of an acid?
A substance that can donate a proton.
What is the pH of a 0.1 mol dm-3 HCl solution?
1.00
How do you calculate the moles of sodium ethanoate from its mass?
Moles sodium ethanoate = mass / M_r = 1.1 / 82 = 0.0134 mol.
What characterizes the buffer region in a weak acid and strong base titration?
The pH rises quickly and then levels off.
What should be done when approaching the endpoint of a titration?
Add alkali in smaller volumes.
What is the relationship between [HIn] and [In-] at the end-point of a titration?
[HIn] = [In-].
How do you calculate the pH of a strong base?
Use the K_w expression to find [H⁺(aq)] from the concentration of hydroxide ions.
How do you calculate pH from [H+]?
pH = -log[H+].
How do you calculate the concentration of propanoic acid from its pH?
Use the K_a expression and the pH to find [H⁺] and then calculate [HA].
What is the pH when 15 cm³ of 0.5 mol dm⁻³ HCl is reacted with 35 cm³ of 0.55 mol dm⁻³ NaOH?
pH = 13.37.
What is the formula to calculate the pH of a buffer solution?
pH = -log[H+].
What is the color change for methyl orange in an acid-base titration?
Red in acid to yellow in alkali (orange at the end point).
How do you calculate the moles of ethanoic acid in the buffer solution?
Moles ethanoic acid = concentration × volume = 0.200 × 0.500 = 0.100 mol.
What is the purpose of maintaining a constant temperature during titration?
To improve the accuracy of pH measurements.
How do you determine which reactant is in excess during a neutralization reaction?
Compare the moles of acid and base added.
How do you calculate the pH of a diluted strong acid?
[H+] = [H+] old x (old volume / new volume).
How can you determine the pKa from a pH curve?
The pH at half neutralization (½ V) will equal the pKa.
What is the dissociation expression for weak acids?
HA + H₂O ⇌ H₃O⁺ + A⁻.
How do you calculate the moles of OH- when using a diprotic acid like H₂SO₄?
Moles of OH- = moles of Ba(OH)₂ x 2.
What is the relationship between [H+] and [OH-] in pure water?
[H+] = [OH-]
What is the pH range for strong acids and weak bases at the equivalence point?
Less than 7.
What is the pH at the equivalence point for a strong acid and strong base titration?
pH 7.
What is the reaction when a small amount of acid is added to a buffer?
CH₃CO₂⁻ (aq) + H⁺ → CH₃CO₂H (aq)
What components make up a basic buffer solution?
A weak base and a salt of that weak base.
What does a larger K_a value indicate?
A stronger acid.
What is the total volume used in pH calculations for neutralization?
Total volume = volume of acid + volume of base added.
How do you find the new concentration of H+ after diluting an acid?
[H+(aq)] = [H+(aq) old] x (old volume / new volume).
What is the pH after reacting 35 cm³ of 0.5 mol dm⁻³ H₂SO₄ with 30 cm³ of 0.55 mol dm⁻³ NaOH?
pH = 0.55.
How does temperature affect the pH of pure water?
Increasing temperature decreases pH due to increased [H+] concentration.
What is the Ka value used in the buffer calculations?
K_a = 1.7 x 10⁻⁵ mol dm⁻³.
What is the effect on the moles of salt when alkali is added to a buffer?
The moles of salt increase by the same amount as the alkali added.
How does Le Chatelier's principle apply to indicators?
In an acidic solution, H+ ions push the equilibrium towards reactants, showing the acidic color.
Why does the pH of a buffer remain constant when diluted?
The ratio of [HA]/[A⁻] stays constant as both concentrations are diluted by the same proportion.
How do you calculate the moles of the original acid in a neutralization reaction?
Moles = concentration x volume.
What is the pH of a 0.01 mol dm⁻³ ethanoic acid solution?
3.38.
How does the concentration of hydrogen ions relate to strong acids?
The concentration of hydrogen ions in a monoprotic strong acid is the same as the concentration of the acid.
How do you calculate the moles of ethanoic acid in a buffer solution?
Moles ethanoic = conc x vol = 0.1 x 0.045 = 0.0045 mol.
How do you find the concentration of CH₃CO₂H after adding NaOH?
[CH₃CO₂H] = moles excess CH₃CO₂H / total volume (dm³).
What is the first step in constructing a pH curve?
Calibrate the pH meter by measuring the known pH of a buffer solution.
What is the effect of diluting a buffer solution with water on its pH?
Diluting a buffer solution with water will not change its pH.
What happens to the pH of a buffer solution when small amounts of alkali are added?
The pH stays fairly constant due to the buffer's ability to produce more H⁺ ions.
What is the equilibrium expression for a buffer solution containing ethanoic acid?
[CH₃CO₂H (aq)] [CH₃CO₂⁻ (aq)] [H⁺ (aq)] = Kₐ.
What is the first step in calculating pH for strong acid and strong base neutralizations?
Work out moles of the original acid and hence moles of H+.
How is pH calculated from the concentration of H+ ions?
pH = -log[H+].
What is the relationship between K_a and pK_a?
pK_a = -log K_a.
What happens when sodium hydroxide is added to a weak acid to create a buffer?
It partially neutralizes the weak acid, producing salt.
What happens to the moles of buffer acid when a small amount of alkali is added?
The moles of the buffer acid reduce by the number of moles of alkali added.
When should phenolphthalein be used as an indicator?
In titrations with strong bases but not weak bases.
What is the significance of the steep part of the curve in a weak acid and strong base titration?
It indicates a rapid change in pH, typically between pH 7 and 9.
What assumptions are made when calculating the pH of a weak acid?
What is the ionic product of water (Kw) at 25°C?
1 x 10^-14 mol² dm^-6
What is the pH of a buffer made from 45 cm³ of 0.10 mol dm⁻³ ethanoic acid and 50 cm³ of 0.15 mol dm⁻³ sodium ethanoate?
pH = 4.99.
What is the reaction when a small amount of alkali is added to a buffer?
CH₃CO₂H (aq) + OH⁻ → CH₃CO₂⁻ (aq) + H₂O (l)
What is the pH of the buffer solution after adding 0.005 mol of NaOH?
The pH is 4.91.
How do you calculate the concentration of salt formed in a neutralization reaction?
[A-] = moles OH- added / total volume (dm³).
What happens at half equivalence in a weak acid-strong base neutralization?
[HA] = [A-] and pH = pKa.
What is the Bronsted-Lowry definition of a base?
A substance that can accept a proton.
What happens to the moles of buffer salt when a small amount of acid is added?
The moles of the buffer salt reduce by the number of moles of acid added.
What defines the end-point of a titration?
The point when the color of the indicator changes.
What formula is used to calculate the concentration of excess H+ ions?
[H+] = moles excess H+ / total volume (dm³).
What is the formula for calculating the new pH when diluting an acid?
pH = -log[H+].
What is the formula for calculating pH?
pH = - log [H+]
How do you find [H+] from pH?
[H+] = 1 x 10^-pH
What is the pH of water at 50°C if Kw = 5.476 x 10^-14?
6.6
At half the neutralization volume for weak acids, what is true about the concentrations?
[HA] = [A-].
In the example with HCl and NaOH, what is the pH after reacting 45 cm³ of 1.0 mol dm⁻³ HCl with 30 cm³ of 0.65 mol dm⁻³ NaOH?
pH = 0.47.
What is the pH of a buffer made by adding 1.1 g of sodium ethanoate into 100 cm³ of 0.40 mol dm⁻³ ethanoic acid?
pH = 4.29.
What is the significance of the steep part of the titration curve?
It indicates a rapid change in pH, where the indicator should change color.
