20 Questions
What is the mole fraction of methyl alcohol in a 5.2 molal aqueous solution of CH3OH?
0.086
What is the normality of a 2 M H2SO4 solution?
2
Which of the following acids is a weak acid?
HF
What is the mole fraction of C2H5OH in a solution that contains 46 grams of ethanol and 64 grams of methanol?
0.42
What is the concentration of a solution prepared by dissolving 5g of NaCl in 500 ml of distilled water in ppm?
1000 ppm
What is a Lewis base?
A chemical compound that has the tendency to donate an electron pair
What is the definition of an acid according to the Arrhenius theory?
A substance that increases the concentration of the hydronium ion when dissolved in water
What happens to the equilibrium when HB > HS+ in the leveling effect?
The equilibrium lies to the right
What is the limitation of the Arrhenius theory?
It does not account for the existence of hydronium ions and hydroxide ions in solution
What is the effect of a less basic solvent on the dissociation of acids?
Acids are not leveled and HClO4 is stronger than the other
What is the definition of a Brønsted-Lowry acid?
A substance that donates a proton
What is the conjugate base of an acid?
Everything that remains of the acid molecule after a proton is lost
What is a characteristic of a strong acid?
It dissociates completely in water to produce H+(aq)
What is the advantage of the Brønsted-Lowry theory over the Arrhenius theory?
It can explain the behavior of a wider range of substances
What is the definition of a Lewis acid?
A substance that has a tendency to accept an electron pair
What is the characteristic of a weak acid in an equilibrium reaction?
The equilibrium lies far to the left
What is the correct formula for calculating the pH of a strong acid solution?
pH = -log [H+]
What is the correct formula for calculating the concentration of OH- in a solution?
[OH-] = Kw/[H+]
What is the result of the equation pH + pOH = pKw?
pH + pOH = 14
What is the characteristic of the conjugate base of a weak acid?
It is a relatively strong conjugate base
Study Notes
Volumetric Analysis
- Volumetric analysis is a type of quantitative analysis that involves the measurement of the volume of a solution required to react with a known volume of another solution.
Weak Acids
- A weak acid is an acid that does not dissociate completely in water, but instead reaches an equilibrium.
- Examples of weak acids include phosphoric acid (H3PO4), acetic acid (CH3COOH), and benzoic acid (C6H5COOH).
- A weak acid has a strong conjugate base.
Strong Acids
- A strong acid is an acid that dissociates completely in water to produce H+ (aq).
- Examples of strong acids include hydrochloric acid (HCl), sulfuric acid (H2SO4), and perchloric acid (HClO4).
- The equilibrium of a strong acid lies far to the right, meaning that almost all the original acid is dissociated.
Acid Strength
- Acid strength is defined by the equilibrium position of its dissociation reaction.
- A strong acid is one for which the equilibrium lies far to the right, meaning that almost all the original acid is dissociated.
- A weak acid is one for which the equilibrium lies far to the left, meaning that only a small amount of the acid is dissociated.
Arrhenius Theory of Acids and Bases
- Arrhenius theory states that an acid is a substance that increases the concentration of H+ ions in solution, while a base is a substance that increases the concentration of OH- ions in solution.
- The theory is limited in that it only applies to substances that dissolve in water and does not account for the acidic or basic properties of substances in non-aqueous solutions.
Brønsted-Lowry Theory of Acids and Bases
- Brønsted-Lowry theory states that an acid is a substance that donates a proton (H+), while a base is a substance that accepts a proton.
- The theory is more comprehensive than Arrhenius theory and can be applied to substances in both aqueous and non-aqueous solutions.
Lewis Theory of Acids and Bases
- Lewis theory states that an acid is a substance that accepts an electron pair, while a base is a substance that donates an electron pair.
- The theory is more comprehensive than Arrhenius and Brønsted-Lowry theories and can be applied to substances in both aqueous and non-aqueous solutions.
The Leveling Effect
- The leveling effect refers to the phenomenon where the strength of an acid is governed by the solvent in which it is dissolved.
- In a solvent with a high dielectric constant, such as water, acids are leveled to a common strength.
Calculation of pH
- pH is calculated as -log[H3O+] or -log[H+].
- The concentration of H+ ions can be calculated using the dissociation constant (Ka) and the initial concentration of the acid.
Problems
- Calculate the mole fraction of C2H5OH in a solution containing 46g of ethanol and 64g of methanol.
- Calculate the molality of a 5.2 molal aqueous solution of methyl alcohol.
- Calculate the concentration of a solution prepared by dissolving 5g of AgNO3 in 100ml of water.
- Calculate the percentage by weight of a solution prepared by dissolving 200g of Na2SO4 in 500ml of water.
- Calculate the molarity of a solution prepared by dissolving 4g of NaOH in 500ml of water.
This quiz covers volumetric analysis in analytical chemistry, including weak acids and calculating mole fractions in solutions.
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