All questions of Acids and Bases for ACT Exam

Qualitative Analysis

The common ion effect can be used in qualitative analysis to help identify the presence of certain ions in a solution. This effect is based on the principle that the solubility of a compound is reduced when a common ion is added to the solution.

How it works

When a common ion is added to a solution that contains a sparingly soluble salt, the equilibrium shifts toward the formation of solid precipitate. This results in the precipitation of the less soluble compound, which can be used to identify the presence of a specific ion in the solution.

Example

For example, if you suspect the presence of chloride ions in a solution, you can add a solution of silver nitrate (AgNO3), which contains the common ion Ag+. If a white precipitate forms, it indicates the presence of chloride ions in the solution, as silver chloride (AgCl) is a sparingly soluble salt.

Application in Qualitative Analysis

The common ion effect is commonly used in qualitative analysis to identify the presence of various ions in a solution. By understanding the solubility behavior of different compounds in the presence of common ions, chemists can determine the composition of unknown solutions.

Conclusion

In conclusion, the common ion effect is a valuable tool in qualitative analysis, allowing chemists to identify the presence of specific ions in a solution based on their solubility behavior. By utilizing this effect, researchers can gain valuable insights into the composition of various chemical samples.

Explanation:

pKa of water (pKWat) at 298K:
- The pKa of water at 298K is approximately 14.
- This value indicates the acidity or basicity of water at a specific temperature.

pKa Value:
- The pKa value is the negative logarithm of the acid dissociation constant (Ka).
- It is used to quantify the strength of an acid in a solution.

pKWat at 298K:
- At 298K, the pKWat value of water is 14, indicating that water is neutral (neither acidic nor basic) at this temperature.
- The pH of pure water at 298K is 7, which is considered neutral.

Significance:
- Understanding the pKWat value is essential in various chemical and biological processes.
- It helps in determining the behavior of water in different environments and reactions.

Conclusion:
- In the given options, the correct answer is 'A) 14' for the pKWat value at 298K.
- Knowing this value contributes to a deeper comprehension of the properties and interactions of water in scientific studies.

Hydroxide ion as a Bronsted Base

Hydroxide ion (OH-) is indeed a Brønsted base. This can be explained based on the Brønsted-Lowry definition of acids and bases. According to this definition, an acid is a substance that donates a proton (H+ ion) while a base is a substance that accepts a proton.

Explanation:
- Hydroxide ion, OH-, can accept a proton (H+) from another substance, which means it acts as a base by accepting a proton.
- When hydroxide ion accepts a proton, it forms water (H2O), indicating its basic behavior.
- In the reaction: OH- + H+ -> H2O, hydroxide ion is acting as a base by accepting the proton (H+).
- Therefore, based on the Brønsted-Lowry definition, hydroxide ion is classified as a base.

In conclusion, hydroxide ion is considered a Brønsted base because it has the ability to accept a proton from another substance, which aligns with the fundamental principles of Brønsted-Lowry acid-base theory.

Hydrolysis
Hydrolysis is the reverse process of Neutralization. In neutralization, an acid and a base react to form a salt and water. On the other hand, in hydrolysis, a salt reacts with water to form an acid and a base.

Process
- During hydrolysis, the salt dissolves in water and the ions of the salt separate.
- The ions then react with water molecules to form an acid and a base.
- This reaction occurs because the salt ionizes in water, leading to the formation of an acid and a base.

Example
For example, when sodium acetate (CH3COONa) is dissolved in water, it undergoes hydrolysis to form acetic acid (CH3COOH) and sodium hydroxide (NaOH). The reaction can be represented as follows:
CH3COONa + H2O → CH3COOH + NaOH

Significance
Hydrolysis is an important process in various chemical reactions and industries. It is used to break down salts into their constituent acids and bases. This process is also crucial in understanding the behavior of different compounds in aqueous solutions.
In conclusion, hydrolysis is the reverse process of neutralization where a salt reacts with water to form an acid and a base. It plays a significant role in various chemical reactions and industries.

Normal salt:

NaCl, or sodium chloride, is a normal salt. Normal salts are formed by the reaction between an acid and a base, where the acid donates a proton (H+) and the base donates a hydroxide ion (OH-). In the case of NaCl, sodium hydroxide (NaOH), which is a base, reacts with hydrochloric acid (HCl), which is an acid, to form NaCl.

Properties of NaCl:

- NaCl is a white crystalline solid at room temperature and is highly soluble in water.
- It is commonly known as table salt and is used in various culinary applications as a seasoning and preservative.
- When dissolved in water, NaCl dissociates into sodium ions (Na+) and chloride ions (Cl-), making it a strong electrolyte.

Uses of NaCl:

- Apart from its culinary uses, NaCl is also used in industries such as chemical manufacturing, pharmaceuticals, and water treatment.
- It is essential for maintaining proper electrolyte balance in the human body and is used in medical treatments for conditions like dehydration.

In conclusion, NaCl is classified as a normal salt due to the way it is formed through a neutralization reaction between an acid and a base. Its properties and widespread uses make it a crucial compound in various industries and in our daily lives.

Explanation:

b) Solubility Product:
- Ksp stands for the solubility product constant.
- It is the equilibrium constant for a solid substance dissolving in an aqueous solution to form a saturated solution.

a) Soluble Product:
- For the dissociation of an electrolyte AxBy, the solubility product expression is given as [Ay]x[Bx]y.
- Here, [Ay] and [Bx] represent the concentrations of the ions produced when the electrolyte dissociates.
- The product of these ion concentrations raised to their respective stoichiometric coefficients gives the value of Ksp.

Conclusion:
- Therefore, Ksp refers to the solubility product constant, which is determined by the concentrations of the ions produced when an electrolyte dissociates in a solution.

Solubility of a Salt

The solubility of a salt refers to the maximum amount of the salt that can dissolve in a given amount of solvent at a specific temperature. The solubility is typically expressed in moles per liter (M) or molarity.

Determining Solubility

To determine the solubility of a salt, it is necessary to conduct an experiment in which the salt is added to a solvent and the amount that dissolves is measured. If all of the salt dissolves, the solubility is considered to be "infinite" or "very soluble." However, if only a portion of the salt dissolves, the solubility is finite and can be quantified.

Significance of Solubility

The solubility of a salt is an important characteristic because it determines whether a solution can be formed. If a salt is soluble, it will readily dissolve in a solvent to form a homogeneous solution. On the other hand, if a salt is insoluble, it will not dissolve or only dissolve to a very limited extent.

Solubility of a Salt

In the given question, it states that a salt is soluble if the solubility is greater than 0.1 M. This means that if the solubility of a salt is higher than 0.1 M, it is considered soluble. Therefore, option 'D' is the correct answer.

Explanation

The options provided in the question are:

a) less than 0.01 M
b) in between 0.01 M and 0.1 M
c) greater than 0.01 M
d) greater than 0.1 M

Option 'A' states that the solubility is less than 0.01 M. This implies that the salt dissolves in a very limited amount and is considered to be insoluble.

Option 'B' states that the solubility is in between 0.01 M and 0.1 M. This indicates that the salt partially dissolves but does not fully dissolve. It is considered to be partially soluble or sparingly soluble.

Option 'C' states that the solubility is greater than 0.01 M. This covers a wide range of solubilities, including both soluble and partially soluble salts.

Option 'D' states that the solubility is greater than 0.1 M. This indicates that the salt fully dissolves in a substantial amount and is considered to be soluble.

Conclusion

In conclusion, a salt is considered soluble if its solubility is greater than 0.1 M. This means that the salt fully dissolves in a significant amount when added to a solvent.

Answer:

A Lewis base is a species that donates an electron pair in a chemical reaction. In other words, it is a substance that can accept a proton or donate an electron pair to form a coordinate covalent bond. Among the given options, ammonia (NH3) is a Lewis base.

Explanation:

Definition of Lewis Base:
A Lewis base is a substance that donates an electron pair in a chemical reaction. It is also known as an electron pair donor. Lewis bases are characterized by having at least one lone pair of electrons that can be donated to form a coordinate covalent bond.

Analysis of the Given Options:
a) Ammonia (NH3): Ammonia is a Lewis base because it has a lone pair of electrons on the nitrogen atom that can be donated to form a coordinate covalent bond. It can act as a Lewis base by donating its lone pair of electrons to a Lewis acid.

b) Magnesium chloride (MgCl2): Magnesium chloride is not a Lewis base because it does not have any lone pairs of electrons available for donation. It is a compound formed by the transfer of electrons from magnesium to chlorine, resulting in the formation of ionic bonds.

c) Aluminium chloride (AlCl3): Aluminium chloride is not a Lewis base because it does not have any lone pairs of electrons available for donation. It is an example of a Lewis acid, which is a species that accepts an electron pair.

d) Sodium ion (Na+): Sodium ion is not a Lewis base because it does not have any lone pairs of electrons available for donation. It is a cation formed by losing an electron, and cations are generally not Lewis bases.

Conclusion:
Based on the analysis of the given options, the correct answer is option 'A' - ammonia (NH3). Ammonia is a Lewis base because it has a lone pair of electrons available for donation, which allows it to act as an electron pair donor in chemical reactions.

Explanation:

pH:
- pH is a measure of the acidity or alkalinity of a solution. It is defined as the negative logarithm of the concentration of hydrogen ions ([H+]) in a solution.
- Mathematically, pH = -log[H+].

Concentration of Hydrogen Ion:
- The concentration of hydrogen ions ([H+]) in a solution can be calculated using the formula [H+] = 10^(-pH).
- This means that the concentration of hydrogen ions is equal to 10 raised to the power of negative pH.

Therefore, the correct option is Option B: [H+] = 10^(-pH), as it correctly represents the relationship between pH and the concentration of hydrogen ions.

Explanation:

pH and pOH relationship:
- The relationship between pH and pOH can be expressed as pH + pOH = 14.
- Therefore, if the pH of a substance is 3, then the pOH can be calculated as follows:
pOH = 14 - pH
pOH = 14 - 3
pOH = 11

Therefore, the pOH of the substance with a pH of 3 is 11.

Protophilic substance cannot act as both acid and base

Protophilic substances refer to molecules or ions that are capable of accepting a proton but not donating a proton. This means that they can act as bases by accepting a proton, but they cannot act as acids by donating a proton.

Amphoteric substance
- Amphoteric substances are capable of acting as both an acid and a base depending on the reaction conditions. They can either donate or accept a proton, making them versatile in their reactivity.

Amphiprotic substance
- Amphiprotic substances are molecules or ions that can both donate and accept a proton. They can act as both an acid and a base in different chemical reactions.

Ampholyte
- Ampholytes are substances that can behave as both an acid and a base depending on the medium they are in. They can donate or accept protons in different situations.

In conclusion, while amphoteric substances, amphiprotic substances, and ampholytes can all act as both acids and bases, protophilic substances lack the ability to donate protons and therefore cannot act as acids.

The conjugate pair in the equation is NH3 and NH4+.

Calculation of Ionic Product of Water at 298K:

- The ionic product of water (Kw) is the product of the concentrations of H+ ions and OH- ions in water at a specific temperature.
- At 298K, the value of the ionic product of water is 1 x 10^-14 mol^2/L^2.

Explanation:

- The ionic product of water is represented by the equation Kw = [H+][OH-].
- At 298K, the concentration of H+ ions and OH- ions in pure water is approximately 1 x 10^-7 mol/L each.
- Therefore, Kw = (1 x 10^-7)(1 x 10^-7) = 1 x 10^-14 mol^2/L^2.

Importance of Kw:

- The value of the ionic product of water is essential in determining the pH and pOH of a solution.
- It helps in understanding the ionization of water and the behavior of acidic and basic solutions.

In conclusion, the value of the ionic product of water at 298K is 1 x 10^-14 mol^2/L^2. This value is crucial in various chemical calculations and understanding the properties of aqueous solutions.

Buffer solutions are solutions that resist changes in pH when small amounts of acid or base are added to them. They are typically composed of a weak acid and its conjugate base or a weak base and its conjugate acid. The ability of a buffer solution to maintain its pH depends on the presence of both the weak acid or base and its conjugate pair.

When a weak base is added to a buffer solution, the buffer is destroyed. This is because the weak base reacts with the weak acid present in the buffer to form their respective conjugate acid and base. This reaction consumes the weak acid and weak base, disrupting the balance of the buffer system. As a result, the pH of the solution will change significantly, and the buffer will no longer be able to resist changes in pH.

The addition of a strong acid or base does not necessarily destroy a buffer solution. Strong acids and bases are completely dissociated in water and do not have conjugate pairs. Therefore, they do not participate in the buffer system. Instead, they directly change the concentration of hydrogen ions (H+) or hydroxide ions (OH-) in the solution, leading to a significant change in pH.

The addition of a weak acid to a buffer solution does not necessarily destroy the buffer. The weak acid will simply increase the concentration of its conjugate base, helping to maintain the buffer system.

The addition of a salt to a buffer solution also does not destroy the buffer. Salts are composed of cations and anions, and their presence does not significantly affect the buffer system as long as they do not react with the weak acid or base.

In summary, the buffer solution is destroyed when a weak base is added because it reacts with the weak acid in the buffer, disrupting the balance of the buffer system. The addition of a strong acid or base, weak acid, or salt does not destroy the buffer.

Calculation of pH of Ammonium Acetate Solution

Ammonium acetate is a salt formed by the reaction of acetic acid and ammonium hydroxide. When dissolved in water, it dissociates into ammonium ions (NH4+) and acetate ions (CH3COO-).

Step 1: Calculate the concentration of NH4+ and CH3COO-
- The initial concentration of NH4+ is the same as the concentration of ammonium acetate, as it fully dissociates.
- The initial concentration of CH3COO- is also the same as the concentration of ammonium acetate, as it fully dissociates.

Step 2: Calculate the equilibrium concentration of acetic acid (CH3COOH)
- Due to the reaction NH4+ + CH3COO- ⇌ CH3COOH + NH3, the concentration of CH3COOH increases by the same amount as the NH4+ ion concentration.

Step 3: Calculate the equilibrium concentration of NH3
- Due to the reaction NH4+ + CH3COO- ⇌ CH3COOH + NH3, the concentration of NH3 increases by the same amount as the CH3COO- ion concentration.

Step 4: Calculate the pH of the solution
- Use the Henderson-Hasselbalch equation: pH = pKa + log([A-]/[HA]).
- Substitute the values for pKa, [A-] (CH3COO-), and [HA] (CH3COOH) to find the pH of the solution.

Therefore, the pH of the ammonium acetate solution is 7.48 (option D).

To find the value of the degree of dissociation, we need to use the equilibrium constant expression for the dissociation of formic acid. Formic acid (HCOOH) dissociates into hydrogen ions (H+) and formate ions (HCOO-).

The balanced chemical equation for the dissociation of formic acid is:

HCOOH ⇌ H+ + HCOO-

The equilibrium constant expression for this reaction is given by:

K = [H+][HCOO-]/[HCOOH]

Given that the concentration of formic acid (HCOOH) is 0.1 M and K is 1.77 x 10^-4, we can substitute these values into the equilibrium constant expression:

1.77 x 10^-4 = [H+][HCOO-]/0.1

Now, let's assume that the degree of dissociation of formic acid is x. This means that at equilibrium, the concentration of hydrogen ions ([H+]) and formate ions ([HCOO-]) will be x, and the concentration of undissociated formic acid ([HCOOH]) will be (0.1 - x).

Substituting these values into the equilibrium constant expression, we get:

1.77 x 10^-4 = x * x / (0.1 - x)

Now, we can solve this equation to find the value of x, which represents the degree of dissociation.

By solving this equation, we find that x is approximately 0.042 or 4.2%.

Therefore, the correct answer is option B: 4.2.

Explanation:
The degree of dissociation of ammonium hydroxide (NH4OH) increases in the presence of ammonium chloride (NH4Cl) due to the process of hydrolysis of the salt.

Hydrolysis:
Hydrolysis is a chemical reaction in which a compound reacts with water to produce ions. In the case of ammonium chloride, it undergoes hydrolysis in an aqueous solution:

NH4Cl + H2O → NH4OH + HCl

This reaction results in the formation of ammonium hydroxide (NH4OH) and hydrochloric acid (HCl).

Common Ion Effect:
The common ion effect is a phenomenon in which the presence of a common ion reduces the degree of dissociation of a weak electrolyte. In this case, the common ion is the ammonium ion (NH4+), which is present in both ammonium hydroxide and ammonium chloride.

When ammonium chloride is dissolved in water, it dissociates into ammonium ions (NH4+) and chloride ions (Cl-). The ammonium ions released from ammonium chloride increase the concentration of ammonium ions in the solution.

Due to the common ion effect, the increased concentration of ammonium ions from the dissociation of ammonium chloride suppresses the dissociation of ammonium hydroxide. The presence of more ammonium ions shifts the equilibrium of the hydrolysis reaction towards the reactant side, reducing the concentration of hydroxide ions (OH-) in the solution. As a result, the degree of dissociation of ammonium hydroxide increases.

Summary:
In summary, the degree of dissociation of ammonium hydroxide increases in the presence of ammonium chloride due to the hydrolysis of ammonium chloride. The common ion effect caused by the presence of ammonium ions from the dissociation of ammonium chloride suppresses the dissociation of ammonium hydroxide and leads to an increase in its degree of dissociation.

Proton Donor Explanation:
Proton donors are substances that are capable of donating a proton (H+ ion) in a chemical reaction. This process is essential in acid-base chemistry and is commonly seen in reactions involving acids.

Protongenic Substance:
- A protonic substance is often referred to as protogenic.
- Protogenic substances have the ability to donate protons, making them proton donors.
- They play a crucial role in acid-base reactions by releasing protons to react with other substances.

Example:
- One common example of a protogenic substance is hydrochloric acid (HCl).
- In a solution of HCl, the hydrogen atom can dissociate from the chloride ion, resulting in the donation of a proton.

Significance:
- Understanding proton donors is essential in the study of acid-base chemistry.
- Proton donors help in identifying the acidic nature of a substance and predicting its behavior in chemical reactions.
- They are integral to the concept of pH and the measurement of acidity in solutions.
In conclusion, a proton donor is a protogenic substance that has the ability to donate protons in chemical reactions, playing a key role in acid-base chemistry.

The Arrhenius Theory and Non-Aqueous Solutions

The Arrhenius theory, proposed by Svante Arrhenius in 1884, is a widely accepted theory that explains the behavior of acids and bases in aqueous solutions. According to this theory, acids are substances that release hydrogen ions (H+) in solution, while bases are substances that release hydroxide ions (OH-) in solution. However, the Arrhenius theory is not applicable to non-aqueous solutions and fails to explain their acidic and basic behavior.

Lack of Water Molecules

One of the main reasons why the Arrhenius theory fails in non-aqueous solutions is the absence of water molecules. In aqueous solutions, water molecules play a crucial role in the dissociation of acids and bases. Water molecules can act as a medium for the ions to move around and react with each other. However, in non-aqueous solvents, such as organic solvents like ethanol or acetone, there are no water molecules present to facilitate the ionization process.

Alternative Theories

To explain the acidic and basic behavior in non-aqueous solutions, alternative theories have been proposed. Some of these theories include:

1. Brønsted-Lowry Theory: This theory defines acids as proton (H+) donors and bases as proton acceptors. According to this theory, the solvent plays a crucial role in the behavior of acids and bases. In non-aqueous solvents, the solvent molecules themselves can act as proton acceptors or donors, leading to different acid-base behavior compared to aqueous solutions.

2. Lewis Theory: The Lewis theory defines acids as electron pair acceptors and bases as electron pair donors. This theory is more general and can explain the behavior of acids and bases in both aqueous and non-aqueous solutions. In non-aqueous solvents, Lewis acids and bases can interact through electron transfer, coordination, or complexation reactions.

Conclusion

In summary, the Arrhenius theory, which explains the behavior of acids and bases in aqueous solutions, is not applicable to non-aqueous solutions. The absence of water molecules in non-aqueous solvents prevents the ionization process necessary for the Arrhenius theory. Instead, alternative theories such as the Brønsted-Lowry theory and Lewis theory are more suitable for explaining the acidic and basic behavior in non-aqueous solutions. These theories take into account the different properties and interactions that occur in non-aqueous solvents, leading to a more comprehensive understanding of acid-base behavior in these systems.

The Lewis concept of acids and bases, proposed by Gilbert N. Lewis in 1923, provides a broader understanding of acid-base behavior beyond the traditional Arrhenius and Brønsted-Lowry theories. According to the Lewis concept, an acid is defined as a substance that can accept a pair of electrons, while a base is a substance that can donate a pair of electrons. This concept helps explain the behavior of protonic acids, which are substances that can donate a proton (H+) in a chemical reaction.

Explanation:
- The Lewis concept of acids and bases is a more inclusive theory that goes beyond the limitations of the Arrhenius and Brønsted-Lowry theories. It focuses on the electron-pair transfer in chemical reactions.
- According to the Lewis concept, an acid is a substance that can accept a pair of electrons to form a coordinate covalent bond. This means that acids are electron pair acceptors.
- On the other hand, a base is a substance that can donate a pair of electrons to form a coordinate covalent bond. Bases are electron pair donors.
- Protonic acids are substances that can donate a proton (H+) in a chemical reaction. In the Lewis concept, this behavior can be explained by the fact that the proton can accept a pair of electrons from a base, forming a coordinate covalent bond.
- When a protonic acid donates a proton, it becomes a conjugate base, which is the species that remains after the acid has donated a proton.
- In the Lewis concept, amphoteric substances are substances that can act as both acids and bases, as they can both accept and donate a pair of electrons. This behavior is explained by their ability to form coordinate covalent bonds with other substances.
- Lewis acids and bases can also form complexes with each other, where the Lewis acid accepts a pair of electrons from the Lewis base, forming a coordinate covalent bond.
- Salt is not specifically explained by the Lewis concept of acids and bases, as it refers to the product of a neutralization reaction between an acid and a base, according to the Arrhenius or Brønsted-Lowry theories.

In summary, the Lewis concept of acids and bases provides a more comprehensive explanation of acid-base behavior, including the behavior of protonic acids and amphoteric substances. It focuses on the transfer of electron pairs in chemical reactions, allowing for a broader understanding of acid-base interactions.