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Hydrolysis

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Intros
Lessons
  1. What is hydrolysis?
  2. Salts dissolving in water.
  3. Which ions react with water?
  4. Dissolving salts: effect on pH.
  5. Amphiprotic ions: using Ka and Kb.
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Examples
Lessons
  1. Predict the effect on pH when dissolving the following salts in water.
    Predict the effect on pH when the following salts are added to neutral water at 25oC, explaining your answer:
    1. NH4Cl
    2. KI
    3. Na2CO3
Topic Notes
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Introduction to Salt Hydrolysis

Welcome to our exploration of salt hydrolysis, a fascinating concept in chemistry that plays a crucial role in understanding acid-base reactions. Salt hydrolysis occurs when a salt dissolves in water, causing a change in the solution's pH. This process is essential in various chemical applications and everyday life. To kick off our learning journey, I've prepared an introduction video that will visually demonstrate the key principles of salt hydrolysis. This video will help you grasp the concept more easily, showing how different ions interact in solution. You'll see firsthand how some ions act as spectator ions, while others actively participate in the hydrolysis process. Understanding salt hydrolysis is vital for predicting the acidity or basicity of salt solutions, which has implications in fields ranging from environmental science to pharmaceuticals. As we delve deeper into this topic, you'll discover how salt hydrolysis connects to broader chemical concepts, enhancing your overall chemistry knowledge.

Understanding Spectator Ions

What Are Spectator Ions?

Spectator ions are ions that remain unchanged during a chemical reaction. These ions do not participate in the formation of new compounds and are present in the same form in both the reactants and products. Understanding spectator ions is crucial for simplifying chemical equations and focusing on the actual reactive species in a solution.

Identifying Spectator Ions

Learning how to determine spectator ions is an essential skill in chemistry. To identify spectator ions, follow these steps:

  1. Write the complete ionic equation for the reaction.
  2. Compare the ions present in the reactants and products.
  3. Identify ions that appear unchanged on both sides of the equation.

These unchanged ions are your spectator ions. They can be removed from the equation to create a net ionic equation, which focuses on the actual chemical change occurring.

Examples of Spectator Ions

Common examples of spectator ions include:

  • Sodium (Na+) and chloride (Cl-) ions in many reactions involving aqueous solutions
  • Potassium (K+) ions in reactions with potassium salts
  • Nitrate (NO3-) ions in reactions involving nitrate compounds

Spectator Ions in Strong Acids and Bases

Strong acids and strong bases play a significant role in understanding spectator ions. These compounds dissociate completely in aqueous solutions, often resulting in spectator ions. For example:

  • Strong acids like HCl, HNO3, and H2SO4 dissociate completely, often leaving H+ ions as reactive species and their anions as spectators.
  • Strong bases such as NaOH and KOH dissociate fully, typically with OH- as the reactive ion and their cations as spectators.

Importance of Recognizing Spectator Ions

Identifying spectator ions is crucial for:

  • Simplifying chemical equations
  • Focusing on the actual chemical changes occurring in a reaction
  • Understanding the true nature of reactions in solution
  • Predicting reaction outcomes more accurately

Practical Applications

The concept of spectator ions has practical applications in various fields:

  • Water treatment: Understanding which ions are spectators helps in designing effective purification processes.
  • Industrial chemistry: Identifying non-reactive ions can lead to more efficient chemical processes.
  • Environmental science: Recognizing spectator ions aids in analyzing water quality and pollution effects.

Common Misconceptions

It's important to note that spectator ions are not always obvious. Some common misconceptions include:

  • Assuming all ions from strong electrolytes are spectators
  • Overlooking the possibility of ion pairing in concentrated solutions
  • Forgetting that spectator ions can still affect solution properties like conductivity

Conclusion

Understanding spectator ions is fundamental in chemistry. By mastering how to determine spectator ions, especially in reactions involving strong acids and strong bases, you can simplify complex chemical processes and gain deeper insights into reaction mechanisms. This knowledge not only aids in academic pursuits but also has significant applications in various scientific and industrial fields. Remember, while spectator ions don't participate in the chemical change, they still play a role in the overall solution properties and should not be completely disregarded in broader chemical contexts.

The Process of Salt Hydrolysis

Salt hydrolysis is a fascinating chemical process that occurs when certain salts dissolve in water, leading to changes in the solution's pH. This phenomenon plays a crucial role in various chemical reactions and has significant implications in fields ranging from chemistry to biology. Let's dive into the details of salt hydrolysis and explore its mechanisms using the example of ammonium chloride.

Understanding Salt Hydrolysis

When a salt dissolves in water, it separates into its constituent ions. In some cases, these ions can interact with water molecules, leading to the formation of new compounds. This interaction between the salt's ions and water is called hydrolysis. The process can result in the production of either hydrogen ions (H+) or hydroxide ions (OH-), which ultimately affects the pH of the solution.

Types of Salt Hydrolysis

There are three main types of salt hydrolysis:

  1. Hydrolysis of salts of weak acids and strong bases
  2. Hydrolysis of salts of strong acids and weak bases
  3. Hydrolysis of salts of weak acids and weak bases

The type of hydrolysis that occurs depends on the nature of the acid and base that formed the salt.

Ammonium Chloride: A Case Study

Let's examine the hydrolysis of ammonium chloride (NH4Cl) as an example. Ammonium chloride is a salt formed from a weak base (ammonia) and a strong acid (hydrochloric acid). When it dissolves in water, the following reaction occurs:

NH4Cl (s) NH4+ (aq) + Cl- (aq)

The ammonium ion (NH4+) undergoes hydrolysis, while the chloride ion (Cl-) does not. The hydrolysis equation for the ammonium ion is:

NH4+ (aq) + H2O (l) NH3 (aq) + H3O+ (aq)

Breaking Down the Hydrolysis Equation

In this equation:

  • NH4+ represents the ammonium ion
  • H2O is water
  • NH3 is ammonia
  • H3O+ is the hydronium ion (which contributes to the acidity of the solution)

The double arrow () indicates that this is an equilibrium reaction, meaning it can proceed in both directions.

Effect on pH

As the hydrolysis reaction produces hydronium ions (H3O+), the solution becomes acidic. This means that when ammonium chloride dissolves in water, the resulting solution will have a pH less than 7. The exact pH will depend on the concentration of the salt and the extent of hydrolysis.

Factors Affecting Salt Hydrolysis

Several factors can influence the extent of salt hydrolysis:

  • Temperature: Higher temperatures generally increase the rate of hydrolysis
  • Concentration: The concentration of the salt affects the equilibrium of the hydrolysis reaction
  • Nature of the salt: Salts formed from weak acids or weak bases are more likely to undergo significant hydrolysis

Importance of Salt Hydrolysis

Understanding salt hydrolysis is crucial in many areas of chemistry and biology. It helps explain why some salt solutions are not neutral and can affect chemical reactions, biological processes, and even industrial applications. For instance, in agriculture, the hydrolysis of fertilizer salts can impact soil pH, which in turn affects plant growth.

Conclusion

Types of Salt Hydrolysis

Introduction to Salt Hydrolysis

Salt hydrolysis is a fascinating chemical process that occurs when certain salts dissolve in water. This reaction can significantly affect the pH of the resulting solution, making it acidic, basic, or neutral. Understanding the different types of salt hydrolysis is crucial for various applications in chemistry and everyday life.

Acidic Hydrolysis

Acidic hydrolysis occurs when a salt formed from a strong acid and a weak base dissolves in water. In this case, the cation (positively charged ion) from the weak base undergoes hydrolysis, producing hydronium ions (H3O+) and increasing the acidity of the solution. A common example is ammonium chloride (NH4Cl), where the ammonium ion (NH4+) hydrolyzes to produce a slightly acidic solution.

Basic Hydrolysis

Basic hydrolysis takes place when a salt composed of a strong base and a weak acid dissolves in water. Here, the anion (negatively charged ion) from the weak acid undergoes hydrolysis, generating hydroxide ions (OH-) and increasing the basicity of the solution. Let's explore this further with the example of sodium ethanoate.

Example: Sodium Ethanoate (CH3COONa)

When sodium ethanoate dissolves in water, it dissociates into sodium ions (Na+) and ethanoate ions (CH3COO-). The sodium ion, being from a strong base, doesn't hydrolyze. However, the ethanoate ion, derived from the weak acetic acid, undergoes hydrolysis:

CH3COO- + H2O CH3COOH + OH-

This reaction produces hydroxide ions, making the solution basic. The pH of the resulting solution will be greater than 7, typically around 8-9, depending on the concentration.

Neutral Hydrolysis

Neutral hydrolysis occurs when a salt formed from a strong acid and a strong base dissolves in water. In this case, neither the cation nor the anion undergoes significant hydrolysis, resulting in a neutral solution with a pH close to 7. Sodium chloride (NaCl) is a classic example of a salt that undergoes neutral hydrolysis when dissolved in water.

Factors Determining the Type of Hydrolysis

The nature of the salt components plays a crucial role in determining the type of hydrolysis that occurs. Here are the key factors:

  • Strength of the parent acid: If the salt contains an anion from a weak acid, it's more likely to undergo basic hydrolysis.
  • Strength of the parent base: If the salt contains a cation from a weak base, it's more likely to undergo acidic hydrolysis.
  • Relative strengths: When both the acid and base components are weak, the relative strengths determine the overall pH of the solution.

Practical Applications

Understanding salt hydrolysis is essential in various fields, including:

  • Environmental science: Predicting the pH of natural water bodies affected by dissolved salts
  • Agriculture: Managing soil pH for optimal crop growth
  • Pharmaceuticals: Formulating buffer solutions for drug stability
  • Industrial processes: Controlling chemical reactions and product quality

Conclusion

Salt hydrolysis is a fundamental concept in chemistry that explains how different salts can affect the pH of aqueous solutions. By understanding the principles of acidic, basic, and neutral hydrolysis, we can predict and control the properties of salt solutions in various applications. Whether you're a student, researcher, or industry professional, grasping these concepts will enhance your understanding of chemical processes and their real-world implications.

Amphiprotic Ions and Their Behavior

Amphiprotic ions, also known as amphoteric ions, play a fascinating role in the world of chemistry, particularly in salt hydrolysis. These unique chemical species have the ability to act as both acids and bases, depending on the environment they're in. This dual nature makes them essential in various chemical processes and reactions.

Understanding Amphiprotic Ions

Amphiprotic ions are molecules or ions that can both donate and accept protons (H+ ions). This characteristic allows them to behave as acids in some situations and bases in others. The term "amphiprotic" comes from the Greek words "amphi" (meaning "both") and "protos" (meaning "first" or "most important").

The Hydrogen Oxalate Ion: A Perfect Example

To better understand the concept of amphiprotic ions, let's consider the hydrogen oxalate ion (HC2O4-) as an example. This ion is particularly interesting because it clearly demonstrates the dual nature of amphiprotic species:

  • As an acid: HC2O4- + H2O C2O42- + H3O+
  • As a base: HC2O4- + H2O H2C2O4 + OH-

In the first reaction, the hydrogen oxalate ion acts as an acid by donating a proton to water, forming the oxalate ion and a hydronium ion. In the second reaction, it behaves as a base by accepting a proton from water, producing oxalic acid and a hydroxide ion.

The Importance of Ka and Kb Values

When dealing with amphiprotic ions, the acid dissociation constant (Ka) and base dissociation constant (Kb) play crucial roles in determining their overall behavior in solution. These constants help us predict whether an amphiprotic ion will act predominantly as an acid or a base in a given situation:

  • Ka represents the strength of the ion as an acid
  • Kb represents the strength of the ion as a base

For the hydrogen oxalate ion:

  • Ka = 5.9 × 10-5
  • Kb = 6.4 × 10-11

Since Ka is significantly larger than Kb, we can conclude that the hydrogen oxalate ion behaves more as an acid than a base in aqueous solutions. This means that in most cases, it's more likely to donate a proton than accept one.

The Role of Amphiprotic Ions in Salt Hydrolysis

Salt hydrolysis occurs when a salt dissolves in water and reacts with it, potentially changing the pH of the solution. Amphiprotic ions play a significant role in this process, as they can influence the acidity or basicity of the resulting solution based on their Ka and base dissociation constant values.

For example, when sodium hydrogen oxalate (NaHC2O4) dissolves in water, the hydrogen oxalate ion undergoes hydrolysis. Since its Ka is greater than its Kb, the solution will become slightly acidic. This principle applies to many other salts containing amphiprotic ions, making it essential in predicting the pH of salt solutions.

Applications and Importance

Understanding amphiprotic ions and their behavior is crucial in various fields:

  • Biochemistry: Many biological molecules, including amino acids, exhibit amphiprotic properties.
  • Environmental science: Amphiprotic species play roles in natural water systems and soil chemistry.
  • Industrial processes: Knowledge of amphiprotic behavior is essential in designing and optimizing chemical reactions and separations.

In conclusion,

Practical Applications of Salt Hydrolysis

Understanding Salt Hydrolysis

Salt hydrolysis is a fundamental chemical process that occurs when certain salts dissolve in water, resulting in a change in the solution's pH. This phenomenon has far-reaching implications across various scientific disciplines and industries. Let's explore how salt hydrolysis finds practical applications in chemistry, biology, and environmental science.

Applications in Chemistry

In the field of chemistry, salt hydrolysis plays a crucial role in numerous processes and applications. One significant area is buffer solutions, where salt hydrolysis helps maintain a stable pH in chemical reactions. For instance, in analytical chemistry, understanding salt hydrolysis is essential for accurate titrations and pH measurements. Additionally, the concept is vital in the production of various chemicals and pharmaceuticals, where controlling pH is critical for product quality and efficacy.

Importance in Biology

Salt hydrolysis has profound implications in biological systems. In the human body, for example, the hydrolysis of salts helps maintain the delicate pH balance necessary for optimal cellular function. This process is particularly important in blood pH regulation, where bicarbonate ions act as a buffer system. Moreover, salt hydrolysis is crucial in understanding enzyme activity, as many enzymes are pH-sensitive and require specific conditions to function properly. In agriculture, knowledge of salt hydrolysis is essential for soil management and plant nutrition, as it affects nutrient availability and uptake by plants.

Environmental Science Applications

In environmental science, salt hydrolysis is a key concept in understanding and addressing various ecological issues. One prominent example is acid rain formation, where the hydrolysis of certain atmospheric pollutants leads to the creation of acidic precipitation. This understanding is crucial for developing strategies to mitigate environmental damage. Furthermore, salt hydrolysis is important in water treatment processes, particularly in adjusting the pH of drinking water and wastewater. In marine biology, the concept helps explain the ocean's natural buffering capacity, which is vital for marine life and global climate regulation.

Real-World Scenarios

The practical applications of salt hydrolysis extend to numerous real-world scenarios. In the food industry, understanding this process is crucial for food preservation and flavor enhancement. For instance, the hydrolysis of sodium acetate in certain food products can affect their taste and shelf life. In the textile industry, salt hydrolysis is utilized in dyeing processes to achieve desired colors and fastness. In forensic science, knowledge of salt hydrolysis can be applied in crime scene investigations, particularly in analyzing soil samples and understanding the degradation of certain evidence types.

Conclusion

Salt hydrolysis, while a seemingly simple concept, has wide-ranging applications across various scientific fields and industries. From maintaining the delicate balance in our bodies to addressing global environmental challenges, understanding this process is crucial. As we continue to advance in science and technology, the importance of salt hydrolysis in practical applications is likely to grow, opening up new avenues for research and innovation in chemistry, biology, environmental science, and beyond.

Conclusion

In this article, we've explored the fascinating world of salt hydrolysis and spectator ions, two crucial concepts in chemistry. We've learned how salt hydrolysis affects solution pH and the role of spectator ions in chemical reactions. The introduction video provided a visual foundation for understanding these complex topics. Remember, grasping these concepts is essential for success in chemistry studies and beyond. Salt hydrolysis helps explain why some salt solutions aren't neutral, while understanding spectator ions simplifies chemical equations. These principles are fundamental to many chemical processes in both academic and real-world applications. We encourage you to revisit the video and article content to reinforce your understanding. Consider exploring related topics or practicing problem-solving to further solidify your knowledge. Chemistry is a journey of discovery, and mastering these concepts will open doors to deeper scientific understanding. Keep exploring, questioning, and learning!

What is Hydrolysis?

What is hydrolysis? Salts dissolving in water.

Step 1: Introduction to Hydrolysis

Hydrolysis is a chemical process that involves the splitting of a molecule by water. In the context of salts dissolving in water, hydrolysis refers to the reaction of water with the ions produced when a salt dissolves. This process can affect the pH of the solution, making it either more acidic or more basic depending on the nature of the ions involved.

Step 2: Understanding Spectator Ions

When salts dissolve in water, they dissociate into their constituent ions. Some of these ions do not participate in further chemical reactions and are known as spectator ions. Spectator ions simply remain in the solution without affecting the pH. For example, in a solution of sodium chloride (NaCl), the sodium (Na+) and chloride (Cl-) ions are spectator ions because they do not react with water.

Step 3: Dissociation of Salts in Water

When a salt dissolves in water, it dissociates into its positive and negative ions. For instance, a salt MX will dissociate into M+ and X- ions. This dissociation is usually complete for salts that are highly soluble in water. The dissociation can be represented by the equation: MX (in water) M+ + X-.

Step 4: Interaction of Ions with Water

Once the salt has dissociated, the ions may interact with water molecules. This interaction can lead to hydrolysis reactions. For example, the M+ ion might react with water to form a weak acid, while the X- ion might react to form a weak base. These reactions can change the pH of the solution. However, not all ions will react with water; those that do not are the spectator ions.

Step 5: Predicting Hydrolysis Reactions

To predict whether a hydrolysis reaction will occur, one must consider the nature of the ions. Ions derived from strong acids or strong bases typically do not hydrolyze and are spectator ions. For example, the chloride ion (Cl-) from hydrochloric acid (HCl) is a spectator ion. Conversely, ions from weak acids or bases are more likely to hydrolyze. For instance, the acetate ion (CH3COO-) from acetic acid (CH3COOH) can react with water to form hydroxide ions (OH-), making the solution basic.

Step 6: Using Ka and Kb to Determine pH Changes

The extent of hydrolysis and the resulting pH change can be quantified using the acid dissociation constant (Ka) and the base dissociation constant (Kb). These constants help determine the strength of the acid or base formed during hydrolysis. For example, if an ion hydrolyzes to form a weak acid, the Ka value will indicate how much the acid dissociates in water, thus affecting the pH. Similarly, the Kb value will indicate the extent of dissociation for a weak base.

Step 7: Amphiprotic Species and pH

Some ions can act as both acids and bases; these are known as amphiprotic species. An example is the bicarbonate ion (HCO3-), which can either donate a proton to form carbonate (CO32-) or accept a proton to form carbonic acid (H2CO3). The behavior of amphiprotic species in water can further complicate the pH changes resulting from hydrolysis.

Step 8: Practical Implications of Hydrolysis

Understanding hydrolysis is crucial in various fields, including environmental science, medicine, and industrial processes. For instance, the hydrolysis of salts in natural water bodies can affect aquatic life by altering the pH. In medicine, the hydrolysis of certain drugs can influence their efficacy and stability. In industrial processes, controlling the pH through hydrolysis reactions is essential for optimizing chemical reactions and product quality.

FAQs

Here are some frequently asked questions about salt hydrolysis and spectator ions:

  1. What is meant by hydrolysis of salt?

    Salt hydrolysis refers to the reaction between a salt and water, where the salt's ions interact with water molecules to produce either an acidic or basic solution. This process occurs when the salt of a weak acid or weak base dissolves in water, affecting the solution's pH.

  2. How do you identify the spectator ion?

    Spectator ions can be identified by comparing the ionic equation of a reaction. Ions that appear unchanged on both sides of the equation are spectator ions. They don't participate in the chemical reaction and remain in their aqueous form throughout the process.

  3. What is an example of a hydrolyzed salt?

    A common example of a hydrolyzed salt is sodium acetate (CH3COONa). When dissolved in water, the acetate ion (CH3COO-) reacts with water to produce acetic acid and hydroxide ions, resulting in a basic solution. The reaction can be represented as: CH3COO- + H2O CH3COOH + OH-

  4. Is OH- a spectator ion?

    OH- (hydroxide ion) is not typically a spectator ion. It often participates actively in reactions, especially in acid-base chemistry. However, its role depends on the specific reaction. In some cases, it might be a product or reactant, while in others, it could be part of a neutralization reaction.

  5. How do you write a hydrolysis equation?

    To write a hydrolysis equation, follow these steps: 1) Identify the salt and its dissociation products. 2) Determine which ion (cation or anion) will react with water. 3) Write the reaction of that ion with water, showing the equilibrium. For example, for NH4Cl: NH4+ + H2O NH3 + H3O+

Prerequisite Topics for Understanding Hydrolysis

Hydrolysis is a fundamental concept in chemistry that involves the breakdown of chemical compounds through their reaction with water. To fully grasp this process, it's crucial to have a solid understanding of several prerequisite topics. These foundational concepts provide the necessary context and knowledge to comprehend the intricacies of hydrolysis reactions.

One of the key prerequisites is ionic equations and formulae. Understanding how to write and interpret ionic equations is essential for representing hydrolysis reactions accurately. These equations show the dissociation of compounds in water and the subsequent interactions between ions, which is at the heart of hydrolysis.

Closely related to ionic equations is the concept of ion formation. In hydrolysis, compounds often dissociate into ions when they interact with water. Knowing how ions form, particularly hydroxide ion formation, is crucial for understanding the products of hydrolysis reactions and their effects on solution properties.

Another critical prerequisite is the understanding of strong and weak acids and bases. Hydrolysis often involves the reaction of salts derived from weak acids or bases with water. The strength of the acid or base determines the extent of hydrolysis and its effect on the solution's pH. This knowledge is essential for predicting the outcome of hydrolysis reactions.

Building on this, familiarity with mixing strong acids and bases provides insight into more complex hydrolysis scenarios. While hydrolysis typically involves weaker electrolytes, understanding the behavior of strong acids and bases in solution helps in comparing and contrasting different types of aqueous reactions.

The concept of buffer solutions is also relevant to hydrolysis. Some hydrolysis reactions can create buffer systems, which resist changes in pH. Understanding how buffers work is crucial for predicting the pH stability of solutions undergoing hydrolysis.

Lastly, knowledge of the acid dissociation constant (and its counterpart, the base dissociation constant) is vital. These constants quantify the strength of acids and bases, which directly influences the extent of hydrolysis. They help in calculating the pH of solutions resulting from hydrolysis reactions and in predicting the direction of equilibrium in these processes.

By mastering these prerequisite topics, students can develop a comprehensive understanding of hydrolysis. This foundation enables them to analyze, predict, and explain hydrolysis reactions with confidence, setting the stage for more advanced studies in chemistry and related fields.

In this lesson, we will learn:

  • The meaning of the term spectator ion and to identify them in salt and water interactions.
  • To predict hydrolysis reactions and changes in pH of water when salt solutions are made.
  • How to use Ka and Kb to determine pH changes when amphiprotic species are produced in solution.

Notes:

  • Recall that strong acids and strong bases completely dissociate in water. Salts that are water-soluble are also assumed to completely dissociate in water. This means that interactions between water and a water-soluble salt MX can be put in an equation:

    MX = H2O → M+ + X- + H2O

  • Some but not all aqueous ions react with water and this can have a major effect on pH.
    Strong acids dissociate completely in water, so their conjugate bases are such poor bases that they can’t go back to being the conjugate acid. Once they become the conjugate base, they stop reacting – they are ‘spectator’ ions. The conjugate pair of any strong acid or strong base is a spectator ion.
    There are some general and specific spectator ions that should be remembered when learning about hydrolysis of salts:
    • The M+ metal ions of group 1 (alkali metals) and group 2 (alkali earth metals) are spectator ions.
    • The ions I-, Br-, Cl-, NO3- and ClO4- are spectator ions as they are the conjugate bases of strong acids.
    • Once you have identified any spectator ions formed in solution from a salt and water interaction, they can be ignored in any reaction to water.

  • The ions that are not spectator ions can react with water in a hydrolysis reaction. Hydrolysis is the breaking down of a compound (in a chemical reaction) by water. This can cause changes in pH because salts contain oppositely charged ions that dissociate in solution. If one of the ions is a spectator ion but the other (the counter-ion) is not, then the effect on water will be asymmetrical! See below for two examples:
    • Ammonium chloride, NH4Cl is soluble in water and the dissociation can be written in an equation:

      NH4Cl → NH4+ + Cl-

      The two ions that make ammonium chloride have an asymmetric effect on water; chloride, Cl- is a spectator ion but ammonium, NH4+, isn’t! The result is an unopposed hydrolysis reaction of the NH4+ ions with neutral water:

      NH4+ + H2O ⇌\rightleftharpoons NH3 + H3O+

      As the equation shows, H3O+ is a product (the ammonium ion is a weak acid) so the resultant solution is more acidic. The overall effect of adding ammonium chloride to water is a lowering of pH.

    • Sodium ethanoate, CH3COONa is soluble in water. When it dissociates, the Na+ ion is a spectator but the ethanoate ion is not. A hydrolysis reaction can be shown with the equation:

      CH3COO- + H2O ⇌\rightleftharpoons CH3COON + OH-

      The ethanoic acid formed is a moderately ‘strong’ weak acid, but because all of this acid will have come from the ethanoate originally formed, the net effect is OH- ions being made, so the resultant solution is more basic. The overall effect of adding sodium ethanoate to water is a rise in pH.

  • There will be some instances where the salt dissolved in water gives two spectator ions – in this case, the resultant solution is neutral.

  • In some cases, the ions produced when salts dissolve in water will be amphiprotic; molecules that are capable of accepting and donating protons (all amphiprotic molecules are amphoteric molecules):
    • For example: hydrogen oxalate, HC2O4- has two carboxylic acid groups. One is still protonated and could donate a proton, behaving as an acid. The other has already been deprotonated; it could be re-protonated, behaving as a base if this happened. Amphiprotic molecules can and will take part in reactions to accept and donate a proton, but will do one more than the other. The Ka and Kb values for your amphiprotic molecule will tell you if it is a stronger base or acid (the Ka or Kb value will be larger).
      This greater acid/base behaviour will give you the net effect on the pH of the solution.