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What is Salt Hydrolysis? - Definition & Examples

What is Salt Hydrolysis? - Definition & Examples
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  • 0:04 Definitions
  • 1:30 Salts of Strong Acids…
  • 2:29 Salts of Weak Acids &…
  • 3:28 Salts of Strong Acids & Bases
  • 4:11 Salts of Weak Acids & Bases
  • 4:27 Lesson Summary
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Lesson Transcript
Instructor: Kimberly Uptmor

Kimberly has a bachelor's degree in Secondary Education: Science and has master's in Curriculum and Instruction. Currently, she teaches 7th grade through college level classes.

Salt is an important substance for the human body. Made from an acid and a base, salt can react with water and produce acidic, basic, or neutral solutions. In this lesson, we will learn about salt hydrolysis and how to determine if the salt is acidic, basic, or neutral.

Definitions

Salt has often held a bad reputation for being harmful to the body. However, some bodily functions, such as nerve impulses, blood pressure, and digestion, would not be possible if salt wasn't involved. Salt is an ionic compound that is made from the reaction of an acid and a base solution. Salts help the body by making solutions that are acidic, basic, or neutral. Depending on the situation, your body needs different types of solutions to function and maintain its natural processes. Let's begin with a few definitions before jumping into the lesson.

  • An ion is a charged atom that is made from losing or gaining electrons.
  • A hydroxide ion (OH-) is produced when the conjugate base accepts a proton from water and causes the solution to become basic
  • A conjugate acid is a substance formed when the base gains a hydrogen ion.
  • A conjugate base is a substance formed when the acid loses a hydrogen ion.
  • A hydronium ion (H3O+) is produced when the conjugate acid donates a proton to water, causing the solution to become acidic.

Now we have enough review of terms to understand salt hydrolysis, which is when salt completely dissociates in water and its anion or cation reacts with the water to produce hydroxide ions or hydronium ions that affect the pH of the solution.

Salts of Strong Acids and Weak Bases

Salt formed from a strong acid and a weak base will make an acidic solution when added to water. The reason this occurs is because when the salt dissociates, the conjugate acid of the weak base will donate a proton, or one hydrogen ion, to water and form hydronium. NH4NO3 is a salt that comes from a strong acid, HNO3, and a weak base, NH3. When added to water, the salt dissociates into NH4+ and NO3- ions. The NH4+ ion, which is a conjugate acid of the weak base, reacts with water by donating one hydrogen to water and forming hydronium.

Let's look at these equations to see how the salt dissociates and how the conjugate acid of the weak base, or the ammonium ion, reacts with water:

NH4NO3(s)<-->NH4+(aq) + NO3-(aq)

NH4+(aq) + H20(l) <--> NH3(aq) + H3O+(aq)

With more hydronium ions (H3O) in the water, the solution becomes more acidic than basic.

Salts of Weak Acids and Strong Bases

Now let's look at the opposite. If you have a salt that is formed from a weak acid and a strong base, this will make a basic solution when added to water. This occurs because, when the salt dissociates, the conjugate base of the weak acid will accept a proton, or hydrogen, from water and forms hydroxide. KF is a salt that comes from a strong base, KOH, and a weak acid, HF. When added to water, the salt dissociates into a K+ ion and F- ion. The F- ion, which is the conjugate base of the weak acid, reacts with water by accepting one hydrogen atom from water and forming hydroxide.

Let's look at these equations to see how the salt dissociates and how the conjugate base of the weak acid, or the fluoride ion, reacts with water:

KF(s) <--> K+(aq) + F-(aq)

F-(aq) + H2O(l) <--> HF(aq) + OH-(aq)

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