Difference Between Alkali and Metal Hydroxide

Main Difference – Alkali vs Metal Hydroxide

A hydroxide is any chemical compound containing one or more –OH groups. In a hydroxide, the –OH groups act as anions. This anion is in combination with a cation, usually a metal ion or an organic group. Alkali hydroxides are compounds containing an alkali metal cation bonded to a –OH anion. Alkali metal cations can be formed from alkali metal atoms, which are the group 1 elements. Metal hydroxides are compounds containing any metal cation bonded to one or more –OH groups. These metal cations include cations formed from elements in group 1, group 2 and also d block elements. The main difference between alkali hydroxides and metal hydroxides is that alkali hydroxides are essentially composed of a metal cation formed from group 1 elements whereas metal hydroxides are composed of metal cations formed from any metal element.

Key Areas Covered

1. What is Alkali Hydroxide
     – Definition, Formation, Properties, Examples
2. What is Metal Hydroxide
    – Definition, Formation, Properties, Examples
3. What is the Difference Between Alkali and Metal Hydroxide
     – Comparison of Key Differences

Key Terms: Alkali Hydroxide, Alkali Metal, Anion, Bases, Cation, Hydroxide, Metal Hydroxide

What is Alkali Hydroxide

Alkali hydroxides are chemical compounds containing a group 1 metal cation and a –OH anion. These are ionic compounds. The group 1 elements are Lithium, Sodium, Potassium, Rubidium, Caesium and Francium. All these elements except Francium can form hydroxides because Francium is a radioactive element. Therefore, the list of alkali hydroxides is as follows.

• Lithium hydroxide
• Sodium hydroxide
• Potassium hydroxide
• Caesium hydroxide

All these hydroxides are strong bases and are very corrosive. They have different uses depending on the basicity and chemical composition. Alkali hydroxides are formed when the metal reacts with water. Group 1 metals react with water resulting in an explosive reaction. The reaction gives alkali hydroxide and hydrogen gas. For example,

Na   +   H₂O     →      NaOH   +   H₂

The reaction between alkali metal oxide and water also yields the hydroxide. For example,

Na₂O   +   H₂O     →      2NaOH  

Figure 1: Sodium Hydroxide

However, concentrated alkali hydroxides are the strongest bases among all. The basicity of these hydroxides increases when going down the group; i.e. Lithium hydroxide is the least basic compound of the group and Caesium hydroxide is the highest basic compound. All alkali hydroxides are white crystalline solid compounds and dissolve very well in water.

What is Metal Hydroxide

Metal hydroxides are chemical compounds containing a metal cation and –OH anion. These are ionic compounds. Metals can be group 1 elements (except hydrogen), group 2 elements, d block elements and f block elements including few p block elements as well.

Metal hydroxides can be found in different colors based on the type of metal cation present in the compound. For example, chromium hydroxide is green colored; ferric hydroxide is red colored, cobalt(II) hydroxide is green colored, etc.

Figure 2: Cobalt(II) Hydroxide

Metal hydroxides are considered as strong bases. That is because these compounds can release –OH groups which cause the basicity of a solution. The number of –OH ions present in a metal hydroxide (or the number of –OH groups it can release) depends on the oxidation state of the metal cation.

Difference Between Alkali and Metal Hydroxide

Definition

Alkali Hydroxide: Alkali hydroxides are chemical compounds containing a group 1 metal cation and a –OH anion.

Metal Hydroxide: Metal hydroxides are chemical compounds containing a metal cation and –OH anion.

Number of OH Groups

Alkali Hydroxide: Alkali hydroxides contain one –OH group per molecule.

Metal Hydroxide: Metal hydroxides contain one or more –OH groups depending on the oxidation state of the metal cation.

Color

Alkali Hydroxide: Alkali hydroxides are white crystalline solids.

Metal Hydroxide: Metal hydroxides can be in different colors depending on the type of metal cation.

Basicity

Alkali Hydroxide: Alkali hydroxides are the strongest bases among all bases.

Metal Hydroxide: Metal hydroxides are basic compounds.

Examples 

Alkali Hydroxide: Alkali hydroxides include Lithium hydroxide, Sodium hydroxide, Potassium hydroxide, Rubidium hydroxide, and Caesium hydroxide.

Metal Hydroxide: Metal hydroxides include a wide variety of compounds such as aluminum hydroxide, ferrous hydroxide, magnesium hydroxide, etc.

Conclusion

Alkali chemical elements are group 1 elements. They are called alkali because the compounds they form are basic. Metals are chemical elements that can remove electrons to form cations. Metals include elements in group 1, group 2, d block elements, f block elements and a few of p block elements. The main difference between alkali hydroxides and metal hydroxides is that alkali hydroxide is essentially composed of a metal cation formed from group 1 elements whereas metal hydroxides are composed of metal cations formed from any metal element.

Reference:

1.  “Hydroxide.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 20 July 1998, Available here.
2. “Alkali hydroxide.” Wikipedia, Wikimedia Foundation, 4 July 2017, Available here.
3. “Metal hydroxide.” Wikipedia, Wikimedia Foundation, 10 Nov. 2017, Available here.

Image Courtesy:

1. “SodiumHydroxide” By Walkerma – Own work (Public Domain) via Commons Wikimedia
2. “Cobalt(II) hydroxide (2)” By Chemicalinterest – Own work (Public Domain) via Commons Wikimedia