Difference between Alkali and Base - Definitions, Examples, Practice Problems & FAQs

Do you know what are the applications of substances which are basic in nature in our day-to-day life?

There are numerous applications such as the production of paper, detergents, and soap all use sodium hydroxide. Soap and detergents are essential commodities. You must have seen that they dissolve quickly in water.

So can we say that all basic substances are soluble in water?

Well, that’s not true. Not all basic substances are water-soluble. Hence, to avoid confusion there’s a separate category for the basic substances which are soluble in water. Let’s find out and discuss that special category of basic substances and the difference between them.

Table of Content

• What is a Base?
• What is an Alkali?
• Difference Between Alkali and Base
• Practice Problems
• Frequently Asked Questions - FAQs

What is a Base?

There are three different conceptual definitions of bases:

1. Arrhenius Concept: Base is the substance that produces $OH{ }^{-}$in an aqueous solution. Examples include NaOH, $Ca(OH{)}_2$, etc.
2. Bronsted-Lowry Concept: According to this theory, a base is a substance that has the ability to accept protons (H+).
3. Lewis Concept: According to lewis's concept, the substance which donates a lone pair of electrons is known as the base. For example: NH₃ is lewis's base as it can donate a pair of electrons.

What is an Alkali?

The word "alkali," which is derived from Arabic, means calcined ashes. Alkalis are water-soluble bases. All alkalis are bases but not all bases are alkalis. Because all bases might not easily dissolve in the water. An alkali tastes bitter and changes red litmus paper to blue. The alkali solution has a pH that is higher than 7.

Examples:

Sodium hydroxide (NaOH) — caustic soda, Potassium hydroxide (KOH)— caustic potash, Calcium hydroxide Ca(OH)₂ — limewater etc.

Difference Between Alkali and Base

Practice Problems

Q1. Bleaching powder has pH value greater than 7 and it's an alkaline substance. Is this statement correct or not?

Answer: (B)

Solution: (CaOCl₂) is the chemical formula for calcium oxychloride, also known as bleaching powder. It has a pH value 13 so it is basic in nature. Moreover, bleaching powder can be easily dissolved in water making the solution alkaline. Hence, bleaching powder is an alkali.

Q2. Which of the following is a base but not an alkali?

A. NaOH
B. ZnO
C. KOH
D. Ca(OH)2

Answer: (B)

Solution: Alkali substances are those bases which are soluble in an aqueous medium. This means all alkalis are bases but not all bases are alkalis. NaOH, KOH, Ca(OH)2 are water soluble bases, so they are included in the alkali category whereas ZnO is not a water-soluble substance. Hence, it won’t be considered as alkali. So, option B is the correct choice.

Q3. Al(OH)3 is a/an

A. Acid
B. Base
C. Alkali
D. Mixture

Answer: (B)

Al(OH)3 is a base but it’s not an alkali. Aluminium hydroxide (Al(OH)3) is not soluble in water. As a results, it is not an alkali. Hence, all bases are not alkalis, but all alkalis are bases.

Q4. What will be the pH of alkaline substances?

A. Less than 7
B. Greater than 7
C. Equals to 7
D. None of the above

Answer: (B)

Solution: Just like any other base the alkali solution has a pH that is higher than 7. For example pH of NaOH is close to 10.

Frequently Asked Questions (FAQs)

Q1. Is milk acidic or alkaline?

Answer: The pH range of the milk is 6.5 to 6.7. So, milk is slightly acidic in nature, but very near to the pH 7. Therefore, if the litmus paper is used, the result on the litmus paper would be neutral to slightly acidic.

Q2. Why NaOH is referred to as caustic soda?

Answer: Lye, also known as Caustic Soda, is an alkali salt. It is sodium hydroxide's common name. Because this salt corrodes the tissues of both plants and animals, it has earned this name.

Q3. What is the application of alkali substances?

Answer: The production of paper, detergents, and soap all use sodium hydroxide. In addition to being used as the electrolyte in alkaline, Ni-Cd, and Ni-MH batteries. Moreover, to make acidic soil alkaline, potassium hydroxide is used by the farmers which make the plants grow better. .

Q.4 Can acid be neutralised by an alkali?

Answer: Yes, acid can be easily neutralised by alkali substances. A neutralisation reaction occurs when the H+ of acid balances the OH- ion of the base to produce water and salt. The most common example would be the neutralisation reaction of HCl & NaOH.

$HCl \left(aq\right)+NaOH \left(aq\right)\to NaCl \left(aq\right)+H_{2}O \left(l\right)$

In this reaction H+of HCl balances the OH- ion of NaOH to produce water and salt (NaCl).