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Difference Between Alkali and Base is that Alkali compounds are bases that dissolve in water. Whereas, base neutralizes acid.
- Alkali is known to be a hydroxide of alkali metals and alkaline earth metals. Typically, they do not have Ammonia or NH3.
- Thus, as per this Lewis Concept, NH3 is not an alkali even though it is a base. The bases that are dissolved in water in order to form OH- are alkalis. However, this reaction also excludes NH3.
- Thus, the major difference between alkali and base is that alkali is a subset of bases. Hence, it proves that all alkali are bases but not all bases are alkalis.
Alkali and bases are metal oxides, metal hydroxides, metal carbonates and carbonates of molten hydrogen. There are several bases which are insoluble in water. In case the base dissolves in the water, it is an alkali.
Read Also: Acids and Bases
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Key Terms: Alkali, Bases, NaOH, NH3, Ions, Valence Electrons, Ionization, Dissociation, Bronsted Lowry Concept, Arrhenius concept, Lewis Concept
What is Alkali?
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An alkalai is a substance that produces hydroxides ions when dissolved in water. Alkalis are known to be water-soluble bases.
- The word "alkali," has been derived from Arabic, meaning calcined ashes.
- Alkalis have this characteristic of only acting as an alkali after being dissolved in water.
- It takes less energy to remove the outermost electron from an alkali metal.
- The alkali metals are considered soft, glossy, and light. They are soft because they have a weaker metallic bond.
- They are used to balance the pH of water. Its melting temperatures and densities are both low.
- When an alkali is mixed in water, the resulting solution is clear which means transparent.
- Alkalis have potent bases that change the color of litmus paper from red to blue.
- It is used to keep sewage sludge in place and to minimize odor.
- Alkali metals are good conductors of electricity and are considered as reactive metals.
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What is Base?
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A base is a material which is generally used to neutralize acids. Here are some examples of bases i.e., Metal Oxide and Metal hydroxides which react with acid to create neutral substances.
Bases increase the OH- ions concentration when they dissolve in water. Bases are used in digestive medication, soaps, detergents, and cleansers, among other things.
- When bases react with acids, they generally form molecules and water.
- They are unpleasant to taste, a characteristic shared by all bases. They, like acids, can be powerful or weak. Those that are really potent can burn the skin and are extremely corrosive.
- A strong base refers to a base which is soluble in water. Example of a strong base: NaOH. Weak base refers to the base which does not dissolve in water. Example of weak base: NH3.
There are three general definitions of bases, namely:
Arrhenius Concept
As per the Arrhenius concept, any compound which provides OH- ions in its aqueous solution is a base. It is about all hydroxides of alkali metals and alkaline earth metals bases, including NaOH, Ca(OH)2 etc.
Bronsted Lowry Concept
Any compound which can accept a proton, that is, H+ ion is a base. Thus, it means even H2O is capable of acting as a base because it can accept a proton to form hydronium ion i.e., H3O+ ion. This concept covers almost all bases, yet not all bases because not all of them extract the H+.
Lewis Concept
Any compound, as per Lewis Concept, which can donate a lone pair or can donate a pair of electrons is a base.
Also read: Properties of Bases
Difference Between Alkali and Base
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Some of the many differences between alkali and base include:
| Type | Alkali | Base |
|---|---|---|
| Meaning | Alkali refers to the bases which can be soluble in water. | Bases which cannot be soluble in water. |
| Nature | All alkalis are considered bases. | All bases are not considered alkali |
| Formation | It forms carbonates and hydroxides | It forms hydroxide or lone pairs |
| Texture | Soft and lustrous in texture | Slippery in texture |
| Strength | Alkali’s strength depends upon the nature and concentration of ionic salt | The base’s strength depends upon the concentration of hydroxide ions |
| Example | Potassium Hydroxide, Sodium Hydroxide | Zinc hydroxide, Copper Oxide |
Things to Remember
- One difference between a base and an alkali is that alkalis are ionic compounds that can break when dissolved in a polar protic solution, whereas bases can be either ionic or non-ionic.
- CuO, ZnO, and NH3 are all covalent compounds that serve as bases.
- The ionic alkalis NaOH and KOH are crucial alkalis.
- It has been said that all alkalis are bases, but not all bases are alkalis.
- Bases are divided into two parts I.e., strong base and weak base.
- Alkalis are sour in taste whereas bases are bitter.
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Sample Questions
Ques. Why are lemons sour in taste? (2 marks)
Ans. If you've ever actually eaten out of a lemon, you already know how sour they can be. This is due to the presence of citric acid, a weak organic acid present in a variety of fruits and vegetables. Citric acid stimulates taste cells on the sides and centre of your tongue when you take a bite of lemon.
Ques. Give a reason why distilled water does not contain electricity whereas rainwater contains? (2 marks)
Ans. Rainwater contains dissolved gases such as Sulphur dioxide and carbon dioxide, whereas distilled water is relatively pure which does not possess any ions. Carbonic acid is formed when these gases are dissolved in water. Hydrogen ions and carbonate ions are formed when carbonic acid dissociates. The conduction of electricity is caused by these ions. As a result, distilled water does not conduct electricity, whereas rainwater does.
Ques. A student dropped a few marbles into a test tube containing dilute hydrochloric acid. After that, the gas was routed through lime water. In lime water, what changes would you notice? What happens if there is too much gas in the lime water? Explain the observation with the help of balanced chemical equations. (4 marks)
Ans. Calcium carbonate is the chemical formula for marble. Calcium chloride, water, and carbon dioxide are formed when dilute HCl is introduced to calcium carbonate. The reaction's chemical equation is as follows:
CaCO3 + 2HCl → CaCl2 + H2O + CO2
Due to the creation of calcium carbonate, carbon dioxide gas makes lime water milky. The chemical equation for the reaction between lime water and carbon dioxide is shown below.
Ca(OH)2 + CO2 → CaCO3 + H2O
Excess CO2 causes milkiness to diminish because Ca(HCO3)2 is generated, which is water soluble.
CaCO3 + H2O + CO2 → Ca(HCO3)2
Easily soluble in water
Ques. To disinfect the water tank, a sanitary worker applies a white chemical with a strong chlorine gas odor. (3 marks)
(I) Write down the chemical compound's name and formula.
(ii) Provide a chemical equation for its manufacture.
(iii) Describe its two other purposes besides disinfection.
Ans. To disinfect the water tank, a sanitation worker applies a white chemical with a strong chlorine gas odor.
(i) Bleaching Powder is the chemical compound's name (Calcium oxychloride). CaOCl2 is its chemical formula.
(ii) It's made when chlorine reacts with dry-slaked lime.
Ca(OH)2 +Cl2 →CaOCl2 +H2O
(iii) Bleaching powder is used in the textile sector to bleach cotton and linen, in the paper industry to bleach wood pulp, and in the laundry to bleach washed garments.
Many chemical industries utilize it as an oxidizing agent.
Ques. A chemical compound is left behind after bee stings, which causes pain and discomfort. Identify the chemical compound. Determine the type of substance that, when applied to the sting area, can provide relief. (1 mark)
Ans. Methanoic acid is a chemical compound. The formula is HCOOH. NaHCO3 or milk of magnesia are two substances that may provide relief. They will neutralize the reaction because they are base.
Ques. Give reason why A tarnished copper vessel regains its shine when rubbed with lemon. (1 mark)
Ans. Lemon is acidic in nature. When a tarnished copper vessel is rubbed with a lemon, the basic copper oxide or copper carbonate combines with the acid (citric acid) in the lemon to generate a salt, which is then washed away with water.
Ques. Explain Why should curd or sour things not be stored in brass or copper vessels? (2 marks)
Ans. Brass and copper are considered as metal.
Lactic acid is found in curd and other sour foods (C3H6O3). When metals react with acids, salt, and hydrogen gas are produced. And when sour things such as curd are stored in brass or copper vessels, the lactic acid in the curd reacts with the metals, causing corrosion and the creation of toxic ions that cannot be digested.
Ques. “Sodium hydrogen carbonate is a basic salt”. Define this statement. How can it be converted into washing soda? (2 marks)
Ans. Sodium hydrogen carbonate is a salt which can be formed by the reaction between sodium hydroxide (a strong base) and carbonic acid (weak acid). It is, therefore, a weak basic salt. Heating and crystallisation are the various methods that helps to convert it to washing soda. A reaction of the same is as followed:
2NaHCO3 → Na2CO3 → CO2 +H2O.
Ques. Name the conjugate bases of the Bronsted acids HF, H2SO4, and HCO– ? (1 mark)
Ans. F–, HSO4–, and CO32– are the conjugate bases for the Bronsted acids.
Ques. What is Lime water? (1 mark)
Ans. Lime water can be defined as a saturated aqueous solution of calcium hydroxide.
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