Acid And Base Difference: Introduction, Definition, General Properties

Edited By Team Careers360 | Updated on Jul 02, 2025 05:24 PM IST

In our day-to-day life, we use many chemicals that scientists call acids and bases. From cleaning agents to the food we eat, we often come across them in our everyday life. For example, the orange juice or lemon water we drink contains citric acid (also spelt as Vitamin C), the vinegar we use to change the texture of food contains acetic acid, the diary products we eat has lactic acid, the baking soda we use in cooking, soaps and detergents we use for washing cloths are included under bases. Thus, acid and base can be defined as chemicals that play a vital role in chemistry as well as in our daily chores.

This Story also Contains

Introduction
Acid: Definition
Acid: General Properties
Base: Definition
Bases: General Properties
Acids and Bases: Definition in Chemistry
Acidity and Basicity
pH Scale: Acidic and Basic Nature Indicator
Acid and bases: Difference

Acid And Base Difference: Introduction, Definition, General Properties

Introduction

Acids and bases refer to the form of popular chemicals which interact with each other resulting in the formation of salt and water. They play an important role in chemistry and also in our daily life. Some of them taste sweet, some are sour, some are bitter and some are salty.

Acid: Definition

The term acid belongs to the Latin word ‘acidus’ which means ‘sour’. Therefore, anything that tastes sour contains an acid. For example, lemon juice, vinegar, tomato juice etc, all taste sour which must contain an acid. Aqueous solutions of acids generally taste sour.

Thus, acids can be defined in various ways. According to Liebig (1838),

“An acid is a compound which contains hydrogen that can be replaced partially or wholly by a metal or a group of elements acting as metal (termed as acidic hydrogen or replaceable hydrogen) to produce a salt.”

For example, HCl, H2SO4, HNO3 etc.

Acid: General Properties

Acids are sour in taste.
They are corrosive.
They are good conductors of electricity.
They turn blue litmus paper red.
They possess a pH value always less than 7.
They show acidic properties only in the presence of water.
Their aqueous solutions conduct electricity.
They react with certain metals and evolve hydrogen gas.

Base: Definition

Bases, in contrast to acids, are the molecules or ions that are capable of accepting a proton from an acid. They are soapy to the touch with a slippery texture and are bitter. A base is usually the oxides or the hydroxides of a metal, which can react with an acid to produce salt and water.

Alkalis refer to those bases that are soluble in water. For example, KOH, Ca(OH)2, NaOH etc. It is thus, important to remember all alkalis are bases but all bases are not alkalis.

Bases: General Properties

Bases are bitter in taste.
The aqueous solutions of bases give a soapy touch.
When dissolved in water they yield hydroxide ions (OH-). Thus, in an aqueous solution, they act as good conductors of electricity.
They turn red litmus paper blue.
Bases possess a pH value always greater than 7 which is between 8 - 14.The more the pH value more is the basicity.
They chemically react with acids to produce salt and water.

Acids and Bases: Definition in Chemistry

In order to define acids and bases, three theories have been put forth namely, Arrhenius theory, Lowry- Bronsted theory and the Lewis theory of acids and bases.

Based on these theories, acids and bases can be defined as follows:

Arrhenius theory of acids and bases states that “an acid yields H+ ions in a solution while a base in solution produces OH- ions.”
According to Lowry- Bronsted theory, “An acid is a proton donor and a base is a proton acceptor.”
Lewis theory defines “acids as electron pair acceptors while bases as electron pair donors.”

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Acidity and Basicity

In chemistry, there exist three types of terms to define the chemical characteristics of substances i.e. acidic, basic and neutral.

All these terms are related to the number of hydrogen ions a compound can generate in the solution of water.

Thus, the basicity of an acid can be defined as the number of H atoms in one molecule of acid that can be replaced by a metal. Also, it is the no. of H+ ions that can be replaced by one molecule of that acid.

For example, HCl (Monobasic), H2SO4 (Dibasic), H3PO4 (tribasic)

The acidity of bases is the number of hydroxyl ions (OH- ions) which can be produced per molecule of a base in its aqueous solution.

For example, NaOH (monoacidic), Mg(OH)2(diacidic), Al(OH)3(triacidic)

pH Scale: Acidic and Basic Nature Indicator

The pH of a solution indicates the potency of hydrogen that describes which solution is more acidic or more basic than the other.
A pH scale introduced by S P Sorensen (1909) usually expresses the acidity or basicity of a solution in terms of H+ ion concentration.

pH= -log [H+]

pH= -log[OH-]

Acidic solutions have a pH of less than 7 and thus they taste sour. The lower the pH value, the more acidic is the solution.
In contrast, basic solutions have a pH greater than 7 and thus they taste bitter. The more the pH, the more basic is the solution.
Neutral solutions or pure water possess a pH of 7.

Acid and bases: Difference

Difference in definition:

An acid is a substance that has a pH value of less than 7 in its aqueous solution. Acids donate H+ ions to bases. They are also called proton donors or electron-pair acceptors.

A base (alkali) is a substance that has a ph value of greater than 7 in its aqueous solution. Bases donate OH- ions. They are also called proton acceptors or electron pair donors.

Difference in Formula:

The chemical formula for most acids starts with H.

For Example, Nitric acid (HNO3), Carbonic acid in soft drinks (H2CO3), Boric acid (H3BO3), Hydrochloric acid (HCl) etc.

The chemical formula for most bases (compounds) has OH at the end. For example, Calcium hydroxide or slaked lime, Ca(OH)2 (paper, flocculant), Magnesium hydroxide Mg (OH)2 or milk of magnesia, Sodium hydroxide (NaOH) or caustic soda

Difference in pH:

Acids have a pH of less than 7.0. The more the pH value is less that 7 more is the acidity of the solution.

On the other hand, Bases have a pH higher than 7.0, and could even go up to 14 if the bases are very strong.

Difference in physical characteristics:

Acids, when dissolved in water, become sticky with a burning sensation.

They change the blue litmus paper to red.

They taste sour and are a good conductor of electricity.

They react with bases to neutralize their properties.

They liberate H+ ions when reacting with active metals.

While bases,

When dissolved in water, they taste bitter.

They change the red litmus paper into blue.

They become slippery to the touch.

They react with acids to neutralize their respective properties.

Difference in Strength:

The strength of an acid depends on the concentration of hydronium (H3O+) ions.

While the strength of the base depends on the concentration of hydroxide (OH-) ions.

Difference in Dissociation:

Acids when mixed with water dissociate and release H+ ions.

While bases when mixed with water dissociate and release OH- ions.

Difference in uses:

Acids are used as household cleaning agents, in leather processing and carbonated drinks, preservatives and fertilizers.

Bases are used in soaps, detergents, antacids etc.

Frequently Asked Questions (FAQs)

1. How can acids and bases be identified?

To identify whether a substance is an acid or base, count the number of hydrogen on each substance before and after the reaction.

If the number has decreased that substance is the acid (which donates H+ ions). And if the number of hydrogen has increased that substance is the base (accepts H+ ions)

2. What makes a substance an acid or a base?

An acid is a substance containing hydrogen ions. If the solution contains more hydronium ions (H3O+) than hydroxyl ions (OH-), then the given solution can be said to be an acid. Similarly, if the solution contains more hydroxyl ions (OH-) than hydrogen ions (H+), then the given solution is a base.

3. How can acids and bases be differentiated?

Any chemical substance with a pH value between 0-7 is known to be acid while a pH value between 7-14 is a base. Acids turn litmus paper red while bases turn litmus paper blue. Acids taste sour and bases taste bitter.

4. What is the importance of acids in everyday life?

Acids play significant roles within the human body. The presence of hydrochloric acid (HCl) in the stomach helps digestion by breaking down complex food molecules into simpler forms. In addition, the orange juice or lemon water we drink contains citric acid or Vitamin C, the vinegar we use to change the texture of food contains acetic acid, and the dairy products we eat contain lactic acid.

5. Acids can react with metals. Yes/No. If yes, explain.

Yes, acids react with the metal to form the corresponding salt and liberate hydrogen gas.

Acid + Metal → Salt + Hydrogen Gas

For example: H2SO4 + Mg → MgSO4 + H2↑

(Acid) (Metal) (Salt) (H2 gas)

6. What is the fundamental difference between acids and bases?

Acids are proton donors, while bases are proton acceptors. This means acids release hydrogen ions (H+) in solution, whereas bases accept hydrogen ions or release hydroxide ions (OH-) in solution. This fundamental difference is the basis for their contrasting properties and behaviors in chemical reactions.

7. What are the limitations of the Arrhenius theory of acids and bases?

The Arrhenius theory has several limitations: it only applies to aqueous solutions, doesn't explain the basic nature of substances like ammonia (which don't produce OH- ions), and can't account for acid-base reactions in non-aqueous solvents. These limitations led to the development of more comprehensive theories like Brønsted-Lowry and Lewis theories.

8. How does the Lewis theory further expand the concept of acids and bases?

The Lewis theory defines acids as electron pair acceptors and bases as electron pair donors. This definition broadens the concept of acid-base reactions beyond proton transfer, including reactions where no protons are involved. It can explain reactions like the formation of complex ions and some organic reactions, making it the most comprehensive acid-base theory.

9. Why do acids typically taste sour while bases taste bitter?

The sour taste of acids is due to the interaction of hydrogen ions (H+) with taste receptors on the tongue. Bases, on the other hand, taste bitter because of the interaction of hydroxide ions (OH-) or the basic substance itself with different taste receptors. These taste differences are a sensory manifestation of the chemical properties of acids and bases.

10. How do acids and bases conduct electricity in solution?

Acids and bases conduct electricity in solution due to the presence of mobile ions. When dissolved in water, acids release hydrogen ions (H+) and their corresponding anions, while bases produce hydroxide ions (OH-) and their cations. These ions can carry electric charge through the solution, allowing for electrical conductivity. The strength of the acid or base and its concentration affect the degree of conductivity.

11. What is neutralization, and how does it relate to acid-base reactions?

Neutralization is a reaction between an acid and a base that produces water and a salt. In this process, the H+ ions from the acid combine with the OH- ions from the base to form water molecules. The remaining ions form a salt. For example, HCl + NaOH → H2O + NaCl. Neutralization reactions are important in many applications, from controlling soil pH in agriculture to treating industrial waste.

12. How does the concept of Lewis acids and bases apply to coordination compounds?

In coordination compounds, the central metal ion acts as a Lewis acid (electron pair acceptor), while the ligands act as Lewis bases (electron pair donors). This interaction forms coordinate covalent bonds. For example, in the complex ion [Cu(NH3)4]2+, the Cu2+ ion is the Lewis acid, accepting electron pairs from four NH3 molecules (Lewis bases). This concept explains the formation and stability of many metal complexes and is crucial in understanding transition metal chemistry and catalysis.

13. How do organic acids differ from inorganic acids in their properties and behavior?

Organic acids, such as carboxylic acids, typically have a -COOH functional group and are generally weaker than inorganic acids. They often have larger molecules, which can affect their solubility and reactivity. Inorganic acids, like HCl or H2SO4, are usually stronger, more reactive, and often consist of simpler molecules. The difference in strength affects their behavior in solutions, their ability to donate protons, and their roles in various chemical and biological processes.

14. What is the significance of pKa values in acid-base chemistry?

The pKa value is the negative logarithm of the acid dissociation constant (Ka). It indicates the strength of an acid – the lower the pKa, the stronger the acid. pKa values are crucial for predicting the behavior of acids and bases in solution,

15. What is a conjugate acid-base pair?

A conjugate acid-base pair consists of two species that differ by a single proton. When an acid donates a proton, it becomes its conjugate base. Similarly, when a base accepts a proton, it becomes its conjugate acid. For example, HCl (acid) and Cl- (conjugate base) form a conjugate acid-base pair. Understanding these pairs helps predict the direction of acid-base reactions.

16. How do amphoteric substances behave in acid-base reactions?

Amphoteric substances can act as both acids and bases, depending on the reaction conditions. They can donate protons in the presence of a base and accept protons in the presence of an acid. Water is a common example of an amphoteric substance. Understanding amphoterism is crucial for predicting the behavior of certain compounds in different chemical environments.

17. What is the role of water in acid-base reactions?

Water plays a crucial role in acid-base reactions as both a solvent and a reactant. As a solvent, it facilitates the dissociation of acids and bases. As a reactant, it can act as both an acid and a base (amphoteric). In aqueous solutions, acids react with water to produce hydronium ions (H3O+), while bases react to produce hydroxide ions (OH-). Water's ability to participate in proton transfer reactions is fundamental to understanding acid-base behavior in aqueous solutions.

18. How does temperature affect the strength of acids and bases?

Temperature can influence the strength of acids and bases by affecting their degree of ionization. Generally, as temperature increases, the ionization of weak acids and bases increases slightly, making them behave more like strong acids or bases. However, temperature also affects the autoionization of water, which can impact the pH scale. Understanding these temperature effects is crucial in predicting acid-base behavior in various environmental and industrial conditions.

19. How do polyprotic acids differ from monoprotic acids in their acid-base behavior?

Polyprotic acids can donate more than one proton per molecule, while monoprotic acids can only donate one. This means polyprotic acids undergo stepwise dissociation, with each step having its own dissociation constant (Ka). For example, H2CO3 can donate two protons: H2CO3 ⇌ H+ + HCO3- and then HCO3- ⇌ H+ + CO32-. This stepwise dissociation results in more complex titration curves and buffer systems compared to monoprotic acids.

20. How does the Arrhenius theory define acids and bases?

The Arrhenius theory defines acids as substances that increase the concentration of hydrogen ions (H+) in aqueous solution, while bases are substances that increase the concentration of hydroxide ions (OH-) in aqueous solution. This theory is limited to aqueous solutions and doesn't account for all acid-base behaviors.

21. How does the Brønsted-Lowry theory expand on the definition of acids and bases?

The Brønsted-Lowry theory defines acids as proton donors and bases as proton acceptors. This broader definition allows for acid-base reactions in non-aqueous solutions and explains the behavior of substances like ammonia, which acts as a base by accepting protons without producing hydroxide ions. It also introduces the concept of conjugate acid-base pairs.

22. How do Lewis acids and bases differ from Brønsted-Lowry acids and bases?

Lewis acids and bases are defined by their ability to accept or donate electron pairs, respectively, while Brønsted-Lowry acids and bases are defined by their ability to donate or accept protons. This means that Lewis theory can explain acid-base behavior in reactions where no proton transfer occurs, such as in the formation of coordination compounds. For example, BF3 is a Lewis acid because it can accept an electron pair, but it's not a Brønsted-Lowry acid as it doesn't donate protons.

23. How do acid-base reactions in non-aqueous solvents differ from those in water?

Acid-base reactions in non-aqueous solvents can behave differently due to the solvent's properties. Unlike water, which can act as both an acid and a base, some non-aqueous solvents may be purely basic (like liquid ammonia) or acidic. This affects the definition of acids and bases in these solvents and can lead to different equilibria and reaction products. For example, in liquid ammonia, acids are defined as substances that produce ammonium ions (NH4+). Understanding these differences is crucial in organic synthesis and in studying reactions under anhydrous conditions.

24. What is the relationship between acid strength and the stability of its conjugate base?

There's an inverse relationship between acid strength and the stability of its conjugate base. Strong acids have weak conjugate bases, while weak acids have strong conjugate bases. This is because a strong acid readily donates its proton, forming a stable conjugate base that has little tendency to accept the proton back. Conversely, a weak acid holds onto its proton more tightly, forming a less stable conjugate base that more readily accepts protons. This relationship is key to predicting the direction of acid-base reactions.

25. What is the difference between an Arrhenius base and a Brønsted-Lowry base?

An Arrhenius base is defined as a substance that increases the concentration of hydroxide ions (OH-) when dissolved in water. A Brønsted-Lowry base, on the other hand, is defined as a proton acceptor. The Brønsted-Lowry definition is broader and includes substances that don't produce OH- ions but can still accept protons. For example, ammonia (NH3) is a Brønsted-Lowry base because it can accept a proton to form NH4+, but it's not an Arrhenius base because it doesn't directly produce OH- ions in solution.

26. How do acids and bases interact with metals, and what are the products?

Acids generally react with metals to produce hydrogen gas and a salt. The general reaction is: Metal + Acid → Salt + Hydrogen gas. For example, Zn + 2HCl → ZnCl2 + H2. However, not all metals react with acids; noble metals like gold and platinum are resistant. Bases, particularly strong bases, can also react with some metals (especially amphoteric metals like aluminum) to produce hydrogen gas and a complex ion. For example, 2Al + 2NaOH + 6H2O → 2Na[Al(OH)4] + 3H2. Understanding these reactions is crucial in metallurgy and chemical processing.

27. What is a titration, and how does it help determine acid or base concentration?

A titration is a laboratory technique used to determine the concentration of an acid or base in solution. It involves the controlled addition of a solution of known concentration (the titrant) to a solution of unknown concentration until the reaction is complete (the endpoint). By measuring the volume of titrant needed to reach the endpoint, and knowing the stoichiometry of the reaction, the concentration of the unknown solution can be calculated. Titrations are widely used in analytical chemistry for quantitative analysis.

28. What is the role of acid-base chemistry in biological systems?

Acid-base chemistry plays a crucial role in biological systems. It's essential for maintaining pH balance in bodily fluids, which is critical for enzyme function, protein structure, and cellular processes. For example, blood pH is tightly regulated through buffer systems. Acid-base reactions are also involved in digestion, where stomach acid helps break down food, and in the transport of CO2 in blood. Understanding acid-base chemistry is fundamental to biochemistry, physiology, and medicine.

29. How do acids and bases affect the color of indicators?

Acid-base indicators are weak organic acids or bases that change color depending on the pH of the solution. In acidic solutions, the indicator exists in its protonated form, displaying one color. In basic solutions, it loses a proton and shows a different color. For example, litmus is red in acidic solutions and blue in basic solutions. This color change is a visual representation of the solution's pH.

30. What is the pH scale, and how does it relate to acid and base strength?

The pH scale is a logarithmic measure of the hydrogen ion concentration in a solution, ranging from 0 to 14. A pH of 7 is neutral, below 7 is acidic, and above 7 is basic. The lower the pH, the stronger the acid; the higher the pH, the stronger the base. Each unit change in pH represents a tenfold change in H+ concentration, making it a powerful tool for comparing acid and base strengths.

31. What is the autoionization of water, and why is it important in acid-base chemistry?

The autoionization of water is the process where water molecules react with each other to produce equal amounts of hydrogen ions (H+) and hydroxide ions (OH-). This reaction is represented as: H2O ⇌ H+ + OH-. The product of [H+] and [OH-] is always constant at 1 x 10-14 at 25°C, known as the ion product of water (Kw). This concept is fundamental to understanding pH and the behavior of acids and bases in aqueous solutions.

32. What is the difference between strong and weak acids or bases?

Strong acids and bases ionize completely in solution, while weak acids and bases only partially ionize. For example, HCl (strong acid) dissociates completely into H+ and Cl- ions in water, whereas CH3COOH (weak acid) only partially dissociates. This difference affects their reactivity, pH in solution, and ability to conduct electricity. Strong acids and bases have a more pronounced effect on pH than weak ones at the same concentration.

33. How do buffers maintain pH, and what is their composition?

Buffers are solutions that resist changes in pH when small amounts of acid or base are added. They typically consist of a weak acid and its conjugate base (or a weak base and its conjugate acid) in roughly equal concentrations. When an acid is added, the conjugate base neutralizes it; when a base is added, the weak acid neutralizes it. This ability to neutralize both acids and bases allows buffers to maintain a relatively constant pH, which is crucial in many biological and chemical processes.

34. What is the common ion effect, and how does it influence acid-base equilibria?

The common ion effect occurs when an ion that is part of the equilibrium system is added from an external source. This addition shifts the equilibrium according to Le Chatelier's principle. For example, adding sodium acetate (CH3COONa) to a solution of acetic acid (CH3COOH) increases the concentration of acetate ions, pushing the equilibrium towards the undissociated acid. This effect is important in understanding buffer solutions and in predicting the behavior of weak acids and bases in various solutions.

35. What is hydrolysis, and how does it relate to salts in solution?

Hydrolysis is the reaction of a salt with water, which can affect the pH of the solution. When a salt dissolves in water, its ions can interact with water molecules, potentially producing H+ or OH- ions. The nature of this interaction depends on whether the salt is derived from a strong or weak acid/base. For example, sodium acetate (from a weak acid and strong base) undergoes hydrolysis to produce a basic solution, while ammonium chloride (from a weak base and strong acid) produces an acidic solution. Understanding hydrolysis is crucial for predicting the pH of salt solutions.

36. How do indicators work in acid-base titrations, and what is an endpoint?

Indicators are weak acids or bases that change color at specific pH ranges. In a titration, the indicator is added to the analyte solution. As the titrant is added, the pH changes gradually until the equivalence point is reached. The endpoint is the point at which the indicator changes color, signaling that the titration is complete. Ideally, the endpoint should coincide with the equivalence point. Different indicators change color at different pH ranges, so choosing the right indicator is crucial for accurate titrations. Understanding indicator behavior helps in selecting the appropriate indicator for specific acid-base titrations.

37. What is a buffer capacity, and how is it measured?

Buffer capacity is the amount of acid or base that a buffer solution can neutralize before significant pH change occurs. It's a measure of the buffer's effectiveness in resisting pH changes. Buffer capacity is typically highest when the concentrations of the weak acid and its conjugate base are equal. It can be measured experimentally by titrating the buffer with strong acid or base and observing the pH change. A higher buffer capacity means more acid or base can be added before the pH changes significantly. Understanding buffer capacity is crucial in preparing effective buffers for various applications in chemistry and biology.

38. How do acid-base properties influence the behavior of amino acids and proteins?

Amino acids and proteins contain both acidic and basic groups, making them amphoteric. Their behavior depends on the pH of the solution. At low pH, amino acids are protonated and act as cations; at high pH, they're deprotonated and act as anions. The pH at which an amino acid carries no net electrical charge is called its isoelectric point. This amphoteric nature affects protein solubility, structure, and function. For example, enzymes have optimal pH ranges for activity, and changes in pH can denature proteins by altering their structure. Understanding these properties is crucial in biochemistry and molecular biology.