Acids and Bases - Definition, Properties, Examples, FAQs

Q: Give any two metal carbonate examples.

Metal carbonates are Na 2 CO 3 , CaCO 3 .

Acids and Bases - Definition, Properties, Examples, FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 05:03 PM IST

To discuss the properties of acids and bases we first have to study about what acid and base are.
Acid: The word acid comes from the Latin word acidus, which means "sour taste." When acidic chemical compounds dissolve in water, they produce a sour or acidic flavor. Even after the loss of a hydrogen ion from its molecule, an acid can remain energetically favorable.

Acids cause litmus to turn Red. The pigment in the litmus paper reacts with the H⁺ ions, causing chemical modifications in which the chemical bonds are tuned to reflect longer wavelength light, giving it a red appearance to human eyes. The absorption of blue to green wavelengths occurs when the pigment in litmus paper reacts with the H⁺ ions in an acid. Acids mostly oxidize other chemical molecules or alter the color of a product. Acids can be organic or inorganic, with the former having a carboxyl group, hydroxyl group, and hydrogen atoms, while the latter has a metal ion.

Bases: Bases are distinguished by their slick texture and harsh flavour. Alkali is a term used to describe bases that can dissolve in water. The chemical reaction of bases reacting with acids to produce salt and water is known as neutralization.

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Bases turn to be a reddish-blue colour in the presence of litmus. The following is the explanation behind the colour change: The OH^- ions, or hydroxyl ions, react with the colour in the litmus paper in distinct ways. When it reacts with the hydroxyl ion, it absorbs green and red wavelengths and reflects short wavelengths, giving it a blue colour.

The colour of the indicators can be changed by the bases. In the presence of a base, phenolphthalein turns pink.

Other than these acids and bases can also be differentiated on the basis of pH value if any solution shows pH value less than 7 then it is said to be acidic nature and if it is greater than 7 then solution is said to be of basic nature while if the pH shown by solution is exactly 7 then it is said to be of neutral nature. Acid and base combine to form salt and water. Salts are formed when an acid and a base react, which is known as a neutralization reaction. Salts are ionic compounds made up of a cation and an anion, where the cation is not H+ and the anion is not OH^-.

Physical and chemical properties of acids and bases can be discussed as follows:

1. Physical properties of acids and bases: Physical properties of acids and bases generally depend upon their looks like their color, solubility, taste and appearance.

a. Color: Mineral acids are colorless liquids, however impurities in sulphuric acid can cause it to turn yellow. Some organic acids are solids with a white color while bases are colorless in nature except hydroxide of copper and iron.

b. Taste: Acids are basically sour in taste like citric acid while bases are of bitter taste.

c. Touch: Acids have no particular touchy appearance while bases are slippery to touch.

d. Solubility: Acids are generally soluble in water while bases are not soluble in water.

Many acids are toxic if consumed and should not be tasted. The acid becomes a neutral chemical after it binds to the base. This reaction frequently results in the formation of water and salt. When strong acids react with strong bases, this is a common occurrence. The acids are the generators of electricity. The batteries are utilized to generate electricity outside of this. A strong acid is one that conducts electricity well, while a weak acid is one that conducts electricity poorly.

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Chemical properties of acids and bases

Chemical properties generally based on the chemical reactions of acids and bases with other metals or gases

a. Reaction of acids and bases with metals:

When a metal reacts with an acid, hydrogen is usually displaced from the acid. Hydrogen gas is formed as a result of this process. The metals react with the residual acids to generate a salt. For instance, consider the reaction of sulphuric acid with zinc.

The metal reacts with alkalis (water-soluble bases) to form salt and hydrogen gas. To explain this we can take the example of zinc reacting with sodium hydroxide

b. Reaction of acids with carbonates and bicarbonates of metals

Salt, carbon dioxide, and water are produced when metal carbonates/metal bicarbonates react with acids. For instance, sodium carbonate/sodium bicarbonate reacts with hydrochloric acid. Metal carbonate react with acid is shown in the following example:

While bases will not react with metal carbonate or metal bicarbonate.

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c. Metal oxides and non-metal oxides with acids and alkalis

Salt and water are produced when metal oxides react with acids. For instance, consider the reaction between copper oxide and weak hydrochloric acid.

Metal oxides reacts with acids while in case of bases non-metal oxides react with them and form salt and water. Reaction between non-metal oxide and base can be shown as:

d. Base and acid reactions with each other

Acids and bases react with each other and produce salt and water. Neutralization reactions are the reactions that occur when acids and bases react to form salts. For this instance we can take the example of a reaction occurring between sodium hydroxide and hydrochloric acid.

The reaction of an acid and a base always produces salt and water, which is known as neutralization. One H+ ion of acid is neutralized by one OH– ion of base in a neutralization process. Complete neutralization occurs when all of the H+ ions in the acidic solution are neutralized by the corresponding number of OH– ions in the basic solution. The total number of H+ and OH– ions produced by each acid and base determines the relative amounts of acid and base necessary for full neutralization.

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Frequently Asked Questions (FAQs)

1. Give any two metal carbonate examples.

Metal carbonates are Na₂CO₃, CaCO₃.

2. Which of the following is not a property of acids? a. Sour in taste b. Reacts with metal oxides c. Slippery in touch d. Reacts with metal oxide to form salt.

Acids have no particular texture so the option c is not a property of acid all other resembles the properties of acids.

3. Acid plus base gives?

Acid and base react with each other from salt and water and the reaction is said to be a neutralization reaction.

4. Bases are …… in taste.

Bases are bitter in taste.

5. What defines an acid in chemistry?

An acid is a substance that donates protons (H+ ions) in aqueous solutions. It increases the concentration of hydrogen ions when dissolved in water, typically resulting in a pH below 7. Acids have a sour taste, react with metals to produce hydrogen gas, and turn blue litmus paper red.

6. How do we define a base in chemistry?

A base is a substance that accepts protons (H+ ions) or donates hydroxide ions (OH-) in aqueous solutions. It decreases the concentration of hydrogen ions when dissolved in water, typically resulting in a pH above 7. Bases have a bitter taste, feel slippery to the touch, and turn red litmus paper blue.

7. What is the Arrhenius theory of acids and bases?

The Arrhenius theory defines acids as substances that produce hydrogen ions (H+) in aqueous solutions, and bases as substances that produce hydroxide ions (OH-) in aqueous solutions. This theory is limited to water-based solutions and doesn't account for all acid-base behaviors.

8. 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 amphoteric substances, which can act as both acids and bases depending on the context.

9. What is the Lewis theory of acids and bases?

The Lewis theory defines acids as electron pair acceptors and bases as electron pair donors. This definition further expands the concept of acids and bases beyond proton transfer, allowing for the explanation of acid-base behavior in reactions where no protons are involved, such as in some metal complex formations.

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

Acid-base chemistry is fundamental to biological systems. It's crucial for maintaining pH homeostasis in cells and body fluids, enzyme function (as most enzymes are pH-sensitive), oxygen transport by hemoglobin, and many metabolic processes. Understanding acid-base balance is essential in physiology and medicine, particularly in diagnosing and treating conditions like acidosis and alkalosis.

11. How does the presence of a common ion affect the solubility of a sparingly soluble salt?

The presence of a common ion decreases the solubility of a sparingly soluble salt through the common ion effect. This effect shifts the solubility equilibrium towards the solid phase, reducing the amount of dissolved salt. This principle is important in analytical chemistry for precipitating and separating ions, and in environmental chemistry for understanding the behavior of minerals in natural waters.

12. How do we measure the strength of an acid or base?

The strength of an acid or base is measured by its ability to ionize in solution. For acids, we use the acid dissociation constant (Ka), while for bases, we use the base dissociation constant (Kb). The negative logarithm of these values gives us pKa and pKb, respectively. The lower the pKa, the stronger the acid; the lower the pKb, the stronger the base.

13. What is the pH scale and how does it relate to acidity and basicity?

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. Each unit change in pH represents a tenfold change in H+ concentration. The pH scale helps quantify the acidity or basicity of a solution.

14. How do indicators work in acid-base chemistry?

Indicators are weak acids or bases that change color at specific pH ranges. They work by undergoing a structural change when protonated or deprotonated, which alters their light absorption properties and thus their color. Different indicators change color at different pH values, allowing for the visual determination of a solution's approximate pH.

15. What is a buffer solution and how does it work?

A buffer solution is a mixture that resists changes in pH when small amounts of acid or base are added. It typically consists of a weak acid and its conjugate base (or a weak base and its conjugate acid) in roughly equal concentrations. Buffers work by neutralizing small additions of H+ or OH- ions, maintaining a relatively stable pH.

16. How do we calculate pH from hydrogen ion concentration?

The pH is calculated as the negative logarithm (base 10) of the hydrogen ion concentration: pH = -log[H+]. For example, if [H+] = 1 × 10^-3 M, then pH = -log(1 × 10^-3) = 3. This logarithmic relationship means that each unit change in pH represents a tenfold change in [H+].

17. What is the difference between strong and weak acids?

Strong acids completely ionize in aqueous solutions, releasing all their protons. Weak acids only partially ionize, reaching an equilibrium between the acid and its ions. Strong acids have very low pKa values (typically < 0), while weak acids have higher pKa values. The strength of an acid affects its reactivity and its ability to change the pH of a solution.

18. How do conjugate acid-base pairs work?

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. When a base accepts a proton, it becomes its conjugate acid. In any acid-base reaction, the conjugate base of a strong acid is a weak base, and vice versa. This relationship is crucial in understanding acid-base equilibria.

19. What is the autoionization of water and why is it important?

The autoionization of water is the process where water molecules react with each other to produce hydronium (H3O+) and hydroxide (OH-) ions: H2O + H2O ⇌ H3O+ + OH-. This reaction establishes the ion product of water (Kw), which is constant at a given temperature (Kw = [H+][OH-] = 1 × 10^-14 at 25°C). This concept is fundamental to understanding pH and pOH calculations.

20. How do polyprotic acids differ from monoprotic acids?

Polyprotic acids can donate more than one proton per molecule, while monoprotic acids can only donate one. Polyprotic acids undergo stepwise dissociation, with each step having its own Ka value. Generally, Ka1 > Ka2 > Ka3, meaning the first proton is easiest to remove, and subsequent protons become progressively harder to remove. This affects their titration behavior and buffer capacity.

21. What is a salt and how does it relate to acids and bases?

A salt is an ionic compound formed by the neutralization reaction between an acid and a base. Salts can be neutral, acidic, or basic depending on the strength of the acid and base from which they're formed. The process of salt hydrolysis, where salt ions react with water, can affect the pH of aqueous solutions, leading to acidic, basic, or neutral salt solutions.

22. How does temperature affect acid-base equilibria?

Temperature changes can shift acid-base equilibria according to Le Chatelier's principle. For endothermic reactions, increasing temperature favors the products, while for exothermic reactions, decreasing temperature favors the products. In water, higher temperatures increase Kw, affecting pH calculations. Temperature also influences reaction rates and the strength of hydrogen bonding in solutions.

23. What is the common ion effect and how does it impact acid-base equilibria?

The common ion effect occurs when an ion already present in a solution is added, typically through a salt. This addition shifts the equilibrium to favor the reactants, according to Le Chatelier's principle. In acid-base chemistry, this can suppress the ionization of a weak acid or base, affecting the pH and buffer capacity of the solution.

24. How do we determine the pH of a polyprotic acid solution?

Determining the pH of a polyprotic acid solution involves considering multiple dissociation steps. We typically focus on the first dissociation step, as it contributes most significantly to the [H+]. For subsequent steps, we consider the relative magnitudes of the Ka values. If Ka values differ by more than 10^3, we can often simplify calculations by considering only the first dissociation.

25. What is the Henderson-Hasselbalch equation and how is it used?

The Henderson-Hasselbalch equation relates the pH of a buffer solution to the pKa of the weak acid and the concentrations of the acid and its conjugate base: pH = pKa + log([A-]/[HA]). This equation is used to calculate the pH of buffer solutions, design buffers with specific pH values, and understand how buffer composition affects pH.

26. 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 amphoteric substance. Understanding amphoterism is crucial for predicting the behavior of certain metal hydroxides and amino acids in different pH environments.

27. What is a titration curve and what information can we derive from it?

A titration curve is a plot of pH versus the volume of titrant added during an acid-base titration. It provides information about the strength of the acid or base, the equivalence point (where moles of acid = moles of base), and the buffer regions. The shape of the curve and the pH at the equivalence point can help identify whether the titration involves strong or weak acids/bases.

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

Lewis acids and bases are defined by electron pair acceptance and donation, respectively, while Brønsted-Lowry acids and bases are defined by proton donation and acceptance. The Lewis definition is broader and includes reactions where no proton transfer occurs, such as in the formation of coordination compounds. This allows for the explanation of acid-base behavior in non-aqueous systems and gas-phase reactions.

29. What is the role of solvents in acid-base chemistry?

Solvents play a crucial role in acid-base chemistry by influencing the behavior of dissolved species. The ability of a solvent to accept or donate protons (its proticity) affects the strength of acids and bases dissolved in it. Protic solvents like water can participate in hydrogen bonding and acid-base reactions, while aprotic solvents cannot. The dielectric constant of the solvent also affects the degree of ionization of dissolved species.

30. How do we calculate the pH of a mixture of a weak acid and its salt?

To calculate the pH of a mixture of a weak acid and its salt (a buffer solution), we use the Henderson-Hasselbalch equation: pH = pKa + log([salt]/[acid]). This calculation assumes that the concentrations of the acid and salt are similar and that the acid is weak. For more accurate results in extreme cases, we may need to consider the acid dissociation equilibrium explicitly.

31. What is the significance of pKa in organic chemistry?

In organic chemistry, pKa is crucial for predicting the behavior of functional groups in different pH environments. It helps in understanding the acidity or basicity of organic compounds, their reactivity, and their ability to act as leaving groups in substitution reactions. pKa values are also important in predicting the direction of organic reactions and in designing synthetic strategies.

32. How do we predict the pH of salt solutions?

To predict the pH of salt solutions, we consider the acid-base properties of the ions formed when the salt dissolves. Salts of strong acids and strong bases produce neutral solutions. Salts of weak acids and strong bases produce basic solutions due to hydrolysis of the anion. Salts of strong acids and weak bases produce acidic solutions due to hydrolysis of the cation. For salts of weak acids and weak bases, we compare the Ka and Kb values to determine the resulting pH.

33. What is the difference between equivalence point and endpoint in a titration?

The equivalence point is the theoretical point in a titration where the moles of acid exactly equal the moles of base added. The endpoint is the experimentally observable point, usually indicated by a color change of an indicator. Ideally, these points should coincide, but in practice, there's often a slight difference. Choosing an appropriate indicator that changes color close to the equivalence point pH is crucial for accurate titrations.

34. How do organic acids compare to inorganic acids in terms of strength?

Organic acids are generally weaker than inorganic acids due to the electron-donating nature of alkyl groups, which stabilize the conjugate base. Inorganic acids often have more electronegative atoms that can better stabilize the negative charge of the conjugate base. However, the strength of organic acids can be increased by the presence of electron-withdrawing groups near the acidic proton.

35. What is the concept of leveling effect in acid-base chemistry?

The leveling effect occurs when a solvent limits the maximum acidity or basicity that can exist in that solvent. In water, for example, all strong acids are "leveled" to the strength of the hydronium ion (H3O+), and all strong bases are leveled to the strength of the hydroxide ion (OH-). This effect is important when comparing acid or base strengths in different solvents.

36. How do buffer capacity and buffer range relate to each other?

Buffer capacity is the amount of acid or base a buffer can neutralize before significant pH changes occur. Buffer range is the pH range over which a buffer is effective, typically within ±1 pH unit of the buffer's pKa. A buffer has its maximum capacity at the midpoint of its range (where pH = pKa). Understanding both concepts is crucial for designing effective buffers for specific applications.

37. How do we determine if a polyprotic acid is diprotic or triprotic from its titration curve?

A polyprotic acid's titration curve will show multiple equivalence points, one for each acidic proton. A diprotic acid will have two equivalence points, while a triprotic acid will have three. The spacing and relative positions of these points on the curve can provide information about the relative strengths of each acidic proton. The number of buffer regions in the curve also corresponds to the number of acidic protons.

38. What is the relationship between Ka and Kb for a conjugate acid-base pair?

For a conjugate acid-base pair, the product of Ka and Kb is equal to Kw, the ion product of water (Ka × Kb = Kw = 1 × 10^-14 at 25°C). This relationship allows us to calculate Kb if we know Ka, and vice versa. It also implies that the stronger an acid, the weaker its conjugate base, and vice versa. This concept is crucial for understanding the relative strengths of acids and bases.

39. How does the presence of electron-withdrawing or electron-donating groups affect acid strength?

Electron-withdrawing groups increase acid strength by stabilizing the conjugate base through delocalization of the negative charge. This makes it easier for the acid to donate a proton. Conversely, electron-donating groups decrease acid strength by destabilizing the conjugate base, making it harder for the acid to donate a proton. This principle is important in organic chemistry for predicting and comparing the acidities of different compounds.

40. What is the significance of pKa in drug design and pharmacology?

In drug design and pharmacology, pKa is crucial for predicting a drug's behavior in the body. It affects the drug's solubility, absorption, distribution, and excretion. The pKa determines whether a drug will be ionized or non-ionized at physiological pH, which impacts its ability to cross cell membranes and its distribution in different body compartments. Understanding pKa is essential for optimizing drug efficacy and minimizing side effects.

41. How do we calculate the pH of a solution of a weak base?

To calculate the pH of a weak base solution, we first determine the OH- concentration using the base dissociation constant (Kb) and the initial concentration of the base. We then calculate pOH = -log[OH-], and finally pH = 14 - pOH (at 25°C). This process often involves solving a quadratic equation if we can't make simplifying assumptions about the degree of dissociation.

42. What is the concept of microscopic and macroscopic dissociation constants?

Microscopic dissociation constants (k) refer to the individual proton removal steps in a polyprotic acid, considering all possible routes of deprotonation. Macroscopic dissociation constants (K) are the overall constants we typically measure and use in calculations. For a diprotic acid, K1 = k1 + k2, and K2 = (k3 × k4) / (k1 + k2). Understanding this distinction is important for accurately describing the behavior of polyprotic acids and their conjugate bases.