Acid-Base Solutions: Definition, Acid-Base Theory, Properties and Types

Acid-Base Solutions: Definition, Acid-Base Theory, Properties and Types – Acid and alkaline solutions are two groups of chemical compounds that are widely found and used in everyday life. Therefore, this is an important topic in learning chemistry, especially for those who don't understand it. Check out the further discussion below.

Acid-Base Solutions: Definition, Acid-Base Theory, Properties and Types

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Acid and base solutions are solutions with a degree of acidity or alkalinity of a substance depending on the number of H+ (acid) and OH- (base) ions present in the substance and also the degree of ionization of the substance. The level of acidity and alkalinity is expressed by pH. This understanding of Acid and Base solutions is very necessary as the foundation of knowledge for understanding the next chemistry material, namely calculating the level of acidity or alkalinity of something substance.

Acid Base Theory

Acids and bases (alkalis) have been known for a long time and we have often encountered them in everyday life. For example, tartaric acid in grapes, citric acid in oranges, acetic acid in vinegar, sulfuric acid in battery water and various other substances. Meanwhile, we find alkaline substances in lime water, soap, ulcer medicine, and various other substances. There are several acid-base theories that can be distinguished, including the following:

Stevante Arrhenius' Acid-Base Theory

Stevante Arrhenius put forward an Acid-Base theory that:

an acid is a substance that when dissolved in water will produce H+ ions where these H+ ions will be the only positive ions in solution. Meanwhile, a base is a substance which, when dissolved in water, will ionize to produce OH- ions, and these OH- ions will be the only negative ions in the solution.

Bronstead Lowry's Acid-Base Theory

J.N Bronstead and T.N. Lowry put forward another theory about acids and bases. According to this theory, acids are proton donors and bases are proton acceptors. From this definition, an acid will form a conjugate after releasing a proton, and a base will also form a conjugate after accepting a proton. So in this conjugate acid-base theory, the term "acid-base pair" or "conjugate acid-base" is known.

After knowing the Bronstead Lowry Acid-Base Theory, we can determine that a substance containing hydrogen is included in the group of acidic or basic substances. What about compounds/substances that are aprotic (do not contain H), how do you determine their acid or base properties?

Lewis Acid Base Theory

A chemist G.N Lewis also put forward the theory of acids and bases. According to this theory, a base is a substance that has one or more lone pairs of electrons that can be donated to another substance thus forming a coordinate covalent bond, while an acid is a substance that can accept lone pairs of electrons the.

A substance that is a base according to Lewis' acid-base theory is also a base according to Bronstead Lowry's theory.

Properties and Types of Acid and Base Solutions

Properties of Acid Solutions

In the world of chemistry, an acid is a chemical compound which when dissolved in water will produce a solution with a pH lower than 7. Acids can also be interpreted as substances that can give protons (H+ ions) to other substances (which are called bases), or can accept lone pairs of electrons from a base.

Examples of acids in daily life include vinegar containing acetic acid, oranges containing citric acid, and wine contains tartaric acid, apples contain malic acid, vitamin C contains ascorbic acid, and eye drops contain acid borate.

The properties of acidic solutions, including namely:

• Has a sour taste
• Can turn blue litmus red
• Can conduct electricity (strong acid)
• When dissolved in water, it releases hydrogen ions (H+)
• Corrosive to metal
• Can neutralize alkaline

Acid Solution Type

There are two types of acidic solutions, namely strong acids and weak acids. The presence of rust on iron is one of the characteristics indicating that acid is corrosive to metal.

If an acid is dissolved in such a way that almost all of the H+ ions are released, it is called a strong acid. If only a small portion of H+ ions is released, the acid is called a weak acid. Strong acids can conduct electricity, while weak acids can barely conduct electricity.

Examples of substances that are classified as Strong Acids include: stomach acid (hydrochloric acid = HCl), sulfuric acid (H2SO4), sulfite acid (H2SO3), bromide acid (HBr), nitric acid (HNO3) and nitric acid (HNO2).

Examples of substances that include Weak Acids include: carbonic acid (H2CO3), acetic acid (CH3COOH), sulfidic acid (H2S), cyanide acid (HCN) and phosphoric acid (H3PO4).

Properties of Alkaline Solutions

Bases are chemical compounds that absorb hydronium ions when dissolved in water. Bases have a pH greater than 7. When dissolved in water it decomposes into hydroxyl ions (OH–) and metal positive ions (but not always). Therefore, a base can conduct electric current.

Examples of bases that are often encountered in everyday life include ulcer drugs containing magnesium hydroxide (Mg (OH) 2) and aluminum hydroxide (Al (OH) 3); body wash containing sodium hydroxide (NaOH); baby bath soap containing potassium hydroxide (KOH); deodorants contain aluminum hydroxide (Al (OH)3) and floor cleaners contain ammonium hydroxide (NH4OH).

The properties of bases include:

• Feels slippery when in contact with skin (not to be tried on skin, dangerous)
• Can turn red litmus to blue
• Can conduct electricity (strong base)
• When dissolved in water, it releases hydroxyl ions (OH–)
• Can neutralize acids

Types of Alkaline Solutions

If when the base is dissolved and almost all the ions (OH–) are released then the base is called a strong base. Examples of strong bases, such as sodium hydroxide (NaOH), calcium hydroxide (KOH), barium hydroxide (Ba (OH)2).

However, if only a small portion of OH- is released then the base is called a weak base. Examples of weak bases include ammonium hydroxide (NH4(OH) and aluminum hydroxide (Al (OH)3).

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Strength of Acids and Bases

The strength of acids and bases is determined by the degree of ionization (α), how much H+ and OH− ions are released. Acids and bases in water will experience decomposition reactions into ions which are equilibrium reactions. Therefore, the strength of acids and bases can be expressed by their equilibrium constants, namely, the acid ionization constant (Ka) and the base ionization constant (Kb).

For example, in water HCl almost completely dissociates into H+ ions and Cl− ions, whereas HF only partially decomposes into H+ ions and F− ions. Therefore, HCl is referred to as a strong acid and HF is referred to as a weak acid. Likewise, in water NaOH almost completely decomposes into Na+ ions and OH− ions, while NH3 only partially decomposes into NH4+ ions and OH− ions. NaOH is referred to as a strong base and NH3 is referred to as a weak base.

Acid ionization constant (Ka)

In general, the equilibrium reaction for HA acid solution in water can be written as follows.

HA(aq) ⇌ H+(aq) + A−(aq)

The acid ionization constant Ka can be formulated as follows.

K_a = \frac{[H^+][A^-]}{[HA]}
strong acids (example: HCl, HBr, HI, HNO3, HClO4, H2SO4)
In water, almost all strong acids decompose into their ions, so the degree of ionization α ≈ 1. Thus, the Ka value of a strong acid is very large. For very large Ka values, it can be assumed that the acid completely dissociates into its ions and the H+ ion concentration can be calculated from the acid concentration ([HA]equilibrium ≈ [HA]initial = Ma) and the valence the sour. The valence of an acid is the number of H+ ions produced per molecule of acid.

[H^+] = valency_a \times M_a
weak acids (example: HF, HCN, HNO2, CH3COOH, H2CO3)
In water, only some weak acids decompose into their ions, so the degree of ionization is 0 < α < 1. If the initial concentration of the weak acid solution HA is expressed as Ma, then:

HA(aq) ⇌ H+(aq) + A−(aq)

At first: Mom
Reaction: −αMa + αMa + αMa
Equilibrium: (1 − α)Ma αMa αMa

K_a = \frac{(\alpha M_a)(\alpha M_a)}{((1 – \alpha) M_a)}
K_a = \frac{\alpha^2}{1 – \alpha} M_a
If the value of α is very small (α ≪ 1), then it can be assumed that the value is (1 − α) ≈ 1, so the Ka equation for a weak acid can be written as follows:

K_a = \alpha^2 M_a
\alpha = \sqrt{\frac{K_a}{M_a}}
So, to calculate the concentration of H+ ions, you can use the value of Ka or the value of α.

[H^+] = \sqrt{K_a \times M_a} or [H^+] = \alpha \times M_a

Base ionization constant (Kb)

In general, the equilibrium reaction of LOH base solution in water can be written as follows.

LOH(aq) ⇌ L+(aq) + OH−(aq)

The base ionization constant Kb can be formulated as follows.

K_b = \frac{[L^+][OH^-]}{[LOH]}
strong bases (example: NaOH, KOH, Ca (OH)2, Sr (OH)2, Ba (OH)2)
In water, almost all strong bases break down into their ions, so the degree of ionization α ≈ 1. Thus, the Kb value of a strong base is very large. For very large Kb values, it can be assumed that the base completely dissociates into its ions and OH− ion concentration can be calculated from the base concentration ([LOH]equilibrium ≈ [LOH]initial = Mb) and valence the base. Base valence is the number of OH− ions produced per base formula unit.

[OH^-] = valency_b \times M_b
weak base (example: NH3, CH3NH2, C6H5NH2)
In water, only some weak bases break down into their ions, so the degree of ionization is 0 < α < 1. If the initial concentration of a weak base LOH solution is expressed as Mb, then:

LOH(aq) ⇌ L+(aq) + OH−(aq)

At first: Mb
Reaction: −αMb + αMb + αMb
Balance: (1 − α)Mb αMb αMb

K_a = \frac{(\alpha M_b)(\alpha M_b)}{((1 – \alpha) M_b)}
K_a = \frac{\alpha^2}{1 – \alpha} M_b
If the value of α is very small (α ≪ 1), then it can be assumed that the value is (1 − α) ≈ 1, so the Kb equation for a weak base can be written as follows:

K_b = \alpha^2 M_b
\alpha = \sqrt{\frac{K_b}{M_b}}
So, to calculate the concentration of OH− ions, you can use the Kb value or the α value.

[OH^-] = \sqrt{K_b \times M_b} or [OH^-] = \alpha \times M_b

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pH (Degrees of Acidity)

The degree or degree of acidity of the solution depends on the concentration of H+ ions in the solution. The greater the concentration of H+ ions, the more acidic the solution is. In 1909, Søren P. L. Sørensen proposed a concept of pH which expresses the degree of acidity of a solution as a function of the concentration of H+ ions in the solution. The pH function is expressed as the negative logarithm of the concentration of H+ ions in a solution.

pH = –log[H^+]
The concept of pH makes it easy to express the concentration of H+ ions and their changes are sometimes very small. For example, the concentration of H+ ions in a 0.1 M acetic acid solution is about 0.001 M and the concentration of H+ ions in distilled water is about 1 × 10−7 M. If expressed in pH, then the pH of the 0.1 M vinegar solution is 3 and the pH of the distilled water is 7.

From the two examples, it can be seen from the concentration of H+ ions that a 0.1 M vinegar solution ([H+] = 0.001 M = 1 × 10−3 M) is more acidic than distilled water ([H+] = 1 × 10−7 M). However, the pH of 0.1 M acetic acid solution (pH = 3) is lower than distilled water (pH = 7). So, the more acidic the solution, the lower the pH value. Vice versa, the more alkaline the solution, the greater the pH value.

Acid Base Indicator

As the introduction described at the beginning of the discussion, in ancient times before the introduction of the acid-base theory, people distinguished acids and bases by tasting them.

But at present, various indicators have been known to distinguish acids and bases. Apart from being a safe and practical method, indicators are also able to provide more relevant results.

Litmus paper

One indicator that is often used is litmus paper. There are two types of litmus paper namely blue litmus paper and red litmus paper.

Red litmus paper will turn blue when exposed to a base, but if exposed to an acid or a neutral substance it will not change color.

Blue litmus paper will turn red when exposed to acids, but if exposed to bases or neutral substances it will not change color.

Universal Indicator

Litmus paper can only compare a substance including acid or base, then indicator paper is developed again.

Universal indicator paper is able to show the level of acidity and alkalinity of a substance.

By comparing the colors obtained for each substance tested with standard paper on universal indicators, we can determine the acidity level of a substance.

Solution Indicator

Examples of indicators for this solution are methyl red, methyl orange, bromothymol blue, and several other solutions. This indicator works exactly the same as litmus paper, this solution will change color if exposed to acids or bases.

Thus the review from About the knowledge.co.id about Acid Base Solution, Hope it is useful.