It is one of the constituents of gastric juice which aids in the digestion process. HCl can be synthesized according to the following reaction by warming aqueous solution crystals of sodium chloride with sulphuric acid. NaCl aq. + H2SO4 (aq.) ——-> 2 HCl (aq) + Na2SO4aq. It is soluble in water and combines with alkali to form salt and water. HCl is very useful. HCl can be distinguished from a base by using indicators like turmeric, pH paper, litmus paper, etc. Dry HCl gas does not change the color of indicators because of the absence of H3O+ ions. In this article, we will discuss the acidic behavior of hydrochloric acid and compare the same with other acids. So, what is the ph of HCl? The pH of HCl generally lies around 3 classifying it as a strong acid. It is a strong acid because it dissociates completely in an aqueous solution to release H+ ions and Cl- ions. Acid is considered a strong acid if it completely dissociates to form H+ ions. We will study more about its fundamentals and concepts in detail. Stay connected.
Why is HCl a Strong Acid?
Why is HCl a Strong Acid?
Acids release H+ or H3O+ ions on dissolving in water. Some acids dissociate completely while some acids dissociate partially, and an equilibrium is established. HCl behaves like a strong electrolyte. HCl dissociates completely according to the following equation. HCl (aq.) + H2O(l) —–> H3O+(aq.) + Cl-(aq.) On the reaction of HCl with water, HCl completely breaks down to release hydronium and chloride ions. Cl- is the conjugate base. A strong acid leads to the formation of a weak conjugate base. It is believed that the weaker the conjugate base is, the stronger is the acid. For strong acids, the value of pKa is less than -1.74. For HCl, pKa is -6.3. pKa is inversely proportional to acidity.
What are Acids?
What are Acids?
Various scientists have given different definitions of acid. Some of them are-
Type of Acids (explained on the basis of Arrhenius Theory)
Type of Acids (explained on the basis of Arrhenius Theory)
Which is More Acidic? HCl, HBr, or HI
Which is More Acidic? HCl, HBr, or HI
According to Arrhenius’s theory, acids dissociate to release H+ ions in water. The acid which releases H+ ion more easily is considered to be a stronger acid. A weak bond will break easily to release the constituent ions. Longer bonds are weaker. Large-sized anions form longer and weak bonds and relatively small-sized anions form short and stable bonds. The decreasing order of size of anions is I->Br->Cl-
Thus, the strength of the bond follows the order HIHCl
Which is More Acidic? HCl or H2SO4
Which is More Acidic? HCl or H2SO4
Both are considered to be very strong acids and electrolytes. It is a common misconception that sulphuric acid is stronger because it is diprotic and HCl is monoprotic. The compound which releases proton more easily is considered to be a better acid. HCl (aq) —–> H+ (aq) + Cl- (aq) H2SO4(aq) —–> H+ (aq) + HSO4- (aq) HCl is more acidic because the Cl- ion so formed on dissociation is a weaker conjugate base than HSO4-. HSO4- is stabilized by resonance. For HCl, the pKa value is -6.3, while for H2SO4, it is ~-3. Thus, HCl releases the H+ ion more easily than H2SO4. HCl is a stronger acid than H2SO4.
Which is More Acidic? HCl or CH3COOH
Which is More Acidic? HCl or CH3COOH
HCl is a strong electrolyte, while acetic acid is a weak electrolyte. For the same concentration of HCl and CH3COOH, the dissociation of HCL is 100%, while it is less than 5% for acetic acid. HCl (aq) ——> H+(aq) + Cl- (aq) CH3COOH(aq) ⇌ CH3COO-(aq) + H + (aq) Thus, the amount of H+ ions released is relatively less for acetic acid. Most of the acetic acid is in undissociated form. Since fewer protons are dissociated from acetic acid, it is a weaker acid. HCl is a stronger acid than acetic acid.
How to calculate the pH of HCl?
How to calculate the pH of HCl?
pH is used for measuring the concentration of H+ ions in a substance. Concentration is measured in terms of molarity, i.e., the number of moles of H+ ions per liter of solution. pH is calculated by taking the negative logarithmic value of H+ ions concentration. pH= – log10[H+]
A standard pH scale ranges from 0 to 14. For a neutral solution, the pH is 7. It indicates that the concentration of H+ in pure water is 10-7M. In an aqueous solution, both water and acid contribute to increasing H+ ion concentration. The dissociation of water follows the given equation. Kw is the dissociation constant of water. 2H2O(l) ⇋ H3O+(aq) + OH-(aq) Keq = [OH-][H3O+]/[H2O] Kw = [OH-][H3O+] = 10^-14 For water, [OH-] = [H3O+] = 10^-7 The dissociation of acid follows the given equation HCl aq + H2O(l) ⇋ H3O+(aq) + Cl-(aq) Here, the concentration of H3O+ is equal to the concentration of HCl. pH + pOH = 14 For measuring pH, we adopt different methods depending on the concentration of HCl.
Case 1: When the concentration of HCl is greater than ~10-5 M
Here, the concentration of HCl is considered to be high, and we assume that acid is the only source of all the H+. Example 1: 10-3M solution of HCl we assume, [H+ ]=10-3M. In the logarithmic bracket, we put a unitless quantity. Hence, we divide the given concentration by a unit concentration to obtain a unitless quantity. pH = -log10(10-3 M/1M) = -log10(10-3) = 3log10(10) =3 Example 2: 2* 10-2M solution of HCl pH= -log10(210-2 M/1M) = -log10(210-2) = -log10(2) – log10(10-2) = -log10(2)+2 = -0.301+2 = 1.699
Case 2: Concentration of HCl is less than 10-5 M
In this case, the concentration of HCl is not considered to be high, and we consider the H+ ions coming from water. Example For 10-8M HCl In water [OH-] = [H3O+] = x Kw = [OH-][H3O+] = x(10-8 +x) = 10-14 We solve the equation x^2 + 10^-8x – 10^-14 = 0 to get x which gives [OH-] x = 9.5* 10-8 pOH = -log109.5 * 10-8M1M = -log10(9.5*10-8) = -log10(9.5) – log10(10-8) = -log10(9.5) + 8 = -0.98 + 8 pOH =7.02 pH+pOH =14 pH = 6.98
HCl Properties
HCl Properties
HCl Uses
HCl Uses
Conclusion
Hydrochloric acid is a strong acid. It dissociates completely in water to give H+ ions. Three theories have been successful in explaining the meaning of acid. The three theories are- Arrhenius Theory, Brönsted-Lowry Concept, and Lewis Acid-base concept. On the basis of strength, acids can be classified as strong and weak. On the basis of the number of ionizable hydrogen, acids can be classified as monoprotic and polyprotic. On the basis of concentration, acids can be classified as dilute and concentrated. On the basis of source, acids can be classified as organic and inorganic. On the basis of the presence of O, acids can be classified as oxyacid and hydracid. Considering the various factors affecting acidity, we can conclude that the acidity order is HI>HBr>HCl HCl>H2SO4 HCl>CH3COOH To measure the pH of HCl, we ignore the contribution of water for highly concentrated solutions, while for very dilute solutions, we consider the contribution from water. Happy Learning
