# Question Video: Determining Which Acid Is the Strongest Given the πΎ_π Values Chemistry

The following is a list of acids and their acid dissociation constants: i. Nitrous acid (HNOβ), πΎ_(π) = 4.1 Γ 10β»β΄ mol/L. ii. Hypochlorous acid (HClO), πΎ_(π) = 3.0 Γ 10β»βΈ mol/L. iii. Ethanoic acid (CHβCOOH), πΎ_(π) = 1.8 Γ 10β»β΅ mol/L. iv. Methanoic acid (HCOOH), πΎ_(π) = 1.8 Γ 10β»β΄ mol/L. What is the strongest acid?

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### Video Transcript

The following is a list of acids and their acid dissociation constants. (i) Nitrous acid, HNO2, πΎ π equals 4.1 times 10 to the negative fourth moles per liter. (ii) Hypochlorous acid, HClO, πΎ π equals 3.0 times 10 to the negative eighth moles per liter. (iii) Ethanoic acid, CH3COOH, πΎ π equals 1.8 times 10 to the negative fifth moles per liter. (iv) Methanoic acid, HCOOH, πΎ π equals 1.8 times 10 to the negative fourth moles per liter. What is the strongest acid?

To answer this question, we need to use the provided acid dissociation constants to determine which of the four acids is the strongest.

An acid dissociation constant is the equilibrium constant for the reaction of an acid with water. It can be used as a quantitative measurement of how strong a particular acid is. In its most basic form, we can state that the acid dissociation constant is equal to the concentration of the products divided by the concentration of the reactants. Letβs see how this equation can be applied to the dissociation of a generic weak acid in water.

For this generic reaction equation, the acid dissociation constant can be expressed as πΎ π equals the concentration of H+ times the concentration of Aβ divided by the concentration of HA. If the strength of the acid were to increase, then more of the acid molecules would dissociate in water and the equilibrium would shift to the right. So, at equilibrium, a stronger acid will have a lower HA concentration and higher H+ and Aβ concentrations than a weaker acid. This means that the numerator of the πΎ π equation will be larger, while the denominator will be smaller, resulting in a larger πΎ π value.

From this, we can see that as acid strength increases, so too will the acid dissociation constant. So, to determine which acid is the strongest, we need to identify which acid has the largest πΎ π value. Of the acids provided, the acid with the largest acid dissociation constant is nitrous acid. Therefore, the strongest acid is nitrous acid, HNO2.