Acid Strength and Ka Classify each acid as strong or weak....

Acid Strength and $K_{\mathrm{a}}$ Classify each acid as strong or weak. If the acid is weak, write an expression for the acid ionization constant $\left(K_{a}\right) .$ $$\begin{array}{l}{\text { a. HF }} \\ {\text { b. HCHO }} \\ {\text { c. } \mathrm{H}_{2} \mathrm{SO}_{4}} \\ {\text { d. } \mathrm{H}_{2} \mathrm{CO}_{3}}\end{array}$$

Acid Strength and $K_{\mathrm{a}}$
Classify each acid as strong or weak. If the acid is weak, write an
expression for the acid ionization constant $\left(K_{a}\right) .$
$$\begin{array}{l}{\text { a. HF }} \\ {\text { b. HCHO }} \\ {\text { c. } \mathrm{H}_{2} \mathrm{SO}_{4}} \\ {\text { d. } \mathrm{H}_{2} \mathrm{CO}_{3}}\end{array}$$

Key Concepts

Acid Strength

Acid strength refers to the ability of an acid to donate a proton (H?) in solution. Strong acids completely dissociate in aqueous solutions, meaning virtually all acid molecules donate their protons, whereas weak acids only partially dissociate, establishing an equilibrium between the undissociated acid and its ions.

Acid Ionization Constant (Ka)

The acid ionization constant, Ka, quantifies the extent of ionization of a weak acid in solution. It is defined by the equilibrium expression formed from the concentrations of the dissociated ions and the remaining undissociated acid, providing a measure of the acid's strength and its tendency to donate a proton.

Equilibrium Expressions

An equilibrium expression is used to describe the state of a chemical reaction when both the forward and reverse reactions occur at the same rate. For weak acids, the Ka expression is derived from the concentration of the products (H? and the conjugate base) divided by the concentration of the undissociated acid, all at equilibrium, highlighting the reversible nature of the acid's dissociation.

Dissociation Reaction of Acids

The dissociation reaction for an acid in water involves the acid donating a proton to water, resulting in the formation of hydronium ions (or simplified as H?) and its conjugate base. This reaction can be complete for strong acids or partial for weak acids, and understanding this process is essential for writing accurate Ka expressions and classifying acid strength.

Transcript

00:01 So our first acid here is hf.

00:02 And now, this is just an exception you have to remember.

00:06 All the other halides, so hcl, hbr, et cetera, they're strong acids.

00:13 Hf, the weird one out, is a weak acid.

00:16 The reason is that fluorine is a small atom.

00:19 It doesn't handle the negative charge very well.

00:21 And so this is just something you need to remember.

00:24 Hf, the reaction of it in water, if this is still an acid, so it's going to give up h -plus, so it's going to form the fluoride ion and h3o plus.

00:38 See the basically there's a transfer of an h plus over here.

00:42 You get an extra one so two versus three and a positive charge.

00:47 I'm going to make a quick point.

00:50 This is an acid and you know that it is because when it's mixed with water it produces h3o plus.

00:57 That is what it means to be an acid.

00:59 Do not forget that.

01:01 Our task here is to figure out what kas and so this is just a a a a a is.

01:04 From our equilibrium unit, the mass action expression.

01:08 We take the product of the concentration of fluoride times h -3o -plus, the two things on the right, over the concentration of hf.

01:17 We don't say over the concentration of water because that doesn't really have meaning.

01:20 It's a liquid.

01:21 We ignore that in the mass action expression.