In workshop today we will explore two classes of compounds known as acids and ba
ID: 484063 • Letter: I
Question
In workshop today we will explore two classes of compounds known as acids and bases. Acids were first identified as compounds that tease sour while bases were first identified as compounds that feel slippery and taste bitter. today there are 3 prevailing theories that define acids and bases. We will spend most of our time in genChem using the Bronsted-Lowry Theory. Strong acids dissociate completely in aqueous solution. This means that every strong acid molecule in the solution will lose its acidic protons. Weak acids however, do not completely dissociate in aqueous solution. A weak acid will still donate protons, but not every single molecule will dissociate. Weak acids are known to result in an equilibrium in aqueous solution. Every weak acid has a defined acid dissociation constant, K_a (where the subscript a stands for acid). Like all dissociation constants k_a tells you how far in the forwards direction a reaction will proceed until it reaches equilibrium. For weak acids, k_a is thus a measure of acid dissociation. Consider the weak acid, nitrous acid (HNO_2) with K_a = 5.6 times 10^-4 a) Write the equilibrium reaction for the aqueous dissociation of this acid. b) In the space above, label the acid, base, conjugate acid and conjugate base. c) Now let's try and draw a picture that models the microscopic behavior of this acid. What do you expect to see in solution on a molecular level when the HNO_2 reaches equilibrium in an aqueous solution? Before you draw your picture make sure that EVKRVONE in your group is comfortable predicting the solution composition at equilibrium. Do you expect all of the acid to dissociate? If not. what do you expect to see Do you think you need to include water molecules in your diagram? How are you going to model/depict the molecules? Do you need to include a legend for clarity? Take a moment to discuss these questions in your group and when you are sure you all agree draw your picture in the space provided.Explanation / Answer
For the weak acid
a) balanced equation,
HNO2 + H2O <=====> NO2- + H3O+
acid base conjugate conjugate
base acid
b) labelled above are all the acid, base, conjugate acid and conjugate base in the reaction
c) Weak acids dissociate only partially in solution
At equilibrium we would see,
say we start with 6 molecules of HNO2 in solution, at equilibrium,
number of NO2- species = 2
number of HNO2 species = 4
number of H3O+ species = 2
We do not have to show water molecules in it.