AICE Chemistry Acids and Bases

Acids These are chemical compounds that can be identified because they start with the element Hydrogen. They have the generic formula “HX”. The “X” part can be either a non-metal or a polyatomic. If the “X” is a non- metal, we have a binary acid. If the “X” is a polyatomic, we have an oxy-acid.

Examples Binary Acids HCl HBr H 2 S Oxy-Acids HNO 3 H 2 SO 4 HC 2 H 3 O 2 H 3 PO 4

Acid Names Binary acids are named according to the format “hydro _______ ic acid” The prefix “hydro” means binary acid. All that you need in the space is usually the root of the non- metal’s name. Oxy-acids are named according to the format “_________-ic acid. There is no “hydro” here – these are not binary acids. All that you need in the space is usually the root of the polyatomic’s name.

Examples Binary Acids HCl = hydrochloric acid HBr = hydrobromic acid H 2 S = hydrosulfuric acid (this one is a bit of an exception – we use the full name of sulfur because it sounds better than “hydrosulfic” acid) Oxy-acids HNO 3 = nitric acid H 2 SO 4 = sulfuric acid ( again, a bit of an exception for the same reason noted in the binary name example) HC 2 H 3 O 2 = acetic acid H 3 PO 4 = phosphoric acid (another exception)

Some Related Vocabulary We will eventually discuss the chemical behavior associated with acids losing the hydrogen atoms attached to the “X” part. From the formulas, you can see that different acids have different numbers of H atoms attached to that “X”. Since an H atom is nothing more than a proton (and a bonding electron), we have: – Monoprotic acids – that have only 1 H atom attached to the “X”. – Diprotic acids – that have 2 H atoms attached to the “X”. – Triprotic acids – that have 3 atoms attached to the “X”.

Examples and Practice H 2 CrO 4 HI H 2 CO 3 HF H 3 PO 4 H 2 Cr 2 O 7 H 2 SO 4 Describe each of the acids to the left in terms of the vocabulary already covered so far.

Chemical Behaviors Acids react with metal carbonates to produce aqueous “salt”, gaseous carbon dioxide, and water. This is the pattern for both binary and oxy- acids. Note that a bicarbonate will yield the same results. Acids react with metals to produce hydrogen (diatomic) and an aqueous “salt”. Definition – a “salt” is simply an ionic compound produced during a reaction involving an acid. It contains the metal cation and the anion of the acid (the “X” part). Note – there are some very significant exceptions to this pattern.

Write Equations for the Following: Aqueous hydrobromic acid reacts with solid potassium carbonate. Aqueous acetic acid reacts with solid sodium bicarbonate. Several pieces of zinc are added to a flask containing aqueous nitric acid. A piece of magnesium ribbon is added to a beaker of sulfuric acid.

Ionization – Another Chemical Behavior Ionization is the term given to the reaction that occurs when an acid is dissolved in water. Unlike the dissolving of an ionic compound – a physical change – ionization is actually a chemical reaction between the acid and the water. In the reaction, the H atom proton leaves the “X” part and attaches itself to the two lone pairs of electrons on the water molecule. The product particle has the formula H 3 O +1 and is called the hydronium ion. The other product particle is an anion of the “X” part. It has a charge because it keeps the H atom’s electron when the H leaves.

Look at the Equations Given: Hydrochloric acid is dissolved in water -Even though the given says “dissolved” in water, since this is an acid we have to realize that this is actually a chemical reaction. -So it is written as: HCl + H 2 O  H 3 O + + Cl -

Another Example: Nitric acid is dissolved in water: The fact that this is an oxy-acid does not change the format of the reaction and equation. The H atom is leaves the nitrate and attaches to the water forming hydronium. The nitrate ion is the other product. HNO 3 + H 2 O  H 3 O + + NO 3 -1

What about Diprotic Acids? These will be a bit more complicated. The key to these is to remember that in an ionization, one H atom leaves the acid, bonds with the water to form hydronium, and the remaining particle is “one more negative” than it was before the ionization. What you will see is that a diprotic acid will undergo two separate ionizations. Likewise, a triprotic acid will undergo three separate ionizations.

Consider Sulfuric Acid Sulfuric acid is H 2 SO 4 and is obviously diprotic. Its two separate ionizations are presented below. 1 st Ionization: H 2 SO 4 + H 2 O  H 3 O + + HSO nd Ionization HSO H 2 O  H 3 O + + SO 4 -2

A Quick Check: Write the set of ionizations that occur in phosphoric acid.

Stoich VIII for Acids This is actually easier for acids than it was in the Equilibrium unit. Your typical focus is going to be on calculating the concentration of hydronium in the solution. What makes this relatively easy is that ionization is always a one-to-one ratio.

An Example: Consider the ionization of HCl from an earlier slide: HCl + H 2 O  H 3 O + + Cl - As you can see, the ratio of HCl to H 3 O + is one-to-one. (coefficients) Therefore, whatever the concentration of the HCl solution is, the [H 3 O + ] will be the same – all of the HCl actually becomes H 3 O +.

What That Means: If we are told that the [HCl] is molar, then the [H 3 O + ] is the same thing – M. For the time being (it gets a bit more complicated when we learn about weak acid equilibrium) … Whatever the concentration of the acid solution is – we will simply state that the concentration of hydronium is simply the same thing.

Why the Concern? We will need to be able to specify the concentration of H 3 O + in order to calculate the pH of an acid (and eventually a base) solution.

pH pH is a numerical scale that is used to describe the relative acidity of a given solution. Important to keep in mind that pH is calculated using the [H 3 O + ], but pH is NOT the actual concentration of anything. The pH scale was developed in order to facilitate greater understanding – the general public was essentially lost when a discussion included a concentration – measured in moles/liter

Think about it… You are trying to communicate information about the relative acidity of a solution and you tell the listener that the system is molar. And they think that you are talking about teeth. But, if you tell the listener that the solution has a pH = 3, they are far more comfortable – even though they probably do not have enough of a Math background to understand how pH is calculated.

Comparing The solution is molarThe pH of the solution is 3

The pH Equation pH = - log [H 3 O + ] Which is: the pH of solution is the opposite of the base 10 log of the concentration of the hydronium in the solution.

The pH Scale This is a numerical scale that presents the relative acidities and basicities of acid and base solutions. It commonly runs from 0 to 14. Next slide show the structure of the scale.

Visual of the pH Scale