Section 6.3—Acidity, pH How does concentration of acid affect the pH of a sports drink?

A Review of Acids & Bases

Acids – Arrhenius Definition Produce Hydronium ion (H 3 O +1 ) in water Hydronium ion is water + a hydrogen cation H O H water H +1 H O H H By this definition, if an acid is to give a H +1 to water, then all acids will have hydrogen as the cation (first element written).

How do Acids produce Hydronium? H O H H - water acid Hydrogen cation with some anion

How do Acids produce Hydronium? H O H H - +1

How do Acids produce Hydronium? H O H H +1 - Hydronium ion Anion

Bases – Arrhenius Definition Bases produce the hydroxide ion in water H O Hydroxide Ion

Characteristics of Acids & Bases BasesAcids Produce H 3 O +1 (hydronium ion) in water Produce OH -1 (hydroxide ion) in water Tastes sourTastes Bitter React with active metals to form hydrogen gas Feels slippery

Strength versus Concentration

Strong versus Weak Acids Strong acid Most of the acid molecules have donated the H +1 to water How many hydronium ion – anion pairs can you find? How many intact acid molecules can you find? 3 1

Strong versus Weak Acids + - Weak acid Only a few of the acid molecules have donated the H +1 to water How many hydronium ion – anion pairs can you find? How many intact acid molecules can you find? 1 3

Concentrated versus Dilute solute solvent Lower concentration Not as many solute (what’s being dissolved) particles Higher concentration More solute (what’s being dissolved) particles

Combinations of Concentration & Strength DiluteConcentrated A lot of acid added & most dissociates Not much acid added, but most of what’s there dissociates A lot of acid added, but most stays together Not much acid added and most of what is there stays together Strong Weak

Acids and Bases as Electrolytes Acids and bases dissociate into ions in water Free-floating ions in water conduct electricity Acids & Bases are electrolytes Strong acids and bases are strong electrolytes Weak acids and bases are weak electrolytes

pH

Is a scale to measure the acidity of a sample pH Scale 114 Highly acidicVery basic (not acidic) neutral 7 Chapter 6 will give more detail about how pH is calculated!

pH is a Logarithmic Scale Logarithm –The number of times a base must be multiplied by itself to reach a given number # of multiples Base # you’re trying to reach

Calculating pH pH scale – Logarithmic scale of the acidity of a solution The pH scale uses base “10” pH has not units [ ] = concentration in Molarity

The “-” in the pH equation Because pH is the negative log of concentration of hydronium, as concentration increases, the pH goes down. The lowest pH is the highest concentration of hydronium

What does a “log” scale really mean? pH x more acidic 100x more acidic 1000x more acidic Level of acidity increases Every change of 1 in pH shows a change of 10x in concentration of hydronium

An example of calculating pH Example: Find the pH if the concentration of [H 3 O +1 ] is 0.25 M

An example of calculating pH pH = 0.60 Example: Find the pH if the concentration of [H 3 O +1 ] is 0.25 M

An example of calculating hydronium Example: Find the [H 3 O +1 ] if the pH is 2.7

An example of calculating hydronium H 3 O +1 = M Example: Find the [H 3 O +1 ] if the pH is 2.7

Auto-ionization of Water Water will split into ions  2 H 2 O  H 3 O +1 + OH -1 Water will do this to make sure that at 25°C the following is true:  [H 3 O +1 ] × [OH -1 ] = 1 × So if you know the hydronium concentration at 25°C (which can be found from pH), then you can also find the hydroxide concentration

An example of calculating hydroxide Example: Find the [OH -1 ] if the pH is 10.7

An example of calculating hydroxide Example: Find the [OH -1 ] if the pH is 10.7 H 3 O +1 = 2.0 × M OH -1 = M

Let’s Practice #1 Example: Find the pH if the concentration of [H 3 O +1 ] is 2.5 × M

Let’s Practice #1 pH = 4.6 Example: Find the pH if the concentration of [H 3 O +1 ] is 2.5 × M

Let’s Practice #2 Example: Find the [OH -1 ] if the pH is 3.6

Let’s Practice #2 Example: Find the [OH -1 ] if the pH is 3.6 H 3 O +1 = 2.5 × M OH -1 = 4.0 × M

Let’s Practice #3 Example: Find the [H 3 O +1 ] if the pH is 11.2

Let’s Practice #3 H 3 O +1 = 6.3 × M Example: Find the [H 3 O +1 ] if the pH is 11.2