Acids and Bases

Video 11.1Acids and Bases

What is an electrolyte?

A substance that dissolves in water and conduct electricity. Acids and bases are electrolytes.

◦Acid: Substance that, when dissolved in water, increases the concentration of hydrogen H+ (or hydronium H3O+) ions.◦Acids have a sour taste and can burn your skin.

◦Acids react vigorously with metals to make H2

◦pH is less than 7◦On table K

Arrhenius

Base: Substance that, when dissolved in water, increases the concentration of hydroxide ions.

Bases have a bitter taste and are corrosive.

pH>7 On Table L

Arrhenius

If an acid is added to a base, it results in neutralization, where all properties of the acid and base are lost. The products are a salt and water.

NaOH + HCl H2O + NaCl

Salt is another name for solid ionic compounds containing elements other than H+ and OH-. Salts are electrolytes with high mp and bp.

Arrhenius

1. H2SO4 + LiOH H2O + Li2SO4

2. KOH + HNO3 KNO3 + H2O

Label and name the acid, base and salt:

Acid Base Salt

Base Acid Salt

1. NaOH + HF

2. Ca(OH)2 + H2SO4

Identify the salt produced:

H2O + NaF

H2O + CaSO4

Make sure you check your compounds with the criss cross rule for ions!

Video 11.2Alternate Acid Base Theory

◦Acid: Proton donor◦Base: Proton acceptor

Brønsted–Lowry : BAAD

Protons refer to hydrogen ions.

H H+

HCO3−

HSO4−

H2O

These all have hydrogen atoms to donate and a negative charge that

would attract H+

If it can act as either an acid or a base it is amphiprotic.

What Happens When an Acid Dissolves in Water?

Water acts as a Brønsted–Lowry base and removes a proton (H+) from the acid.

As a result, the conjugate base of the acid and a hydronium ion are formed.

Conjugate Acids and Bases:

Reactions between acids and bases always yield their conjugate bases and acids.

Strong acids and bases are completely dissociated in water to make a lot of H+or OH-.

Weak acids and bases only dissociate partially in water to make a small amount of H+or OH-.

How is strength different from concentration?

Acid and Base Strength

Strength refers to the amount of ions a substance makes when it breaks down.

Concentration refers to the amount of the substance initially, before it breaks down. This is usually measured in molarity (mol/L).

Strength versus Concentration

Video 11.3pH and indicators

pH

How Do We Measure pH? For less accurate

measurements, one can use◦Litmus paper “Red” paper

turns blue above ~pH = 8

“Blue” paper turns red below ~pH = 5

◦An indicator

How Do We Measure pH?

For more accurate measurements, one uses a pH meter, which measures the voltage in the solution.

Earth’s Natural Litmus Hydrangeas are blue when the acidity of

the soil is between 5-5.5 and red if the acidity is between 6.5-7.5. A mix of colors can be seen between 5.5-6.5.

If the pH goes up one, the concentration of hydrogen ions decreases by 10. The solution is more basic.

If the pH goes down one, the concentration of hydrogen ions increases by 10. The solution is more acidic.

pH is a logarithmic scale

If the pH changes from 3 to 4, how much more basic is the solution?

If the pH = 3 and the hydrogen concentration increases by 100 times, what is the new pH?

If the pH = 8 and the hydrogen ion concentration decreases by 10,000 times, what is the new pH?

Examples

If NaOH is tested with methyl orange, what color will it be?

At what pH will bromocrescol green turn yellow?

What type of solution will turn bromothymol blue, yellow?

At what pH will both bromothymol and thymol blue be yellow?

Indicators

yellow

3.8

acidic

7.6-8

Why won’t methyl orange be good at determining the difference between an acid and a base?

Which indicator is the best to test the difference between a strong and weak base?

What color change will be seen if NaOH is added to HCl with methyl orange?

What color change will be seen if nitric acid is added to lithium hydroxide using bromocrescol green?

Examples

Bases and acids can both be yellowThymol blue

Red to yellow

Blue to yellow

Video 11.4Titrations

ACID + BASE SALT + WATER

Salt is another name for any ionic substance. They can conduct electricity.

HCl + NaOH NaCl + H2O

Neutralization

acid base salt

Titrations are used to find the concentration of a solution. Usually the concentration of the base is unknown, so a known acid is added to the base until the solution neutralizes.

The endpoint, or the point where the solution is neutral and the titration is over, is marked by a faint pink color in the solution (due to phenolphthalein).

Titrations

To calculate the molarity of the unknown use the formula on Table T:

MAVA=MBVB

Titrations

1. What is the molarity of NaOH if 100.mL of 3.00M HCl is titrated with 200.mL of NaOH?MAVA=MBVB(3.00)(100) = x(200) x = 1.50M2. What is the molarity of 100.0mL HCl if it is

neutralized by 250mL of 2.0M NaOH?MAVA=MBVB (x)(100) = (2.0)(250) x = 5.0M

Examples

The titration formula only works if the acid and the base have equal numbers of H+ and OH-. If not, the acid side must be multiplied by the number of hydrogen ions and the base side must be multiplied by the number of hydroxide ions in the formulas.◦ What is the molarity of a solution of Ca(OH)2 if

750mL of it is titrated with 250mL of 3.5M H3PO4?

3MAVA = 2MBVB

3(3.5)(250) = 2(x)(750) x = 1.75M

Exceptions

0.6mL 15.4mL

15.4-.6 = 14.8mL released from the burette.

How much acid was released?

How much acid is in each burette?