presentation preparation of solutions of acids and bases

8/13/2019 Presentation PREPARATION OF SOLUTIONS OF ACIDS AND BASES

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What is an ACID?

pH less than 7

Neutralizes bases

Forms H+

ions in solution Corrosive-reacts with mostmetals to form hydrogen gas

Good conductors of electricity


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Common Acids

HCl - hydrochloric- stomach acid

H2SO4- sulfuric acid - car batteries

HNO3

nitric acid - explosives

HC2H3O2- acetic acid - vinegar

H2CO3-carbonic acidsodas

H3PO4- phosphoric acid -flavorings
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What is a BASE?

pH greater than 7

Feels slippery

Dissolves fats and oilsUsually forms OH

-ions in

solutionNeutralizes acids


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Common Bases

NaOH- sodium hydroxide (LYE) soaps, drain

cleaner

Mg (OH)2- magnesium hydroxide-antacidsAl(OH)3-aluminum hydroxide-antacids,

deodorants

NH4OH-ammonium hydroxide-ammonia
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Preparation of solutions

Always add acid to a large volume of water.The solution may then be diluted with additional

water to make one liter.

Because mixing acid with water is an exothermicreaction, be sure to use glassware capable of

withstanding the temperature change (e.g., Pyrex or

Kimax).Sulfuric acid is particularly reactive with water.

Add the acid slowlyto the water while stirring.


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MAKING MOLAR (M)

SOLUTIONS

A 1 Molar solution (1M) contains 1 mole of solute

dissolved in a solution totaling 1 liter.

If you use water as the solvent, it must be distilled

and deionized. Do not use tap water.

A mole is the molecular weight (MW) expressed

in grams (sometimes referred to as the grammolecular weight (gMW) of a chemical). Thus, 1

M = 1 gMW of solute per liter of solution.


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solution

Using 70% concentrated Nitric Acid as an example:70% Nitric Acid means that 100 grams of this acidcontains 70 grams of HNO3.

To calculate the Molarity of a 70 wt. % Nitric Acid thenumber of moles of HNO3present in 1 liter of acid needs

to be calculated. Knowing the density of the acid to be 1.413 g/mL, we

can calculate the weight of 1 L of 70% HNO3to be 1413grams. Knowing that the solution is 70 wt % would thenallow the number of grams of HNO

3to be calculated:

(0.700)(1413g) = 989.1 grams HNO3per liter.

Dividing the grams of HNO3by the molecular weight ofHNO3(63.01 g/mole) gives the number of moles ofHNO3/ L or Molarity, which is 15.7 M.


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The Molarity Calculator Equation:The following equation is used for calculatingMolarity where the concentration is given in wt

%: [(% x d) / MW] x 10 = MolarityWhere: % = Weight %; d = Density (or specificgravity); MW = Molecular Weight (or FormulaWeight).The above equation can then be used tocalculate the Molarity of the 70 wt % NitricAcid:

[(70 x 1.413) / 63.01] x 10 = 15.7 M

N lit f id b


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Normality of an acid or base

from its Molarity There is a relationship between normality and molarity.

Normality can only be calculated when we deal with

reactions, because Normality is a function of equivalents.

Normality refers to compounds that have multiple chemical

functionalities, such as sulfuric acid, H2SO4. 1 M solution of H2SO4 will contain only one mole of

H2SO4 in 1 liter of solution, but if the solution is titrated

with a base, it will be shown to contain two moles of acid.

This is because a single molecule of H2SO4contains twoacidic protons (H+ Ions). Thus, a 1 M solution of

H2SO4 will be 2 N. The 'Normality' of a solution is the

'Molarity' multiplied by the number of equivalents per

mole.


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Percent Solutions

Mass percent solutions are defined based on the

grams of solute per100 grams of solution.

Example: 20 g of sodium chloride in 100 g of solution is

a 20% by mass solution.

Volume percent solutions are defined as milliliters of

solute per 100 mL of solution.

Example: 10 mL of ethyl alcohol plus 90 mLof H2O (making approx. 100 mL of solution) is a 10% by

volume solution.


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Neutralization of an acid and a base

Introduction and Definitions:

A salt is any compound which can be derived from the

neutralization of an acid and a base.

The word "neutralization" is used because the acid and baseproperties of H+and OH-are destroyed or neutralized. In the

reaction, H+ and OH- combine to form HOH or water

molecules.

A neutralization is a type of double replacement reaction. A

salt is the product of an acid-base reaction and is a much

broader term then common table salt as shown in the first

reaction.


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The following are some examples of

neutralization reactions to form salts.

a. HCl + NaOH --> NaCl + HOH

b. H2SO4+ 2 NH4OH --> (NH4)2SO4+ 2 HOH

c. 2 NaOH + H2CO3--> N2CO3+ 2 NaOH

To the solution will be neutralized when the

number of moles of H+equals the number of molesof OH-.


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Stomach Antiacids:

Antiacids are supposed to decrease the amount of

hydrochloric acid in the stomach by reacting with

excess acid. They are used in the treatment of gastric

hyperacidity and peptic ulcers. Some of the ingredients in antacids are: Magnesia

(MgO), milk of magnesia (Mg(OH)2, calcium

carbonate (CaCO3), sodium bicarbonate (NaHCO

3),

dihydroxyaluminum sodium carbonate

(NaAl(OH)2CO3), aluminum hydroxide gel (Al(OH)3).

Several of these will habe top be recognized as

Bronsted bases.


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Buffer

A bufferis a solution of a weak acid and itsconjugate base that resists changes in pH inbothdirectionseither up or down.

A buffer works best in the middle of its range,where the amount of undissociated acid is aboutequal to the amount of the conjugate base.

One can soak up excess protons (acid), theother can soak up excess hydroxide (base).

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Buffer Capacity

The bu ffer capacity is a measure of the

strengthof the buffer, its ability to maintain the

pH following addition of strong acid or base.

The greater the concentrat ions of the buffer

components, the greaterits capacity to resist pH

changes.

The closerthe component concentrations are

to each other, the greaterthe buffer capacity.


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The relation between buffer capacity and pH change.

When strong b ase is

added, the pH increasesleast for the most

con centrated buffer.

This graph shows the final pH values for four different buffer solutions after

the addition of strong base.


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Buffer Range

The bu ffer range is the pH range over which the buffer is

effective.

Buffer range is related to the ratio of buffer component

concentrations.

[HA]

[A-]The closer is to 1, the more effective the buffer.

If one component is more than 10 times the other, buffering

action is poor. Since log10 = 1, bu ffers have a usablerange with in 1 pH unit o f the pKaof th e acid

component .


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Preparing a Buffer in Real Life

To prepare 1.00 L of buffer containing 0.100 M tris at pH 7.60. When we say

0.100 M tris, we mean that the total concentration of tris plus tris H+ will be

0.100M.

Procedure:1. Weigh out 0.100 mol tris hydrochloride and dissolve it in abeaker containing about 800 mL water and a stirring bar.

2. Place a pH electrode in the solution and monitor the pH.

3. Add NaOH solution until the pH is exactly 7.60.4. Transfer the solution to a volumetric flask and wash the

beaker and stirring bar a few times. Add the washings to the

volumetric flask.

5. Dilute to the mark and mix.P.202


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Buffer capacity

The amount of H+or OH-

that buffered solution canabsorb without a

significant

change in pH

Buffer capacity measures how well a solution resists changesin pH when acid or base is added.

The greater the buffer capacity, the less the pH changes.


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pKa= 4.76

22

pH 7 __

_

_

_

_

_

0 equiv. of NaOH 1.0

added

Buffering range: only

small pH changes

result from addition ofbase or acid

Titration of acetic acid with sodium hydroxide

50% dissociation


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Ionization of acetic acid:

Resisting changes both ways23

OH- H2O

Acetic acid HAc Ac- Acetate

(CH3COOH) (CH3COO-)

H+


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Insights for the Future

pH control is important, as many enzymes havea narrow range in which they function optimally.

Buffering capability is essential for the well-

being of organisms, to protect them fromunwelcome changes in pH.

For example, your stomach is about pH 1, yetthe adjacent portion of your intestine is near pH

7 Many compounds and macromolecules in

addition to bicarbonate can serve a bufferingfunctionproteins comprise one of the major

classes.

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presentation preparation of solutions of acids and bases

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