acids bases salts

E X P E R I ME N T 7

G R OU P S 8 & 9

parts

I. Electrolytes and Common

Household Items

I. Conductivity Test

II. Preparation of 1 M NaOH using NaOH

pellets

III. Preparation of 0.1 M from 1 M NaOH

IV. Titration of an Acid and a Base

concepts

o Electrolyte

oAcids

o Bases

o Neutralization

o Salts

o pH

electrolytes and common

household items

concepts electrolyte

a substance that, when dissolved in water, results in a

solution that can conduct

electricity

concepts acids

GENERAL PROPERTIES

sour taste color changes in plant dyes react with certain metals React with carbonates and bicarbonates to produce CO2 gas

Aqueous acid solutions conduct electricity

concepts bases

GENERAL PROPERTIES

bitter taste slippery color changes in plant dyes aqueous base solutions conduct

electricity

concepts acids vs. bases

ACIDS BASES

ARRHENIUS

CONCEPT

Ionize in water

solution to produce

H+(aq) or H3O+

Ionize in water

solution to produce

OH-(aq)

BRNSTED-LOWRY

CONCEPT

Proton donors Proton acceptors

LEWIS

CONCEPT

Electron-pair

acceptors Electron-pair donors

concepts neutralization

a reaction between an acid and a base.

aqueous acid-base reactions produce water and a salt

acid + base salt + water

concepts salts

ionic compounds made up of a cation other than H+

and an anion other than OH-

or O2-

concepts pH

measure of acidity the negative logarithm of the hydrogen ion

concentration (in mol/L):

concepts pH

INDICATORS

litmus paper phenolphthalein congo red pH paper

procedure electrolytes and common

household items

NaOH NH4Cl HCl HC2H3O2 NaCl C12H22O11 C2H5OH H2O

Test with litmus paper, phenolphthalein, and congo red Classify whether acidic, basic, or neutral Test pH using pH paper

procedure electrolytes and common

household items

shampoo conditioner feminine

wash

liquid

sosa

liquid

soap

fruit

juice

softdrink

Test with litmus paper, phenolphthalein, and congo red Classify whether acidic, basic, or neutral Test pH using pH paper

results

Reagents

0.1 M

Solutions

Classification pH Classification

of Acid/Base

NaOH Base 12 Strong Base

NH4Cl Base 8 Weak Base

HCl Acid 2 Strong Acid

HC2H3O2 Acid 2 Strong Acid

NaCl Neutral 7 -

H2O Neutral 7 -

C6H12O11 Neutral 7 -

C2H5OH Base 12 Strong Base

results Solution

Litmus

Paper Phenolphthalein Congo Red Classification

Shampoo R-R

B-R Colorless Red Base

Conditioner B-B-

R-R Colorless Red Acid

Feminine

Wash

B-B

R-R Colorless Colorless Acid

Liquid

Sosa

R-B

B-B Violet Red Base

Liquid

Soap

R-B

B-B Colorless Red Base

Softdrink B-R

R-R Cloudy Dark violet Acid

Fruit

Juice

R-R

B-R Cloudy Violet Acid

concepts

o strong electrolytes

o weak electrolytes

o non-electrolytes

conductivity test

concepts

dissociate completely into

ions and create a large current

strong electrolytes

dissociate into ions very little, and most of

their molecules remain intact.

weak electrolytes

procedure conductivity test

Test conductivity of the solutions in 1-a

results

Reagents

0.1 M Solutions Conductivity

Classification (based

on conductivity)

NaOH Good Strong Electrolyte

NH4Cl Good Strong Electrolyte

HCl Good Strong Electrolyte

HC2H3O2 Weak Weak Electrolyte

NaCl Good Strong Electrolyte

H2O - Non-electrolyte

C12H22O11 - Non-electrolyte

C2H5OH - Non-electrolyte

concepts

o Concentration of solution

o Molarity

preparation of 1 M

NaOH using NaOH pellets

concepts concentration

a measure of the quantity of solute dissolved in a given

quantity of solution

concepts molarity

molar concentration, which is the number of

moles of solute per liter of

solution

procedure

Calculate the weight of NaOH pellets needed to prepare 50.0 mL of 1 M NaOH

Weigh pellets in a watch glass and dissolve in 50 mL water

Transfer in 100-mL volumetric flask and dilute to the mark with water

preparation of 1 M

NaOH using NaOH pellets

results

1 mol NaOH x 0.1 L x 40 g NaOH = 4g NaOH in

1 L 1 mol NaOH the beaker

concepts

o dilution

preparation of 0.1 M

NaOH from 1 M NaOH

concepts dilution

a procedure for preparing a less concentrated solution from

a more concentrated solution.

procedure

Determine volume of NaOH from available concentration needed to

prepare 100 mL of 0.1 M NaOH

Dilute the measured volume to 100.00 mL with water in a

volumetric flask

M1V1=M1V2

preparation of 0.1 M

NaOH from 1 M NaOH

results

M1V1=M1V2

1M (V1) = 0.1 M (250 mL)

V1 = 25 mL

concepts

o titration

o equivalence point

o indicator

o end point

titration of an acid

with a base

concepts titration

a method of determining the concentration of a solution by

monitoring its reaction with a

solution of known concentration.

concepts equivalence

the point at which the acid has completely reacted with or been

neutralized by the base

point

concepts indicators

are substances that have distinctly different colors in acidic and basic

media.

concepts end point

the pH at which the indicator changes color.

procedure titration of an acid

with a base

Wash base buret with soap and water then rise with 0.1 M NaOH.

Fill buret with 0.1 M NaOH and

remove airspace

Pipet a 10-mL aliquot of the unknown acid in an erlenmeyer flask, add 50 mL water then add

2-3 drops phenolphtalein. Titrate until pink

coloration. Calculate molarity of unknown acid

solution

results

Trial 1 Trial 2 Trial 3

Volume of

0.1 M NaOH 2.8 mL 2.9 mL 3 mL

Volume of

unknown

acid solution 2mL 2mL 2mL

Molarity of

unknown

acid solution 0.14 M 0.145 M 0.15

Average

molarity of

unknown acid

solution

0.145 M

5

results Trial 1:

MacidVacid=MbaseVbase Macid(2 mL) = (0.1 M)(2.8 mL)

Macid = 0.14 M Trial 2:

MacidVacid=MbaseVbase Macid(2 mL) = (0.1 M)(2.9 mL)

Macid = 0.145 M

Trial 3:

MacidVacid=MbaseVbase Macid(2 mL) = (0.1 M)(3 mL)

Macid = 0.15 M

guide

1. From your results, what relationship can

you draw between the acidity/basicity of a

substance and its electrolyte property?

There is a direct relationship between the acidity/basicity

of a substance and its ability to conduct electricity. Strong

acids/bases have stronger conductive ability because of

their almost complete dissociation in an aqueous

substance. Although other properties must be considered

if an acid/base is also a salt, whether weak or strong, when

dissolved in water, it is also a good conductor of electricity.

questions

guide

2. Why are electrolytes conductors of

electricity?

Electrolytes dissociate in aqueous solutions, thus they are ionized. Positively charged ions move toward the negative

electrode and negatively charged ions move to the positive

electrode. This resembles the movement of electrons along a metal

wire which explains the conductive property of electrolytes.

questions

conclusion

Electrolytes are compounds that dissociate into

its constituent ions. Strong acids/bases completely

dissociate. Thus make a good conductor because

there is abundance in ions that would complete an

electrical circuit. Weak acids and bases, on the other

hand, do not completely dissociate. This partial

dissociation causes their low conductivity because

there is a low availability of ions that would complete

the circuit. Non-electrolytes do not produce ions at

all because they exist as uncharged molecules.

recommendation

It is recommended that one be careful and

observant in using indicators when getting the pH of

the solution in order to obtain accurate results. For

the preparation of the titrant, one must accurately

measure the weight of NaOH pellets and the volume

of water to use. It must also be completely dissolved

in water before being diluted in a 100mL volumetric

flask. During the titration, one must be careful in

transferring of the titrant to the unknown solution in

order to avoid over-titration.

references

Chang, R. (2010). Chemistry (10th ed.). New

York, NY: McGraw-Hill.

Silberberg, M.S. (2009). Chemistry: the

molecular nature of matter and change (5th

ed.). New York, NY: McGraw-Hill.