Experiment no. 7Acid, Bases and Salts

Butial, John RexDizon, Dan Ronsley

Manlapaz, Patrick EvandelVicedo, Viviene Neriz

Group no. 7, Chem 14.1, WEGI, Mr. Ralph Julius L. MendozaMarch 18, 2009

<Abstract>

Keywords:

Introduction

Experimental

1. Electrolytes

Five drops of 0.1 M solutions of NaOH, NH4Cl, HC2H3O2, NaCl, C2H5OH, C12H12O11, HCl, NH4OH, HOAc + NaOH, HCl + NaOH, NH4OH + HCl and distilled water was placed in separate test tubes and was tested using the following indicators: litmus paper, phenolphthalein and congo red. Color was taken note of and the substances were classified into acids, bases and salts.

The pH oh each substance was obtained using a pH paper.

Equal volumes, specifically 1 ml of 1 M HCl and 1 M NaOH was mixed in a test tube. Indicators were used to test the mixture. This procedure was repeated by using 1 M acetic acid in place of HCl.

2. Conductivity Test

The conductivity of the above solution was tested using the conductivity apparatus.

3. Preparation of 1 M NaOH using NaOH pellets

The weight of NaOH needed to prepare 100.00 mL of 1 M NaOH was calculated. The calculated amount of pellets was weighed in a watch glass and was dissolved in 50 mL water.

4. Preparation of 0.1 M NaOH from available concentration of NaOH

The volume of NaOH from available concentration needed to prepare 100 mL of 0.1 M NaOH was determined. The measured volume to from procedure A was dilute to 100.00 mL distilled water in a volumetric flask.

5. Titration of an Acid with a Base

The base buret was washed thoroughly with soap and water and was rinsed with 3 mL portions of the standard base, 0.1 M NaOH. The buret was filled with 0.1 M sodium hydroxide, NaOH and the air space was removed at the tip. Zero reading was set and the buret was clamped into the iron stand.

10 mL aliquot of the unknown acid was transferred into an Erlenmeyer flask. 50 mL of distilled water and 2-3 drops of phenolphthalein was added. The acid was titrated with the standard base until the appearance of the first appearance of a permanent light pink coloration. The final reading was recorded and three trials were conducted. Finally, the molarity of the unknown acid solution was calculated. Results

I. Electrolytes

II. Preparation of 1 M NaOH using NaOH pellets

Calculations:

1 M NaOH = Xg NaOH 40g NaOH 100g x 1 mL x 1 L

1 g 100 mL 0.1 = x

40

x = 4g NaOH Pellets

III. Preparation of 0.1 M NaOH from available concentration of NaOH

Calculations:

(1 M)(x) = (0.1 M NaOH final) (100 mL NaOH + H20 Final)

x= 10 mL NaOH initial

IV. Titration of an Acid with a base TRIAL

No. 1 No. 2 No. 3 No. 4 NO.5Volume of 0.10 M NaOH

6.3 6.3 6.6 6.8 6.6

Volume of unknown acid solution

10 mL

10 mL

10 mL

10 mL

10 mL

Molarity of unknown acid solution

0.663 0.068 0.066 0.068 0.066

Average Molarity of unknown acid solution:0.0662

Calculations:

MA = MBVB

VA

MA = (0.1) (0.0063) 0.01

Discussion

Acid is a substance that produces H+ (aq) ions in aqueous solutions. Strong acids ionize completely or almost completely in dilute aqueous solutions; weak acids ionize only slowly.

Base is a substance that produces OH- (aq) ions in aqueous solutions. Strong bases are soluble in water and are dissociated completely. Weak bases ionize only slowly.

Salt is a compound that contains a cation other than H+ and an anion other than OH- or O2-.

Aqueous solution of both acids and base conduct electricity because they are ionized/dissociated completely.

The indicators used were litmus paper, pH paper, phenolphthalein, and congo red.

Indicators are weak acids or bases with differently colored acid and base forms.

Since color change often accompanies chemical change, you might suspect that a chemical reaction is responsible for indicator action. This indeed is the case.

Indicators are weak acids or bases with differently colored acid and base forms.

The indicator reaction is pH dependent because it involves either the release or capture of hydrogen ions:

HIn H+ + In-

where "HIn" and "In" stand for the indicator molecule with and without an attached hydrogen ion.

The two forms of the indicator molecule have noticeably different colors. For example, phenolphthalein has a clear HIn form and a red-violet In form. When there are equal amounts of HIn and In, the solution looks pink/cloudy. Adding a drop of acid adds H+ ions which react with the In- ions to form HIn, and the solution becomes more clear. Adding a drop of base converts HIn to In, and the solution becomes more pink/red violet.

Litmus paper

Litmus is a weak acid. It has a seriously complicated molecule which we will simplify to HLit. The "H" is the proton which can be given away to something else. The "Lit" is the rest of the weak acid molecule.

There will be an equilibrium established when this acid dissolves in water. Taking the simplified version of this equilibrium:

The un-ionised litmus is red, whereas the ion is blue.

Now use Le Chatelier's Principle to work out what would happen if you added hydroxide ions or some more hydrogen ions to this equilibrium.

Adding hydroxide ions:

Adding hydrogen ions:

If the concentrations of HLit and Lit - are equal:

At some point during the movement of the position of equilibrium, the concentrations of the two colors will become equal. The colour you see will be a mixture of the two.

The reason for the inverted commas around "neutral" is that there is no reason why the two concentrations should become equal at pH 7. For litmus, it so happens that the 50 / 50 colour does occur at close to pH 7 - that's why litmus is commonly used to test for acids and alkalis. As you will see below, that isn't true for other indicators.

Phenolphthalein

Phenolphthalein

Phenolphthalein is another commonly used indicator for titrations, and is another weak acid.

In this case, the weak acid is colorless and its ion is bright pink. Adding extra hydrogen ions shifts the position of equilibrium to the left, and turns the indicator colorless. Adding hydroxide ions removes the hydrogen ions from the equilibrium which tips to the right to replace them - turning the indicator pink.

Type: HIn + H2O In- + H3O+

pK: 9.5Approximate pH range for color change: 8.0-9.8Color of acid form: clearColor of base form: red-violet

Congo Red

Approximate pH range for color change: 3.0-5.0Color of acid form: blueColor of base form: red

For part A electrolytes, the different reagents were tested using the following instruments: phenolphthalein, congo red, pH paper, litmus paper and conductivity apparatus. Through these indicators, properties like acidity, conductivity, the strength and weakness of acid/ base and the electrolyte property were obtained.

For 0.1 M sodium hydroxide, the red litmus paper turned blue, and the blue litmus paper turned red, indicating that the reagent is basic. Its pH is 14, and through the conductivity apparatus, it was identified that it is a strong

Electrolytes are compounds that ionize or dissociate into their constituent ions to produce aqueous solutions that conduct an electric current.

Strong electrolytes are ionized or dissociated completely or very nearly completely, in dilute aqueous solutions. Strong electrolytes include strong acids, strong bases and strong salts.

Weak electrolytes conduct electricity poorly in dilute aqueous solutions.

Non-electrolytes exist as molecules in aqueous solutions, and such solutions do not conduct electric current.

Electric current is carried through aqueous solution by the movement of ions. The strength of an electrolyte depends on the number of ions in solution and also on the charges of these ions.

pH

a measure of the acidity or basicity of a solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions (H+). Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations. The pH scale is not an absolute scale; it is relative to a set of standard solutions whose pH is established by international agreement.

Guide Questions & Answers

Conclusion and Recommendations

References

I hereby certify that I have given substantial contributions to this report.

-----------------------------------Butial, John Rex

-----------------------------------Dizon, Dan Ronsley

-----------------------------------Manlapaz, Patrick Evandel

-----------------------------------Vicedo, Viviene Neriz