General chemistry Lab 2

Chemistry

Analytical Chemistry

Gravimetric Analysis

Oxidation and Reduction Reactions

Instrumental AnalysisChemical Analysis

Qualitative Analysis

Physical Chemistry

Biochemistry

Change in oxidation number

Quantitative Analysis

Volumetric Analysis

No Change in oxidation number

Neutralization Reactions

Complex formation Reactions

Precipitation Reactions

Organic Chemistry

Inorganic Chemistry

Neutralization Reactions

Neutralization Reactions:

is a reaction between an acid and a base. Generally , aqueous acid-base reactions produce water an a salt.

acid + base = salt + water

For example:

HCl + NaOH → NaCl + H2O

Titration

A solution of accurately known concentration, called a standard solution, is added gradually to analyte solution (unknown concentration solution), until the chemical reaction between the two solutions is complete.

If we know the volumes of the standard and unknown solutions used in the titration. Along with the concentration of the standard solution, we can calculate the concentration of the unknown solution.

( N x V ) standard solution ( x V` ) unknown solutions = N`

Equivalent pointThe point where the reaction theoretically complete.

End pointThe point at which the reaction is observed to be complete.

Acid-Base Indicators

- An acid-base indicator is either a weak organic acid or weak organic base that exhibits a color change as the concentration of hydrogen (H+) or hydroxide (OH-) ions changes in an aqueous solution.

- Indicator: substances that have distinctly different colors in acidic and basic.

- Also Known As: pH indicator.

- for every equivalence point, (must) there is suitable indicator.

- Indictors dose not change colour sharply at one particular pH, they change over a narrow range of pH.

pH of solution

pH solution

pH = 7 Neutralization

pH > 7 Basic

pH < 7 Acidic

Examples of Indicators

Indicator pH Acidic medium

Basicmedium

M.O 3.1- 4.4 red Yellow

Ph.ph 8.3 - 10 Colorless Red - pink

pH Indicator

Strong acid and strong base 1-14 All Indicator

Weak acid and strong base pH > 7 ph.ph

strong acid and weak base pH < 7 M.O

Weak acid and weak base pH (Very little) -------

Expressions of concentration of solution

weight of solute Weight percent = x 100 weight of solution

volume of soluteVolume percent = x 100 volume of solution

weight of solute (in g)Weight volume percent = x 100 volume of solution (in mL)

Expressions of concentration of solution

Molarity (M): the number of moles of solute in one liter of solution. n M = VL

Molality: the number of moles of solute dissolved in one kilogram of solvent. n m = KgNormality (N): the number of gram equivalents of solute per liter of solution. Eq N = VL

Expressions of concentration of solution

Grams per unit volume = the number of grams dissolved in one liter of solution. Strength of the solution = Normality X Equivalent weight

Exp1:Titration of Hydrochloric Acid with Sodium HydroxideStrong acid and strong base

Purpose: To determine the concentration of the basic solution by titrating it with an acidic solution of known concentration.

Titration of Hydrochloric Acid with Sodium HydroxideStrong acid and strong base

Principle: An aqueous solution of hydrochloric acid, HCl(aq), is a strong acid.An aqueous solution of sodium hydroxide, NaOH(aq), is a strong base.

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(L)

The aqueous solution of a salt of a strong acid and a strong base will have a pH = 4 -10.

so the suitable indicator is: ph.ph and MO.

Titration of Hydrochloric Acid with Sodium HydroxideStrong acid and strong base

Tools:

- 50‐mL Buret

- 250‐mL conical flasks

- Buret funnel

- Two 250‐mL beaker

- 10‐mL pipette

-Pipette pump.

Titration of Hydrochloric Acid with Sodium HydroxideStrong acid and strong base

Materials:

- NaoaH(aq)

- HCL(aq)

- Phenolphthalein

- Methyl-orange

- Distilled water

Titration of Hydrochloric Acid with Sodium HydroxideStrong acid and strong base

Procedure:

1- wash the tools by: a- tap water b- distilled water c- solution if need it.

2- Add the base solution from the beaker to the buret (use a funnel to pour). Move the funnel around while adding to ensure the sides of the buret are coated with base.

3- Pour more of the sodium hydroxide solution into the buret until it is near the 0.00 mL mark. Open the stopcock to allow several drops to rinse through the tip of the buret. This should eliminate any air bubbles in the buret tip.

Titration of Hydrochloric Acid with Sodium HydroxideStrong acid and strong base

Procedure:4- Draw 10 mL of the acid solution into the volumetric pipette and transfer this solution into an Erlenmeyer flask. Add 2‐3 drops of phenolphthalein to the acid solution in the flask.

5- Place the flask under the buret and start adding the base solution to the Erlenmeyer flask. When pink starts to develop, add the solution more slowly. At this point you should add one drop at a time followed by swirling until a very light pink color persists for at least 30 seconds. Remember, the lighter the pink the better!!!

6- Record the final reading of the buret. Wash the contents of the flask down the drain with water.

Titration of Hydrochloric Acid with Sodium HydroxideStrong acid and strong base

Procedure:

7- Refill the buret with more sodium hydroxide solution if necessary. Pipette another sample of acid and add the phenolphthalein as before and titrate as before.

8. Conduct additional titrations until three of them differ by no more than 1.0%.

9. calculate the concentration of NaOH and its strength

NaOH (N = ----)(v= ???)

HCL (N = 0.1)(V=10ml) + Ph.ph

Titration of Hydrochloric Acid with Sodium HydroxideStrong acid and strong base

calculations:

Experience initial reading final reading volume Average

1

2

3

Volume of NaOH:-----------

Titration of Hydrochloric Acid with Sodium HydroxideStrong acid and strong base

calculations:

concentration of ( NaOH )

( N x V )acid = ( N` x V` )base

( N x V )HCL = ( N` x V` )NaOH

( N x V )HCL

N`NaOH =

V`NaOH

(0.1 x 10 )HCL N`NaOH = ???

N`NaOH = --------------------------- N

Titration of Hydrochloric Acid with Sodium HydroxideStrong acid and strong base

calculations:

concentration of ( NaOH ) by (C g / L)