Experiment no: 1

Name of the experiment: determination of purity % of NaOH.

Object:

1. To know how purity% of NaOH is determined.

Theory:

A common problem in chemistry is determining whether or not a substance is

impure and to what extent it is impure. Chemicals used in experiments or for commercial

purposes often need to be pure to ensure safety and efficiency during reactions, but

determining whether or not a given substance is pure can be difficult. If the chemical is an

acid or a base, titration with a standardized solution can be used to assess its purity.

In a generic titration, “one solution of known concentration is used to determine the

concentration of another solution through a monitored reaction.”1 An acid-base titration

works on the principle that the acidic solution will combine the basic solution to neutralize,

altering the pH of the solution.

H3O+(aq) + OH- (aq) 2H2O(l) (1)

Eq. 1 shows that when equal moles of the H3O+ion and the OH- ion are present, the solution

is completely neutralized. 2 When this dynamic equilibrium occurs in a titration, it is called

the equivalence point, and at that point a given reaction has a characteristic pH. Thus,

indicators, substances that can change color depending on the pH, are valuable tools for

monitoring the progress of titration reactions. A few drops of indicator are added to one of

the solutions and the other solution is added dropwise. When the moles of acid and base are

equivalent, the equivalence point is reached and adding one more drop of the titrant will

cause the indicator to change color, signaling the end point of the reaction. The end point

occurs just after the equivalence point, but the extra titrant required to reach the end point is

negligible in calculations.

The titration method is useful in determining purity only if a standardized solution,

one with a known molarity, is available for the titration. If a known volume of standardized

solution is used in a titration, then the moles of both acid and base can be determined. From

the moles, the mass of the pure substance can be determined and compared to the mass of

the impure substance to find the percent purity.

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In this experiment, a sodium hydroxide, NaOH, solution was standardized by

titration with pure hyrdrochloric acid, HCl.

2NaOH + H₂SO₄ --> 2H2O + Na₂SO₄ (2)

This reaction was monitored using phenolphthalein indicator, which changes from clear to

pink near a pH of 8, corresponding to the pH at the reaction’s equivalence point.

Material Safety Data Sheet for NaOH:

Potential Health Effects

First Aid Measures Handling and Storage

Stability and Reactivity

Inhalation: Severe irritant. Effects from inhalation of dust or mist vary from mild irritation to serious damage of the upper respiratory tract, depending on severity of exposure. Symptoms may include sneezing, sore throat or runny nose. Severe pneumonitis may occur. Ingestion: Corrosive! Swallowing may cause severe burns of mouth, throat, and stomach. Severe scarring of tissue and death may result. Symptoms may include bleeding, vomiting, diarrhea, fall in blood pressure. Damage may appears days after exposure. Skin Contact: Corrosive! Contact with skin can cause irritation or severe burns and scarring with greater exposures. Eye Contact: Corrosive! Causes irritation of eyes, and with greater exposures it can cause burns that may

Inhalation: Remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Call a physician. Ingestion: DO NOT INDUCE VOMITING! Give large quantities of water or milk if available. Never give anything by mouth to an unconscious person. Get medical attention immediately. Skin Contact: Immediately flush skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Call a physician, immediately. Wash clothing before reuse. Eye Contact: Immediately flush eyes with plenty of water for at least 15 minutes, lifting lower and upper eyelids occasionally. Get medical attention immediately.

Note to Physician: Perform endoscopy in all

Handling: Wash thoroughly after handling. Do not allow water to get into thecontainer because of violent reaction. Minimize dust generation and accumulation.Do not get in eyes, on skin, or on clothing. Keep container tightly closed. Avoidingestion and inhalation. Discard contaminated shoes. Use only with adequateventilation.Storage: Store in a tightly closed container. Store in a cool, dry, well-ventilated areaaway from incompatible substances. Keep away from metals. Keep away from acids.Store protected from moisture. Containers must be tightly closed

Chemical Stability: Stable at room temperature in closed containers under normalstorage and handling conditions.Conditions to Avoid: Moisture, contact with water, exposure to moist air or water,prolonged exposure to air.Incompatibilities with Other Materials: Water, metals, acids, aluminum, zinc,tin, nitromethane, leather, flammable liquids, organic halogens, wool.Hazardous Decomposition Products: Toxic fumes of sodium oxide.Hazardous Polymerization: Will not occur.

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result in permanent impairment of vision, even blindness. Chronic Exposure: Prolonged contact with dilute solutions or dust has a destructive effect upon tissue. Aggravation of Pre-existing Conditions: Persons with pre-existing skin disorders or eye problems or impaired respiratory function may be more susceptible to the effects of the substance.

cases of suspected sodium hydroxide ingestion. In cases of severe esophageal corrosion, the use of therapeutic doses of steroids should be considered. General supportive measures with continual monitoring of gas exchange, acid-base balance, electrolytes, and fluid intake are also required.

to prevent theconversion of NaOH to sodium carbonate by the CO2 in air.

Physical and Chemical Properties:

Physical state and appearance: Solid

Odor: Odorless. Molecular Weight: 40 g/mole Color: White. pH (1% soln/water): 13.5 [Basic.] Boiling Point: 1388°C (2530.4°F) Melting Point: 323°C (613.4°F) Specific Gravity: 2.13 (Water = 1) Solubility: Easily soluble in cold water.

Stability: The product is stable. Incompatibility with various substances: Highly reactive with metals.                                  Reactive with oxidizing agents, reducing agents, acids, alkalis, moisture

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Mechanism:

When 2-3 drops of phenolthalein are added to NaOH solution chemical reaction takes place between them and solution becomes pink colored.

Colorful (Pink)

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During titrartion H₂SO₄ is added to the solution and the colored compound reacts with it to form colorless phenolphthalein and the end point of the titration is reached.

Apparatus:

Mug, balance, burner, beaker, buret,pipet.

Calculation:

NaOH 10ml (1% solution)

H₂SO₄ 25ml (.1M H₂SO₄ )

Initial reading of H₂SO₄

Final reading of H₂SO₄

Difference Average

25 36.2 11.2 11.2536.2 47.3 11.3

Purity% of NaOH = 11.25×6 = 67.5%

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Procedure:

10ml H₂SO₄ is taken in a beaker

2-3 drops of phenolphthalein added

Solution preparation(Pink colored)

25ml H₂SO₄ is taken in Burret(.1M)

H₂SO₄ is added to the solution slowly and solution is shaked after adding each drop of

H₂SO₄

End point is reached when solution becomes colorless

The process is repeated

Result:

The purity% of NaOH is 67.5.

Conclusion:

From the experiment we have learrned the process of determining purity% of NaOH which has increased our knowledge.

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