experiment 2 preparation of solution

7/28/2019 Experiment 2 Preparation of Solution

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THE PHILIPPINE WOMENS UNIVERSITYAnalytical Chemistry

Laboratory Activity/Experiment

Group No. : _________Section/Room : _________Date Performed: _________

Experiment No. 2

Preparation of Solutions

Introduction

Solutions are most commonly used reagents in the laboratory. When a substance called soluteis dissolved in another substance called the solvent, a solution is formed. Vinegar is a solutionof acetic acid (the solute) in water (the solvent). The concentration of a solution represents theamount of solute dissolved in a unit amount of solvent or of solution. Concentration is usually

expressed in one of the following ways: as percentage concentration (%), molar concentration(M), as molal concentration (m), or as normal concentration (N).

Percent by mass (%w/w) is the mass of the solute divided by the mass of the solution (mass

of solute plus mass of solvent), multiplied by 100. Volume percent or volume/volume

percent most often is used when preparing solutions of liquids. Volume percent

(%v/v) is defined as volume of solute divided by the volume of the solutionmultiplied by 100. Molarity(M) is probably the most commonly used unit of concentration. Itis the number of moles of solute per liter of solution. Molality (m) is the number of moles ofsolute per kilogram of solvent.Normality (N) is equal to the gram equivalent weightof a soluteper liter of solution. A gram equivalent weight or equivalent is a measure of the reactive capacityof a given molecule.

Dilution is adding solvent to a solution. Adding solvent results in a solution of lower

concentration. You can calculate the concentration of a solution following a dilutionby applying this equation:

MiVi = MfVf

where M is molarity, V is volume, and the subscripts i and f refer to the initial and final values.

Another way of expressing the concentration of solutions is mole fraction. This is the number ofmoles of a compound divided by the total number of moles of all chemical species in thesolution.

Objective:At the end of the experiment, the student shall be able to:

1. Prepare solutions of different concentrations;2. apply the techniques in the dilution of solutions; and3. Compute the mass of solute needed to prepare a certain concentration of the

solution.

Materials:2-Volumetric flask (100 mL) measuring pipette (5 ml) medicine droppermeasuring pipette (10 mL) water bath stirring rodBeaker 100 mL wash bottle

Preparation and Performance Rating

A. Before the Activity

(5 pts) Attendance ____(10 pts) Lab. Gown/Apron ____

(5 pts) Lab Manual ____

B. During the Activity

(10 pts) Organization/Orderliness____

(10 pts) Cooperation/Behavior ____(10 pts) Knowledge (Quiz) ____

(50pts) Total _______Written Report

A. Group

(30 pts) Data/Results ____B. Individual

(5 pts) Readability ____

(10 pts) Answer to question/s ____(5 pts) Neatness ____

(50 pts) TotalOverall All Total ______


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Procedure:A. Solid solute

1. Wash all glassware apparatus with soap and water ; rinse with distilled and allow todry in an upside down position.

2. Compute for the mass of Sodium hydroxide necessary to prepare 100 mL of a 0.50M sodium hydroxide.

3. Weigh out accurately into a beaker the amount of Sodium hydroxide needed.4. Dissolve the NaOH with about 30 mL of distilled water with stirring (done under the

hood while beaker is immerse in a water bath)

5. Pour the NaOH solution in a 100-mL capacity volumetric flask and rinse the beakerwith about 5 mL of distilled water twice. Pour the washings into the volumetric flaskalso.

6. Add distilled water (dilution) up to the 100-mL mark of the flask.7. Stopper the flask and shake (by turning the flask upside down) the solution.8. Transfer the prepared solution into a reagent bottle and label the bottle as 0.50 M

NaOH.

B. Dilution process1. Compute the volume of 18 M Sulfuric acid needed to prepare 100 mL of 3 M H2SO4.

Use the dilution formula.2. Transfer about 30 mL of distilled water into the volumetric flask and carefully pour the

measured volume of 12 M H2SO4 (#1). Always pour the acid to the water3. Fill the flask up to the 100-mL mark with distilled water . Stopper and mix thoroughly.4. Transfer to a reagent bottle and label with 3 M H2SO4 .

C. Prepare 100 mL of 10% Sodium chloride .1. Compute for the amount of NaCl needed to prepare the solution.2. Weigh the NaCl in a beaker and dissolve with about 30 mL of distilled water.3. Transfer the solution in the volumetric flask and rinse the beaker twice with 5 mLof

distilled water, with washings added to the flask.4. Dilute with distilled water up to the 100-mL mark. Stopper and mix thoroughly.5. Transfer in a reagent bottle and label with 10% NaCl.

Data and Results:

Solution Volume of solution(mL)

Mass ofsolute (g)

Volume ofsolute (mL)

Volume ofsolvent(mL)

0.50 M NaOH

3 M H2SO4

10% NaCl

Computation:

Conclusion:

Questions:1. Why is it necessary to shake the volumetric flask at the end of the preparation?2. Why is distilled water used in this experiment rather than tap water?


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3. What is the concentration of 1.60 g of Na2CO3 in 200 cm3 solution?

experiment 2 preparation of solution

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