Experiment 2 Preparation of Solution

THE PHILIPPINE WOMEN’S UNIVERSITY  Analytical  Analytical Chemistry Laboratory Activity/Experiment

Group No. : _________  Section/Room : _________  Date Performed: _________  Experiment No. 2 Preparation of Solutions

Preparation and Performance Rating A. Before the Activity (5 pts) Attendance ____  (10 pts) Lab. Gown/Apron ____  (5 pts) Lab Manual Manual ____  B. During the Activity (10 pts) Organization/Orderliness____  (10 pts) Cooperation/Behavior ____  (10 (10 pts) pts) Know Knowle ledg dgee (Qui (Quiz) z) ____  ____  (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) Total Overall All Total

Introduction Solutions are most commonly used reagents in the laboratory. When a substance called solute is dissolved in another substance called the solvent, a solution is formed. Vinegar is a solution of acetic acid (the solute) in water (the solvent). The concentration of a solution represents the amount of solute dissolved in a unit amount of solvent or of solution. Concentration is usually expressed in one of 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 preparing solutions of liquids. Volume percent (%v/v) is defined as as volume of solute divided by the volume of the solution multiplied by 100. Molarity( Molarity(M) M) is probably the most commonly used unit of concentration. It is the number of moles of solute per liter of solution. Molality (m) is the number of moles of  solute per kilogram of solvent. Normality (N) is equal to the gram equivalent weight  of a solute per liter of solution. A gram equivalent weight or equivalent is a measure of the reactive capacity of 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 following a dilution dilution by applying this equation: MiVi = Mf Vf 

where M is molarity, V is volume, and the subscripts i and f refer to the initial and final values.  Another way of expressing  Another expressing the the concentration concentration of of solutions solutions is mole fraction. fraction. This is the number of  of  moles of a compound divided by the total number of moles of all chemical species in the solution. Objective:  At the end end of the experimen experiment, t, the student student shall shall be able to: 1. Prep Prepare are solutio solutions ns of differ different ent conce concentra ntration tions; s; 2. app apply ly the techn techniqu iques es in the the dilution dilution of of solution solutions; s; and 3. Compute the mass of solute solute needed needed to prepare a certain certain concentration concentration of the solution. Materials: 2-Volumetric flask (100 mL) measuring pipette (10 mL) Beaker 100 mL

measuring pipette (5 ml) water bath wash bottle

medicine dropper  stirring rod

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Procedure:  A. Solid solute 1. Wash all glassware apparatus with soap and water ; rinse with distilled and allow to dry in an upside down position. 2. Compute for the mass of Sodium hydroxide necessary to prepare 100 mL of a 0.50 M 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 beaker  with about 5 mL of distilled water twice. Pour the washings into the volumetric flask also. 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 process 1. Compute the volume of 18 M Sulfuric acid needed to prepare 100 mL of 3 M H 2SO4. 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 H 2SO4 (#1). Always pour the acid to the water  3. 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 H 2SO4 . 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 of  solute (g)

Volume of  solute (mL)

Volume of  solvent (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?

3. What is the concentration of 1.60 g of Na 2CO3 in 200 cm 3 solution?