BASIC LABORATORY EQUIPMENT

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Chemistry - FALL 2019

LAB EXPERIMENT 1: REACTIONS OF GROUPS III, IV AND V OF CATIONS

OBJECTIVES:

To further understand cation classification. To get introduced to the chemistry laboratory. To learn how to recognize cations of Groups III, IV and V.

INTRODUCTION

Qualitative and Quantitative Chemical Analysis

The fact that certain ions will form hardly soluble precipitates of specific color when reacting under controlled conditions is used to identify those ions. For example, Ag+ cation will form white AgCl precipitate if HCl, NaCl or any other Cl --containing electrolyte is added to the solution. In other words, we have used qualitative chemical analyses to identify certain substance (qualitative relates to the property and type of substance). Qualitative chemical analysis usually refers to the systematic procedure of proving the presence (or absence) of a substance, usually an ion.

Another important thing in chemistry is to determine the amount of substance present in a sample. In order to do this, quantitative chemical analysis is used (quantity is the amount). It is important to note that qualitative analysis has to precede quantitative, as is it first necessary to determine the type of substance and then its amount.

Flame Tests

Flame test is another type of qualitative analysis. It was noted that the salts of some elements belonging to the Group I and Group II of the periodic table (not Group I and Group II cations) color the flame in a specific way. If an inert platinum wire is immersed in a concentrated solution of these salts and then burned in flame, that flame will get characteristic color. For example, Ba gives yellowish-green color, Ca gives orange-red and Sr carmine red color. This is another type of test which will be used in today’s lab.

This phenomenon happens as a consequence of the fact that when a particle absorbs light or any other form of energy, it gets excited. In other words, if a substance is heated, enlightened or gets exposed to mechanical energy, its own energy level gets higher. An example is (the only)

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hydrogen electron. In its unexcited state, it is described by four quantum numbers: n=1, l=0, m=0 and s=1/2. If an H atom absorbs enough energy to enable passage of its electron to a higher energy level, it will take up one of four possible orbitals available at the higher level (2s, 2px, 2py

or 2pz). If energy input was even higher, it would pass to energy level 3 (n=3) and take up one of nine possible orbitals. If energy input was high enough, electron will get free from nuclear attraction force and will leave an atom ionizing it (turning it into cation).

If energy absorption does not cause ionization, excitation state is unstable and will not last for long time period, since an atom always tends to get stabilized by releasing excess energy. This energy is released through light emission and released light wavelength corresponds to atomic energy levels. If the wavelength belongs to the visible spectrum, it will be visible to the naked eye. Since excitation energy of Group I and some Group II elements from the periodic table is relatively low, as these atoms contain one or two electrons, light emission of these elements belongs to the visible spectrum. Different flame coloration primarily depends on two factors; the number of valence electrons and total number of electrons.

Group III Cations

The members of Group III are the following cations: Fe2+, Fe3+, Al3+ and Cr3+. These cations can be precipitated as hydroxides in the presence of ammonia. Therefore, their group reagent is NH4OH. This group will be tested in today’s lab using FeCl3 (iron(III) chloride) as a source of Fe3+ cations.

Group IV Cations

The following cations belong to this group: Mn2+, Ni2+, Co2+ and Zn2+. They are usually precipitated as sulfides using (NH4)2S as a group reagent. ZnCl2 (zinc chloride) will be used as a source of Zn2+ ions to test Group IV cations reactions.

Group V Cations

Group V cations are Ba2+, Sr2+ and Ca2+. These ions form soluble sulfides and insoluble carbonates in neutral and alkaline solutions. Group reagent is (NH4)2CO3. We will use BaCl2

(barium chloride) as a source of Ba2+ ions to test the reactions of Group V cations. Additionally, SrCO3 (strontium carbonate) and CaCO3 (calcium carbonate) will be used for flame test.

Group VI Cations

Group VI cations are: Mg2+, K+, Na+ and NH4+. These cations cannot be precipitated with any

group reagent mentioned for the previous five groups.

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SAFETY MEASURES

H2SO4 is a strong acid and has to be handled in chemical hood. NaOH is a strong base and is a corrosive substance. NH4OH and (NH4)2S are very hazardous in the case of skin contact (corrosive and irritant), eye contact (irritant) or ingestion. They may cause damage to mucous membranes and respiratory tract. Handle carefully in the chemical hood. All chemicals are to be handled with care and according to assistant’s instructions. Wearing protective clothes (lab coat and gloves) is mandatory throughout whole exercise. In the case of spills, inform your instructor and clean carefully. In the case of skin or eye contact, immediately inform your instructor and wash with a plenty of water.

MATERIALS AND METHODS

Chemicals:

Iron(III) chloride – FeCl3

Ammonium hydroxide – HN4OH Potassium ferrocyanide – K4[Fe(CN)6] Sodium hydroxide - NaOH Ammonium sulfide - (NH4)2S Sodium hydrogen phosphate – Na2HPO4

Zinc chloride – ZnCl2

Barium chloride – BaCl2

Ammonium carbonate – (NH4)2CO3

Sulfuric acid – H2SO4

Potassium chromate – K2CrO4

Strontium carbonate – SrCO3

Calcium carbonate – CaCO3

Lab equipment:

Test tubes Test tube rack Droppers Chemical hood Watch glass

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Inoculating loop Lab burner

Procedure:

Obtain 0.1 M solutions of compounds to be tested from your assistant. During this exercise, you will be using 1 ml of reagent per reaction. Use separate dropper for every reagent. Note that NH4OH, (NH4)2S and H2SO4 are available in chemical hood.

Take FeCl3 solution and put 1 ml in each of five test tubes. Fe3+ ion will be tested by the addition of the following reagents: NH4OH, K4[Fe(CN)6], NaOH, (NH4)2S and Na2HPO4.

Observe the reaction outcome and record observations on the report sheet attached to this handout.

Take ZnCl2 solution and put 1 ml into each of three test tubes. Zn2+ ion will be tested on the following substances: NaOH, (NH4)2S and K4[Fe(CN)6]. Record your observations.

Take BaCl2 and place 1 ml of this reagent in four test tubes. Ba2+ ion will be tested using (NH4)2CO3, H2SO4, Na2HPO4 and K2CrO4. Record your observations.

Perform flame tests for Ba2+, Sr2+ and Ca2+ cations according to assistant’s instructions. Note the color of each flame on the report sheet.

REPORT SHEET

PRE-LAB QUESTIONS

1. Differentiate between qualitative and quantitative chemical analysis.

2. What is the goal of flame test?

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3. What is the common property of all Group V cations?

4. What is the only non-metal cation mentioned in labs so far.

EXPERIMENT RESULTS

Group III Cations: Reactions of Fe3+

Reaction with: Precipitating compound Precipitate appearanceNH4OH

K4[Fe(CN)6]

NaOH

(NH4)2S

Na2HPO4

Group IV Cations: Reactions of Zn2+

Reaction with: Precipitating compound Precipitate appearanceNaOH

(NH4)2S

K4[Fe(CN)6]

Group V Cations: Reactions of Ba2+

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Reaction with: Precipitating compound Precipitate appearance(NH4)2CO3

H2SO4

Na2HPO4

K2CrO4

Group V cations: Flame tests

Cation Flame colorBa2+

Sr2+

Ca2+

POST-LAB QUESTIONS

1. Write molecular, ionic and net ionic equation for the following reactions of Fe3+ ion.

Reaction with NH4OHMolecular:

Ionic:

Net ionic:

Reaction with K4[Fe(CN)6]Molecular:

Ionic:

Net ionic:

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Reaction with Na2HPO4

Molecular:

Ionic:

Net ionic:

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Chemistry - FALL 2019

LAB EXPERIMENT 2: pH VALUE (CALCULATIONS AND EXPERIMENTAL DETERMINATION)

OBJECTIVES:

To get familiar with the concept of pH in chemistry. To learn how to calculate pH of a solution. To determine pH experimentally using indicator strips and pH meter.

INTRODUCTION

Acids and Bases

When talking about the concept of pH value, we usually think of strong acids and bases with toxic and corrosive nature. However, the majority of acids and bases are weak. For example, Vitamin B and aspirin are weak acids, while caffeine, nicotine and indigo are weak bases.

To decide if an acid or a base is strong or weak, one should consider how well it dissociates (ionizes) in water. For example, any acid HA will react with water in the following way:

HA(aq) + H2O(l) → H3O+(aq) + A-

(aq)

If an acid is a stronger protein donor than hydronium ion (H3O+), it will give its proton to water and dissociate completely. Such as acid is considered to be strong. On the other hand, weak acids are weaker proton donors than hydronium ion, which means that a reaction between a weak acid and a water molecule is reversible; acid HA will donate its proton to water to form H 3O+, but H3O+ will donate its proton to A- to form HA at the same time.

If a substance HA is a weaker proton donor than H2O, it will receive a proton from water, as in the following reaction:

HA(aq) + H2O(l) → H2A+(aq) + OH-

(aq)

Such compounds are termed strong bases. These bases are removing a proton from water and forming OH- (hydroxide) ion, therefore completely ionizing in water.

The following are the general rules for classification of acids and bases:

1. Any protein donor stronger than H3O+ is a strong acid in water.

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2. If a substance is a protein donor of strength between H3O+ and H2O, it is a weak acid.3. Any protein acceptor stronger than H2O (weaker protein donor) is a weak base.4. Any protein acceptor stronger than OH- is a strong base.

Therefore, the concentration of H3O+ and OH- ions is a measure of how strong acids and bases are.

pH Value

Water is an amphoteric substance, that is, it can act both as an acid and a base and is capable of self-ionization, which is shown in the following reaction:

H2O(l) + H2O(l) → H3O+(aq) + OH-

(aq)

At 25 C, only two out of 10⁰ 9 water molecules self-ionize. The product of H3O+ and OH- is the ionic product of water, Kw, which is 1.0 x 10-14 at 25 C:⁰

[H3O+][OH-] = 1.0 x 10-14

[H3O+] = [OH-] = 1.0 x 10-7

If an acid is added to this solution, hydronium ion concentration goes above 1.0 x 10-7, while hydroxide ion concentration decreases, but never reaches zero. If base is added, OH-

concentration goes above 1.0 x 10-7, while H3O+ concentration decreases, but never reaches zero.

A good way of presenting such small concentrations of these two ions is pH value scale. pH is a negative logarithm of hydronium ion concentration and is a dimensionless unit:

pH = -log[H3O+]

On the other hand, H3O+ concentration can be calculated if pH of a solution is known:

[H3O+] = 10-pH mol/l

pOH is a negative logarithm of hydroxide ion concentration:

pOH = -log[OH-]

[OH-] = 10-pOH mol/l

pKw is a negative logarithm of ionic product of water:

pKw = -logKw = -log(1.0 x 10-14) = 14

pH + pOH = pKw

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pH + pOH = 14

Figure 3: pH value chart.

pH Calculations (Examples)

1. pH of a solution is 6.6. Calculate the concentration of H+ and OH- ions. What is pOH of that solution?

[H+] = 10-pH

[H+] = 10-6.6 = 2.5 x 10-7 M

[OH-] = Kw / [H+]

[OH-] = 1.0 x 10-14 / 2.5 x 10-7 = 0.4 x 10-7 = 4 x 10-8 M

pOH = 14 – pH = 14 – 6.6 = 7.4

2. What is the pH and OH- concentration in a solution of pOH = 1?

pH = 14 – pOH = 14 – 1 = 13

[OH-] = 10-pOH = 10-1 = 0.1 M

Measuring pH Value

pH value can be measured in different ways. Today, we will use two methods:

1. Universal pH indicator strips are using different color combinations to show pH of a solution.

2. pH meters are giving the most accurate measurements. They are using electric potential in a glass electrode whose potential depends on hydronium ion concentration in a

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solution. The result is shown on a display. When used, pH meter should first be calibrated with one or two buffers of known pH value.

SAFETY MEASURES

All acids have characteristic unpleasant odors which is why they should be prepared in chemical hood. Strong acids and bases are corrosive substances. Although they are available as diluted solutions, it is obligatory to wear lab coat and protective gloves. Any spills should be immediately reported and carefully cleaned. In case of skin or eye contact, inform you assistant immediately.

MATERIALS AND METHODS

Chemicals:

100 mM HCl 1 mM HCl 100 mM CH3COOH 1 mM CH3COOH 100 mM NaOH 1 mM NaOH 100 mM Na2HPO4

1 mM Na2HPO4

100 mM KCl 1 mM KCl

Lab equipment:

Erlenmeyer flasks pH indicator strips pH meter.

Procedure:

Necessary solutions of HCl (hydrochloric acid), CH3COOH (ethanoic or acetic acid), NaOH (sodium hydroxide), Na2HPO4 (sodium hydrogen phosphate) and KCl (potassium chloride) are available in the lab.

Measure pH of every solution using pH indicator strips. Record values on the report sheet.

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Measure pH of every solution using pH meter. Record values on the report sheet. Obtain household products available in the laboratory. Measure their pH using indicator

strips. Record pH values and acid/base nature of those products on the report sheet.

REPORT SHEET

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PRE-LAB QUESTIONS

1. Differentiate between an acid and a base.

2. Calculate the pH and pOH of 1.2 x 10-3 M HCl solution.

3. Calculate pH, pOH and [OH-] of 0.1 M HNO3 solution.

4. If a solution X has pH = 5, which of the following is true:a. Solution X is neutral.b. H3O+ ion concentration is higher than OH- concentration.c. OH- ion concentration is higher than H3O+ concentration.

EXPERIMENT RESULTS

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Table 6.1: pH values of acid, base and salt solutions.

Solution pH by indicator strips

pH by pH meter Type of solution

100 mM HCl1 mM HCl100 mM CH3COOH1 mM CH3COOH100 mM NaOH1 mM NaOH100 mM Na2HPO4

1 mM Na2HPO4

100 mM KCl1 mM KCl

Table 6.2: pH values of common household products.

Product pH by indicator strips Acid/base/neutralApple juiceLiquid soapClothes detergentTable saltSugar

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Chemistry - FALL 2019

LAB EXPERIMENT 3: MAKING BRASS COINS

Chemicals:

20 mL 10 % Sodium hydroxide 2 spoon tips Zinc powder Hydrochloric acid Ethanol

Equipment:

Beakers Tongs Tripod Bunsen burner Glass pointer for mixing Copper coins

Background

Zinc coats itself with a very thin but hard oxide layer. It has to be treated in alkaline environment so that the Zinc oxide can go into the solution.

ZnO + H2O + 2 OHˉ -> [Zn(OH)4] 2 ˉ

The zinc powder is coated on the surface with the zinc oxide (ZnO). This oxide goes in alkaline medium as Tetrahydroxozincat. The released zinc atoms together with the copper atoms of the coin produce brass.

Zn + Cu -> ZnCu

The heating speeds up brass formation.

Protocol

Copper coin must be clean (put it in the hydrochloric acid and later on in the alcohol. After that clean it under tap water).

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1. Place the clean copper coin in beaker and soak it with 20% sodium hydroxide (Attention: evaporates!) and 2 spoon tips of Zinc powder.

2. Put the beaker on Tripod over the Bunsen burner. Heat it up with mixing until boiling.3. Turn off the Bunsen burner and let the coin sit in the mixture in the beaker for some time.4. Take the coin with the tongs and rinse it longer under tap water.5. Turn on the Bunsen burner. Heat up the coin (hold it with the tongs only on the edge). Do

not bring it to glow phase. The coin should be “gold” (brass).

Disposal:

Put the Zinc solution though the filter paper. Collected Zinc powder can be reused again.

PRE-LAB QUESTIONS

1. Differentiate between metals and nonmetals.

3. Explain the formation of Zinc oxide.

POST-LAB ASSIGNMENT

Explain if the Zinc powder is toxic and bring the arguments for it.

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Chemistry - FALL 2019

LAB EXPERIMENT 4: AMYLASE IN HONEY

Chemicals:

Lugol solution soluble starch honey

Equipment:

Waterbath Erlenmayer flasks

Background

Bees produce enzyme amylase which is responsible for breaking of bonds in the starch. This enzyme can be found in the honey during production process.

Starch has the ability to react with Iodine from Lugol solution. During this reaction it makes colorated complex. However, this reaction is not possible with fake honey since it is made from crystal sugar. Iodine forms a blue to black complex with starch, but does not react with glucose. If iodine is added to a glucose solution, the only color seen is the red or yellow color of the iodine

Protocol

Take two honey samples: one which is real honey and the second one which is fake honey. Add soluble starch in it and heat it in water bath at 35-40 °C for one hour with mixing from time to time for better solving.

The real honey is able to break the starch. The fake honey does not have amylase so the starch will stay intact.

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After one hour add Lugol solution to both probes. The probe which is blue colored is real honey and the one which changes the color to red/orange (color of Lugol solution) is fake honey.

PRE-LAB QUESTIONS:

1. Explain the Lugol solution (how to make it and its purpose).

2. Differentiate between monosaccharides, polysaccharides and oligosaccharadies.

3. Explain the purpose of starch in plants

POST-LAB ASSIGNEMENT:

1. Explain the chemical background of color changing between real and fake honey (short essay).

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Chemistry - FALL 2019

LAB EXPERIMENT 5: SAPONIFICATION

!!!SAFETY!!! Be sure to exercise caution when dispensing the 9 M NaOH. If the chemical comes into contact with your skin, immediately rinse with water for a minimum of fifteen minutes and notify your instructor.Personal Protective Equipment (PPE) required: safety goggles, lab coat, closed-toe shoes

Chemicals:

Warm olive/coconut oil (preheated by instructor)Food coloring9 M sodium hydroxide solutionassorted fragrances stearic acid

Equipment:

Tall 250 mL beaker Plastic stirring rodsGlass pipettesPipette bulbs

Background

Making soap was a long and arduous process. First, the fat had to be rendered (melted and filtered). Then, potash solution was added. Since water and oil do not mix, this mixture had to be continuously stirred and heated sufficiently to keep the fat melted. Slowly, a chemical reaction called saponification would take place between the fat and the hydroxide which resulted in a liquid soap. When the fat and water no longer separated, the mixture was allowed to cool. At this point salt, such as sodium chloride, was added to separate the soap from the excess water. The soap came to the top, was skimmed off, and placed in wooden molds to cure. It was aged many months to allow the reaction to run to completion.

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All soap is made from fats and oils, mixed with alkaline (basic) solutions. There are many kinds of fats and oils, both animal and vegetable. Fats are usually solid at room temperature, but many oils are liquid at room temperature. Liquid cooking oils originate from corn, peanuts, olives, soybeans, and many other plants. For making soap, all different types of fats and oils can be used – anything from lard to exotic tropical plant oils.Saponification reaction: Fat + Lye -> Soap + GlycerolProtocol

1. Your instructor has a beaker of olive oil, preheated to 35°C, at the front bench. Pour 10 ml of the warm oil into a tall 250 mL beaker.

2. Prior to beginning the reaction, choose your fragrance. You may choose one of the following: holiday candy, island coconut, yuzu, energy, lavender, white tea & ginger, fresh cut grass, plumeria, lilac, oatmeal milk & honey, sandalwood, relaxing, cedarwood, cinnamon, amyris, vanilla.

3. Add 1-2 drops of desired fragrance, using the pipet provided at front bench; do not mix fragrances.

4. Add 3 ml of 9 M sodium hydroxide solution to the beaker. This is approximately two full dropper squirts.

5. Use the plastic stirring rod to mix. You must stir for 20-45 minutes; you may choose to take turns with your lab partner. The mixture will slowly become smoother and more opaque; it should thicken to a pudding-like consistency.

6. After approval by your instructor, add 2-3 drops of desired food coloring. Stir.7. Add a dash (approximately 1/8 teaspoon) of stearic acid. This will serve as a hardener for

the liquid soap. Stir.8. Pour into chosen mold shape. Label with your names and lab section number.9. After pouring into the mold, the process will continue on its own. The soap will heat up

and liquefy again, then cool off slowly, harden and dry. So, the soap must be left undisturbed for at least 12 hours. You will pick up your finished soap in lab next week.

Report

Experimental ObservationsYou may make observations after the soap has dried; it will be returned in lab section or lecture.

1. Does it smell like any soap that you have used?2. Wash your hands with your soap. Does it lather like regular soap?3. Does it clean your hands as well as regular soap? Explain.

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Now rinse your hands thoroughly just in case your soap contains any unreacted sodium hydroxide.

PRE-LAB QUESTIONS:

1. Differentiate between saturated and unsaturated fatty acids

2. What is the purpose of sodium hydroxide in the saponification process?

POST-LAB ASSIGNMENTS:

1. Describe the lye types that can be used in saponification process (short essay).

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