inorganic chemistry laboratory experimental report

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HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY Office of International Study Program

Faculty of Chemical Engineering

INORGANIC CHEMISTRY LABORATORY

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CONTENT

UNIT 2: Alkaline Earth Metals (Group IIA) ... 3

UNIT 6: Hydrogen - Oxygen - Sulfur (𝐻2 – 𝑂2 – 𝑆) ... 10

UNIT 8: Copper-Silver- Gold (𝐶𝑢 – – 𝐴𝑔 𝐴𝑢) (GROUP IB) ... 18

UNIT 10: Group VIB (CHROMIUN)... 28

UNIT 12: transition metal Iron-Cobalt-Nickel (𝐹𝑒 − 𝐶𝑜 − 𝑁𝑖) (GROUP VIIIB) ... 33

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UNIT 2: ALKALINE EARTH METALS (GROUP IIA)

I. Experiment determinations:

- The location of the alkalien-earth metals in the periodic table, their electron configuration, oxidation state and chemicals properties.

- Water hardness and method for softening water.

II. Experimental Results:

1. Experiment 1: Observation of the color of alkaline earth metal flame

Produce:

- Dip a clean filter paper into a saturated 𝐶𝑎𝐶𝑙2 - Hold it over the flame

- Observe the color of the flame

- Repeat with saturated solutions of 𝑆𝑟𝐶𝑙2and 𝐵𝑎𝐶𝑙2 Phenomenon of flame’s color:

o 𝐶𝑎𝐶𝑙2: orange-red o 𝑆𝑟𝐶𝑙2: red o 𝐵𝑎𝐶𝑙2: yellow-green

Explanation:

- When absorbing energy from the flame, electrons jump from lower energy level to higher one and then emitted energy in the form of photons to return to their initial states. Each

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different color's flame. Conclusion:

Burning alkaline-earth metal cation (in a compound with a suitable anion) will give specific flame color. In the group IIA, from top to bottom (Ca, Sr, Ba), the flame color will change from red to yellow, which can be understood by the increasing of energy due to the radius is increase, the electrons easily move to a higher energy level.

2. Experiment 2: Reaction of an alkaline earth metal with H O 2

Prepare 2 test tubes adding Observe the state of mixture and reaction at room temperature and the reaction occurs very slowly, the color of solution turns to light pink and s small

amount of gas appears.

- At high temperature, the reaction occurs quicker, the pink color becomes darker and spread throughout the solution, more gas

appeared.

- When 𝑁𝐻4𝐶𝑙 is added, the color of solution fades until it turns to colorless, at the same

- Creation of 𝐻2 gas that escaped air bubbles and 𝑀𝑔(𝑂𝐻)2 that covered the

surface of Mg slows down the reaction.

𝑀𝑔 + 2𝐻2𝑂 → 𝑀𝑔(𝑂𝐻)2+ 𝐻2

- Mg(OH)2 dissolve partly in water, producing OH- that turning

phenolphthalein into pink at the interface between Mg and water.

𝑀𝑔( )𝑂𝐻2⇌𝑀𝑔2++ 2𝑂𝐻− - At high temperature, 𝑀𝑔(𝑂𝐻)2 is more

soluble in water, making the solution color darker. At the same time, the coverage of 𝑀𝑔( )𝑂𝐻2 decreases making the first reaction occur stronger, creating more air bubbles.

- When 𝑁𝐻4𝐶𝑙 is added, it dissolves 𝑀𝑔(𝑂𝐻)2, which released the surface of Mg, making the reaction between Mg and

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time, more gas releases. After that, the solution turns to pink again.

𝐻2𝑂 occurred more stronger and increased the a mount of 𝐻2 air bubbles. 𝑀𝑔(𝑂𝐻)2+ 𝑁𝐻4𝐶𝑙 ⇄ 𝑀𝑔𝐶𝑙2+ 𝑁𝐻3+ 𝐻2𝑂

- At the same time, 𝑀𝑔(𝑂𝐻)2 is dissolved, the equilibrium of reaction is shifted to the backwards direction, which making 𝑂𝐻− decrease therefore phenolphthalein turned back to being colorless. - Pink color reappears due to 𝑁𝐻3 is

produced in the reaction and 𝑂𝐻− from the dissolution of 𝑀𝑔( )𝑂𝐻2.

Conclusion: Alkaline-earth metals react weakly with water at room temperature, but react

strongly when heated or in the presence of suitable catalyst.

3. Experiment 3: Alkaline earth metal hydroxide synthesis 3.1) synthesis and properties of 𝑴𝒈(𝑶𝑯)𝟐

Synthesis 𝑀𝑔(𝑂𝐻)2 from sodium hydroxide and magnesium salt, then centrifuge to get the solid. Decant the liquid and

- The precipitate absolute dissolved making the

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React with 𝑁𝑎𝑂𝐻 - Test tube 3:

React with 𝑁𝐻4𝐶𝑙

- The precipitate dissolved making the colorless solution, the pungent

- Prepare 4 separate test tubes containing 1 mL of 𝐵𝑎2+, 𝑆𝑟2+, 𝐶𝑎2+, 𝑀𝑔2+ 0.5M solutions - Add 0.5 mL of 1M 𝑁𝑎𝑂𝐻 solution to each of test tubes

- Observe the formation of precipitate and compare the precipitate quantity Phenomenon:

- White precipitate created in all test tubes.

- The amount of precipitate increase in order of 𝐵𝑎2+, 𝑆𝑟2+, 𝐶𝑎2+ and 𝑀𝑔2+ Reactions and Explanation:

𝑀𝑔2++ 2𝑂𝐻−⇄𝑀𝑔( )𝑂𝐻2 𝑆𝑟2++ 2𝑂𝐻−⇄ ( )𝑆𝑟𝑂𝐻2 𝐶𝑎2++ 2𝑂𝐻−⇄ ( )𝐶𝑎𝑂𝐻2 𝐵𝑎2++ 2𝑂𝐻−⇄𝐵𝑎 𝑂𝐻( )2

From 𝑀𝑔 𝐵𝑎 to , the atomic radius increases leading to the decrease in the attractive force of nucleus on its valence electrons. Moreover, due to oxygen has a high electronegativity which pulls electrons to itself, making the hydroxyl group highly polar making it easy to be dissolved in water.

Conclusion: Hydroxide of alkaline earth metals can be synthesized by the reaction between

their soluble salt with strong basic hydroxide solution. From 𝑀𝑔 𝐵𝑎 to , the solubility of these hydroxide decreases.

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salts

1) Slowly add 0.5 mL of 2N sulfuric acid to 4 separate test tubes Then centrifuge . the solutions to observe the

- White precipitate but less than others

- The biggest amount of - From 𝑀𝑔 𝐵𝑎 to , the radius of ion

𝑋2+ increases, so the polarizability of it in water and hydrate energy decreases. Moreover, the activation of the cations is larger than lattice energy. From these reasons above, the solubility decreases from 𝑀𝑔 to 𝐵𝑎.

- When adding excess 𝐻2𝑆𝑂4, the concentration of 𝑆𝑂42− increases, making the equilibrium shifts to the forward direction reaction, increasing the amount of precipitate.

Conclusion: The solubility of alkaline earth metals decrease from 𝑀𝑔 𝐵𝑎 to .

5. Experiment 5: Evaluation of water hardness

Produce:

- Extract 10ml hard water by using pipet 10ml into 250ml erlenmeyer flask - Add distilled water in order to obtain around 100ml of volume in total. - Add 5ml buffer solution pH=10, add 4 to 7 drops of ERIO-T indicator color.

- Shake and titrate using 0.02N EDTA solution until the indicator color changes from purple-red to light blue

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Conclusion: The total remaining content of 𝑀𝑔2+ and 𝐶𝑎2+is 14.6 (mN)

6. Experiment 6: Water softening

Conclusion: 𝑋′ < 𝑋 meaning that the amount of 𝑀𝑔2+ and 𝐶𝑎2+ in sample decrease. Water is softened when 𝑁𝑎2𝐶𝑂2 and 𝐶𝑎( )𝑂𝐻2is added.

𝑀𝑔2++ 2𝑂𝐻−⇄𝑀𝑔( )𝑂𝐻2 𝐶𝑎2++𝐶𝑂32−⇄ 𝐶𝑎𝐶𝑂3

III. Questions

1. In reaction 2, explain the role of 𝑵𝑯𝟒𝑪𝒍. Is it compulsory that 𝑵𝑯𝟒𝑪𝒍 be used or are other 𝑵𝑯𝟒 salts also applicable?

𝑁𝐻4𝐶𝑙 is added to react with 𝑀𝑔(𝑂𝐻)2, which covering the surface of 𝑀𝑔. Therefore, it makes the reaction between 𝑀𝑔 and 𝐻2𝑂 occurs more easily.

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𝑀𝑔(𝑂𝐻)2+ 𝑁𝐻4𝐶𝑙 ⇄ 𝑀𝑔𝐶𝑙2+ 𝑁𝐻3+ 𝐻2𝑂

Other 𝑁𝐻4 salts also applicable because 𝐶𝑙− don’t have role in the reaction above. This reaction is basically between 𝑁𝐻4+ and 𝑂𝐻−.

𝑁𝐻4++ 𝑂𝐻−⇄ 𝑁𝐻3+ 𝐻2𝑂

2. Aside from using washing soda (𝑵𝒂𝟐𝑪𝑶𝟑), are there any other methods for softening hard water? Write down the equation for each method.

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UNIT 6: HYDROGEN - OXYGEN - SULFUR

(𝑯

𝟐

– 𝑶 – 𝑺)

𝟐

- Preparation of hydrogen and oxygen gas: by water displacement method. - Chemical properties of hydrogen, oxygen, sulfur:

o Hydrogen: atomic hydrogen is a stronger reducing agent than molecular hydrogen. o Oxygen: oxygen is a strong oxidizing agent, easily oxidizing metals and non-metals

to form oxides. Oxygen also maintains combustion.

o Sulfur: at high temperature, sulfur has strong oxidizing properties.

Experiment Description of interesting experiments and observations.

Explain the phenomenon, writing equation, analysis and conclusion

1. Synthesis of Hydrogen.

- Install the air gathering system.

Introduce five pellets of zinc metal to the test tube prior to adding 5 𝑚𝐿 of concentrated 𝐻𝐶𝑙. Collect the gas produced with a small test tube filled with water upside down in a pot. Igniting the hydrogen gas released at the top of the pipe has

𝑍𝑛 + 2𝐻𝐶𝑙 → 𝐶𝑙𝑍𝑛 2+ 𝐻2↑

Because hydrogen reacts with oxygen mixed in the test tube and in the gas system, there is an explosion. Initially, the amount of oxygen was more, so there was a loud explosion.

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Result:

mMorh’s salt weighed = 12.83g mMorh’s salt theory = 5

2. Experiment 2: Properties of 𝑭𝒆𝟐+ and 𝑭𝒆𝟑+ compounds

+ Tube 2: 𝐻2𝑂2 solution which was previously acidized using

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leftover, the melting cabinet creates a brown soil color that makes the starch turn blue.

2𝐹𝑒3+ + 𝐼 →− 𝐹𝑒2+ + 𝐼2 (charcoal purple) - When KI is excess:

𝐼2 + → 𝐾𝐼𝐾𝐼 3 (brown soil)

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- 𝐹𝑒3+ salt is stable in the air and has oxidation property in acids.

3. Experiment 3: Properties of 𝑪𝒐𝟐+and 𝑵𝒊𝟐+ compounds

- Add 5 drops 𝐶𝑜𝐶𝑙2 and add few drops 2N 𝑁𝑎𝑂𝐻 to 2 test tubes

- The solution’s color is pink. - Blue precipitate appears and changes to the red color

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- Put in 2 test tubes each 5

The color stays unchanged

Air bubbles appear

Precipitate turns gray

Precipitation turns gray and air

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+ Part 1: The precipitate dissolves and creates a yellow

+ Part 1: The precipitate dissolved slightly to create a light pink solution

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- Green precipitate appears.

+ Part 1: The precipitate dissolved to create a pale pink solution

+ Part 2: No phenomenon

𝑁𝑖2+ + 2𝑂𝐻− → 𝑁𝑖(𝑂𝐻)2 ( green)

𝑁𝑖(𝑂𝐻)2+ 𝐻 → + 𝑁𝑖2+ + 2𝐻2𝑂

Before adding HCl and NaOH:

After adding HCl and NaOH:

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- In alkali, hydroxides are more stable and insoluble.

4. Experiment 4: Properties of 𝑪𝒐𝟐+and 𝑵𝒊𝟐+compounds

The color change of 𝑪𝒐𝟐+

- Write letters on filter paper and view the letter color. Dry filter paper by flame.

The Tsugaep reaction of Nickel:

- The letters’s color is pink. Drying by the flames of alcohol lamps. The pink color disappears and the blue purple – color appears instead.

- In the heating process, complex 𝐶𝑜(𝐻2𝑂)62+ loses water to form a smaller complex 𝐶𝑜(𝐻2𝑂)42+ having a blue – purple color.

𝑁𝑖2+ + 2𝑂𝐻− → 𝑁𝑖(𝑂𝐻)2(green)

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- Green precipitate appears then dissolves to creates a dark blue

- The 𝑁𝑖(𝐶4𝐻7𝑁2𝑂2)2 complex has a square shape with weak acidity and basicity in the water or in the diluted NH4OH solution, but it dissolves well in strong acid and base.

Conclusion:

- The complex has a square shape with weak acidity and basicity in the water or in the diluted 𝑁𝐻4𝑂𝐻 solution, but it dissolves well in strong acid and base. Therefore, when replacing 𝑁𝐻4𝑂𝐻 with 𝑁𝑎𝑂𝐻, the enough amount will lead to an appearane of the light red precipitate. On the contrary, adding excess 𝑁𝑎𝑂𝐻 could make the precipitate dissolve immediately. - The Tsugaep reaction is used to calculate and quantify 𝑁𝑖2+ in the solution.

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5. Experiment 5: Properties of 𝑪𝒐𝟐+ and 𝑵𝒊𝟐+ compounds

Pink precipitate appears then dissolves shortly afterwards, create a brown solution above, pink below and blue in the middle. When vigorously shaken, the entire solution turns brown.

The solution turns blue

Blue precipitate appears and create a dark blue solution

𝐶𝑜2++ 2𝑂𝐻−→ (𝑂𝐻)𝐶𝑜 2 (pink) 𝐶𝑜(𝑂𝐻)2+ 6 𝑁𝐻3 →

[𝐶𝑜(𝑁𝐻3)6](𝑂𝐻) (brown) 2 The blue color appears because the concentrated 𝑁𝐻4𝑂𝐻 absorbs water from on

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- 𝑁𝑖(𝑂𝐻)2 and 𝐶𝑜(𝑂𝐻)2 are soluble in 𝑁𝐻3 due to their ablility to form stable complexes.

- Both 𝐶𝑜2+ and 𝑁𝑖2+ are able to form complexes with 𝐶𝑙− and those complexes may change

the color of solution.

III. Questions:

1. How are two-valent and three-valent salts synthesized from Fe metal? Write down the reaction equations.

2. How is double salt different from complex salt?

A mixture of many salts that crystallize at the same time.

A compound.

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force between salt molecules. between the central ions and the ligands. Exist in solid form and dissolve

into constituent species in solution.

Exist In both solid and liquid states and still maintain their identity.

Completely dissociate into its ions in

3. What ions are present in the Morh’s salt solution?

The Morh’s salt solution is 𝐹𝑒𝑆𝑂4(𝑁𝐻4)2𝑆𝑂4. 6𝐻2𝑂.

- After dissolving the Morh’s salt in water, two 𝑁𝐻4+, two 𝑆𝑂42−and one 𝐹𝑒2+ will be produced. To prove that:

- Add concentrated 𝑁𝑎𝑂𝐻 solution and heat gently 𝐹𝑒2+ + 2𝑂𝐻− → 𝐹𝑒(𝑂𝐻)2

4𝐹𝑒(𝑂𝐻)2+ 𝑂 + 2𝐻2 2𝑂 → 4𝐹𝑒(𝑂𝐻)3

- There is a mossy green precipitate that rapidly turns brown in the air The presence of 𝐹𝑒2+. - There is a presence of urine gas The presence of 𝑁𝐻4+

𝑁𝐻4+ +𝑂𝐻− →𝑁𝐻3+ 𝐻2𝑂 - Add 𝐵𝑎𝐶𝑙2 salt solution

𝐵𝑎2+ + 𝑆𝑂42−→ 𝐵𝑎𝑆𝑂4

- A white precipitate is formed that is insoluble in strong acids The presence of 𝑆𝑂42−

4. Explain the procedure for the synthesis of Morh’s salt solution.

Dissolve Fe in dilute 𝐻2𝑆𝑂4 to form 𝐹𝑒2+. The heating speeds up the dissolution reaction and it also makes 𝐻2𝑆𝑂4 become denser, which will oxidize 𝐹𝑒2+ to 𝐹𝑒3+.

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Therefore, it is necessary to regularly add water to dilute H2SO4 to limit 𝐹𝑒3+ formation and keep excess 𝐹𝑒 to convert 𝐹𝑒3+ to 𝐹𝑒2+.

When excess Fe is almost gone, filter to remove impurities. Immediately add solid (𝑁𝐻4 2) 𝑆𝑂4to the becher to collect filtered water and stir well to create two saturated copper salt solutions so that the two salt solutions can crystallize at the same time. (𝑁𝐻4)2𝑆𝑂4 act as a reducing agent that will keep 𝐹𝑒2+: from being oxidized to 𝐹𝑒3+ in the double salt. Soak the becher in cold water for a more favorable crystallization process.

5. What reactions are used to detect the presence of 𝑭𝒆𝟐+ and 𝑭𝒆𝟑+?

For the detection of 𝐹𝑒2+: 𝐹𝑒2+ reacts with potassium ferricyanide will form the turnbull blue precipitate of ferrous ferricyanide.

3𝐹𝑒2+ + 2[𝐹𝑒(𝐶𝑁)6]3− → 𝐹𝑒 𝐹𝑒3[ ( )𝐶𝑁6]2

For detection of Fe : Fe reacts with potassium ferrocyanide to form potassium berlin blue 3+3+ precipitate of ferric ferrocyanide.

4𝐹𝑒3++ 3[𝐹𝑒(𝐶𝑁)6]4−→ 𝐹𝑒4[𝐹𝑒( )𝐶𝑁 ]63

6. What kind of reaction as conducted in the experiment 4b? What is it used for?

The Tsugaep reaction is a complexation reaction of 𝑁𝑖( )𝐼𝐼: nickel dimethylglyoximatein dilute 𝑁𝐻3 solution, used for qualitative and quantitative determination of Ni in solution. 2+

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