Sdhaliwal Lab Book

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Sukhkaran Dhaliwal’s Chemistry 12 Lab Book Course: SCH4U Teacher: Mr. J. Linzel

2008/2009

MACLACHLAN COLLEGE

Sukhkaran Dhaliwal

Chemistry 12 Lab Book

2008/2009

Table of Contents (Click on the lab you want go to and it will take you directly there. While viewing the lab, click on its title to go back to the table of contents)

Page No.

Lab One - Determining the Chemical Formula for a Copper Chloride Hydrate Compound .............................................................. 3

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Chemistry 12 Lab Book

2008/2009

Determining the Chemical Formula for a Copper Chloride Hydrate Compound Introduction The mole is essentially a counting unit and is the SI base unit that measures an amount of substance. The substances being measured are typically molecules but may also be atoms, ions, atomic particles, etc. The number of entities of one mole (1 mol) is Avogadro's number, 6.02x1023. This means that one mole of hydrogen and one mole of oxygen will both have 6.02x1023 atoms of their respective element. There is a fundamental relationship that encompasses the number of moles, mass, and molar mass of a substance. It is as follows can be rearranged in various ways to solve for different variables:

n = number of moles m = mass of substance Mr = molar mass of substance The quantitative relationship among reactants and products is called stoichiometry. In chemistry, it is often required to calculate quantities of reactants and products. Stoichiometric calculations are based on the principle that atoms are conserved. This is called the law of conservation of mass. It states that mass is neither created nor destroyed. Simply, the mass of the products in a chemical reaction is always equal to the mass of the reactants due to the law of conservation of mass. Balancing a chemical equation is often required to satisfy the law of conservation of mass. The combustion of methane (CH4) can be used as an example. CH4 + O2

CO2 + H2O

after balancing

CH4 + 2O2

CO2 + 2H2O

If those highlighted coefficients were not there, the original reaction would have lost two atoms of hydrogen and gained one atom of oxygen. Balancing equations are very important in stoichiometry because not only does it follow the laws of conservation of mass, it also reveals to the chemist the number of moles needed to create such a reaction. This also shows the mole ratio of each element to another in the reaction. Physical properties of a substance are characteristics that do not change the chemical nature of matter. They can be observed or measured without changing the composition of matter. Subsequently, 3

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Chemistry 12 Lab Book

2008/2009

chemical properties of a substance are characteristics that change the chemical nature of matter. Some examples of physical properties are appearance, texture, color, odour, melting point, boiling point, density, solubility, and polarity. Some examples of chemical properties include electronegativity, ionization potential, pH balance, reactivity against other chemical substances, heat of combustion, enthalpy of formation, toxicity, chemical stability, flammability, preferred oxidation state(s), coordination number, and malleability. It is important to know in this experiment when determining the empirical formula, the values being calculated will follow the skeleton of: CuxCly · zH2O. In this case x, y, and z are integers which, when known, establish the formula of the compound. When expressing the formula of a compound like this one, where water molecules remain intact within the compound, it is imperative that the formula of the whole H2O be retained. It will just be a coefficient determining the number of water molecules copper chloride combines with.

Safety Precautions Since it was unknown which form of copper chloride was used, the MSDS information for both copper (I) chloride and copper (II) chloride are provided.

Copper (I) Chloride:

Copper (I) Chloride (CuCl) is harmful when swallowed and should not common in contact with eyes, skin, or clothing. It should be kept in a tightly closed container. Hands should also be washed thoroughly after handling. Copper (I) Chloride may cause irritation to the eyes, skin, and respiratory tract. It may also cause gastrointestinal discomfort. The one precaution to be taken when handling or storing Copper (I) Chloride is to keep the container it is in tight closed. It is also suitable for any general chemical storage area. This compound should be disposed in accordance with all applicable federal, state, and local regulations.

Copper (II) Chloride:

Copper (II) Chloride (CuCl2) is harmful when swallowed and should not common in contact with eyes, skin, or clothing. It should be kept in a tightly closed container. Hands should also be washed thoroughly after handling. Copper (II) Chloride may cause irritation to the eyes, skin, and respiratory tract. It may also cause gastrointestinal discomfort. The one precaution to be taken when handling or storing Copper (II) Chloride is to keep the container it is in tight closed. It is also suitable for any general chemical storage area. This compound should be disposed in accordance with all applicable federal, state, and local regulations.

Ethanol:

Exposure to ethanol 95% (C2H5OH) in concentrations below 1000 ppm usually produces no signs of intoxication. Exposure to concentrations over 1000 ppm may cause headaches, irritation of the eyes, nose, and throat, and if continued for an hour, drowsiness and lassitude, loss of appetite and inability to concentrate. This material should be kept in an area suitable for the storage of 4

Sukhkaran Dhaliwal

Chemistry 12 Lab Book

2008/2009

flammable liquids. Container should be bonded and grounded when transferring ethanol. Oxidizing materials and strong acids should be kept away from it. As well, splash-proof chemical safety goggles and rubber gloves should be work at all times during the cleanup process. This compound should be disposed in accordance with all applicable federal, state, and local regulations.

Hydrochloric Acid:

Hydrochloric acid (HCl) causes severe burns and may be fatal if inhaled or swallowed. The vapor is extremely irritating. Hydrochloric acid may cause damage to the respiratory passages and lungs, irritation to the eyes, skin, respiratory tract, and can cause gastrointestinal discomfort. This compound should be kept in a container that is tightly closed, in a cool, well ventilated area away from incompatible materials. Hydrochloric acid should be disposed in accordance with all applicable federal, state, and local regulations.

When carrying out this experiment, goggles and aprons must be worn at all times. Rubber gloves should also be worn when handling certain chemicals. Long hair should be tied back because an open flame is being used.

Aim To review a large a number of chemistry 11 techniques and concepts including: molar stoichiometry, writing chemical equations, balancing, writing formula, and determining empirical formula.

Purpose Determine the formula for a copper chloride hydrate compound. Include the moles of the hydrate.

Method 1. Massed a clean, dry crucible, without a cover, accurately on the analytical balance and recorded the mass (in grams) in the data table. 2. Placed 1.00 gram of unknown hydrated copper chloride in the crucible. Broke up any sizable crystal particles by pressing them against the wall of the crucible. Then massed the crucible and its contents accurately. Recorded the results in the data table. 3. Placed the uncovered crucible on the clay triangle supported by an iron ring. 4. Lit the Bunsen burner away from the crucible and then adjusted the flame so it was 5-10cm away from the bottom of the crucible. See Figure 1. 5. Gently heated the crucible so that all the green crystals completely changed to a brown colour. Heated the sample to a constant mass. See Figure 1. 6. Allowed the sample to cool for 10-15 minutes before massing it. Once cooled, recorded the mass of the crucible (in grams) in the data table. The mass of the evaporated water was found 5

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Chemistry 12 Lab Book

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through simple subtraction. The lid of the crucible was put on while being cooled to minimize rehydration, but ensured the lid was off when massing. Transferred the brown crystals (anhydrous copper chloride) in the crucible to a 50 mL beaker. Rinsed out the crucible with 16 mL of distilled water. The anhydrous copper chloride dissolved in the distilled water. Swirled the beaker around to completely dissolve the crystals. Placed a strip of aluminum wire of 0.25 grams into the beaker so that it was completely immersed. Recorded qualitative observations of what occurred between the aluminum wire and solution with the copper chloride in the data table. Added a few drops of 6M of HCl to dissolve any insoluble aluminum salts and to clear up the solution. This also helped to wash the metal deposits off the aluminum wire. Set up a gravity filter by folding a piece of filter paper conically and placing it in a funnel, which was then placed inside a beaker. Allowed the solution to filter through into the beaker, leaving only and unknown mass of copper in the filter paper. Placed a few drops of 95% ethanol into the gravity filter to ensure that only copper was left in the filter. Removed the filter paper with the copper from the funnel and placed it on a glass disk inside the incubator to dry for two days. Massed the filter paper with the copper. Subtracted the mass of the filter paper and glass disk from the total mass to obtain the mass of the copper in grams.

Crucible (copper chloride hydrate) Iron ring

Retort stand

Flame

Bunsen burner

Figure 1 – Diagram of Apparatus During Dehydration

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Sukhkaran Dhaliwal

Chemistry 12 Lab Book

2008/2009

Materials Table of Materials and Equipment Materials and Equipment

Amount

Hydrochloric acid (HCl) 95% Ethanol (C2H5OH) Copper chloride hydrate Retort stand Crucible Analytical balance Clay triangle Distilled water Goggles Beaker Glass funnel Filter paper Pipette Aluminum wire Bunsen burner

6M 10 mL 1.00 g 1 1 1 1 16 mL 1 50 mL 1 1 1 0.25 g 1

Table 1 – Table of Materials and Equipment

Data Collection Quantitative Table of Various Masses and Mole Values Element/Compound

Mass Before Experiment

Copper

Unknown

Mass After Dehydrating Water

Final Mass

Number of Moles*

0.38 g

1

0.41 g

2

0.21 g

2

Chemical and Empirical Formula*

0.79 g (combined) Chloride

Unknown

Water

Unknown

0.21 g

Table 2 – Table of Masses and Calculated Empirical Formula (quantitative)

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CuCl2 · 2H2O

* Calculations shown in the section below

Sukhkaran Dhaliwal

Chemistry 12 Lab Book

2008/2009

The values for Table 2 were calculated through simple subtraction. The mass of the water was calculated by massing the crucible before and after dehydration and subtracting the two values. The mass of copper was calculated through gravity filtering it through filter paper and the mass of the filter paper was subtracted to determine the mass. Therefore, chlorine was determined through adding the masses of copper and water and then subtracting it from the initial mass, which was 1.00g.

Qualitative Table of Observations During Different Processes Process Dehydrating H2O Rehydrating Anhydrous Copper Chloride with Distilled Water

Adding an Aluminum Strip to the Solution

Observations When dehydrating the water from the copper chloride, it started to turn into brown crystals and there were less and less blue/green crystals visible. This indicated that the copper chloride lacked water and was anhydrous. After all the crystals were brown, the anhydrous was massed three times to ensure it had reached a constant mass. Rehydrating the anhydrous copper chloride was essentially the reverse of dehydrating it. Since it was a brown colour, it became blue/green crystals when placed in distilled water indicating that it was hydrated. As soon as the aluminum strip was placed in the copper chloride hydrate water solution, it began to react. The solution started to bubble and gas was produced. This reaction also released quite a bit of heat. It can be said that this was an exothermic reaction. The copper chloride hydrate also reacted with the aluminum strip producing a single displacement reaction as demonstrated below: 3CuCl2 + 2Al

Removing Copper from Aluminum Strip with Hydrochloric Acid (HCl)

2AlCl3 + 3Cu

Hydrochloric acid was used to remove any remnant copper that was still on the aluminum foil. As the hydrochloric acid was dropped on the aluminum strip, it reacted immediately and was vigorous.

Table 3 – Qualitative Table of Observations

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Chemistry 12 Lab Book

Data Processing and Analysis Mole Calculations

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Chemistry 12 Lab Book

Calculating Percentage Error

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Sukhkaran Dhaliwal

Chemistry 12 Lab Book

2008/2009

The evidence and calculations above demonstrate a very concise argument that shows the empirical and chemical formula of the unknown copper chloride hydrate was:

CuCl2 · 2H2O or Copper (II) Chloride Dihydrate From this chemical formula, it can be deduced that copper, chlorine, and water combine in a 1:2:2 ratio. It also shows that the copper (II) chloride and water combine in a 1:2 ratio. This means that for every mole copper (II) chloride, there will be two times the amount moles of water. More specifically, there was approximately 0.0060 moles of copper, 0.012 moles of chlorine, and 0.012 moles of water. To verify the results, research on the different oxidation states of copper and the different types of copper chloride was carried out. The main oxidation states of copper are +1 and +2. The oxidation state of chlorine is -1. This means that it could have been CuCl or CuCl2 in the compound and would consequently affect the number moles of water in the compound as well. Although CuCl is insoluble in water, it dissolved in aqueous solutions containing suitable donor molecules. It forms complexes with halide ions, but no such ions were present. If CuCl was placed into the distilled water, it wouldn’t dissolve nor would it change colour, but if CuCl2 was placed into the distilled water, it would dissociate because it was in aqueous solution. With this knowledge, the notion of CuCl being present in the copper chloride hydrate compound was eliminated and that it could only have been CuCl2 that was present. The calculations were rather simplistic and didn’t require many steps because two of the three unknown variables (mass and molar of mass of substances) were given. The masses of the different substances were found through the experiment and simple subtraction. The molar masses of these substances were determined by looking at the periodic table. The only unknown value was then the amount of moles of each substance. The one relationship that uses the two known variables to solve for the amount of moles is: This formula was applied to copper, chlorine, and water to establish that amount of moles of each that was in the compound. After this, each value was divided by the lowest of the mole values so that it would produce a whole number, which gave the molar ratio. The values were 1 for copper and 2 respectively for chlorine and water. Therefore, copper, chlorine, and water combined in a 1:2:2 ratio in the copper (II) chloride dihydrate compound. To further support the results attained, the percentage error was calculated. The formula is as follows: In reference to the calculations in the above section, the theoretical yield of copper was calculated to be approximately 0.37g and the actual yield was 0.38g. When those values are substituted into the equation, the percentage error equals to 1.9%, which shows that experiment was conducted very successfully and the results obtained were highly accurate. The very low percentage error is further support that the formula for the copper chloride hydrate compound was precisely predicted. Lastly, to prove that formula was correct, another simple mole calculation can be used to demonstrate the accuracy of the formula. Since the mole ratio for CuCl2 and H2O is 1:2, therefore if the amount of moles were multiplied by two, the results should be approximately accurate to the actual mole value for H2O.

The number of moles calculated is approximately exact to the number of moles calculated in when determining the chemical formula. This is further proof that chemical formula for the unknown copper chloride hydrate compound was: CuCl2 · 2H2O

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Sukhkaran Dhaliwal

Chemistry 12 Lab Book

Cook Book

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2008/2009