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# Decomposition of CuCO3

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• Pages: 4
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• Category: Chemistry

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Cu2O is a red crystalline material, which is produce by the electrolytic or furnace method. CuO is a black powder prepared by the ignition of suitable salts such as carbonate (1)

The mole is the mass of substance that has the same number of particles as atoms in exactly 12g of carbon-12. One mole of any substance contains Avogadroās number 6.02Ć10Ā²Ā³ molĖ1 (2).Avogadro discovered that at room temperature (25Ā°C) and pressure (1 atm), all gases occupy the same volume. 1 mole of any gas will occupy a volume of 24dmĀ³.

CALCULATING THE NEEDED MASS

The best method is to take one of the two equations and try to prove or disprove it. Since equation 2 has only 1 mole of every substance this would be the easiest to work out in terms of ratio. This assumption is made because the equation is āstoichiometricā (3) meaning 1 mole of CuCOŠ· decomposes to exactly 1 mole of CuO and 1 mole of carbon dioxide. However, 24000cmĀ³ would be too much gas to produce in a school lab, as that size of apparatus is not available. Gas syringe will be used but has a maximum of 100cmĀ³, so it would not be sensible to produce 100cmĀ³ of gas because if equation 1 turns out to be correct (which would mean oxygen will also be produced), and there would consequently be more gas. Aiming to produce 75cmĀ³ of gas would leave room for error and the possibility of equation 1 occurring.

Equation 2: CuCOŠ· ā CuO + CO2

If 1 mole of CuCOŠ· produces 24000cmĀ³ of CO2, to produce 75cmĀ³ (for equation 2) we need:

Moles in gas = volume / 24000

= 75 / 24000

Moles in gas = 0.003125 moles

Ratio = CO2 : CuCOŠ·

1 : 1

0.003125 : 0.003125

Moles of CuCOŠ· = 0.003125 moles

R.A.M of CuCOŠ· = 63.5 + 12 + (16 Ć 3)

= 123.5

Mass of CuCOŠ· = 0.003125 Ć 123.5

= 0.3859375

Mass of CuCOŠ· needed to be decomposed = 0.39g (2 s.f)

Equation 1: 2CuCOŠ· ā Cu2O + 2CO2 + Ā½O2

For equation 1, volume of gas that will be produced using 0.39g of CuCOŠ· will be:

Moles of 2CuCOŠ· = mass / R.A.M

= 0.39 / 123.5

Moles of 2CuCOŠ· = 0.003157894 moles

Ratio = 2CuCOŠ· : 2CO2

= 2 : 2

= 0.00315784 : 0.00315784

Moles of 2CO2 = 0.00315784 moles

Volume of 2CO2 = moles Ć 24000

= 0.00315784 Ć 24000

= 75.78816cmĀ³

Volume of 2CO2 = 76cmĀ³

APPARATUS

0.39g of CuCOŠ·
Bunsen burner
Heat proof mat
Tripod
Gauze
Bung
Delivery tube
Gas syringe
Clamp
Scales (capable of weighing out 0.01g)
METHOD

Collect and set up apparatus as shown in the drawing
Ensure the gas syringe is at 0 before the experiment begins.
Place the weighed mass of CuCOŠ· into the conical flask and insert the bung tightly so that no gas escapes.
Light the Bunsen burner and place it underneath the test tube (as shown in the drawing).

Heat the conical flask until the CuCOŠ· has fully decomposed. (This will be indicated by the fact that the bubbling will stop, and there will be a significant colour change of the CuCOŠ· form bluish green to black or red).

Continue to heat even after the bubbling has stopped for about 1 minute. This will ensure that the reaction has completely ended

Leave the apparatus unattended to for a few seconds to ensure all gas has been released.
Then record the reading from the gas syringe which shows the volume of gas produced.
Repeat theses stages thrice, to get a more accurate result. Then take the average for the results.
WHICH EQUATION IS CORRECT?

In previous calculation, 0.39g of CuCOĀ³ should produce 75cmĀ³ of gas, if equation 2 is correct. If this volume of gas or a slightly less volume (to allow for slight gas loss) is obtained during the experiment, then equation 2 is correct. But if more than 75cmĀ³ of gas is produced, then it means that another gas has been produced which will be oxygen. This would then mean that equation 1 is correct.

Also, after the decomposition has fully occurred, you can try to guess which equation is happening through looking at the colour of the substance after decomposition. If itās a red compound, it may be equation 1 occurring due to the Cu2O which is a red crystalline. Whereas if itās a black compound then it may be equation 2 occurring as CuO is a black powder.

SAFETY

CuCOŠ· is harmful; ingestion may cause nausea or vomiting, and inhalation may cause irritation (4).

Care must be taken when dealing with Bunsen burner to avoid been burnt.

REFRENCES

(1)http://www.britannica.com/eb/article?tocId=81944&query=copper%20oxides&ct=eb

(2) OCR Chemistry 1 – p20
(3)http://www.iun.edu/~cpanhd/C101webnotes/quantchem/rxnstoich.html

(4)http://www.ctmsupplies.hemscott.net/Copper%20Carbonate.htm

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