7. Once the end of the syringe has stopped moving record the amount of gas produced and compare it with the estimated values of gas to be produced, whichever value the amount of gas corresponds with will show the correct equation.
Calculations:
Formulas used are:
Moles= mass/M
1 mole of gas occupies 24000cm³ of space under standard conditions.
Equation 1:
2CuCO₃(S) Cu₂O(s) + 2CO₂(g) + ½O(g)
According to this equation, 2 moles of CuCO₃ will produce 2½ moles of gas. So the ratio of copper carbonate to gas is 2:2½.
Equation 2:
CuCO₃ CuO(s) + CO₂(g)
According to this equation, 1 moles of CuCO₃ will produce 1 mole of gas. So the ratio of copper carbonate to gas is 1:1, to make both set of calculations become equal I am doubling the amount of copper carbonate, therefore the new ratio will be 2:2.
To determine the amount of 2CuCO₃ to use so that I will get a sensible amount of gas, I’m going to work out the weight of 1 mole of 2CuCO₃ and use this to work out how much gas the reaction will produce:
2CuCO₃= 2(63.5+12+(16x3)) =247
This number can be rounded up to 250g as such a slight difference between the real mass and the mass used here won’t make a big difference.
1 mole of gas will take up 24000cm³ under standard conditions.
If 250g of 2CuCO₃ is used (250/250=1 mole of 2CuCO₃) the amounts of gas produced will be:
Equation 1- 2:2½ volume of gas produced 2½x24000=60000cm³
Equation 2- 2:2 volume of gas produced 2x24000= 48000cm³
This much gas is far too much to be collected in a normal experiment and the equipment needed is too difficult to find, so I will reduce the amount of 2CuCO₃.
If 25g of 2CuCO₃ is used (25/250=0.1 mole of 2CuCO₃) the amounts of gas produced will be:
Equation 1- volume of gas: 60000x0.1= 6000cm³
Equation 2- volume of gas: 48000x0.1= 4800cm³
This is still far too much gas to be collected.
If 0.25g of 2CuCO₃ is used (0.25/250=0.001mole of 2CuCO₃) the amounts of gas produced will be:
Equation 1- volume of gas: 60000x0.001= 60cm³
Equation 2- volume of gas: 48000x0.001= 48cm³
This is a sensible amount of gas to collect. So 0.25g of 2CuCO₃ will be used and will produce 60cm³ of gas or roughly 50cm³ of gas.
If the results of the experiment show that about 60cm³ of gas is produced then equation 1 is correct and if the amount of gas is about 50cm³ then equation 2 is correct.
Apparatus and Reasons for Choice:
I am using this method of collecting gas because the equipment is easy to find and the actual procedure to collect the gas is also simple.
A glass syringe of 100cm³ is used as it will collect the gas and give a result that may not be very accurate but is accurate enough to work out which equation is correct. Also glass is used because it has a very high melting point so the gas won’t melt the syringe.
A conical flask is used with a rubber bung because the bung will create an airtight seal so that gas can’t leak out or in. The glass won’t melt and won’t react with the chemical substance.
Tripod- holds the conical flask above Bunsen burner.
Bunsen Burner- used as heat source
Gauze mat- to place over tripod and to make sure that the heat is more evenly distributed, also makes sure that the conical flask doesn’t fall through the tripod.
Clamp- to hold syringe in place
Rubber tubing is used as it is flexible and can create an airtight seal connecting the conical flask and syringe.
Spatula- used for measuring out the amount of copper carbonate.
Goggles- used for safety
Experimental errors:
- The leakage of gas, however many precautions you take under normal circumstances, can’t ensure that there will be no leakage of gas. Some of the gas will escape.
- The syringe is not totally accurate and there may be some human error whilst the syringe is being read, also it may be difficult to judge when exactly the gas will have cooled down and it may not have cooled down in 5 minutes.
- The weight of the CuCO₃ measured may not be totally accurate as it is measured to the nearest 0.01g.
- The Bunsen burner may be turned off too quickly if it seems as if the reaction has stopped because the movement of the cylinder end has slowed down so much it seems to have stopped.
Safety Precautions:
An apron must be worn as well as goggles. Also the tripod must not be touched straight after the experiment as it may still be hot and may cause burns.
Bibliography:
Longman Study Guides, Chemistry.
Cambridge Advanced Sciences, Chemistry 1.
, A and AS level Chemistry.
