a) Tetraphosphorus (P4), commonly known as white phosphorus, forms different compounds with chlorine (Cl2) depending on the amount of chlorine present. If chlorine is limited, phosphorus trichloride (PCl3) is formed. If there is an excess of chlorine, phosphorus pentachloride (PCl5) is formed.Write balanced equations for the two reactions of white phosphorous with chlorine.
b) Design an experiment that could be performed to verify each synthesis reaction. Include a hypothesis relating to whether PCl3 or PCl5 will be produced, information about the initial masses you would use, and possible problems that might arise.
c) Explain how your experiment will confirm the conservation of matter for each reaction.
d) Based on the ratio of moles of reactants in each case, predict the product of each trial of your experiment (PCl3 or PCl5) using your chosen initial masses. Explain your reasoning, and show any calculations.
e) Suppose you choose the initial masses so that both reactions produce PCl3. Explain how both of these chemical reactions obey the law of definite proportions, even though they produce different numbers of moles of the product. Justify your answer with calculations.
I know the answers to a and b
We would like for you to do some work on your own. I gave you most of b and a you obtained mostly from Bob Pursley.
So write up c,d,e, and we will critique them for you.
a) Balanced equations for the reactions of white phosphorus (P4) with chlorine (Cl2) are as follows:
1. When there is a limited amount of chlorine:
P4 + 6Cl2 → 4PCl3
2. When there is an excess of chlorine:
P4 + 10Cl2 → 4PCl5
b) To verify each synthesis reaction, you can design the following experiment:
For the reaction with limited chlorine (PCl3 formation):
1. Set up a reaction vessel with a stopper and a delivery tube to collect any gaseous products.
2. Weigh a known mass of white phosphorus (P4) and keep it in the reaction vessel.
3. Add a known amount of chlorine gas (Cl2) in a quantity which is limited.
4. Observe the reaction and collect any gas evolved in the delivery tube.
5. Carefully isolate and collect the resulting phosphorus trichloride (PCl3) formed.
6. Weigh the collected PCl3 and compare the mass with the initially used phosphorus (P4).
For the reaction with excess chlorine (PCl5 formation):
1. Follow the same steps as above, but use an excess of chlorine gas (Cl2) in the reaction vessel.
2. Isolate and collect the resulting phosphorus pentachloride (PCl5) formed.
3. Weigh the collected PCl5 and compare the mass with the initially used phosphorus (P4).
Hypothesis:
For the reaction with limited chlorine, the hypothesis could be that PCl3 will be produced. For the reaction with excess chlorine, the hypothesis could be that PCl5 will be produced.
Initial masses:
For accuracy, you would need to weigh the initial mass of white phosphorus (P4) in both experiments. The mass of chlorine gas (Cl2) can be controlled by using a known volume of the gas and utilizing its molar mass to calculate the amount in moles.
Possible problems:
1. Ensuring procedural accuracy and safety precautions.
2. Controlling the amount of chlorine gas added accurately.
3. Avoiding any losses of gases during the reaction.
4. Proper collection and isolation of the product to prevent contamination.
c) The experiment confirms the conservation of matter for each reaction because the collected mass of the product (PCl3 or PCl5) will be compared to the initially used mass of white phosphorus (P4), assuming no losses occurred during the reaction. If the mass of the product equals the mass of the reactant or is very close, it confirms the conservation of matter.
d) Based on the moles of reactants, we can predict the product of each trial. Here's the reasoning and calculation:
For the reaction with limited chlorine (PCl3 formation):
One mole of white phosphorus (P4) reacts with six moles of chlorine (Cl2) to produce four moles of phosphorus trichloride (PCl3). So, we can use stoichiometry to calculate the expected moles of PCl3 formed. The calculation would be based on the initial moles of P4 and the moles of Cl2 available.
For the reaction with excess chlorine (PCl5 formation):
One mole of white phosphorus (P4) reacts with ten moles of chlorine (Cl2) to produce four moles of phosphorus pentachloride (PCl5). Similar to the previous case, stoichiometry can be employed to calculate the expected moles of PCl5 formed.
e) If the initial masses are chosen so that both reactions produce PCl3, it means that the amount of chlorine gas added is limited enough to form PCl3 exclusively in both cases.
The law of definite proportions states that a chemical compound always contains the same elements in the same proportions by mass. In this case, even though the number of moles produced is different in each reaction, the proportions of the elements (phosphorus and chlorine) in each compound remain the same.
To justify this, you can perform calculations comparing the masses of phosphorus and chlorine in both reactions. If the ratios of these masses are consistently the same, it confirms that the law of definite proportions is obeyed.