Extension Questions- Lab 5 6. Equal volumes of oxygen gas and an unknown gas con

Question

Extension Questions- Lab 5 6. Equal volumes of oxygen gas and an unknown gas contain the same number of molecules. The gases weigh 3.00 g for oxygen and 7.50 g for the unknown gas. Which of the following is the unknown gas? Provide explanation/calculations. a. CO b. CO2 c.NO Compare the experimental value of the molar mass that was measured in this lab (either aluminum or zinc) to the actual molar mass of the metal. Thinking about the experimental procedure completed, provide 2 likely experimental sources of error. For each source of error, explain how it would have caused the identified molar mass to be incorrect. 7. At nighttime, when plants do not have sunlight to undergo photosynthesis but still need to use energy in their cells, they undergo respiration of glucose. The unbalanced reaction is shown below. 8. a. How many grams of oxygen must be a plant utilize to consume 15.0 grams of glucose (C,H1 0) during respiration? b. If the amount of oxygen reacted with the glacose in the reaction in part a was at STP, what volume, in mL, would the oxygen gas occupy? 57

Explanation / Answer

6. equal volumes of O2 and unknown gas

equal volume of gas mean equal moles

volume of gas = moles of gas x 22.4 L

moles O2 = moles unknown gas

moles unknown gas = 3 g/32 g/mol =0.094 moles

molar mass of unknown gas = 7.5 g/0.094 moles = 80 g/mol

So the gas matching this molar mass is,

f. SO3

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7. Likely source of error could be insufficient time given for the reaction. This would result in lower moles and higher molar mass of metal calculated. Another source of error would be if the initial mass was measured incorrectly, this would give lower moles and thus lower molar mass of metal.

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8. balanced equation,

C6H12O6 + 6O2 --> 6CO2 + 6H2O

a. moles glucose = 15 g/180.156 g/mol = 0.0833 moles

moles O2 needed = 0.0833 moles x 6 = 0.500 moles

mass O2 needed = 0.500 moles x 32 g/mol = 16 g

b. volume of O2 = 0.500 moles x 22.4 L x 1000 = 11200 ml

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