Answer:
Let's go through each question one by one to check the correctness and the significant figures:
**Question 1:** A sample of Oxygen gas (O2) has a mass of 27.9 g. How many moles of Oxygen gas (O2) are present in the sample?
Your calculation is correct. You divided the given mass by the molar mass of O2 (32.00 g/mol, which is rounded to four significant figures to match the precision of the given mass of 27.9 g), and you got 0.872 moles of O2, which is rounded to three significant figures, consistent with the given data.
**Question 2:** A cup of water, H2O, contains 240 grams. How many water molecules do you expect to find in a standard cup of water?
Your calculation is correct. You used the molar mass of water (18.015 g/mol) and Avogadro's number (6.022 x 10^23) to find the number of water molecules. You have reported the final answer as 8.0 x 10^24 molecules, which is rounded to two significant figures because the given mass (240 g) has only two significant figures.
**Question 3:** What is the percentage of sulfur in sulfuric acid (H2SO4)?
You calculated the molar mass of H2SO4 correctly and then used it to find the percentage of sulfur. Your final answer is 32.7%, which is correctly rounded to three significant figures as the molar mass of sulfur (32.066 g/mol) is given to five significant figures, and you would typically round to the least number of significant figures in the given data or result.
**Question 4:**
a. What is the empirical formula of a compound that is composed of 44.45 g of carbon, 3.73 g of hydrogen, and 51.82 g of nitrogen and a molecular weight of 81.09 g/mol?
You found the empirical formula to be CHN, which is correct. However, the molecular weight given is not consistent with this empirical formula. The molar mass of CHN would be (12.01 + 1.008 + 14.007) g/mol = 27.025 g/mol. Since the molecular weight is given as 81.09 g/mol, you would divide 81.09 g/mol by the molar mass of the empirical formula (27.025 g/mol) to find the multiplier, which is approximately 3. Thus, the molecular formula would be (CHN)3 or C3H3N3.
b. You correctly calculated that the empirical formula needs to be multiplied by 3 to get the molecular formula, which is C3H3N3.
**Question 5:** An analytical chemist summarized the percent composition of a hydrocarbon in a table in her lab notebook. She noted that the molar mass of the compound was 180.15 g/mol.
You correctly found that the chemist's conclusion of the molecular formula being C8H4O2 is incorrect based on the molar mass and empirical formula. You calculated the empirical formula to be CH2O. Then, you found the molar mass of the empirical formula to be 30.026 g/mol. You correctly divided the given molar mass (180.15 g/mol)
by the molar mass of the empirical formula to get 6. Thus, the molecular formula is (CH2O)6 or C6H12O6, which you correctly identified. The significant figures in your answer are correct since you have based your calculations on the percentages given, which have at most three significant figures.
In summary, all your calculations appear to be correct, and your use of significant figures is appropriate for the data provided and the calculations performed. Good job on the assignment! If you need more detailed explanations or have other questions, feel free to ask.Explanation:
