Questions and Answers
Which of the following numerical expressions gives the number of moles in 5.0g of CaO?
In a lab, a student is given a 21g sample of pure Cu metal. Which of the following pieces of information is most useful for determining the number of Cu atoms in the sample?
A 1.0mol sample of which of the following compounds has the greatest mass?
According to the information in the mass spectrum, the atomic mass of the unknown element is closest to:
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The mass spectrum represented above is most consistent with which of the following elements?
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Based on the mass spectrum of a pure element represented above, the average atomic mass of the element is closest to which of the following?
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Which of the following scientific questions could best be answered based on the results of the BaSO₄ precipitation experiment?
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Which of the following questions can be answered from the results of the experiment involving a metallic element, M?
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A 42.0g sample of a compound containing only C and H was analyzed. What can be determined from this information?
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Study Notes
Molar Mass and Moles
- To calculate the number of moles in a substance, divide the mass of the sample by its molar mass.
- For 5.0g of CaO, the expression is 5.0g / 56 g/mol.
- For 21g of pure Cu, knowing its molar mass helps determine the number of Cu atoms by multiplying moles by Avogadro's number.
Determining Mass of Compounds
- The mass of a sample can be calculated using the formula n×M, where n is the number of moles and M is the molar mass.
- Among compounds, N₂O₅ has the greatest molar mass among options due to the highest number of nitrogen and oxygen atoms.
Isotope Abundance and Average Atomic Mass
- For an unknown element, if the mass spectrum suggests atomic masses of isotopes (90, 92, and 94), the average atomic mass is influenced by these abundances, potentially resulting in an average closer to 91 amu.
- The average atomic mass of Gd is around 157 amu, based on isotope distribution.
Analyzing Mass Spectra
- The average atomic mass from a mass spectrum can indicate an elemental mass of about 186 amu, considering the relative abundances of isotopes (e.g., 185 amu at 40% and 187 amu at 60%).
Purity of Chemicals
- The experiment involving BaCl₂ and Na₂SO₄ can determine the purity of BaCl₂ by comparing the calculated moles of Ba in the precipitate to expected moles based on the mass of BaCl₂ used.
Calculating Molar Mass of Metals
- After heating a metallic sample M to form compound MO and measuring the mass of the resulting compound, the molar mass of M can be calculated by analyzing the differences in masses.
Empirical Formula Determination
- To find the empirical formula of a compound containing only carbon (C) and hydrogen (H), divide the mass of each element by its molar mass to calculate the number of moles, then assess the ratio of these moles.
Studying That Suits You
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Description
Test your knowledge of moles and molar mass with these flashcards from Chemistry Unit 1. Each card presents a scenario requiring you to identify the correct numerical expression to calculate the number of moles for given substances. Perfect for students looking to reinforce their understanding of basic concepts in chemistry.
