Questions and Answers
Which of the following numerical expressions gives the number of moles in 5.0g of CaO?
5.0g ÷ 56 g/mol
Which of the following pieces of information is most useful for determining the number of Cu atoms in a 21g sample of pure Cu metal?
The molar mass of Cu
A 1.0mol sample of which compound has the greatest mass?
N2O5
According to the mass spectrum for an unknown element, the atomic mass is closest to what?
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The mass spectrum represented is most consistent with which element?
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Based on the mass spectrum of a pure element, the average atomic mass of the element is closest to what?
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What scientific question can best be answered based on the experiment with BaCl2?
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What can be calculated from heating a mass of metallic element M to form MO?
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What is the empirical formula of a compound containing 36.0g of C and 6.0g of H?
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What information is helpful in determining whether a powder labeled NaCl is pure?
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What additional information is needed to calculate the mole percent of XCl and ZCl in a mixture?
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What is needed to determine the mole fraction of each gas in a gas mixture?
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How many unpaired electrons are in the atom represented by the electron configuration 1s22s22p63s23p6?
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Which of the following represents the electron configuration of an oxygen atom in the ground state?
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What is the correct electron configuration for a ground-state atom of magnesium?
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Which labeled peak corresponds to the 1s electrons in the photoelectron spectrum and why?
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How is the photoelectron spectrum for boron consistent with the electron shell model?
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How is the photoelectron spectrum for carbon consistent with the electron shell model?
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What helps explain the trend of increasing atomic radius from N to Bi?
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What explains why the atomic radius of K is greater than that of Br?
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What helps explain why the first ionization energy of K is less than that of Ca?
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Why does an atom of Rb gas more easily lose an electron in a chemical reaction than an atom of Li gas?
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Which element reacts with O in a mole ratio of 2 to 1, forming an ionic compound, and why?
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What charge does Al typically have in ionic compounds, and why?
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Study Notes
Moles and Mass Calculations
- Number of moles calculated using mass of sample divided by molar mass (e.g., 5.0g of CaO ÷ 56 g/mol).
- For 21g of copper (Cu), molar mass is essential to find the number of Cu atoms via Avogadro's number.
- The compound with the highest molar mass in a sample of 1.0 mol is N2O5 due to the number of atoms in the molecules.
Atomic Mass and Isotopes
- Average atomic mass from isotopes can be estimated; for unknown elements around 91 amu based on relative abundances.
- Gadolinium (Gd) isotopes suggest an average atomic mass of around 157 amu based on spectrum data.
- A pure element's average atomic mass can be derived from its isotopes, yielding 186.3 amu in a specific example.
Experimental Procedures and Purity
- The purity of BaCl2 can be assessed by comparing moles of Ba in the precipitate with moles in the sample.
- The molar mass of unknown metallic element M can be determined by mass change before and after reaction with oxygen.
- Empirical formulas derived from ratios of moles of C and H can identify substances.
Analytical Techniques
- Mass percent composition aids in determining purity of NaCl, an intensive property.
- Molar masses of components X and Z in a chloride mixture are necessary to calculate mole percent.
- For gas mixtures, molar masses are crucial to find each gas's mole fraction.
Electron Configuration and Spectra
- Atom with electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ has zero unpaired electrons.
- The correct ground-state electron configuration of oxygen reflects eight total electrons.
- Magnesium, with atomic number 12, has a specific electron configuration sequence.
Photoelectron Spectra Insights
- The peak corresponding to 1s electrons is identified based on binding energy; it indicates strong nuclear attraction.
- Boron's photoelectron spectrum illustrates electron subshell occupancy matching its configuration.
- Carbon's spectrum demonstrates equal numbers of electrons across occupied subshells, consistent with its structure.
Atomic Radii Trends
- Increasing atomic radius in the nitrogen group explained by decreasing effective nuclear charge as elements descend the group.
- Potassium (K) has a greater atomic radius than bromine (Br) due to lower effective nuclear charge on valence electrons in K.
Ionization Energy and Atomic Behavior
- First ionization energy of K is lower than Ca due to less effective nuclear charge affecting electron attraction.
- Rubidium (Rb) loses electrons more easily than lithium (Li) because Rb's valence electron is further from its nucleus.
- Elements in the same periodic group, like Cs and Rb, react with oxygen in a fixed mole ratio due to similar valence electron configurations.
Ionic Charges and Reactions
- Aluminum typically has a +3 charge in ionic compounds due to its three valence electrons being easily removed.
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Description
Test your knowledge with this progress check quiz designed for AP Chemistry Unit 1. Answer multiple-choice questions and flashcards focused on moles, mass, and atomic calculation. This interactive quiz will help reinforce your understanding of key concepts in chemistry.