30:11 - stoichiometry PDF

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30/11/2020 1. Caffeine has an empirical formula of C4H5N2O and a molar mass of approximately 200 g/mol. A 375 mL can of soft drink contains 36 mg of caffeine. Determine the molarity (i.e. molar concentration) of caffeine in a can of this soft drink. 2. Identify the overall trend in first ionisation energy for the period 2 elements, i.e. between Li and Ne. Identify any exceptions to this trend.

3. *A common organic solvent only contains carbon, hydrogen, and oxygen. Combustion analysis of 1.000 g of this solvent gives 1.913 g CO2 and 1.174 g H2O. What is the empirical formula?

4. How many grams of Fe2O3 are produced when 56 g of Fe are reacted with 32 g of O2? How many grams of the excess reactant will remain after the reaction is complete? 5. An atom of hydrogen emits a discrete wavelength of electromagnetic radiation at 486 nm as the electron transitions from a higher energy level back to the second energy level n = 2. a. Calculate the energy change, in Joules, associated with this transition. b. A second discrete emission line in an atom of hydrogen has a wavelength of 434 nm as the electron transitions from a higher energy level back to the second energy level (n = 2). Would the change in energy associated with the 434 nm spectral line be greater than, less than, or equal to, that of the 486 nm spectral line? Justify your answer. c. Would the energy level (n) of the electronic transition responsible for the 434 nm spectral line be at a higher energy level or a lower energy level than that of the 486 nm spectral line? Justify your answer. In a separate experiment, a molecule of hydrogen, H2, absorbs a photon of electromagnetic radiation with a wavelength of 300 nm. The energy required to break the bond in H2 gas is 432 kJ mol−1 . d. Calculate the frequency of the photons with a 300 nm wavelength. e. *Calculate the number of joules required to break the bond in a single molecule of H2 gas. Then, determine if the photon has sufficient energy to break the bond in a molecule of hydrogen gas. 6. The S2− ion is isoelectronic with the Ar atom. Write the electron configuration of S2-. From which species, S2− or Ar, is it easier to remove an electron? Explain. 7. How many unhybridized p orbitals are there in an sp hybridised Carbon atom? What is the molecular shape of an sp hybridised Carbon atom? 8. XF2 is the formula of a certain metallic fluoride. What will be the molecular formula of the metallic oxide?

9. Pi bonds are formed by ___? a. b. c. d.

2 p orbitals 2 s orbitals 1 p and 1 s orbital All of the above....