Bootcamp gen chem

Parallax error may occur when: A. an experiment does not account for changes in altitude. B. a measurement is not properly converted between the metric and customary systems. C. a meniscus in a buret is not observed directly straight on. D. an object under water is observed at an angle from above the surface. E. the concentration of an acid to be used in a titration is not first checked against a standard.

C. a meniscus in a buret is not observed directly straight on.

27. Electron affinity measures the: A. tendency to attract electrons towards the atom and form a bond. B. chemical reactivity of the valence electrons of the atom. C. amount of energy absorbed when an electron is added to an atom. D. ease with which an atom gains an electron. E. average distance between the electrons and nucleus.

D. Electron affinity is the measured change in energy (how much energy is released) when an atom gains an electron. This can be restated as the ease with which a neutral atom gains an electron. The tendency to attract electrons towards the atom and form bonds is known as electronegativity, and this value is estimated based on ionization energies and electron affinities. The amount of energy it takes to remove an electron from an atom is known as the ionization energy.

18. An exothermic reaction at equilibrium will proceed at a: A. slower rate while its Kc increases at higher temperatures. B. slower rate while its Kc decreases at higher temperatures. C. faster rate while its Kc increases at higher temperatures. D. faster rate while its Kc decreases at higher temperatures.

Let's solve this by making up an example exothermic reaction (shown below). The general concept of an exothermic reaction is that heat is released, or heat is a product: A + B → C + D + heat From Le Chatlier's principle, increasing the temperature would increase the heat, so therefore the reaction would shift to the left (towards the reactants, [A] and [B]). If the concentrations of [A] and [B] increase, then the overall Kc of the reaction would decrease at higher temperatures, eliminating answer choices A and C. Lastly, increasing the temperature will increase the rates of both the forward and the reverse reactions, so the reaction will proceed at a faster rate. Thus we arrive at answer choice D.

26. Which of the following would be strongly attracted to magnetic fields? A. He B. H2 C. Zn D. O2 E. N2

This question is asking about the properties of diamagnetic and paramagnetic atoms and molecules. A paramagnetic atom or molecule has at least one unpaired electron which will result in a tiny magnetic field that can interact with a larger magnetic field. If all of the electrons are paired within their orbitals, then the molecule is said to be diamagnetic (di- for two) and will not interact with magnetic fields (some diamagnetic molecules may repel magnetic fields). To solve this question, we have to draw out the atomic or molecular orbital diagrams of each answer and determine which one has at least one unpaired electron (or is paramagnetic).