stuff

Which of the following is the electron configuration of an excited atom that is likely to emit a quantum of energy?

1s2 2s22p6 3s13p1

HOCN (aq) → H+ (aq) + OCN− (aq) Ka = 3 x 10-4 The ionization of cyanic acid, HOCN, is represented above. A certain solution of HOCN has a pH of 2.0. What is the approximate concentration of unionized HOCN (aq) in the solution?

3 x 10-1 M

Cu(s) + 4 HNO3(aq) → Cu(NO3)2(aq) + 2 NO2(g) + 2 H20()) Each student in a class placed a 2.00 g sample of a mixture of Cu and Al in a beaker and placed the beaker in a fume hood. The students slowly poured 15.0 mL of 15.8 MHNO3(aq) into their beakers. The reaction between the copper in the mixture and the HNO3(aq) is represented by the equation above. The students observed that a brown gas was released from the beakers and that the solutions turned blue, indicating the formation of Cu<*(aq). The solutions were then diluted with distilled water to known volumes. 2+ The students determined that the reaction produced 0.010 mol of Cu(NO3)2. Based on the measurement, what was the percent of Cu by mass in the original 2.00 g sample of the mixture?

32%

The mass percent of Calcium Carbonate is

75%

To gravimetrically analyze the silver content of a piece of jewelry made from an alloy of Ag and Cu, a student dissolves a small preweighed sample in HNO3(aq). Ag+(aq)and Cu2+(aq) ions form in the solution. Which of the following should be the next step in the analytical process?

Adding a solution containing an anion that forms an insoluble salt with only one of the metal ions

The gases CO2(�) and NH3(�) can be liquefied at 20°C by compressing them to sufficiently high pressures. A student claims that NH3(�) can be liquefied at a lower pressure than CO2(�) can be liquefied. Which of the following is the best justification for this claim?

CO2 is a nonpolar molecule that has London dispersion intermolecular forces that are weaker than the dipole-dipole and London dispersion forces between the polar NH3 molecules.

The diagrams above use arrows to represent the speed of a gas particle. Which of the diagrams best represents the speed of the particles of a gas at a fixed temperature, and why?

Diagram 2, because the particles have a variety of different speeds.

Based on the Brønsted-Lowry theory of acids and bases, which of the following species can act as both a conjugate acid and a conjugate base?

HS-

Real Gas vs. Ideal Gas

Ideal: volume is negligible, low pressure, high temperature, don't have any attraction or repulsion between each other Real: volume is inegligeble, high pressure, low temperature, has few attractions between them

The diagram above represents four cations, all shown to the same scale. Which cation would be predicted by Coulomb's law to have the strongest ion-dipole attraction to water, and why?

Mg2+, because it has the largest charge-to-size ratio.

The effective nuclear charge experienced by the outermost electron of Na is different than the effective nuclear charge experienced by the outermost electron of Ne. This difference best accounts for which of the following?

Na has a lower first ionization energy than Ne.

After completing an experiment to determine gravimetrically the percentage of water in a hydrate, a student reported a value of 38 percent. The correct value for the percentage of water in the hydrate is 51 percent. Which of the following is the most likely explanation for this difference?

Strong initial heating caused some of the hydrate sample to spatter out of the crucible.

In his atomic theory, Dalton proposed that all atoms of a given element are identical. Which of the following observations provides the best evidence that the proposal is incorrect?

The mass spectrum of Cu has a peak at 63amu and another peak at 65amu.

Which of the following is evidence that ionic bonds formed during the precipitation?

The precipitate has a high melting point.

Which of the following best helps to explain why the electron affinity of Br has a greater magnitude than that of I?

There is a greater attraction between an added electron and the nucleus in Br than in I.

Two different ionic compounds each contain only copper and chlorine. Both compounds are powders, one white and one brown. An elemental analysis is performed on each powder. Which of the following questions about the compounds is most likely to be answered by the results of the analysis?

What is the formula unit of each compound?

When asked for highest occupied energy sublevel...

find the longest electron configuration

Coulomb's law

this

Kinetic Molecular Theory rules

this

Which of the following best helps explain why the electronegativity of Cl is less than that of F?

A The mass of the Cl atom is greater than the mass of the F atom.

A student was given two clear liquids; a colorless liquid and a dark-blue liquid. The student was asked to combine the liquids in a beaker and record observations. Which of the following results, if true, would provide the best evidence that a chemical change took place when the liquids were combined? A The resulting mixture was cloudy. B The total volume of the mixture was equal to the sum of the initial volumes. C The resulting liquid was light blue. D The liquids formed two separate layers in the beaker.

A The resulting mixture was cloudy.

the Effective Nuclear Charge can be affected on changing the size of atom.

A higher effective nuclear charge causes greater attractions to the electrons, pulling the electron cloud closer to the nucleus which results in a smaller atomic radius.

K2SO3(aq) + 2 HNO3(aq) → 2 KNO3(aq) + SO2(g) + H2O(l) According to the balanced chemical equation above, when 100.0 mL of 0.100 M K2SO3(aq) is mixed with 100.0 mL of 0.200 M HNO3(aq) at 30°C and 1 atm, the volume of SO2 gas produced is 0.24 L. If it is assumed that the reaction goes to completion, which of the following changes would double the volume of SO2 produced at the same temperature and pressure, and why? (For each change, assume that the other solutions and volumes remain the same.)

C Using 200.0mL of 0.100�K2SO3(��) and 200.0mL of 0.200�HNO3(��), because this provides double the number of moles with the correct stoichiometric ratio

The table above shows the first ionization energy and atomic radius of several elements. Which of the following best helps to explain the deviation of the first ionization energy of oxygen from the overall trend?

There is repulsion between paired electrons in oxygen's 2p orbitals.

Lewis electron-dot diagrams for CO2 and SO2 are given above. The molecular geometry and polarity of the two substances are

different because S has a greater number of electron domains (regions of electron density) surrounding it than C has

bond dissociation energy

energy required to break a covalent bond (triple bond stronger than single bond so N2 higher bond dissociation energy than F2)

electron affinity

how quickly an atom can gain an electron and cl is the highest

According to the VSEPR model, the progressive decrease in the bond angles in the series of molecules CH4, NH3, and H2O is best accounted for by the

increasing number of unshared pairs of electrons

A student combines a solution of NaCl(aq) with a solution of AgNO3(aq), and a precipitate forms. Assume that 50.0 mL of 1.0 M NaCl(aq) and 50.0 mL of 1.0 M AgNO3(aq) were combined. According to the balanced equation, if 50.0 mL of 2.0 M NaCl(aq) and 50.0 mL of 1.0 M AgNO3(aq) were combined, the amount of precipitate formed would

not change, because the amount of AgNO3(aq) did not change

when as atom has an increased oxidation number it is....

oxidized=reducing agent=donates an electron

when as atom has a decreased oxidation number it is....

reduced=oxidizing agent=gains an electron