Chem 10/30/19

What charge does Al typically have in ionic compounds, and why?

+3, because it has three valence electrons.

How many unpaired electrons are in the following? 1s2 2s2 2p6 3s2 3p6

0

2 MnO4-(aq) + 10 Br-(aq) + 16 H+(aq) → 2 Mn2+(aq) + 5 Br2(aq) + 8 H2O(l) How many electrons are transferred in the reaction represented by the balanced equation above?

10

Based on the mass spectrum of a pure element represented above, (185, 40) and (187, 60) the average atomic mass of the element is closest to which of the following?

186.0; the average mass of 186.0 amu was calculated using the assumption that each isotope contributes 50%, which is incorrect based on the mass spectrum. Based on the mass spectrum, the 185 amu isotope has a relative abundance close to 40% and the 187 amu isotope has a relative abundance close to 60%. This predicts an average atomic mass slightly higher than 186 amu

A student obtains a mixture of the chlorides of two unknown metals, X and Z. The percent by mass of X and the percent by mass of Z in the mixture is known. Which of the following additional information is most helpful in calculating the mole percent of XCl(s) and of ZCl(s) in the mixture?

The molar masses of X and Z

H2Se(g) + 4 O2F2(g) → SeF6(g) + 2 HF(g) + 4 O2(g) Which of the following is true regarding the reaction represented above?

The oxidation number of Se changes from -2 to +6.

A 42.0g sample of compound containing only C and H was analyzed. The results showed that the sample contained 36.0g of C and 6.0g of H. Which of the following questions about the compound can be answered using the results of the analysis?

What is the empirical formula of the compound?

exothermic reaction

releases heat, causing the temperature of the immediate surroundings to rise

Atomic mass spectrum

shows relative abundance of each ion; rough average to determine the element ie) image probable Mg or Al

A student combines a solution of NaCl(aq) with a solution of AgNO3(aq), and a precipitate forms. Which of the following is the balanced net ionic equation for the formation of the precipitate?

Ag+(aq)+Cl−(aq)→AgCl(s)

what kind of reaction is Pb2+(aq) + CrO42-(aq) → PbCrO4(s)

precipitation

polar covalent bond

Chemical bond in which electrons are shared unequally between two bonded atoms with different electronegativities.

Rb reacts with O in a mole ratio of 2 to 1, forming the ionic compound Rb2O. Which of the following elements will react with O in a mole ratio of 2 to 1, forming an ionic compound, and why?

Cs, because it is in the same group as Rb.

LEO goes GER

Lose Electrons Oxidation. Gain Electrons Reduction

endothermic reaction

The total making and braking bonds results in a net absorption of energy; absorbs heat and cools the surroundings

A vessel contains a mixture of gases. The mass of each gas used to make the mixture is known. Which of the following information is needed to determine the mole fraction of each gas in the mixture?

molar mass of each gas

Molarity

moles of solute/solution (L) Tip: You can also use mmol (millimoles) and mL (milliliter)

When students added 2.0g of NaI crystals to 100.mL of Pb(NO3)2(aq), a yellow precipitate formed. After the solution was filtered, the yellow solid was dried and weighed. Data from the experiment are shown in the table above. Which of the following claims is best supported by the observations?

A chemical change occurred when a yellow, insoluble compound with a larger mass than the original NaI formed.

Na2CO3(aq)+2HCl(aq)→2NaCl(aq)+H2O(l)+CO2(g) A student combined two colorless aqueous solutions. One of the solutions contained Na2CO3 as the solute and the other contained HCl. The chemical reaction that took place is represented by the equation above. What experimental result would be evidence that a chemical reaction took place when the solutions were combined?

Bubbles formed when the two solutions were combined.

Which of the diagrams above best represents the CH2O molecule, and why?

Diagram 2, because all atoms have a formal charge of 0.

5Fe2+(aq)+MnO4−(aq)+8H+(aq)→5Fe3+(aq)+Mn2+(aq)+4H2O(l) Which of the following represents the oxidation half-reaction based on the balanced ionic equation shown above?

Fe2+(aq)→Fe3+(aq)+e−Fe2+(aq)→Fe3+(aq)+e−

A beaker was half filled with freshly distilled H2O and placed on a hot plate. As the temperature of the water reached 100°C, vigorous bubbling was observed in the beaker. The gaseous contents of the bubbles were analyzed. The presence of which of the following substances would support the claim that the observed phenomenon was a physical change?

H20 (g)

Which of the following is the correct net ionic equation of the neutralization reaction between hydrofluoric acid and sodium hydroxide in aqueous solution?

HF(aq)+OH−(aq)→H2O(l)+F−(aq)HF(aq)+OH−(aq)→H2O(l)+F−(aq)

Which of the following best helps explain why an atom of Rb gas more easily loses an electron in a chemical reaction than an atom of Li gas?

In the Rb atom the valence electron is farther from its nucleus than the valence electron of Li is from its nucleus

Ba2+(aq)+SO42−(aq)→BaSO4(s) A student obtains a 10.0g sample of a white powder labeled as BaCl2. After completely dissolving the powder in 50.0mL of distilled water, the student adds excess Na2SO4(s), which causes a precipitate of BaSO4(s) to form, as represented by the equation above. The student filters the BaSO4(s), rinses it, and dries it until its mass is constant. Which of the following scientific questions could best be answered based on the results of the experiment?

Is the BaCl2(s)BaCl2(s) used in the experiment pure?

Which of the following indicates whether the solid substance represented by the particulate diagram shown above conducts electricity and explains why or why not?

It conducts electricity because electrons are free to move through the substance.

Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g) When the reaction represented above proceeds, heat is produced. Which of the following best describes the reaction?

It is an oxidation-reduction reaction because zinc is oxidized and hydrogen is reduced

HC2H3O2(aq)+OH−(aq)→C2H3O2−(aq)+H2O(l) A student carried out a titration using HC2H3O2(aq) and NaOH(aq). The net ionic equation for the neutralization reaction that occurs during the titration is represented above. The NaOH(aq) was added from a buret to the HC2H3O2(aq) in a flask. The equivalence point was reached when a total of 20.0mL of NaOH(aq) had been added to the flask. How does the amount of HC2H3O2(aq) in the flask after the addition of 5.0mL of NaOH(aq) compare to the amount of HC2H3O2(aq) in the flask after the addition of 1.0mL of NaOH(aq), and what is the reason for this result?

It is less because more HC2H3O2(aq) reacted with the base.

Which of the following is the correct net ionic equation of the reaction that occurs when aqueous solutions of ammonia and hydrochloric acid are combined?

NH3(aq)+H+(aq)→NH4+(aq)NH3(aq)+H+(aq)→NH4+(aq)

A chemistry teacher carried out several demonstrations, and students recorded their observations. For one of the demonstrations, a student concluded that a physical change took place, but not a chemical change. Which of the following observations could the student have made of the results of the demonstration?

One piece of solid substance was changed into small pieces.

When C2H4(g) reacts with H2(g), the compound C2H6(g) is produced, as represented by the equation above. The reaction is correctly classified as which of the following types?

Oxidation-reduction, because H2(g) is oxidized.

I2(aq)+C6H8O6(aq)→C6H6O6(aq)+2I−(aq)+2H+(aq) The compound C6H8O6 reacts with I2 according to the reaction represented by the equation above. The reaction is correctly classified as which of the following types?

Oxidation-reduction, because I2 is reduced.

2 H2O2(aq) → 2 H2O(l) + O2(g) ΔH° = −196 kJ/molrxn The decomposition of H2O2(aq) is represented by the equation above. A student monitored the decomposition of a 1.0 L sample of H2O2(aq) at a constant temperature of 300. K and recorded the concentration of H2O2 as a function of time. The results are given in the table below.

Oxygen is both oxidized and reduced.

The atomic radii of the elements in the nitrogen group in the periodic table are given in the table above. Which of the following best helps explain the trend of increasing atomic radius from N to Bi?

The attractive force between the valence electrons and the nuclei of the atoms decreases.

Which of the following correctly compares the strength of the two carbon-to-carbon bonds in the molecule represented in the Lewis diagram shown above?

The carbon-to-carbon bond on the left is stronger because it is a double bond.

Which of the following best helps to explain why the atomic radius of K is greater than that of Br?

The effective nuclear charge experienced by valence electrons is smaller for K than for Br

Which of the following claims about a binary compound in which the bonding is ionic is most likely to be scientifically valid?

The electronegativity difference between the elements in the compound is relatively large.

A 1.0 mol sample of which of the following compounds has the greatest mass?

The mass of a sample of any compound can be calculated by n×Mn×M, where n is the number of moles of molecules in the sample and MM is the molar mass (mass per mole) of the compound. The compound with molecules containing the greatest number of atoms of N and O has the greatest molar mass. Since each sample contains the same number of molecules (1.0mol of molecules), the sample of N2O5N2O5 has the largest mass.

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? Assume that the pressure and temperature in the lab are 1.0atm and 25°C.

The molar mass of Cu

Photoelectron Spectrum

The peaks in PES spectra correspond to the electrons in different subshells of the atom. The peaks with the lowest binding energy correspond to the valence electrons, while the peaks at the highest binding energy correspond to the inner-shell or core electrons

A student combines a solution of NaCl(aq) with a solution of AgNO3(aq), and a precipitate forms. Which of the following is evidence that ionic bonds formed during the precipitation?

The precipitate has a high melting point

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?

The resulting mixture was cloudy.

Al(s)→Al3+(aq)+3e− Zn2+(aq)+2e−→Zn(s) The half-reactions for the oxidation-reduction reaction between Al(s) and Zn2+(aq) are represented above. Based on the half-reactions, what is the coefficient for Al(s) if the equation for the oxidation-reduction reaction is balanced with the smallest whole-number coefficients?

The smallest whole-number coefficient for Al is 2. The number of electrons in the two half-reactions must be equal. Six electrons are given up by 2 Al atoms in the oxidation half-reaction, and six electrons are added to 3 Zn2+ ions in the reduction half-reaction. In the balanced equation for the reaction, the smallest whole-number coefficients for Al and Al3+ are 2 and the coefficients for Zn2+ and Zn are 3

Which of the following best helps explain why the first ionization energy of K is less than that of Ca?

The valence electron of K experiences a lower effective nuclear charge than the valence electrons of Ca

On the basis of electronegativity differences between atoms, which of the following scientific claims is the most accurate regarding the bonding in Mg(NO3)2(s) ?

There is ionic bonding between Mg2+ ions and NO3− ions.

ionic bond properties

They form crystals. They have high melting points and high boiling points. They have higher enthalpies of fusion and vaporization than molecular compounds. They're hard and brittle. They conduct electricity when they are dissolved in water. They're good insulators

K2SO3(aq)+2HNO3(aq)→2KNO3(aq)+SO2(g)+H2O(l) According to the balanced chemical equation above, when 100.0mL of 0.100MK2SO3(aq) is mixed with 100.0mL of 0.200MHNO3(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 the following changes would double the volume of SO2 produced at the same temperature and pressure? (For each change, assume that the other solutions and volumes remain the same.)

Using 200.0mL of 0.100MK2SO3(aq) and 200.0mL of 0.200MHNO3(aq), because these are the required stoichiometric amounts

A student measures the mass of a sample of a metallic element, M. Then the student heats the sample in air, where it completely reacts to form the compound MO. The student measures the mass of the compound that was formed. Which of the following questions can be answered from the results of the experiment?

What is the molar mass of M?

Based on the Lewis diagram for NH3, shown above, the H-N-H bond angle is closest to which of the following?

With four electron domains around the central N atom, their geometry is tetrahedral (which minimizes repulsion among the four electron pairs). The tetrahedral angle is 109.5°; therefore, the H-N-H bond angle is approximately 109.5°

A student combines a solution of NaCl(aq) with a solution of AgNO3(aq), and a precipitate forms. Assume that 50.0mL of 1.0MNaCl(aq) and 50.0mL of 1.0MAgNO3(aq) were combined. According to the balanced equation, if 50.0mL of 2.0MNaCl(aq) and 50.0mL of 1.0MAgNO3(aq) were combined, the amount of precipitate formed would

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

precipitation reaction

refers to the formation of an insoluble salt when two solutions containing soluble salts are combined. The insoluble salt that falls out of solution is known as the precipitate, hence the reaction's name. Precipitation reactions can help determine the presence of various ions in solution

covalent bond properties

relatively low melting points and boiling points. Covalent compounds usually have lower enthalpies of fusion and vaporization than ionic compounds. Covalent compounds tend to be more flammable than ionic compounds. When dissolved in water, they don't conduct electricity