AP Chemistry Final

1s2 2s2 2p6 3s2 3p6 How many unpaired electrons are in the atom represented by the electron configuration above?

0

At 10.°C, 20.g of oxygen gas exerts a pressure of 2.1atm in a rigid, 7.0L cylinder. Assuming ideal behavior, if the temperature of the gas was raised to 40.°C, what indicates the new pressure and explains why?

2.3atm, because the pressure P increases by the proportion 313/283.

One mole of gaseous HA is placed in a one liter container. At equilibrium it is 18% dissociated according to the equation shown here:

2HA ↔ 2H + A2

The Ksp of BaSO4 is 1.5 x 10-9. What is the molar concentration of Ba2+(aq) in a saturated solution of BaSO4?

3.9 x 10-5 M

What is the pH of a 0.00350 M HNO3 solution?

46

What numerical expression gives the number of moles in 5.0g of CaO?

5.0g56g/mol

A buffer solution is prepared that is 0.50 M in propanoic acid and 0.40 M in sodium propanoate with a solution volume of 1.00 liters. (Ka for propanoic acid = 1.3 x 10-5). What is the pH of the solution when 0.040 mol of HCl(g) is added to the solution? Assume no change in solution volume.

71

A gaseous air‑fuel mixture in a sealed car engine cylinder has an initial volume of 600.mL at 1.0atm. To prepare for ignition of the fuel, a piston moves within the cylinder, reducing the volume of the air‑fuel mixture to 50.mL at constant temperature. Assuming ideal behavior, what is the new pressure of the air‑fuel mixture?

About 12atm, because the volume of the gas mixture decreased by a factor of 12.

The particles in solid KI, a stable ionic compound, are arranged to maximize coulombic attractions while minimizing coulombic repulsions among the particles. Why?

Because it alternates between positive and negative

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.

Equimolar samples of CH4(g) and C2H6(g) are in identical containers at the same temperature. The C2H6(g) deviates much more from ideal behavior than the CH4(g) does. What explains this devastation?

C2H6 molecules have a larger, more polarizable electron cloud than CH4 molecules do.

The gases CO2(g) and NH3(g) can be liquefied at 20°C by compressing them to sufficiently high pressures. A student claims that NH3(g) can be liquefied at a lower pressure than CO2(g) can be liquefied. What justifies 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.

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 what substance would support the claim that the observed phenomenon was a physical change?

H2O(g).

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

HF(aq)+OH−(aq)→H2O(l)+F−(aq)

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. What scientific questions could best be answered based on the results of the experiment?

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

Determine the equilibrium constant.

K = 0.0043

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.

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

The molar mass of each gas

Two sealed, rigid 5.0L containers each contain a gas at the same temperature but at a different pressure, as shown above. Also shown are the results of transferring the entire contents of container 1 to container 2. No gases escape during the transfer. Assuming ideal behavior, what is correct regarding the total pressure of the gases after they are combined?

The total pressure of the gases in the mixture is the sum of the initial pressures of oxygen gas and nitrogen gas because pressure only depends on the total amount of gas when volume and temperature are held constant.

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

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