Chemistry 2- Exam 1

This is for chemistry 2 (college Level)

What are the main differences in SO3 and SO3^2-?

Sulfur trioxide is a neutral molecular compound, sulfite is a polyatomic dianion

Review 1 On Your Own TO Make Sense

Review Activty 1

What are the electronegativity differences for F2, HF, and CsF? Would your team characterize HF as more covalent or more ionic, based on the electronegativity difference?

The electronegativity difference for F2 is 0, for HF it is 1.78, and for CsF it is 3.20 For polarities greater than1.7 the bond is considered to be more ionic than covalent, although it possesses characteristics of both

Why is there no arrow showing a molecular dipole for CO2?

The bond polarities add up to zero in the molecule CO2, resulting in no permanent dipole

If heat is required to liquefy a solid, is ΔHfusion endothermic or exothermic for this process? What is the sign of this process?

Heat is required by endothermic systems. The sign is (+)

If heat must be lost to condense a gas into a liquid, is ΔHvaporization endothermic or exothermic for this process?What is the sign of this process?

Heat is lost when a gas condenses into a liquid, that is an exothermic process. The sign is (-).

What extent of ordering is expected for molecules in the gas phase? What is your team's reasoning?

Very little if any ordering is expected since gas molecules are very far apart relative to their size.

Considering the compounds in the table above are of similar size and mass, what does the increase in theboiling point temperature suggest?

The larger the dipole moment of a molecule the stronger its dipole-dipole interactions will be with other dipolarmolecules. For molecules that are about the same size and mass, the strength of the dipole-dipole attractionsincreases with polarity of the molecule

Which atoms in the periodic table should be most polarizable? Why?

Those atoms lower and further to the left in the periodic table. The larger an atom and the more electrons ithas the more polarizable it should be

Why do these two molecules, having the same formula (C3H8O) and mass, have such different boiling points?

Because their masses are the same the extent of London forces should be similar, and their permanent dipolesshould be close to the same size but propanol can participate in hydrogen bonding that ethyl methyl ethercannot producing stronger intermolecular interactions in its liquid state.

Why does the trend in boiling points in the Group 14 molecules change in a predictable manner?

The trend for the hydrides of Group 14 is due only to the London dispersion force and that force generallycorrelates with molecular mass.

Excluding NH3, H2O, and HF what intermolecular force should be most important for the other compoundsin Groups 15-17?

For the other molecules in the Groups 15-17, the dominant intermolecular force should be the London dispersion force even all of those molecules should have permanent dipoles based on their shapes and bond dipoles, the trend in boiling points correlates with mass than with dipole moments and inversely correlates with dipole moment

Review 2 Activty Page

Review 2

In which state will a substance have the lowest extent of intermolecular interactions? Justify your answer.

In the gaseous state because the molecules are far apart and have limited interactions

In your experience, which of water, pancake syrup and oil, which pours the fastest? Does the type of syrup or oil matter? Why?

Water pours the fastest

Considering that octane molecules are hydrocarbon chains, what should happen to the extent of interaction for a much longer hydrocarbon chain for example cetane, C16H34

The extent of interaction should increase as the chains lengthen, grease has many more units and wax even more than that, as indicated by their increasing viscosities. Wax has such a high viscosity at room temperature it becomes solid.

Petroleum based greases and waxes are also hydrocarbons. How many hydrocarbon units (C-H containing) do you think greases and waxes have generally compared to octane (the basis for gasoline) and methane (the basis for natural gas)? How does that relate to the viscosity

Petroleum based greases and waxes have many more C-H unit that octane or methane. Because of all of the interactions of the C-H units in the long chain in a grease or a wax, these substances are much more viscous than octane and methane.

Ethylene glycol is the most commonly used type of antifreeze added to a car radiator, pure ethylene glycol is about 15 times as viscous as pure water. As water is added to ethylene glycol the viscosity of the solution decreases. What do you think is happening regarding the extent of interaction between the molecules of ethylene glycol when water is added?

The interactions between the ethylene glycol molecules are decreased, therefore resulting in a lower viscosity.

What types of van der Waals forces are primarily responsible the observed effect of water "climbing the walls" of a glass tube?

Water molecules are attracted to the surface of the glass by dipole-ion and hydrogen bonding forces.

What type of van der Waals force will be dominant between atoms of mercury in its liquid phase?

Individual atoms can only exhibit London dispersion forces.

Based on your answer above, how can the downward curve of the meniscus of mercury in a glass tube be explained?

Individual atoms can only exhibit London dispersion forces. There will be limited interactions with the ionic and hydrogen bonding sites of the glass surface between the mercury atoms and the glass.

What is standard atmospheric pressure at sea level in atm and torr?

Standard pressure at sea level is 1 atm (760 torr, 760 mmHg). Boiling.

What common term is normally used to describe the behavior of water at 100 oC and standard atmospheric pressure?

Boiling

The peak of Mt. Everest in Nepal is 29, 028 ft resulting in a very low atmospheric pressure of about 253 torr.1 Based on the graph above what should the boiling point temperature of water be at 250 torr?

Look at Graph, but your answer should be 80-85°C

Considering the following graph of vapor pressure vs. temperature for ethanol (CH3CH2OH), what should its boiling point be at standard atmospheric pressure?

Approximately 88oC. Use the graph to find the answer. Look for the point on the line that corresponds to 760 torr.

Consider the vapor pressure curves of water and ethanol above, how do the vapor pressures of the two liquids compare at a single temperature (it will probably be easier to see the difference at higher temperatures)?

Ethanol has a much higher vapor pressure than water.

When the number of molecules in the gas phase increases, what happens to the gas pressure? Why is that?

The gas pressure increases. By Avogardo's law as the number of gas molecules increases, the pressure increases. According to kinetic molecular theory the number of collisions will increase per unit time.

Considering the scientific definitions of volatile and volatility, is water correctly called a volatile substance?

Water is a volatile substance, although it has very low volatility. It does vaporize and evaporates, although its volatility is much lower than other common substances such as isopropanol.

What is volatile?

substance readily evaporates or is vaporized. Informally knows as explodes

Based on the measured data in the graph above, what change occurs in T as water changes from one state into another state (e.g., the conversion from water to steam)?

T remains constant (or the same) during a phase change. It does not keep increasing until the phase change is complete, ie, all of the ice has melted to liquid

Ice warming from 30K to 250 K

Endothermic

Steam cooling from 450 K to 400K

Exothermic

Water cooling from 350 K to 300 K.

Exothermic

The conversion of water to steam

Endothermic

The conversion from liquid to ice

Exothermic

If all substances have similar heating curves to that shown for water, what does that suggest regarding the change in T as a substance converts from one phase to another?

There is no change in temperature during phase changes as the energy that is released or absorbed is used to change the phase of the matter rather than raise the overall temperature of the substance.

Which of the terms sublimation or deposition makes the most sense for the conversion of a gas phase substance into its solid phase?

Deposition make the most sense since ice is being deposited from the gas phase.

If condensation means the conversion from gas to liquid would it be correct to use it instead of the term you chose for the process of converting a gas to a solid?

No condensation specifically refers to the conversion from gas to liquid.

Which of those terms makes the most sense for the conversion of a solid phase substance into its gas phase? Why did you make that choice?

Since deposition means gas to solid, apparently sublimation must mean solid to gas.

If evaporation means the conversion from liquid to gas would it be correct to use it instead of the term your team chose for the process of converting a solid to a gas?

No again evaporation is specific to the conversion of liquid to gas.

Melting is the common term for the conversion from solid to liquid. Freezing (or fusion) is the appropriate term for conversion from liquid to solid.Melting is the common term for the conversion from solid to liquid. Freezing (or fusion) is the appropriate term for conversion from liquid to solid.Melting is the common term for the conversion from solid to liquid. Freezing (or fusion) is the appropriate term for conversion from liquid to solid. Melting is the common term for the conversion from solid to liquid. Freezing (or fusion) is the appropriate term for conversion from liquid to solid.

Did any one on your team ever notice frost in the freezer? Did any one on you team ever notice that ice cubes seem to disappear if they sit in a frost-free freezer too long? There are specific terms for processes of phase change between solid and gas phases:

sublimation and deposition

Considering a column of air above one square inch of a surface at sea level, the air in that one inch square column must have total weight of how many pounds, kilograms?

14.7 lbs, 6.68 kg (2.2 lbs = 1 kg)

(A) what should happen to the mass is air in a 1 in2 column as you go higher elevations (B)? What effect should that have on the measured atmospheric pressure?

The mass should decrease as the column shortens, this should lower the pressure.

What is the total weight in pounds of air resting on this 8.5 in x 11 in (assuming it is at sea level)?

8.5 in x 11 in = 93.5 in2 93.5 in2 x 14.7 psi = 1400 lbs (corr. sig. fig.)

What should happen to the height, H, of the column of mercury if the atmospheric pressure decreases?

The height will decrease

Consider a less dense liquid than mercury is used to make a barometer. Compared to the column height of mercury at the same pressure, the less dense liquid column height should?

A less dense liquid will rise to an increased height.

If the atmospheric pressure in Denver is 550 mm Hg, what is that pressure in atmospheres?

550 mm Hg x 1 atm/760 mm Hg = 720 atm (corr. sig. fig.)

Atmospheric pressure is reported on American TV in inches Hg rather than in mm Hg. If 1 in = 25.4 mm what is the pressure in mm Hg if the measured pressure is 29.4 in Hg?

550 mm Hg x 1 atm/760 mm Hg = 720 atm (corr. sig. fig.)

Consider that air can lift 760 mm Hg at standard pressure, since mercury is 13.534 times as dense as water, how many mm H2O should the air be able to support?

760 mm Hg x 13.534 = 10285 mm H2O

760 mm Hg is a definition.

What is the pressure in torr if the measured pressure is 0.458 atm?

0.458 atm x 760 torr/atm = 348.1 torr

When the trapped gas pressure is greater than the atmospheric pressure, the measured pressure will equal?

The pressure will measure lower.

When the trapped gas pressure is less than the atmospheric pressure, the measured pressure will equal?

The pressure will measure greater.

When the trapped gas pressure is equal to the atmospheric pressure, the measured pressure will equal?

The measured pressure will be the same as the trapped gas pressure.

What happens to the gas pressure inside of a rigid container when more gas molecules are added at constant temperature?

The pressure increases. Like adding air to a basketball.

What happens to the gas pressure inside of a rigid container when the container is heated containing a fixed number of gas molecules?

The pressure increases. Similar to placing an aerosol can in a fire (Don't do it, it is an explosion hazard).

What happens to the gas pressure inside of a container when the volume of the container is increased at a fixed temperature and containing a fixed number of gas molecules?

The pressure will decrease.

What happens to the temperature of a fixed number of gas molecules when the gas is allowed to expand into a larger volume at fixed pressure?

The temperature decreases. Similar to the cooling effect felt when compressed air is allowed to expand over skin.

What happens to the volume of an expandable container when more molecules of gas are added at fixed temperature and pressure?

The volume increases. Like blowing up a balloon.

What happens to the volume of an expandable container when the gas temperature is raised at a fixed pressure and constant number of molecules of gas?

The volume increases. Like placing a partially inflated balloon into a warm water bath.

Boyle's Law

states that as pressure changes the volume changes inversely if its container is occupied by a constant number of moles of gas at a constant temperature.

Charles's Law

states that as temperature changes the volume will change proportionally if the pressure and number of moles remains constant.

Avogadro's Law

states that as number of moles changes the volume proportionally if the pressure and the temperature are constant.

Gay-Lussac's

law state that the pressure exerted by a gas on its container is proportional to the absolute temperature when the volume and number of moles of gas are held constant

What do all of the gas laws have in common in addition to the same four variables: pressure, volume, number of moles, and temperature?

Two variables are fixed.

At standard temperature and pressure of 1 atm and 0 oC, 1 mol of ideal gas occupies 22.4141 L volume, what is the value of the gas constant? Don't leave out the units!

R = [(1 atm)(22.4 L)]/[(273.15 K)(1 mol)] = 0.08 (atm·L)/(mol·K)(corr. sig. fig if measurements are used)

More precisely it is: 0.08206

Why must the temperature used in all gas calculations in units of Kelvin rather than Celsius or Fahrenheit?

The result of dividing by zero is undefined. Kelvin must be used because all gases exist at some temperature above 0 Kelvin, therefore no there is no possibility of obtaining an undefined result. If Celsius were used, then negative values or a zero value could be obtained but would have no practical meaning.

What number of moles of gas occupy a volume of 10.0 L, at 1.21 atm pressure, and a temperature of 25 oC? R can be looked up in a textbook or online.

Need to find n. Therefore PV = nRT needs to be solved for n. n = PV/RT

n = [(1.21 atm)(10.0 L)]/[(0.08206 {atm·L}/{mol·K})(298.15 K)] = 0.495 mol (corr. sig. fig.)

Which of the following gas molecules should have the largest value of b? (CO2, CO, H2, O2)

b indicates the volume occupied by the gas molecules. CO2 will be the largest molecule and will have the highest value of b, then O2, CO and H2 will have the smallest. The more atoms in the molecule the larger the molecule. Remember that atomic radii decrease as you go from left to right across the periodic table.

What is the density of a gas having a molar mass of 44.01 g/mol and a measured pressure of 0.500 atm at 25 oC?

D = P(MM)/RT = (0.500 atm)(44.01g/mol)/(0.0821)(25+273K) = 0.899 g/L

What would be the correct equation for the determination of molar mass from the measured density and pressure of a gas sample at a fixed temperature?

MM = DRT/P

What is the molar mass of a gas sample if its density is determined to be 0.654 g/L at a pressure of 0.500 atm and a temperature of 298 K?

MM = DRT/P = (0.654 g/L)(0.0821)(298K)/(0.500 atm) = 32.00 g/mol

What variables in ideal gas law must not change for Dalton's law to be valid?

The temperature and volume need to remain constant for Dalton's law to apply.

What is the total pressure in a container into which 1.30 atm N2, 0.24 atm O2, and 0.020 atm CO2 are introduced? (If this isn't very simple, you are doing it incorrectly).

1.30 atm N2 + 0.24 atm O2 + 0.020 atm CO2 = 1.56 atm gas mixture

In the problem above determine the total number of moles of gas if the container has a volume of 0.75 L and the temperature is 0 oC.

nt = PtV/RT nt = [(1.56 atm)(0.75 L)]/[(0.08206 {atm·L}/{mol·K})(273.15 K)] = 0.052 mol (corr. sig. fig.)

Does the total number of moles computed in problem 10 match the sum of the moles computed in problem 11. If so, explain why. If not, explain why there is a difference?

nN2 + nO2 + nCO2 = 0.043 mol + 0.0080 mol + 0.00066 mol = 0.052 mol (corr. sig. fig.)

Review 5

5

In a container of gas, should al of the molecules have the same kinetic energy?

What is kinetic energy?

is the energy of motion.

Which end of the water molecule dipole will interact with the calcium ion in the dissolution of CaCl2?

The oxygen end of the water molecule dipole, which is the more electronegative and will be slightly negative, will interact with the positive calcium ion.

Which intermolecular force would be responsible for the ability of pentane (C5H14) to dissolve a hydrocarbon grease (a mixture of larger alkanes)?

van der Waals forces would explain the interaction between these non-polar molecules.

Based on the nature and strength of their relative intermolecular forces, which of the following should be more soluble in water, CO2 or O2 at 25 oC

CO2 is more soluble in water than O2 due to dipole-dipole interactions between carbon dioxide and the water. Even though CO2 is non-polar, it does have two polarized bonds that are in equal and opposite directions. These can interact with the dipole of the water. O2 is non-polar and will only have van der Waals interactions with the water.

Considering the model above what words are missing the sentences: Saline is a solution___ that consists

of a mixture of salt that has been dissolved into water. Salt is the solute__ and water is the solvent_. (solute, sovent, dissolved, solution)

Why do small bubbles form when heating water, even if the temperature is well below boiling point?

This is most likely due to dissolved atmospheric gases coming out of the water solution upon heating.

Why is it necessary to use the proper capitalization in symbols such as molarity and molality?

Molarity and molality are different quanitites, so you need to correctly express which quantity you are speaking of.

What would would happen if a container that could contain exactly 1.00 L was filled to the brim with water and then 200. g of NaCl were added to it?

The volume of the NaCl would displace an equal amount of water, spilling out of the container.

If 200. g NaCl is about 3.42 moles, what would be the molarity of the solution in the 1.00 L container once all of the salt dissolves?

Molarity = moles/Liters of solution = 3.42 moles/1.00L = 3.42 M

The density of NaCl is 2.165 g/mL, what volume of water would 200. g of NaCl displace?

Density = mass/Volume => Volume = mass/density = 200g/2.165 g/mL = 92.4 mL

What mass of water in kg would remain in the container after 200. g of NaCl was added to the 1.00 L of water? (Assume the density of water is 1.00 g/mL)

1000 mL would have a mass of 1000g. The density tells us that 1 mL of water has a mass of 1g. 92.4 mL would have a mass of 92.4g. Therefore, 1000g – 92.4g = 907.6g of water will be left in the container.

What is the molality of the solution described above after all of the salt has dissolved?

Molality = moles/kg of solvent = 3.42 moles/0.9076 kg = 3.77 m

Is molarity the same thing as molality?

No! Molarity depends on the volume of the solution. Molality depends on the mass of solvent.

Review 5678

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