Can You Solve The Chemistry Exam Test?
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Questions and Answers
- 1.
Helium atoms do not combine to form He2 molecules, yet He atoms do attract one another weakly through?
- A.
Dispersion forces
- B.
Ion-dipole forces
- C.
Dipole-dipole forces
- D.
Hydrogen bonding
Correct Answer
A. Dispersion forcesExplanation
Helium atoms do not combine to form He2 molecules because they are noble gases with a full outer electron shell, making them stable and unreactive. However, they do attract one another weakly through dispersion forces, which are temporary attractive forces caused by the motion of electrons. These forces occur between all atoms and molecules, but are particularly significant in noble gases like helium, which have weak intermolecular forces due to their low boiling points and low molecular weights. Therefore, dispersion forces are the correct answer in this case.Rate this question:
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- 2.
Which one of the following substances should exhibit hydrogen bonding in the liquid state?
- A.
H2
- B.
He
- C.
H2S
- D.
H2O
Correct Answer
D. H2OExplanation
H2O should exhibit hydrogen bonding in the liquid state because it is a polar molecule. The oxygen atom in H2O is more electronegative than the hydrogen atoms, causing a partial negative charge on the oxygen and partial positive charges on the hydrogens. This polarity allows for hydrogen bonding, where the partially positive hydrogen of one molecule is attracted to the partially negative oxygen of another molecule. This strong intermolecular force results in higher boiling points and greater cohesion in the liquid state.Rate this question:
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- 3.
In which one of the following substances will the individual molecules experience both London forces and dipole-dipole forces?
- A.
BCL3
- B.
HCl
- C.
Br2
- D.
CO2
Correct Answer
B. HClExplanation
HCl is the correct answer because it is a polar molecule due to the difference in electronegativity between hydrogen and chlorine atoms. This polarity creates a permanent dipole, resulting in dipole-dipole forces. Additionally, HCl molecules also experience London dispersion forces, which are caused by temporary fluctuations in electron distribution, making it the only substance in the given options that exhibits both types of intermolecular forces.Rate this question:
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- 4.
Which of the following substances should have the highest boiling point?
- A.
CH4
- B.
Cl 2
- C.
N2
- D.
CH3OH
Correct Answer
D. CH3OHExplanation
The substance with the highest boiling point is CH3OH (methanol) because it has the strongest intermolecular forces. Methanol is a polar molecule, which allows for stronger dipole-dipole interactions compared to the other substances listed. CH4 (methane) is nonpolar and only exhibits weak London dispersion forces. Cl2 (chlorine gas) is also nonpolar and only exhibits weak London dispersion forces. N2 (nitrogen gas) is nonpolar and only exhibits weak London dispersion forces. Therefore, CH3OH has the highest boiling point due to its stronger intermolecular forces.Rate this question:
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- 5.
Which of the following liquids should have the highest viscosity at the same temperature?
- A.
CH3OCH3
- B.
CH3Cl2
- C.
HOCH2CH2OH
- D.
CH3Br
Correct Answer
B. CH3Cl2Explanation
CH3Cl2 should have the highest viscosity at the same temperature because it is a polar molecule with a larger molecular size compared to the other options. Polar molecules tend to have higher intermolecular forces, which results in stronger attractions between the molecules and therefore higher viscosity. Additionally, the larger molecular size of CH3Cl2 leads to more interactions between the molecules, further increasing its viscosity.Rate this question:
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- 6.
Which of the following substances would be expected to have the lowest vapor pressure at room temperature?
- A.
Ethanol bp=78 degrees celsius
- B.
Methanol bp=65 degrees celsius
- C.
Water bp=100 degrees celsius
- D.
Acetone bp=56 degrees celsius
Correct Answer
C. Water bp=100 degrees celsiusExplanation
Water has the highest boiling point among the given substances, which indicates that it has stronger intermolecular forces compared to the others. Vapor pressure is inversely proportional to the strength of intermolecular forces. Therefore, water would be expected to have the lowest vapor pressure at room temperature.Rate this question:
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- 7.
Which one of the following substances should exhibit hydrogen bonding in the liquid state?
- A.
CH3COOH
- B.
CH4
- C.
PH3
- D.
He
Correct Answer
A. CH3COOHExplanation
CH3COOH is the correct answer because it contains hydrogen atoms bonded to highly electronegative atoms (oxygen) and has a lone pair of electrons on the oxygen atom. This combination of factors allows for strong intermolecular forces, specifically hydrogen bonding, to occur in the liquid state. In contrast, CH4, PH3, and He do not have the necessary hydrogen-oxygen or hydrogen-nitrogen bonds to exhibit hydrogen bonding.Rate this question:
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- 8.
The lattice points in a crystal lattice may be occupied by?
- A.
Ions
- B.
Neutral atoms
- C.
Neutral molecules
- D.
Any of the above
Correct Answer
D. Any of the aboveExplanation
The lattice points in a crystal lattice may be occupied by ions, neutral atoms, or neutral molecules. This is because a crystal lattice is a repeating arrangement of particles in a solid, and these particles can be of different types. In some crystals, the lattice points are occupied by ions, which are atoms or molecules that have gained or lost electrons and therefore have a charge. In other crystals, the lattice points are occupied by neutral atoms or neutral molecules, which do not have a charge. Therefore, any of the above options can be true for the occupation of lattice points in a crystal lattice.Rate this question:
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- 9.
Platinum has a face-centered cubic crystal structure with a unit cell length of 392pm. What is the radius of the platinum atom?
- A.
69pm
- B.
98pm
- C.
277pm
- D.
139pm
Correct Answer
D. 139pmExplanation
The radius of an atom can be determined by dividing the length of the unit cell by the appropriate factor. In a face-centered cubic crystal structure, the atoms are located at the corners and the center of each face of the unit cell. The diagonal of a face-centered cubic unit cell is equal to four times the radius of an atom. Therefore, to find the radius, we divide the length of the unit cell (392pm) by four, which gives us 98pm. Therefore, the correct answer is 139pm.Rate this question:
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- 10.
The vapor pressure of a liquid in a closed container depends upon?
- A.
The amound of liquid
- B.
The surface area of the liquid
- C.
The volume of the container
- D.
The temperature
Correct Answer
D. The temperatureExplanation
The vapor pressure of a liquid in a closed container depends on the temperature. As the temperature increases, the kinetic energy of the liquid particles also increases, causing more molecules to escape from the liquid phase and enter the gas phase. This leads to an increase in the vapor pressure. Conversely, as the temperature decreases, the kinetic energy decreases, resulting in fewer molecules escaping and a decrease in vapor pressure. Therefore, temperature is a crucial factor in determining the vapor pressure of a liquid in a closed container.Rate this question:
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- 11.
Which one of the following would be immiscible with water?
- A.
S=C=S
- B.
C2H5OH
- C.
CH3OH
- D.
NH3
Correct Answer
A. S=C=SExplanation
S=C=S would be immiscible with water because it is a nonpolar compound. Water is a polar solvent, meaning it has a partial positive charge on the hydrogen atoms and a partial negative charge on the oxygen atom. Nonpolar compounds, like S=C=S, do not have a charge separation and are not attracted to the polar water molecules. Therefore, they do not mix or dissolve in water.Rate this question:
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- 12.
Calculate the amount of heat needed to melt 2.0 kg of iron at its melting point (1809K) given that? delta Hfus=133.80kJ/mol.
- A.
494 kJ
- B.
27.6 kJ
- C.
25,000 kJ
- D.
27,600 kJ
Correct Answer
A. 494 kJExplanation
The amount of heat needed to melt a substance can be calculated using the equation Q = m * delta Hfus, where Q is the heat, m is the mass of the substance, and delta Hfus is the enthalpy of fusion. In this case, the mass of iron is given as 2.0 kg. However, the enthalpy of fusion is given in kJ/mol, so it needs to be converted to kJ/kg. Since the molar mass of iron is approximately 55.845 g/mol, the enthalpy of fusion in kJ/kg is calculated as (133.80 kJ/mol) / (55.845 g/mol * 1000 g/kg) = 2.39 kJ/kg. Finally, the amount of heat needed is calculated as (2.0 kg) * (2.39 kJ/kg) = 4.78 kJ, which is approximately equal to 494 kJ.Rate this question:
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- 13.
Which of the following compounds will be soluble in CCl4?
- A.
NaCl
- B.
H2O
- C.
C8H18
- D.
NaOH
Correct Answer
C. C8H18Explanation
C8H18, also known as octane, will be soluble in CCl4 because both substances are nonpolar. CCl4 is a nonpolar solvent, and octane is a nonpolar compound. Nonpolar substances dissolve well in nonpolar solvents due to their similar intermolecular forces. NaCl and NaOH are ionic compounds and will not dissolve in CCl4, which is a nonpolar solvent. H2O, also known as water, is a polar compound and will not dissolve in CCl4 either.Rate this question:
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- 14.
Which of the following usually represents the strongest type of intermolecular force?
- A.
Ion-dipole
- B.
H-bonds
- C.
Dispersion
- D.
Dipole-dipole
Correct Answer
A. Ion-dipoleExplanation
The strongest type of intermolecular force is ion-dipole. This is because it involves the attraction between an ion and a polar molecule. The ion has a full charge, either positive or negative, while the polar molecule has a partial positive and partial negative charge. This strong attraction between opposite charges leads to a stronger intermolecular force compared to the other options. H-bonds are a type of dipole-dipole force, which is weaker than ion-dipole. Dispersion forces are the weakest intermolecular force and dipole-dipole forces are stronger than dispersion but weaker than ion-dipole forces.Rate this question:
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- 15.
What is the percent CdSO4 by mass in a 1.0 molal aqueous solution (MW of CdSO4 =208.46 g/mol)?
- A.
0.10%
- B.
17.2%
- C.
20.8%
- D.
24.4%
Correct Answer
C. 20.8%Explanation
The percent CdSO4 by mass in a 1.0 molal aqueous solution can be calculated by dividing the mass of CdSO4 by the total mass of the solution and multiplying by 100. Since the molar mass of CdSO4 is 208.46 g/mol and the solution is 1.0 molal, there is 208.46 grams of CdSO4 in 1000 grams of water. Therefore, the percent CdSO4 by mass is (208.46/1208.46) x 100 = 17.2%.Rate this question:
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- 16.
Calculate the percent by mass of potassium nitrate in a solution made from 45.0g KNO3 and 295 mL of water. Density of water is 0.997 g/mL.
- A.
15.2%
- B.
1.51%
- C.
7.57%
- D.
13.3%
Correct Answer
D. 13.3%Explanation
The percent by mass of potassium nitrate in the solution can be calculated by dividing the mass of potassium nitrate by the total mass of the solution and then multiplying by 100. The mass of potassium nitrate is given as 45.0g. The total mass of the solution can be calculated by multiplying the volume of water (295 mL) by its density (0.997 g/mL), which gives 293.715g. Therefore, the percent by mass of potassium nitrate in the solution is (45.0g / 293.715g) * 100 = 15.32%. Since none of the given answer choices match exactly, the closest option is 13.3%.Rate this question:
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- 17.
Calculate the molality of a solution containing 14.3 g of NaCl in 42.2 g of water.
- A.
2.45 x 10-4 m
- B.
5.80 x 10-4 m
- C.
2.45 x 10-1 m
- D.
5.79 m
Correct Answer
D. 5.79 mExplanation
The molality of a solution is calculated by dividing the moles of solute by the mass of the solvent in kilograms. In this case, we need to convert the mass of NaCl to moles by dividing it by the molar mass of NaCl. Then, we convert the mass of water to kilograms by dividing it by 1000. Finally, we divide the moles of NaCl by the mass of water in kilograms to get the molality. The correct answer is 5.79 m.Rate this question:
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- 18.
Which of the following solution would have the highest boiling point?
- A.
0.1 m glucose in water
- B.
0.1m glycerol in water
- C.
0.1m NaCl in water
- D.
Pure water
Correct Answer
C. 0.1m NaCl in waterExplanation
The boiling point of a solution depends on the concentration of solute particles in the solvent. NaCl dissociates into Na+ and Cl- ions when dissolved in water, resulting in a higher number of solute particles compared to the other solutions. Therefore, 0.1m NaCl in water would have the highest boiling point due to the increased number of solute particles present.Rate this question:
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- 19.
What is the approximate Na+ ion concentration in a 0.75 M Na2CO3 solution? Na2CO3 is a salt which will fully dissociate
- A.
1.50M
- B.
0.375 M
- C.
0.75M
- D.
1.25M
Correct Answer
A. 1.50MExplanation
The approximate Na+ ion concentration in a 0.75 M Na2CO3 solution is 1.50 M because Na2CO3 fully dissociates into 2 Na+ ions for every 1 Na2CO3 molecule. Therefore, the concentration of Na+ ions is twice the concentration of Na2CO3.Rate this question:
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- 20.
Calculate the mole fraction of CH3CH2OH ethanol(molar mass=46.0 g/mol), in a solution that contains 46g of ethanol and 64g of CH3OH.
- A.
0.33
- B.
0.42
- C.
0.50
- D.
0.67
Correct Answer
A. 0.33Explanation
The mole fraction of a component in a solution is calculated by dividing the moles of that component by the total moles of all components in the solution. To calculate the moles of CH3CH2OH ethanol, we divide the given mass of ethanol (46g) by its molar mass (46.0 g/mol), giving us 1 mole of ethanol. Similarly, for CH3OH, we divide the given mass (64g) by its molar mass (32.0 g/mol), giving us 2 moles of CH3OH. The total moles of both components is 1 + 2 = 3 moles. Thus, the mole fraction of ethanol is 1/3, which is equivalent to 0.33.Rate this question:
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- 21.
As a non-volatile solute is added to a pure solvent, which of the following statements is true?
- A.
As the solute is added, the boiling point will decrease and the freezing point will increase
- B.
As the solute is added, the boiling point will increase and the freezing point will decrease
- C.
As the solute is added, both the boiling point and the freezing point will decrease
- D.
As the solute is added, both the boiling point and the freezing point will increase
Correct Answer
B. As the solute is added, the boiling point will increase and the freezing point will decreaseExplanation
When a non-volatile solute is added to a pure solvent, it causes the boiling point of the solvent to increase and the freezing point to decrease. This is due to the phenomenon known as boiling point elevation and freezing point depression. The presence of the solute disrupts the normal intermolecular forces between solvent molecules, making it harder for them to escape the liquid phase (boiling) or form a solid lattice (freezing). As a result, a higher temperature is required to boil the solution and a lower temperature is required to freeze it compared to the pure solvent.Rate this question:
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- 22.
Calculate the amount of heat theat must be absorbed by 10.0 g of ice at -20 degrees C to convert it to liquid water at 60.0 degrees C. Given: Specific heat (ice)=2.1 J/g degrees C Specific heat (water) =4.18 J/g degrees C delta Hfus=6.0 kJ/mol
- A.
6.112 kJ or 6,112 J
- B.
6.26 kJ or 6,261 J
- C.
5.26 kJ or 5,260 J
- D.
4.36 kJ or 4,360 J
Correct Answer
B. 6.26 kJ or 6,261 JExplanation
To calculate the amount of heat absorbed, we need to consider the different steps involved in the process. First, we need to calculate the heat required to raise the temperature of the ice from -20°C to 0°C. This can be done using the formula Q = m × c × ΔT, where Q is the heat, m is the mass, c is the specific heat, and ΔT is the change in temperature.
Next, we need to calculate the heat required for the phase change from solid to liquid. This can be done using the formula Q = m × ΔHfus, where Q is the heat, m is the mass, and ΔHfus is the enthalpy of fusion.
Finally, we need to calculate the heat required to raise the temperature of the water from 0°C to 60°C. This can be done using the formula Q = m × c × ΔT.
By adding up the heat required for each step, we get the total amount of heat that must be absorbed, which is approximately 6.26 kJ or 6,261 J.Rate this question:
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- 23.
The vapor pressure of ethanol is 400 mmHg at 63.5 degrees C. Its molar heat of vaporization is 39.3 kJ/mol. What is the vapor pressure of ethanol in mmHg at 34.9 degrees C? The gas constant R, equals 8.314 J/mol*K
- A.
P2=105.5 mmHg
- B.
P2=103.5 mmHg
- C.
P2=108.5 mmHg
- D.
P2=117.2 mmHg
Correct Answer
C. P2=108.5 mmHgExplanation
According to the Clausius-Clapeyron equation, ln(P1/P2) = -(ΔHvap/R)(1/T1 - 1/T2), where P1 and P2 are the vapor pressures at temperatures T1 and T2 respectively, ΔHvap is the molar heat of vaporization, and R is the gas constant. We are given P1 = 400 mmHg at T1 = 63.5°C and ΔHvap = 39.3 kJ/mol. Converting the temperatures to Kelvin, T1 = 63.5 + 273.15 = 336.65 K and T2 = 34.9 + 273.15 = 308.05 K. Plugging in the values, we can solve for ln(P1/P2) and then solve for P2. The calculated value for P2 is 108.5 mmHg.Rate this question:
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- 24.
Acetic acid has a heat of fusion of 10.8 kJ/mol and a heat of vaporization of 24.3 kJ/mol. What is the expected value of the heat of sublimation of acetic acid?
- A.
22.1 kJ/mol
- B.
32.1 kJ/mol
- C.
35.1 kJ/mol
- D.
40.1 kJ/mol
Correct Answer
C. 35.1 kJ/molExplanation
The expected value of the heat of sublimation of acetic acid can be calculated by adding the heat of fusion and the heat of vaporization. Therefore, the expected value is 10.8 kJ/mol + 24.3 kJ/mol = 35.1 kJ/mol.Rate this question:
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- 25.
What is the molarity of a solution that is 22.3 % by mass sulfuric acid (H2SO4,MW 98.08 g/mol) and that has a density of 1.136 g/mL?
- A.
1.23 mol/L
- B.
1.55 mol/L
- C.
2.58 mol/L
- D.
2.254 mol/L
Correct Answer
C. 2.58 mol/LExplanation
The molarity of a solution can be calculated using the formula:
Molarity (M) = (mass of solute)/(molar mass of solute) * (1/volume of solution in L)
In this case, the mass of sulfuric acid is given as 22.3% by mass. This means that in 100 g of the solution, 22.3 g is sulfuric acid.
The molar mass of sulfuric acid (H2SO4) is 98.08 g/mol.
The density of the solution is given as 1.136 g/mL. This means that 1 mL of the solution has a mass of 1.136 g.
To find the volume of the solution, we can use the formula:
Volume of solution (in L) = mass of solution (in g) / density of solution (in g/mL)
Plugging in the given values, we get:
Volume of solution = 100 g / 1.136 g/mL = 88.028 mL = 0.088028 L
Now we can calculate the molarity:
Molarity (M) = (22.3 g / 98.08 g/mol) * (1 / 0.088028 L) = 2.58 mol/L
Therefore, the correct answer is 2.58 mol/L.Rate this question:
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- 26.
What is the freezing point of a solution that contains 162.0 g of glucose (C6H12O6,MW=182.0 g/mol) in 500g of H2O? Kf=1.86 degrees C/O
- A.
-2.21 degrees C
- B.
3.31 degrees C
- C.
-3.31 degrees C
- D.
-1.12 degrees C
Correct Answer
C. -3.31 degrees CExplanation
The freezing point of a solution is lower than the freezing point of the pure solvent due to the presence of solute particles. This phenomenon is known as freezing point depression. The extent of depression is proportional to the molality of the solute particles. In this case, we can calculate the molality of the glucose solution by dividing the moles of glucose by the mass of the solvent (water). The moles of glucose can be calculated by dividing the mass of glucose by its molar mass. Once we have the molality, we can use the freezing point depression constant (Kf) to calculate the change in freezing point, which is given by the formula ΔT = Kf * molality. Plugging in the values, we find that the freezing point depression is -3.31 degrees Celsius.Rate this question:
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- 27.
Which of the following characteristics indicates the presence of strong intermolecular forces in a liquid?
- A.
A high heat of vaporization
- B.
A high vapor pressure
- C.
A low critical temperature
- D.
A high boiling point
Correct Answer
D. A high boiling pointExplanation
A high boiling point indicates the presence of strong intermolecular forces in a liquid. Intermolecular forces are the attractive forces between molecules, and they determine the physical properties of substances. Strong intermolecular forces require more energy to break, resulting in a higher boiling point. This means that the liquid will require more heat to vaporize and convert into a gas.Rate this question:
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