Chemistry Tutor Competency Quiz

1. Which physical method of separating mixtures would you use to separate colors in a dye?

Chromatography

Separating funnel

Centrifugation

Simple distillation

Chromatography is a physical method of separating mixtures based on the differences in the components' ability to be carried by a mobile phase. In the case of separating colors in a dye, chromatography can be used because different colors have different affinities for the mobile phase. As the mobile phase moves through a stationary phase, the colors will separate based on their interactions with the stationary phase, allowing for the individual colors to be collected and analyzed.

Explanation

Chromatography is a physical method of separating mixtures based on the differences in the components' ability to be carried by a mobile phase. In the case of separating colors in a dye, chromatography can be used because different colors have different affinities for the mobile phase. As the mobile phase moves through a stationary phase, the colors will separate based on their interactions with the stationary phase, allowing for the individual colors to be collected and analyzed.

2. Which list of formulas represents compounds, only?

CO₂, H₂O, NH₃

H₂, N₂, O₂

H₂, Ne, NaCl

MgO, NaCl, O₂

The given list of formulas, CO₂, H₂O, NH₃, represents compounds only because these formulas consist of multiple elements chemically bonded together. CO₂ is the formula for carbon dioxide, which is a compound composed of carbon and oxygen atoms. H₂O is the formula for water, which is a compound composed of hydrogen and oxygen atoms. NH₃ is the formula for ammonia, which is a compound composed of nitrogen and hydrogen atoms. In contrast, the other options contain elements or compounds that are not chemically bonded together.

Explanation

The given list of formulas, CO₂, H₂O, NH₃, represents compounds only because these formulas consist of multiple elements chemically bonded together. CO₂ is the formula for carbon dioxide, which is a compound composed of carbon and oxygen atoms. H₂O is the formula for water, which is a compound composed of hydrogen and oxygen atoms. NH₃ is the formula for ammonia, which is a compound composed of nitrogen and hydrogen atoms. In contrast, the other options contain elements or compounds that are not chemically bonded together.

3. A single protron has what electrical charge?

No Charge

Positive Charge

Negative Charge

Either a Positive or Negative Charge

A single proton has a positive charge because it contains one unit of positive electrical charge. Protons are subatomic particles found in the nucleus of an atom and are positively charged, while electrons, which orbit the nucleus, have a negative charge. The positive charge of a proton is equal in magnitude to the negative charge of an electron, resulting in a neutral atom.

Explanation

A single proton has a positive charge because it contains one unit of positive electrical charge. Protons are subatomic particles found in the nucleus of an atom and are positively charged, while electrons, which orbit the nucleus, have a negative charge. The positive charge of a proton is equal in magnitude to the negative charge of an electron, resulting in a neutral atom.

4. A triple bond consists of _________________.

Three sigma bonds

One sigma and two pi bonds

Three pi bonds

Two sigma and one pi bond

A triple bond consists of one sigma bond and two pi bonds. The sigma bond is formed by the overlap of two atomic orbitals head-on, while the pi bonds are formed by the sideways overlap of p orbitals. The presence of two pi bonds in a triple bond allows for greater electron density and a stronger bond compared to a double bond, which consists of one sigma and one pi bond.

Explanation

A triple bond consists of one sigma bond and two pi bonds. The sigma bond is formed by the overlap of two atomic orbitals head-on, while the pi bonds are formed by the sideways overlap of p orbitals. The presence of two pi bonds in a triple bond allows for greater electron density and a stronger bond compared to a double bond, which consists of one sigma and one pi bond.

5. Which of the following statements describes the difference between endothermic and exothermic chemical reactions?

Energy is conserved in endothermic reactions but is not conserved in exothermic reactions.

Endothermic reactions involve changes in the nucleus of an atom, but exothermic reactions do not involve changes in the nucleus.

Energy is absorbed in endothermic reactions but is released in exothermic reactions.

Endothermic reactions occur when electrons are shared between atoms, but exothermic reactions occur when electrons are transferred between atoms.

Endothermic reactions involve the absorption of energy, while exothermic reactions involve the release of energy. This means that in endothermic reactions, energy is taken in from the surroundings, while in exothermic reactions, energy is given off to the surroundings.

Explanation

Endothermic reactions involve the absorption of energy, while exothermic reactions involve the release of energy. This means that in endothermic reactions, energy is taken in from the surroundings, while in exothermic reactions, energy is given off to the surroundings.

6. Which of the following is an intensive property?

Mass

Volume

Density

Length

An intensive property is a property that does not depend on the amount or size of the substance. Density is an intensive property because it is a ratio of mass to volume, meaning it remains constant regardless of the amount of substance present. In contrast, mass, volume, and length are extensive properties, as they depend on the amount or size of the substance.

Explanation

An intensive property is a property that does not depend on the amount or size of the substance. Density is an intensive property because it is a ratio of mass to volume, meaning it remains constant regardless of the amount of substance present. In contrast, mass, volume, and length are extensive properties, as they depend on the amount or size of the substance.

7. The process of splitting atoms is called ____________.

Nuclear fusion

Nuclear fission

Radioactive decay

None of the above

Nuclear fission is the correct answer because it refers to the process of splitting atoms. In nuclear fission, the nucleus of an atom is split into two or more smaller nuclei, releasing a large amount of energy. This process is commonly used in nuclear power plants and atomic bombs. Nuclear fusion, on the other hand, is the process of combining two or more atomic nuclei to form a larger nucleus, which also releases a significant amount of energy. Radioactive decay, while related to nuclear processes, does not involve the splitting of atoms.

Explanation

Nuclear fission is the correct answer because it refers to the process of splitting atoms. In nuclear fission, the nucleus of an atom is split into two or more smaller nuclei, releasing a large amount of energy. This process is commonly used in nuclear power plants and atomic bombs. Nuclear fusion, on the other hand, is the process of combining two or more atomic nuclei to form a larger nucleus, which also releases a significant amount of energy. Radioactive decay, while related to nuclear processes, does not involve the splitting of atoms.

8. If 87.5 percent of a sample of pure 131I decays in 24 days, what is the half-life of 131I?

6 days

8 days

12 days

14 days

The half-life of a radioactive substance is the time it takes for half of the sample to decay. In this question, we are given that 87.5 percent of the sample decays in 24 days. Since half of the sample decays in the half-life, we can calculate the half-life by dividing 24 days by 87.5 percent, which is equivalent to multiplying by 100 and then dividing by 87.5. This calculation gives us a half-life of 8 days.

Explanation

The half-life of a radioactive substance is the time it takes for half of the sample to decay. In this question, we are given that 87.5 percent of the sample decays in 24 days. Since half of the sample decays in the half-life, we can calculate the half-life by dividing 24 days by 87.5 percent, which is equivalent to multiplying by 100 and then dividing by 87.5. This calculation gives us a half-life of 8 days.

9. Which equation represents an oxidation reduction reaction?

CH₄ + 2O₂ ==> CO₂ + 2H₂O

H₂SO₄ + Ca(OH)₂ ==> CaSO₄ + 2H₂O

MgCrO₄ + BaCl₂ ==> MgCl₂ + BaCrO₄

Zn(NO₃)₂ + Na2CO₃ ==> 2NaNO₃ + ZnCO₃

The equation CH₄ + 2O₂ ==> CO₂ + 2H₂O represents an oxidation-reduction reaction because there is a transfer of electrons between the reactants and products. In this reaction, methane (CH₄) is oxidized to carbon dioxide (CO₂) by gaining oxygen (O₂), while oxygen (O₂) is reduced to water (H₂O) by gaining hydrogen (H₂). This transfer of electrons indicates a redox reaction, which is characteristic of oxidation-reduction reactions.

Explanation

The equation CH₄ + 2O₂ ==> CO₂ + 2H₂O represents an oxidation-reduction reaction because there is a transfer of electrons between the reactants and products. In this reaction, methane (CH₄) is oxidized to carbon dioxide (CO₂) by gaining oxygen (O₂), while oxygen (O₂) is reduced to water (H₂O) by gaining hydrogen (H₂). This transfer of electrons indicates a redox reaction, which is characteristic of oxidation-reduction reactions.

10.

What is the fourth most abundant element in the universe in terms of mass?

Sodium

Boron

Helium

Carbon

Carbon is the correct answer because it is the fourth most abundant element in the universe in terms of mass. It is found in various forms, such as graphite and diamond, and is a key component of organic compounds. Carbon is essential for life on Earth and plays a crucial role in many biological processes.

Explanation

Carbon is the correct answer because it is the fourth most abundant element in the universe in terms of mass. It is found in various forms, such as graphite and diamond, and is a key component of organic compounds. Carbon is essential for life on Earth and plays a crucial role in many biological processes.

11. Molecular Orbital Theory describes the respective bond orders in H₂ , H₂ + , and H₂ – as _____________.

1, 0, and 0

1, 0, and ½

1, ½, and ½

1, ½, and 0

The Molecular Orbital Theory describes the respective bond orders in H₂, H₂+, and H₂- as 1, ½, and ½. In H₂, both hydrogen atoms contribute one electron to form a bonding molecular orbital, resulting in a bond order of 1. In H₂+, one hydrogen atom donates both its electrons to form a bonding molecular orbital, while the other hydrogen atom remains unaltered, resulting in a bond order of ½. In H₂-, one hydrogen atom retains both its electrons to form an antibonding molecular orbital, while the other hydrogen atom donates both its electrons to form a bonding molecular orbital, resulting in a bond order of ½.

Explanation

The Molecular Orbital Theory describes the respective bond orders in H₂, H₂+, and H₂- as 1, ½, and ½. In H₂, both hydrogen atoms contribute one electron to form a bonding molecular orbital, resulting in a bond order of 1. In H₂+, one hydrogen atom donates both its electrons to form a bonding molecular orbital, while the other hydrogen atom remains unaltered, resulting in a bond order of ½. In H₂-, one hydrogen atom retains both its electrons to form an antibonding molecular orbital, while the other hydrogen atom donates both its electrons to form a bonding molecular orbital, resulting in a bond order of ½.

12. The proper name for N₂O₅ is _______________.

Nitrogen pentoxide

Dinitrogen pentoxide

Nitrous oxide

Pentaoxidgen dinitride

The proper name for N₂O₅ is dinitrogen pentoxide because the compound consists of two nitrogen atoms (di-) and five oxygen atoms (-pentoxide).

Explanation

The proper name for N₂O₅ is dinitrogen pentoxide because the compound consists of two nitrogen atoms (di-) and five oxygen atoms (-pentoxide).

13. Body temperature is 98.6°F. What is the temperature in °C?

32 degrees

37 degrees

39 degrees

40 degrees

To convert Fahrenheit to Celsius, you can use the formula: °C = (°F - 32) / 1.8. Plugging in the given temperature of 98.6°F into the formula, we get (98.6 - 32) / 1.8 = 66.6 / 1.8 = 37°C. Therefore, the correct answer is 37 degrees.

Explanation

To convert Fahrenheit to Celsius, you can use the formula: °C = (°F - 32) / 1.8. Plugging in the given temperature of 98.6°F into the formula, we get (98.6 - 32) / 1.8 = 66.6 / 1.8 = 37°C. Therefore, the correct answer is 37 degrees.

14. How many moles of solid Ba(NO3)2 should be added to 300. milliliters of 0.20-molar Fe(NO3)3 to increase the concentration of the NO3¯ ion to 1.0-molar? (Assume that the volume of the solution remains constant.)

0.060 mole

0.12 mole

0.24 mole

0.30 mole

To increase the concentration of the NO3- ion to 1.0-molar, the moles of NO3- ions in the solution need to be equal to the moles of NO3- ions in the solid Ba(NO3)2. Since the molar ratio between Ba(NO3)2 and NO3- ions is 1:2, we need half the moles of Ba(NO3)2 to achieve the desired concentration.

Given that the volume of the solution remains constant, we can use the formula:

Moles = Molarity × Volume

Moles of NO3- ions in the solution = 0.20 mol/L × 0.300 L = 0.060 mol

Therefore, 0.060 mole of solid Ba(NO3)2 should be added to achieve the desired concentration of the NO3- ion.

Explanation

To increase the concentration of the NO3- ion to 1.0-molar, the moles of NO3- ions in the solution need to be equal to the moles of NO3- ions in the solid Ba(NO3)2. Since the molar ratio between Ba(NO3)2 and NO3- ions is 1:2, we need half the moles of Ba(NO3)2 to achieve the desired concentration.

Given that the volume of the solution remains constant, we can use the formula:

Moles = Molarity × Volume

Moles of NO3- ions in the solution = 0.20 mol/L × 0.300 L = 0.060 mol

Therefore, 0.060 mole of solid Ba(NO3)2 should be added to achieve the desired concentration of the NO3- ion.

15. Mass of an empty container = 3.0 grams Mass of the container plus the solid sample = 25.0 grams Volume of the solid sample = 11.0 cubic centimeters The data above were gathered in order to determine the density of an unknown solid. The density of the sample should be reported as

0.5 g/cm3

0.50 g/cm3

2.0 g/cm3

2.00 g/cm3

The density of a substance is calculated by dividing its mass by its volume. In this case, the mass of the solid sample is determined by subtracting the mass of the empty container from the mass of the container plus the solid sample, which is 25.0 grams - 3.0 grams = 22.0 grams. The volume of the solid sample is given as 11.0 cubic centimeters. Dividing the mass (22.0 grams) by the volume (11.0 cubic centimeters) gives a density of 2.00 g/cm3.

Explanation

The density of a substance is calculated by dividing its mass by its volume. In this case, the mass of the solid sample is determined by subtracting the mass of the empty container from the mass of the container plus the solid sample, which is 25.0 grams - 3.0 grams = 22.0 grams. The volume of the solid sample is given as 11.0 cubic centimeters. Dividing the mass (22.0 grams) by the volume (11.0 cubic centimeters) gives a density of 2.00 g/cm3.