Step-by-Step Guidance for Chem 111 Exam #1 Questions

Q1. Is morphine, C17H19NO3, an element or a compound?

Background

Topic: Classification of Matter

This question tests your understanding of the difference between elements and compounds, and how to identify them based on chemical formulas.

Key Terms:

• Element: A pure substance consisting of only one type of atom.

• Compound: A pure substance made from two or more different elements chemically bonded together.

Step-by-Step Guidance

1. Look at the chemical formula: C17H19NO3.

2. Identify how many different types of atoms are present (C, H, N, O).

3. Recall that an element contains only one type of atom, while a compound contains more than one.

Try solving on your own before revealing the answer!

Final Answer: Compound

Morphine contains carbon, hydrogen, nitrogen, and oxygen atoms, so it is a compound.

Q2. Are poppy flowers that contain morphine a pure substance, heterogeneous mixture, or homogeneous mixture?

Background

Topic: Classification of Matter

This question tests your ability to distinguish between pure substances and mixtures, and to identify the type of mixture.

Key Terms:

• Pure substance: Matter with a fixed composition (element or compound).

• Heterogeneous mixture: A mixture with visibly different parts or phases.

• Homogeneous mixture: A mixture that is uniform throughout.

Step-by-Step Guidance

1. Consider what poppy flowers are made of (many substances, including morphine).

2. Think about whether the composition is uniform or not throughout the flower.

3. Recall the definitions of pure substance, heterogeneous mixture, and homogeneous mixture.

Try solving on your own before revealing the answer!

Final Answer: Heterogeneous mixture

Poppy flowers contain many substances and are not uniform throughout, so they are a heterogeneous mixture.

Q3. Which properties of morphine are extrinsic? (Circle all that apply)

Background

Topic: Intensive vs. Extensive Properties

This question tests your understanding of the difference between intrinsic (intensive) and extrinsic (extensive) properties.

Key Terms:

• Intensive property: Does not depend on the amount of substance (e.g., density, melting point).

• Extensive property: Depends on the amount of substance (e.g., mass, volume).

Step-by-Step Guidance

1. Review the list of properties: volume, appearance, odor, density, mass, melting point.

2. Identify which properties change if you have more or less morphine.

3. Recall that extrinsic (extensive) properties depend on sample size.

Try solving on your own before revealing the answer!

Final Answer: Volume and mass

Volume and mass are extrinsic properties because they depend on the amount of morphine present.

Q4. Rhodium-101: Fill in the blanks

Background

Topic: Isotopes and Atomic Structure

This question tests your ability to determine the number of protons, electrons, and neutrons in an isotope.

Key Terms and Formulas:

• Atomic number (Z): Number of protons.

• Mass number (A): Number of protons + neutrons.

• Isotope: Atoms of the same element with different numbers of neutrons.

Step-by-Step Guidance

1. Find rhodium's atomic number (Z) using the periodic table.

2. Recall that the number of protons equals the atomic number.

3. For a neutral atom, the number of electrons equals the number of protons.

4. Calculate the number of neutrons: $\text{Neutrons} = \text{Mass number} - \text{Atomic number}$

Try solving on your own before revealing the answer!

Final Answer:

Rhodium-101 has 45 protons, 45 electrons, and 56 neutrons.

Q5. An element X has 42 protons and 54 neutrons. Fill in the blanks.

Background

Topic: Isotopes, Ions, and Atomic Structure

This question tests your ability to identify elements, calculate mass numbers, and determine electron counts for ions.

Key Terms and Formulas:

• Element symbol: Use the periodic table to match atomic number to element.

• Mass number (A): $A = \text{protons} + \text{neutrons}$

• Cation: Positive ion (electrons removed).

• Anion: Negative ion (electrons added).

• Full chemical symbol: $^{A}_{Z}\text{Element}$

Step-by-Step Guidance

1. Find the element with atomic number 42 using the periodic table.

2. Calculate the mass number: $A = 42 + 54$

3. For the cation X2+, subtract 2 electrons from the neutral atom's electron count.

4. For the anion X3-, add 3 electrons to the neutral atom's electron count.

5. Write the full chemical symbol for the isotope with 42 protons and 52 neutrons: $A = 42 + 52$

Try solving on your own before revealing the answer!

Final Answer:

a) Mo b) 40 electrons c) 96 d) 47 electrons e) 94Mo

Q6. Choose the transition (in a hydrogen atom) below that corresponds to the absorption of the shortest wavelength photon.

Background

Topic: Atomic Spectra and Energy Transitions

This question tests your understanding of energy transitions in hydrogen atoms and their relationship to photon wavelength.

Key Terms and Formulas:

• Absorption: Electron moves to a higher energy level.

• Wavelength ($\lambda$): Shorter wavelength means higher energy.

• Energy difference: $\Delta E = -2.178 \times 10^{-18} \left( \frac{1}{n_2^2} - \frac{1}{n_1^2} \right)$

Step-by-Step Guidance

1. Identify which transitions are absorption (electron moves to higher n).

2. Recall that the largest energy difference corresponds to the shortest wavelength.

3. Compare the energy differences for each transition.

Try solving on your own before revealing the answer!

Final Answer: n = 1 to n = 3

This transition involves the largest energy jump, resulting in the shortest wavelength photon absorbed.

Q7. Which statement(s) about Rutherford’s gold foil experiment are correct?

Background

Topic: Atomic Structure and Historical Experiments

This question tests your knowledge of the gold foil experiment and its implications for atomic theory.

Key Terms:

• Gold foil experiment: Experiment that led to the discovery of the atomic nucleus.

• Alpha particles: Helium nuclei used in the experiment.

Step-by-Step Guidance

1. Review the statements and recall the main findings of Rutherford's experiment.

2. Identify which statements accurately describe the experiment and its results.

3. Remember that the experiment disproved the plum pudding model and led to the nuclear model.

Try solving on your own before revealing the answer!

Final Answer:

Correct statements: a, c, e

Q8. Which statements are part of the nuclear model of the atom that arose out of Rutherford’s gold foil experiment?

Background

Topic: Atomic Models

This question tests your understanding of the features of the nuclear model of the atom.

Key Terms:

• Nuclear model: Model with a dense, positively charged nucleus and electrons orbiting around it.

Step-by-Step Guidance

1. Review the statements and recall the characteristics of the nuclear model.

2. Identify which statements match the nuclear model (dense nucleus, electrons outside).

3. Exclude statements that describe earlier or later models (plum pudding, Bohr, etc.).

Try solving on your own before revealing the answer!

Final Answer:

Correct statements: c

Q9. Mercury melts at 234.3 K and boils at 629.9 K. What is the physical state at 204 ºF?

Background

Topic: Phase Changes and Temperature Conversion

This question tests your ability to convert between Fahrenheit and Kelvin and determine physical states based on melting and boiling points.

Key Formulas:

• $T_C = \frac{5}{9}(T_F - 32)$

• $T_K = T_C + 273.15$

Step-by-Step Guidance

1. Convert 204 ºF to Celsius using $T_C = \frac{5}{9}(204 - 32)$

2. Convert Celsius to Kelvin using $T_K = T_C + 273.15$

3. Compare the Kelvin temperature to the melting and boiling points of mercury.

Try solving on your own before revealing the answer!

Final Answer:

204 ºF = 362 K; Mercury is a liquid at this temperature.

Q10. When 3.000 g of carbon dioxide is decomposed, 0.819 g of carbon and 2.181 g of oxygen are obtained, regardless of the source. What fundamental law(s) does this experiment illustrate?

Background

Topic: Laws of Chemical Combination

This question tests your understanding of the law of definite proportions and conservation of mass.

Key Terms:

• Law of definite proportions: A compound always contains the same elements in the same proportion by mass.

• Conservation of mass: Mass is neither created nor destroyed in a chemical reaction.

Step-by-Step Guidance

1. Compare the mass of carbon and oxygen obtained to the total mass of carbon dioxide.

2. Consider whether the proportions are constant regardless of the source.

3. Recall which laws are illustrated by constant composition and total mass conservation.

Try solving on your own before revealing the answer!

Final Answer:

Law of definite proportions and conservation of mass

Q11. A photon has 3.20 x 10-19 J of energy. Calculate the frequency of this photon in KHz (kilohertz).

Background

Topic: Quantum Theory and Photons

This question tests your ability to use Planck's equation to relate energy and frequency, and convert units.

Key Formula:

• $E = h\nu$

• $\nu = \frac{E}{h}$

• 1 Hz = 1 s-1; 1 KHz = 103 Hz

Step-by-Step Guidance

1. Write down the energy of the photon: $E = 3.20 \times 10^{-19}$ J

2. Recall Planck's constant: $h = 6.626 \times 10^{-34}$ Js

3. Calculate frequency: $\nu = \frac{E}{h}$

4. Convert the result from Hz to KHz by dividing by $10^3$.

Try solving on your own before revealing the answer!

Final Answer:

Frequency = 4.83 x 1014 KHz

Q12. An electron in a hydrogen atom is excited from n = 1 to n = 2. Does the electron emit or absorb energy?

Background

Topic: Atomic Spectra and Energy Transitions

This question tests your understanding of energy absorption and emission in atomic transitions.

Key Terms:

• Absorption: Electron moves to a higher energy level (requires energy).

• Emission: Electron moves to a lower energy level (releases energy).

Step-by-Step Guidance

1. Identify the direction of the transition (n = 1 to n = 2 is upward).

2. Recall that moving to a higher energy level requires energy input.

Try solving on your own before revealing the answer!

Final Answer: Absorb

The electron absorbs energy to move from n = 1 to n = 2.

Q13. What is the wavelength (in nm) of the photon required for the n = 1 to n = 2 transition in hydrogen?

Background

Topic: Atomic Spectra Calculations

This question tests your ability to calculate the wavelength of a photon for a specific electronic transition using the Rydberg formula.

Key Formulas:

• $\frac{1}{\lambda} = R_H \left( \frac{1}{n_1^2} - \frac{1}{n_2^2} \right)$

• $R_H = 1.097 \times 10^7$ m-1

• Convert meters to nanometers: $1 \text{ m} = 10^9 \text{ nm}$

Step-by-Step Guidance

1. Plug in $n_1 = 1$ and $n_2 = 2$ into the Rydberg formula.

2. Calculate $\frac{1}{\lambda}$ using the values.

3. Invert to find $\lambda$ in meters, then convert to nanometers.

Try solving on your own before revealing the answer!

Final Answer:

Wavelength = 121.6 nm

Q14. In what region of the electromagnetic spectrum does the n = 1 to n = 2 transition occur?

Background

Topic: Electromagnetic Spectrum

This question tests your ability to relate photon wavelength to regions of the electromagnetic spectrum.

Key Terms:

• Ultraviolet (UV): Wavelengths shorter than visible light, typically below 400 nm.

Step-by-Step Guidance

1. Recall the calculated wavelength (from previous question).

2. Compare the wavelength to the ranges for visible, UV, and other regions.

Try solving on your own before revealing the answer!

Final Answer: Ultraviolet

The transition occurs in the ultraviolet region.

Q15. Can we see the n = 1 to n = 2 transition with the human eye?

Background

Topic: Electromagnetic Spectrum and Human Vision

This question tests your understanding of the visible range of the electromagnetic spectrum.

Key Terms:

• Visible light: 400–700 nm

Step-by-Step Guidance

1. Recall the wavelength calculated for the transition.

2. Compare it to the visible range.

Try solving on your own before revealing the answer!

Final Answer: No

The wavelength is outside the visible range, so it cannot be seen by the human eye.

Q16. Would the transition from n = 1 to n = 3 give a higher or lower frequency photon compared to n = 1 to n = 2?

Background

Topic: Atomic Spectra and Energy Transitions

This question tests your understanding of how energy differences relate to photon frequency.

Key Terms:

• Frequency ($\nu$): Higher energy difference means higher frequency.

Step-by-Step Guidance

1. Recall that frequency is proportional to energy difference: $E = h\nu$

2. Compare the energy difference for n = 1 to n = 3 versus n = 1 to n = 2.

Try solving on your own before revealing the answer!

Final Answer: Higher frequency

The n = 1 to n = 3 transition has a larger energy difference, so the photon has a higher frequency.

Q17. Burets are a piece of scientific glassware that allow one to measure volumes while draining out liquid from the bottom. Read the water level in the buret at the beginning and end of this process to the correct number of significant digits and calculate the difference in volume.

Background

Topic: Measurement and Significant Figures

This question tests your ability to read scientific glassware and report values with correct significant figures.

Key Terms:

• Significant figures: The digits in a measurement that are known with certainty plus one estimated digit.

Step-by-Step Guidance

1. Read the initial and final buret levels carefully, noting the smallest division.

2. Record each value with the correct number of significant digits.

3. Subtract the final reading from the initial reading to find the difference in volume.

Try solving on your own before revealing the answer!

Final Answer:

Difference in volume = (initial reading) - (final reading), reported with correct significant figures.

Q18. Circle the least precise type of glassware (graduated cylinder, pipet, or buret).

Background

Topic: Measurement Precision

This question tests your understanding of the precision of different types of laboratory glassware.

Key Terms:

• Precision: How close repeated measurements are to each other.

Step-by-Step Guidance

1. Recall the typical precision of graduated cylinders, pipets, and burets.

2. Compare the number of significant digits each glassware can provide.

Try solving on your own before revealing the answer!

Final Answer: Graduated cylinder

Graduated cylinders are generally the least precise compared to pipets and burets.

Q19. How many atoms of zinc (Zn) are present in 246.1 g of pure zinc?

Background

Topic: Moles and Avogadro's Number

This question tests your ability to convert mass to moles and then to number of atoms using Avogadro's number.

Key Formulas:

• $\text{Moles} = \frac{\text{mass}}{\text{molar mass}}$

• $\text{Atoms} = \text{moles} \times 6.022 \times 10^{23}$

Step-by-Step Guidance

1. Find the molar mass of zinc (Zn) from the periodic table.

2. Calculate the number of moles: $\text{moles} = \frac{246.1}{\text{molar mass of Zn}}$

3. Multiply the number of moles by Avogadro's number to get the number of atoms.

Try solving on your own before revealing the answer!

Final Answer:

Number of atoms = (moles) x (6.022 x 1023), with correct significant figures.