Exam 1 CHEM 106-014

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Questions and Answers

Which scientist is credited with the principle that allows electrons to be described as waves and particles simultaneously?

  • Werner Heisenberg
  • Max Planck
  • Niels Bohr
  • De Broglie (correct)

What does the notation Fe2+ signify in terms of atomic charge?

  • The atom has gained 2 protons
  • The atom has equal numbers of protons and electrons
  • The atom has lost 2 neutrons
  • The atom has lost 2 electrons (correct)

If the density of water is 1 g/ml, which conclusion can be drawn about a solid that sinks when placed in water?

  • It has a density exactly equal to 1 g/ml
  • It has a density greater than 1 g/ml (correct)
  • It has a variable density depending on temperature
  • It has a density less than 1 g/ml

In atomic notation, how many neutrons are present in an atom with 26 protons and a mass number of 33?

<p>17 (C)</p> Signup and view all the answers

What is the net charge of an atom that has 13 protons and 10 electrons?

<p>3+ (C)</p> Signup and view all the answers

What is the degree of uncertainty for Dr. King's porch measurement of 76.445m?

<p>± 0.445 (D)</p> Signup and view all the answers

Which type of balance has the least accuracy based on its uncertainty?

<p>Platform balance, ± 0.1 g (C)</p> Signup and view all the answers

Which statement accurately describes the characteristics of a liquid?

<p>No definite shape and definite volume (B)</p> Signup and view all the answers

Which description best defines the structure of an atom?

<p>Protons and neutrons in nucleus; electrons in orbitals (D)</p> Signup and view all the answers

How can molecules be accurately described?

<p>Two or more atoms chemically joined together (C)</p> Signup and view all the answers

What is the identity of the isotope with 27 protons, 33 neutrons, and 27 electrons?

<p>Cobalt-60 (C)</p> Signup and view all the answers

Which combination will NOT result in a homogeneous mixture?

<p>Mud and water (D)</p> Signup and view all the answers

Which of the following is considered NOT an intensive property?

<p>Mass (A)</p> Signup and view all the answers

How many significant figures are in the number 1.06 × 10²⁴?

<p>Four (D)</p> Signup and view all the answers

What is the correct answer (reported to the proper number of significant figures) for the sum 5.2143 + 0.633 + 12.91?

<p>18.8 (C)</p> Signup and view all the answers

What is the EPA mileage rating of 30 miles per gallon in kilometers per liter?

<p>70 km/L (A)</p> Signup and view all the answers

Which of the following is the Celsius equivalent of 122°F?

<p>64.4°C (A)</p> Signup and view all the answers

What is the temperature in Fahrenheit for 300 K?

<p>351°F (B)</p> Signup and view all the answers

How many grams does 7.98 moles of Krypton (Kr) weigh?

<p>952 g (D)</p> Signup and view all the answers

How many atoms of oxygen are present in 2.50 moles of SO2?

<p>3.01 × 10²⁴ atoms (D)</p> Signup and view all the answers

When waves from two sources interfere destructively, what outcome is observed?

<p>Waves cancel each other (B)</p> Signup and view all the answers

When a wave encounters an obstacle or a slit that is comparable in size to its wavelength, it bends around it. What is this characteristic called?

<p>Diffraction (B)</p> Signup and view all the answers

What is the frequency of electromagnetic radiation with a wavelength of 640 nm?

<p>4.688 × 10^14 Hz (D)</p> Signup and view all the answers

Electromagnetic radiation can behave as which of the following?

<p>Both a wave and particle (C)</p> Signup and view all the answers

What is the mass of a particle with a De Broglie wavelength of 3.45 × 10^-34 m and a velocity of 6.55 m/s?

<p>1.81 × 10^-10 kg (D)</p> Signup and view all the answers

Determine the energy change with an electronic transition from n=3 to n=2 in the hydrogen atom.

<p>-3.03 × 10^-19 J (D)</p> Signup and view all the answers

How many photons correspond to a total energy of 3.83 × 10^-3 J with a wavelength of 3.37 × 10^-7 m?

<p>6.49 × 10^15 photons (C)</p> Signup and view all the answers

What is produced during the process of fireworks observed on Independence Day?

<p>Excitation of electrons followed by emission of light photons (A)</p> Signup and view all the answers

What is the total energy of a UV light source that strikes a metal surface?

<p>3.83 × 10^-3 J (A)</p> Signup and view all the answers

Flashcards

Significant Figures

The number of digits in a measurement that are known with certainty and one uncertain digit.

Conversion of Miles per Gallon to Kilometers per Liter

Converting a given unit of speed or volume from one system (e.g., US customary) to the metric system is calculated by given conversion factors.

Temperature Conversion (Fahrenheit to Celsius)

Formula: °C = (°F - 32) / 1.8

Temperature Conversion (Kelvin to Fahrenheit)

Formula: °F = (K - 273) * 1.8 + 32.

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Moles to Mass Conversion

Mass (g) = Moles *(Molar Mass).

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Atoms in Moles

Number of atoms = (Moles of substance)(Number of atoms per molecule)(Avogadro's number).

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Destructive Interference

Out-of-phase waves having the same amplitude, cancel each other out.

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Atomic Mass Calculation

Weighted average of the masses of naturally occurring isotopes based on their relative abundances. Formula: Average atomic mass = [(fraction of isotope 1) × (mass of isotope 1)] + [(fraction of isotope 2) × (mass of isotope 2)]

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Diffraction

The bending of a wave around an obstacle or a slit that is comparable in size to its wavelength.

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Electromagnetic radiation frequency (v) from wavelength(λ)

The frequency of electromagnetic radiation is related to its wavelength by the speed of light (c): v = c / λ.

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Wave-particle duality

The concept that particles, like electrons, can exhibit wave-like properties and vice versa.

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De Broglie wavelength

The wavelength associated with a particle, calculated from its momentum and Planck's constant.

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Electronic transitions in atoms

Electrons move between energy levels within atoms, emitting or absorbing light corresponding to the energy difference between levels.

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Energy change in hydrogen atom (n=3 to n=2)

The energy change associated with an electron transition from n=3 to n=2 energy level in a hydrogen atom , is -4.09 × 10⁻¹⁹ J.

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Number of photons in a light source

The total energy of a light source, divided by the energy per photon (calculated from the light's wavelength) gives the number of photons involved.

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Fireworks (light)

Fireworks light produced by the excitation of electrons to higher energy levels in atoms of burning metals, followed by the emission of light photons.

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Uncertainty in Measurement (Example)

The degree of error associated with a measurement. It's usually, but not always represented by plus-or-minus, such as ±0.01 g

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Accuracy of Balance

Represents how close a measurement is to the true value. A more accurate scale will have a smaller uncertainty or error

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Liquid Characteristics

Liquids have a definite volume but take the shape of their container.

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Atomic Structure

Atoms consist of a nucleus (containing protons and neutrons) surrounded by orbiting electrons.

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Molecule Definition

A molecule is formed when two or more atoms chemically bond together.

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Isotope

Atoms of the same element that have different numbers of neutrons.

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Homogeneous Mixture

A mixture where the components are evenly distributed and are indistinguishable

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Intensive Property

A property that does not depend on the amount of substance present.

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Density

Density is a measure of how much mass is contained in a given volume. It is calculated by dividing the mass of a substance by its volume. A substance with higher density will sink in a substance with lower density.

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Atomic Notation

Atomic Notation is a shorthand way of representing an atom. It uses the element symbol, the atomic number (number of protons), the mass number (total number of protons and neutrons), and sometimes the charge of the atom. The format is: (atomic number)X(mass number) where X is the element symbol. For example, 12C6 represents a carbon atom with 6 protons and 6 neutrons.

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Number of Protons

The number of protons in an atom's nucleus determines the element. Every atom of a specific element will have the same number of protons. It is also equal to the atomic number. For example, all carbon atoms have 6 protons.

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Number of Neutrons

The number of neutrons in an atom's nucleus determines the isotope of an element. Different isotopes of the same element have the same number of protons but different numbers of neutrons. For example, Carbon-12 and Carbon-14 are both isotopes of carbon, but Carbon-12 has 6 neutrons while Carbon-14 has 8 neutrons.

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Net Charge

The net charge of an atom is determined by the balance between the number of protons (positive charge) and electrons (negative charge). When an atom loses or gains electrons, it becomes an ion with a positive or negative charge, respectively. For example, Na+ has lost an electron, while Cl- has gained an electron.

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Study Notes

Exam 1 CHEM 106-014

  • Exam Format: Multiple Choice. Write the exam version on the scantron.

Question 1

  • Measurement Uncertainty: Dr. King measured a porch 76.445m. The uncertainty is ±0.005m.

Question 2

  • Balance Accuracy: Analytical balance has the least uncertainty (±0.0001g), followed by electronic (±0.001g), beam (±0.01g), and platform (±0.1g) balances.

Question 3

  • Liquid Characteristics: Liquids have a definite volume but no definite shape.

Question 4

  • Atomic Description: Protons and neutrons reside in the nucleus, and electrons orbit around the nucleus.

Question 5

  • Molecule Definition: Molecules are mixtures of two or more elements, with fixed ratios. Another key detail is that they are chemically joined together..

Question 6

  • Isotope Identification: The isotope with 27 protons, 33 neutrons, and 27 electrons is cobalt-60.

Question 7

  • Homogeneous Mixtures: A homogeneous mixture is formed when substances are mixed evenly like sugar in coffee, salt in water, and ice tea, lemonade. Mud and water are heterogeneous.

Question 8

  • Intensive Properties: Intensive properties, like density, melting point, and color, do not depend on the amount of substance. Mass is an extensive property. Boiling point is an intensive property.

Question 9

  • Significant Figures: 6.3 * 3.25 = 20.5 when rounded according to significant figures.

Question 10

  • Significant Figures Count: Three significant figures are present in 0.509, 1.050, and 1.06×10^24.

Question 11

  • Significant Figures in Addition: 5.2143 + 0.633 + 12.91 = 18.8 when rounded correctly to significant figures.

Question 12

  • Unit Conversion: 30 miles per gallon (mpg) equals 70 kilometers per liter (km/L)

Question 13

  • Temperature Conversion: 122°F equals 50.0°C.

Question 14

  • Temperature Conversion (K to °F): 300 K is equal to 81°F

Question 15

  • Molar Mass Calculation (Krypton): 7.98 moles of Krypton has a mass of 560 g.

Question 16

  • Atoms in SO2: 2.50 moles of SO2 contains 1.51 × 10^24 atoms of oxygen.

Question 17

  • Wave Interference: When waves of equal amplitude from two sources interfere out of phase, it's called destructive interference.

Question 18

  • Average Atomic Mass Calculation: The average atomic mass of gallium is 69.72 amu.

Question 19

  • Chloroform Volume: 80 g of chloroform is equivalent to 54.0 mL

Question 20

  • Wave Diffraction: A wave bending around an obstacle is called diffraction.

Question 21

  • Wave Characteristics (a vs b): Wave (a) has a longer wavelength and lower frequency compared to wave (b).

Question 22

  • Firework Light Production: Fireworks utilize the energy released when atoms are excited to higher energy levels and return to original energy levels.

Question 23

  • Light Frequency Calculation: Orange light with a 640-nm wavelength has a frequency of 4.688 × 1014 s-1 .

Question 24

  • Light and Particles: Light can behave as both a wave and a particle; electrons can too.

Question 25

  • De Broglie Wavelength Calculation: Mass of a particle with a De Broglie wavelength of 3.45×10−34 m and velocity of 6.55 m/s is 0.293kg.

Question 26

  • Energy Transition (Hydrogen): The energy change for an electron transitioning from n = 3 to n = 2 in a hydrogen atom is -1.92 × 10−18 J.

Question 27

  • Photons from Ultraviolet Light: With a total ultraviolet light energy of 3.83x10-16 J and wavelength 3.37 × 10-7m, it takes 10 photons.

Question 28

  • Quantum Uncertainty: Werner Heisenberg proved the simultaneous determination of position and speed of electrons is impossible.

Extra Credit Question 1 (a)

  • Density Determination: Based on the image in the graduated cylinder, the possible densities are assigned as follows; L1 < S1 < L2 < S2 < S3

Extra Credit Question 1 (b)

  • Justification for Density Ordering: The liquid layer sits over the solid layers and the relative positions of the solids and liquids remain unchanged. The logic is that layers with greater densities sit below those with lower densities. Objects with similar densities tend to occupy similar positions in the layers. So, if the water layer is above a solid, the solids density has to be smaller.

Question 2

  • Atomic Notation Table: The missing values for the atomic notation table are determined by using concepts like the number of electrons and neutrons, which combined give the mass of the different elements. Net charge can be calculated based on the net number.

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