Q: A sample contains 3.00 moles of carbon atoms. How many atoms are present in the sample?

$$3.00 \times 6.022 \times 10$$^{23}$$ = 1.81 \times 10$$^{24}$$ atoms

Q: A student needs to convert 0.500 kg to grams. What is the correct conversion?

$$0.500 \times 1000 = 500\ \mathrm{g}$$

Question 1

Which experiment provided the first evidence for the existence of the electron, and what was the main conclusion drawn from it?

Accepted Answer

The cathode ray tube experiment; electrons are fundamental particles present in all atoms.

Question 2

A student measures the mass of a liquid as 12.45 g and its volume as 8.2 mL. What is the density of the liquid, reported with the correct number of significant figures?

Accepted Answer

$$\frac{12.45\ \mathrm{g}}{8.2\ \mathrm{mL}} = 1.52\ \mathrm{g/mL}$$

Question 3

Which statement best describes the outcome of Rutherford’s gold foil experiment?

Accepted Answer

Most alpha particles passed through, but some were deflected, indicating a small, dense nucleus.

Question 4

Which of the following is the correct conversion of 25.0 °C to Kelvin?

Accepted Answer

$$25.0 + 273.15 = 298.15\ \mathrm{K}$$

Question 5

Which equation correctly relates the energy of a photon to its frequency?

Accepted Answer

$$E = h 
u$$

Question 6

A sample contains 3.00 moles of carbon atoms. How many atoms are present in the sample?

Accepted Answer

$$3.00 	imes 6.022 	imes 10$$^{23}$$ = 1.81 	imes 10$$^{24}$$ atoms

Question 7

Which of the following best describes the photoelectric effect?

Accepted Answer

Electrons are emitted from a metal surface when it is exposed to light of sufficient frequency.

Question 8

Which formula is used to calculate the wavelength of a particle according to de Broglie’s hypothesis?

Accepted Answer

$$\lambda = \frac{h}{mv}$$

Question 9

An atom has 17 protons and 18 neutrons. What is its mass number and which element is it?

Accepted Answer

Mass number = 35; element = chlorine

Question 10

Which quantum numbers are needed to describe an electron in an atom?

Accepted Answer

Principal ($$n$$), angular momentum ($$l$$), magnetic ($$m_l$$), and spin ($$m_s)$$

Question 11

A student needs to convert 0.500 kg to grams. What is the correct conversion?

Accepted Answer

$$0.500 	imes 1000 = 500\ \mathrm{g}$$

Question 12

Which statement about isotopes is correct?

Accepted Answer

Isotopes of an element have the same number of protons but different numbers of neutrons.

Question 13

Which of the following best explains the uncertainty principle?

Accepted Answer

It is impossible to simultaneously know both the exact position and momentum of a particle.

Question 14

Which equation is used to calculate the energy of a photon given its wavelength?

Accepted Answer

$$E = \frac{hc}{\lambda}$$

Question 15

A hydrogen atom emits light with a wavelength of $$656\ \mathrm{nm} ($$Balmer series). What is the energy of this photon?

Accepted Answer

$$E = \frac{6.626 	imes 10$$^{-34}$$\ \mathrm{J\cdot s} 	imes 3.00 	imes 10^8$\ \mathrm{m/s}}{656 	imes 10$$^{-9}$$\ \mathrm{m}} = 3.03 	imes 10$$^{-19}$$\ \mathrm{J}$$

Question 16

Which rule must be followed when writing quantum numbers for electrons in an atom?

Accepted Answer

No two electrons in the same atom can have the same set of all four quantum numbers.

Question 17

A chemist wants to identify an unknown isotope. The atom has 20 protons and 22 neutrons. What is the isotope?

Accepted Answer

Calcium-42

Question 18

Which of the following best describes the Bohr model of the atom?

Accepted Answer

Electrons orbit the nucleus in fixed energy levels without radiating energy.

Question 19

A hospital uses liquid nitrogen at $$-196\ ^\circ\mathrm{C}$$ for cryopreservation. What is this temperature in Kelvin?

Accepted Answer

$$-196 + 273.15 = 77.15\ \mathrm{K}$$

Question 20

Which of the following is a correct statement about the periodic table?

Accepted Answer

Elements are arranged in order of increasing atomic number.

General Chemistry: Atoms, Measurements, and Quantum Models – Study Notes

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