Q: Which of the following is the correct value for Avogadro’s number ($$N_A$$)?

$$6.022 \times 10$$^{23}$$ things/mol

Q: A student is asked to calculate the number of atoms in $$0.250$$ mol of sodium. Which of the following is the correct calculation?

$$0.250 \times 6.022 \times 10$$^{23}$$

Question 1

Which of the following statements best distinguishes between precision and accuracy in scientific measurements?

Accepted Answer

Precision refers to how close repeated measurements are to each other, while accuracy refers to how close a measured value is to the true value.

Question 2

A student measures the mass of a sample three times and records the following values: 2.51 g, 2.50 g, and 2.52 g. The true mass is 2.75 g. Which statement best describes the measurements?

Accepted Answer

The measurements are precise but not accurate.

Question 3

Which of the following numbers is expressed with the correct number of significant figures for the result of the calculation $$4.56 	imes 1.4$$?

Accepted Answer

$$6.4$$

Question 4

Which of the following is a physical change?

Accepted Answer

Melting of ice

Question 5

A sample contains $$3.01 	imes 10$$^{23}$$ molecules of water. How many moles of water does this sample contain?

Accepted Answer

$$0.500$$ mol

Question 6

Which of the following statements about isotopes is correct?

Accepted Answer

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

Question 7

Which of the following best describes the difference between a compound and a mixture?

Accepted Answer

A compound consists of two or more elements chemically combined in fixed proportions, while a mixture consists of two or more substances physically combined.

Question 8

Which of the following is the correct electron configuration for a neutral atom of carbon ($$Z = 6$$)?

Accepted Answer

$$1s^2$$ $$2s^2$$ $$2p^2$$

Question 9

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

Accepted Answer

Electrons orbit the nucleus in fixed energy levels and can move between levels by absorbing or emitting energy.

Question 10

A student needs to convert $$25.0$$ °C to Kelvin. Which of the following is the correct conversion?

Accepted Answer

$$298.2 K$$

Question 11

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

Accepted Answer

$$E = h 
u$$

Question 12

Which of the following statements about Dalton’s Atomic Theory is NOT correct according to modern understanding?

Accepted Answer

Atoms of a given element are identical in mass and properties.

Question 13

A compound contains $$40.0\%$$ carbon, $$6.7\%$$ hydrogen, and $$53.3\%$$ oxygen by mass. What is the empirical formula of the compound?

Accepted Answer

$$CH_2O$$

Question 14

Which of the following best describes the Heisenberg Uncertainty Principle?

Accepted Answer

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

Question 15

Which of the following is the correct formula for calculating the wavelength ($$\lambda) of a $$particle according to de Broglie’s equation?

Accepted Answer

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

Question 16

A sample of a compound contains $$0.250$$ mol of carbon, $$0.500$$ mol of hydrogen, and $$0.250$$ mol of oxygen. What is the empirical formula of the compound?

Accepted Answer

$$CH_2O$$

Question 17

Which of the following best explains why atomic emission spectra are unique for each element?

Accepted Answer

Each element has a unique number of protons, which determines the energy levels available to its electrons.

Question 18

Which of the following is the correct value for Avogadro’s number ($$N_A$$)?

Accepted Answer

$$6.022 	imes 10$$^{23}$$ things/mol

Question 19

A student is asked to calculate the number of atoms in $$0.250$$ mol of sodium. Which of the following is the correct calculation?

Accepted Answer

$$0.250 	imes 6.022 	imes 10$$^{23}$$

Question 20

Which of the following best describes the difference between an atom and an ion?

Accepted Answer

An atom is neutral, while an ion has a net positive or negative charge due to the loss or gain of electrons.

General Chemistry Exam 1 Study Guide: Measurement, Atomic Theory, and Quantum Mechanics

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