Q: A student is measuring the density of a metal cylinder. The mass is measured as 25.0 g, and the volume is determined by water displacement to be 9.8 mL. What is the density of the cylinder, and which of the following best describes the correct calculation?

$$\text{Density} = \frac{25.0\ \text{g}}{9.8\ \text{mL}} = 2.55\ \text{g/mL}$$

Q: An electron in a hydrogen atom transitions from $$n_i = 4 to$$ $$n_f = 2. $$Using the Bohr model, which equation correctly gives the energy change for this transition?

$$\Delta E = -2.179 \times 10$$^{-18}$$ \left( \frac{1}{2^2$} - \frac{1}{4^2$} \right)\ \text{J}$$

Question 1

A student is measuring the density of a metal cylinder. The mass is measured as 25.0 g, and the volume is determined by water displacement to be 9.8 mL. What is the density of the cylinder, and which of the following best describes the correct calculation?

Accepted Answer

$$	ext{Density} = \frac{25.0\ 	ext{g}}{9.8\ 	ext{mL}} = 2.55\ 	ext{g/mL}$$

Question 2

Which of the following is NOT a correct laboratory safety rule?

Accepted Answer

Dispose of chemicals down the sink unless instructed otherwise.

Question 3

A student determines the boiling point of an unknown liquid to be $$78\ ^\circ	ext{C}. $$Which of the following liquids is most likely the unknown, based on common laboratory chemicals?

Accepted Answer

Ethanol

Question 4

A solution is prepared by dissolving 5.0 g of NaCl in 100 mL of water. After stirring, some solid remains undissolved. What can be concluded about the solution?

Accepted Answer

The solution is saturated with respect to NaCl.

Question 5

An electron in a hydrogen atom transitions from $$n_i = 4 to$$ $$n_f = 2. $$Using the Bohr model, which equation correctly gives the energy change for this transition?

Accepted Answer

$$\Delta E = -2.179 	imes 10$$^{-18}$$ \left( \frac{1}{2^2$} - \frac{1}{4^2$} ight)\ 	ext{J}$$

Question 6

Which electron configuration represents the Fe$$^{3+}$$ ion?

Accepted Answer

$$1s^2$$\ $$2s^2$$\ $$2p^6$$\ $$3s^2$$\ $$3p^6$$\ $$3d^5$$

Question 7

Which set of quantum numbers is NOT allowed for an electron in a 4p orbital?

Accepted Answer

$$n=4,\ l=1,\ m_l=2,\ m_s=+\frac{1}{2}$$

Question 8

Which of the following compounds is named incorrectly?

Accepted Answer

NH$$_3$$: ammonium triiodide

Question 9

Which of the following molecules has a trigonal planar electron group geometry and is nonpolar?

Accepted Answer

BF$$_3$$

Question 10

How many $$\sigma$$ and $$\pi$$ bonds are present in the Lewis structure of CO$$_2$$?

Accepted Answer

2 $$\sigma$$ bonds and 2 $$\pi$$ bonds

Question 11

Which hybridization corresponds to a molecule with 5 electron groups around the central atom?

Accepted Answer

$$sp^3d$

Question 12

A molecule has the following Lewis structure: central atom with 3 single bonds and 1 lone pair. What is the molecular geometry according to VSEPR theory?

Accepted Answer

Trigonal pyramidal

Question 13

Which of the following molecules is polar due to its molecular geometry?

Accepted Answer

H$$_2O$$

Question 14

Which of the following statements about resonance structures is correct?

Accepted Answer

Resonance structures differ only in the arrangement of electrons, not the arrangement of atoms.

Question 15

Which separation technique would be most effective for separating a mixture of sand and salt?

Accepted Answer

Dissolve in water, filter, then evaporate water from filtrate.

Question 16

Given the molecular orbital diagram for O$$_2$$, what is the bond order and magnetic property of the molecule?

Accepted Answer

Bond order = 2, paramagnetic

Question 17

Which of the following best describes Hund's rule?

Accepted Answer

Electrons fill degenerate orbitals singly before pairing.

Question 18

A sample of light emitted from a hydrogen lamp contains a line at $$486\ 	ext{nm}. $$Which transition does this correspond to?

Accepted Answer

$$n_i = 4 to$$ $$n_f = 2$$

Question 19

Which of the following molecules has an expanded octet in its Lewis structure?

Accepted Answer

SF$$_6$$

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