Q: Calculate the percent composition of oxygen in sodium sulfate ($$\mathrm{Na_2SO_4}). ($$Atomic masses: Na = 23, S = 32, O = 16)

$$\displaystyle \frac{64}{142} \times 100 = 45.1\%$$

Question 1

Which of the following best describes effective nuclear charge ($$Z_{eff}) $$and its impact on atomic radius across a period?

Accepted Answer

Effective nuclear charge increases across a period, causing atomic radius to decrease.

Question 2

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

Accepted Answer

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

Question 3

Which of the following ions is paramagnetic?

Accepted Answer

$$\mathrm{Fe$$^{2+}$$}$$

Question 4

Which statement correctly describes Hund’s rule?

Accepted Answer

Electrons fill orbitals singly with parallel spins before pairing.

Question 5

Which of the following elements has the highest first ionization energy?

Accepted Answer

Neon ($$\mathrm{Ne})$$

Question 6

Which of the following is the correct Lewis dot structure for ammonia ($$\mathrm{NH_3$}$$)?

Accepted Answer

N with three single bonds to H and one lone pair on N

Question 7

Which of the following compounds is ionic?

Accepted Answer

Sodium chloride ($$\mathrm{NaCl})$$

Question 8

What is the correct formula for the phosphate ion?

Accepted Answer

$$\mathrm{PO_4$^{3-}}$$

Question 9

Calculate the percent composition of oxygen in sodium sulfate ($$\mathrm{Na_2SO_4}). ($$Atomic masses: Na = 23, S = 32, O = 16)

Accepted Answer

$$\displaystyle \frac{64}{142} 	imes 100 = 45.1\%$$

Question 10

A sample of magnesium nitrate hexahydrate ($$\mathrm{Mg(NO_3$)_2 \cdot 6H_2O}) $$weighs 256 g. How many moles of water are present in the sample? (Molar mass of $$\mathrm{Mg(NO_3$)_2 \cdot 6H_2O} = 256 g/$$mol)

Accepted Answer

6 moles

Question 11

Which of the following is the correct empirical formula for a compound containing 40% carbon, 6.7% hydrogen, and 53.3% oxygen by mass?

Accepted Answer

$$\mathrm{C_2H_4O}$$

Question 12

Which of the following polyatomic ions has a charge of $$-1$$?

Accepted Answer

Nitrate ($$\mathrm{NO_3$^-})$$

Question 13

If 0.50 moles of $$\mathrm{Na_2CO_3}$$ are dissolved in enough water to make 250 mL of solution, what is the molarity of the solution?

Accepted Answer

$$2.0\ \mathrm{M}$$

Question 14

Which of the following best explains why $$\mathrm{F^-} is $$smaller than $$\mathrm{O$$^{2-}$$}$$?

Accepted Answer

$$\mathrm{F^-}$$ has a higher effective nuclear charge than $$\mathrm{O$$^{2-}$$}$$, pulling electrons closer.

Question 15

Which of the following is the correct name for $$\mathrm{$$KNO_3$$}$$?

Accepted Answer

Potassium nitrate

Question 16

A compound contains 0.40 mol of $$\mathrm{Na}$$, 0.20 mol of $$\mathrm{S}$$, and 0.80 mol of $$\mathrm{O}. $$What is its empirical formula?

Accepted Answer

$$\mathrm{Na_2SO_4}$$

Question 17

Which of the following is a diamagnetic species?

Accepted Answer

$$\mathrm{Zn$$^{2+}$$}$$

Question 18

Which of the following is the correct formula for ammonium sulfate?

Accepted Answer

$$\mathrm{(NH_4$)_2SO_4}$$

Question 19

Which of the following statements about valence electrons is correct?

Accepted Answer

Valence electrons are the electrons in the outermost shell and are involved in chemical bonding.

Question 20

A hydrate of copper(II) sulfate has a mass of 250 g. After heating, the mass of anhydrous $$\mathrm{$$CuSO_4$$} is 160 g. $$What is the number of moles of water lost? (Molar mass of $$\mathrm{$$CuSO_4$$} = 160 g/$$mol, $$\mathrm{H_2O} = 18 g/$$mol)

Accepted Answer

5 moles

General Chemistry Study Notes: Periodic Properties, Molecules, and Compounds

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