Chemistry 121 Exam Notes

Chemistry 121 Exam Notes

General Instructions

• Fill in your name and MSU ID# on the scantron (leave the first column blank).
• Use a #2 pencil.
• Version A: Questions 1-40.
• Version B: Questions 51-90.
• Time: 90 minutes.
• Periodic table and list of tables/constants are provided.
• 40 questions, 4 points each.
• Read each question carefully.
• Turn in your scantron after completing the assessment.
• Grades will be posted in D2L after grading.

Question 51

• A deep-sea scuba tank contains helium, oxygen, and traces of other gases.
• The gas in the scuba tank is a homogeneous mixture.

Question 52

• Chemical Property: Flammability.

Question 53

• Given: 125 mL Erlenmeyer flask.
• Convert mL to Liters: $125 \text{ mL} = 0.125 \text{ L}$
  • Answer: 0.125 L

Question 54

• Given: 10K race = 10.0 km, 1 yd = 0.914 m
• Convert km to yards: $10.0 \text{ km} = 10,000 \text{ m}$$\frac{1 \text{ yd}}{0.914 \text{ m}} \times 10,000 \text{ m} = 10,940.9 \text{ yd}$
  • Closest Answer: 10, 900 yd

Question 55

• Element with 12 protons: Mg (Magnesium).

Question 56

• The element with the highest ionization energy is P.

Question 57

• Electron configuration: $1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^{10} 4p^6 5s^2$
• This configuration corresponds to Strontium (Sr).

Question 58

• Ions: $Sr^{2+}$ and $Br^{-}$
• Chemical formula for the binary compound: $SrBr_2$

Question 59

• Sodium sulfite formula: $Na<em>2SO</em>3$

Question 60

• Lewis structure for $OCl_2$: (The description of the correct structure would depend on the provided options. The central O atom is bonded to two Cl atoms, and each atom has lone pairs to fulfill the octet rule).

Question 61

• Phosphine, $PH_3$: 3 covalent pairs and 1 lone pair.

Question 62

• Hydrogen cyanide, $HCN$: 1 single bond and 1 triple bond.
• $H - C \equiv N$

Question 63

• Unbalanced equation: D) $C<em>7H</em>{16} + O<em>2 \rightarrow 7 CO</em>2 + 8 H_2O$
• (Correct balanced equation would be: $C<em>7H</em>{16} + 11O<em>2 \rightarrow 7CO</em>2 + 8H_2O$)

Question 64

• Precipitate formation: KOH (aq) and $Mg(NO<em>3)</em>2$ (aq).

Question 65

• Net ionic equation for $H<em>2SO</em>4$ and $KOH$: $H^+ (aq) + OH^- (aq) \rightarrow H_2O(l)$

Question 66

• Element being reduced in the redox reaction: $H<em>2O</em>2(l) + ClO<em>2(aq) \rightarrow ClO</em>2^-(aq) + O_2(g)$
• Chlorine (Cl).

Question 67

• Oxidation number of chlorine in $LiClO_2$: +3.

Question 68

• Molar mass of $K<em>2SO</em>4$ = 174.259 g/mol
• Moles of $K<em>2SO</em>4$ in 15.0 g:
  $\frac{15.0 \text{ g}}{174.259 \text{ g/mol}} = 0.0861 \text{ mol}$

Question 69

• Given: 4.0 × 10^21 molecules of $H_2O$
• Moles of $H_2O$:
  $\frac{4.0 \times 10^{21} \text{ molecules}}{6.022 \times 10^{23} \text{ molecules/mol}} = 6.6 \times 10^{-3} \text{ mol}$

Question 70

• Reaction: $C<em>3H</em>7SH(l) + 6 O<em>2(g) \rightarrow 3 CO</em>2(g) + SO<em>2(g) + 4 H</em>2O(g)$
• Moles of $O<em>2$ required to produce 4.00 moles of $H</em>2O$:
  $4.00 \text{ mol } H<em>2O \times \frac{6 \text{ mol } O</em>2}{4 \text{ mol } H<em>2O} = 6.00 \text{ mol } O</em>2$

Question 71

• Reaction: $4Al + 3O<em>2 \rightarrow 2Al</em>2O_3$
• Start with 10.0 grams of Al and 19.0 grams of $O_2$
• Molar mass of Al = 26.98 g/mol, Molar mass of $O_2$ = 32.00 g/mol
• Moles of Al: $\frac{10.0 \text{ g}}{26.98 \text{ g/mol}} = 0.371 \text{ mol}$
• Moles of $O_2$: $\frac{19.0 \text{ g}}{32.00 \text{ g/mol}} = 0.594 \text{ mol}$
• Limiting reactant: Al

Question 72

• Molecule with dipole-dipole interaction: $SO_2$

Question 73

• Solution: 100.0 g water, 10.0 g NaCl, 15.0 g methanol
• Mass percent of methanol:
  $\frac{15.0 \text{ g}}{(100.0 + 10.0 + 15.0) \text{ g}} \times 100\% = 12.0\%$

Question 74

• Barium hydroxide: $Ba(OH)_2$, Molar mass = 171.35 g/mol
• Volume = 0.500 L, Concentration = 0.100 M
• Mass of $Ba(OH)_2$
  $0.500 \text{ L} \times 0.100 \text{ mol/L} \times 171.35 \text{ g/mol} = 8.57 \text{ g}$

Question 75

• Dilution: 350 ml of 12.0 M HCl to 1.20 L
• $M<em>1V</em>1=M<em>2V</em>2$
  $12.0 M \times 350 \text{ mL} = M<em>2 \times 1200 \text{ mL}$$M</em>2 = \frac{12.0 \times 350}{1200} = 3.50 M$

Question 76

• Reactants having greater energy than products: Exothermic reaction.

Question 77

• Processes with $\Delta S < 0$: Condensation of water vapor into rain drops.

Question 78

• If the temperature of a reaction increases, the rate of reaction increases.

Question 79

• Rate = k[W]^2.

Question 80

• Equilibrium shift to the left (Mn(OH)2(s) ⇌ Mn2+(aq) + 2 OH-(aq)): add solid NaOH

Question 81

• Equilibrium shift to the left (C(s) + H2O(g) ⇌ CO(g) + H2(g) + heat): decrease temperature

Question 82

• Reaction: 2 NO(g) + O2(g) ⇌ 2 NO2(g)
• Equilibrium concentrations: [NO] = 1.08 × 10^-7, [O2] = 0.500, [NO2] = 0.100
• $K<em>{eq} = \frac{[NO</em>2]^2}{[NO]^2[O_2]} = \frac{(0.100)^2}{(1.08 \times 10^{-7})^2(0.500)} = 1.71 \times 10^{12}$

Question 83

• Grams of $N<em>2$ in an 11.2 liter sample at STP. Molar mass of $N</em>2$ = 28.0134 g/mol.
• At STP, 1 mole of gas occupies 22.4 L.
• Moles of $N_2$: $\frac{11.2 \text{ L}}{22.4 \text{ L/mol}} = 0.5 \text{ mol}$
• Mass of $N_2$: $0.5 \text{ mol} \times 28.0 \text{ g/mol} = 14.0 \text{ g}$

Question 84

• Most gases show variations from ideality at high pressure and low temperature.

Question 85

• A balloon originally had a volume of 4.39 L at 44°C and a pressure of 729 torr. To what temperature must the balloon be cooled to reduce its volume to 3.78 L if the pressure is constant?
• $V<em>1/T</em>1 = V<em>2/T</em>2$
• T1 = 44 + 273.15 = 317.15 K, V1 = 4.39 L, V2 = 3.78 L.
• $T<em>2 = \frac{V</em>2 \times T<em>1}{V</em>1} = \frac{3.78 \times 317.15}{4.39} = 272.76$
• T2 = 272.76 - 273.15 = -0.39 degrees Celsius is about 0.0°C

Question 86

• Image depicting an aqueous solution containing a weak acid (HA).

Question 87

• Given: $[H^+] = 5.0 \times 10^{-3} M$
• $[OH^-]$ concentration:
  $[H^+][OH^-] = 1.0 \times 10^{-14}$
  $[OH^-] = \frac{1.0 \times 10^{-14}}{5.0 \times 10^{-3}} = 2.0 \times 10^{-12} M$

Question 88

• Carbonate buffer system equilibrium: $CO<em>2(g) + 2H</em>2O(l) \rightleftharpoons H<em>2CO</em>3 (aq) \rightleftharpoons HCO<em>3^-(aq) + H</em>3O^+ (aq)$
• $[H<em>2CO</em>3] = 0.56 M$,$[HCO<em>3^-] = 0.0012 M$, $K</em>a = 3.98 \times 10^{-7}$
• Calculate the pH:
  $pH = pK<em>a + log(\frac{[HCO</em>3^-]}{[H<em>2CO</em>3]})$
  $pK_a = -log(3.98 \times 10^{-7}) = 6.40$
  $pH = 6.40 + log(\frac{0.0012}{0.56}) = 6.40 + log(0.00214) = 6.40 + (-2.67) = 3.73$
• pH = 3.73

Question 89

• $^{90}<em>{38}Sr \rightarrow ^{90}</em>{39}Y + ?$
• Radioactive particle emitted: beta particle.

Question 90

• The half-life of 223Ra is 11.4 days. How much of a 200.0 mg sample remains after 25 days?
• $N(t) = N<em>0 (\frac{1}{2})^{\frac{t}{t</em>{1/2}}}$
• $N(25) = 200.0 (\frac{1}{2})^{\frac{25}{11.4}} = 200.0 (0.5)^{2.193} = 200.0 \times 0.219 = 43.8$ mg remaining.