CCC Part A quiz

(Successive Ionization Energies of 3rd Period Elements) Based on this information, which of the following statements is FALSE?

• X has the smallest radius

• Z forms the largest cation

• Y is sodium

• Y is potassium

• V is a semi-metal

Answer explanation

Y cannot be potassium because potassium is in the 4th period, not the 3rd. Therefore, the statement 'Y is potassium' is false. The other statements about the elements' properties are consistent with their positions in the periodic table.

Cows are one of the most significant sources of methane (CH₄) added to the atmosphere. The lower explosive limit (LEL) for methane at SATP is 5.0% v/v. The average cow produces 259 grams of methane per day. Assuming a constant rate of methane emission, how long would it be safe to keep a cow in a 10.0 m³ enclosed space at 25°C and 100 kPa before there is a risk of explosion? The molar volume of a gas at SATP is 24.8 L.

• 30 hours

• 60 hours

• 90 hours

• 600 hours

• 9 hours

Answer explanation

To find the time before reaching the LEL of methane, calculate the volume of methane produced by a cow in 30 hours (259 g/day). At 25°C and 100 kPa, the safe limit is 0.5 m³ of methane in 10 m³, which is reached in 30 hours.

Canada is a world-leader in the production of radionuclides such as technetium-99m, which is used to diagnose bone diseases. ^99mTc has a relative atomic mass of 98.91 amu and exhibits first-order radioactive decay with a half-life of 6.00 hours. If 8.62x10^-12 mol of sodium pertechnetate (Na^99mTcO₄) is injected into a 75 kg adult male patient, what mass of ^99mTc remains after 24 hours?

• 1.46x10^-9 g

• 2.13x10^-10 g

• 3.66x10^-11 g

• 5.33x10^-11 g

• 9.15x10^-11 g

Answer explanation

After 24 hours (4 half-lives), the remaining amount of \(^{99m}Tc\) is calculated using the formula \(N = N_0 (1/2)^{t/t_{1/2}}\). This results in \(5.33 \times 10^{-11} g\), confirming the correct choice.

1) The following data were taken for the addition of solid barium fluoride to enough water to make 100.0 mL of solution. What is the K_sp of barium fluoride: BaF₂ (s) ⇌ Ba²⁺(aq) + F^–(aq)?

• 2.56 x 10^–1

• 6.63 x 10^–6

• 2.41 x 10^-8

• 4.83 x 10^–8

• 6.04 x 10^–9

Answer explanation

To find Ksp for BaF2, use the solubility product expression: Ksp = [Ba^2+][F^-]^2. Given the solubility, calculate the concentrations and substitute into the expression. The correct Ksp is 2.41 x 10^-8.

What is the correct relationship between the following two organic substances?

• non-superimposable mirror images

• identical

• constitutional isomers

• hydrocarbons with different molecular formulae

• geometric isomers

Answer explanation

The correct choice is 'hydrocarbons with different molecular formulae' because the two organic substances differ in their molecular composition, indicating they are not identical or isomers of each other.

1) Hypophosphatemia is a condition of abnormally low phosphate concentration in the human blood stream, occurring in 2% of hospitalized patients. Given the data below, and assuming similar concentrations of both conjugates, determine the most effective buffer combination for a pH of 7.4.

H₃PO₄^–; K_a = 7.2 x 10^-3 H₂PO₄^–; K_a = 6.3 x 10^-8 HPO₄^2–; K_a = 4.2 x 10^-13

• H₃PO₄ and H₂PO₄^–

• H₃PO₄ and HPO₄^2–

• H₂PO₄^– and PO₄^3–

• HPO₄^2– and PO₄

• H₂PO₄^– and HPO₄^2–

Answer explanation

The most effective buffer for pH 7.4 is H2PO4– and HPO4 2–, as they are the conjugate acid-base pair closest to this pH, allowing for optimal buffering capacity.

What is the first change that occurs when I2(s) is heated

slowly at one atmosphere pressure?

• The solid melts

• The solid vaporizes

• The solid breaks into atoms

• The solid becomes darker in colour

Answer explanation

When I2(s) is heated slowly at one atmosphere pressure, the first change is that the solid vaporizes, transitioning directly from solid to gas without melting, due to its sublimation properties.

How can 0.1 g samples of the two white solids, lead(II)

chloride and silver chloride, be distinguished from one

another?

• Add 10 mL of cold water to each. The silver

  chloride will dissolve.

• Add 10 mL of hot water to each. The lead(II)

  chloride will dissolve.

• Add 10 mL of sodium chloride to each solution. The

  lead(II) chloride will become warm and release

  chlorine gas.

• Add 10 mL of zinc chloride solution to each. The

  silver chloride will change to metallic silver.

Answer explanation

Lead(II) chloride is soluble in hot water, while silver chloride is not. By adding 10 mL of hot water, the lead(II) chloride will dissolve, allowing for the distinction between the two solids.

If nitrogen atoms are represented as filled circles and and oxygen atoms as open circles, how much NO₂ can be prepared from the mixture shown?

• 4 molecules

• 5 molecules

• 8 molecules

• 6 molecules

Answer explanation

To form NO2, one nitrogen atom (N) combines with two oxygen atoms (O). The mixture must provide enough N and O. With 8 available oxygen atoms, we can pair them with 4 nitrogen atoms, yielding 8 molecules of NO2.

A gas mixture at 27°C and 760 mm Hg contains 1.0 g

each of He, H₂, N₂ and CO₂. How do their average

molecular speeds compare?

(A) (B)

(C) (D)

• He < H₂ < N₂ < CO₂

• CO₂ < N₂ < He < H₂

• CO₂ < H₂ = N₂ < He

• He = H₂ = N₂ = CO₂

Answer explanation

The average molecular speed is inversely related to the square root of the molar mass. CO2 is the heaviest, followed by N2, He, and H2, which is the lightest. Thus, the order is CO2 < N2 < He < H2.