PRACTICE DAT EXAM #8 - General Chemistry

What is the temperature at which 64 g of O₂ will occupy a volume of 8.2 L at 760 Torr?

[(1)(8.2)]/[(2)(0.082)]

IDEAL GAS LAW: PV=nRT

An element X forms an oxide X₂O₃ with a mass ratio of 0.50 g X / 1 g O. What is the atomic mass of X?

12.0 amu; use dimensional analysis to solve this stoichiometric problem

Which of the following 0.25 M solutions would exhibit the lowest electrical conductivity?

a. HCl

b. K₂SO₄

c. NaCl

d. HF

e. Ba(NO₃)₂

d. HF

In general, strong acids and bases will fully ionize when in contact with water, creating solutions with large electrical conductivity. Of all molecules present, HF is the only one that qualifies as a weak electrolyte, and therefore it will not completely ionize in solution leading to the lowest electrical conductivity of all answer choices present. 

Key Takeaway:

• Strong acids and bases are able to fully dissociate creating solutions with large electrical conductivity. 

For the reaction 2NO_(g) + O_2(g) → 2NO_2(g), the concentration of NO was monitored from 0 to 100 seconds. Given the following data, what is the average rate of disappearance of NO from 0 to 100 seconds?

t (s) | (NO), M

0 | 1.0 x 10^-3

100 | 5.0 x 10^-4

5.0 × 10^-6 M/s

Which of the following reactions will be spontaneous at all temperatures?

A. 2H_2(g) + O_2(g) → 2H₂O_(g) ΔH = –483.6 kJ

B. 2NCl_3(g) → N_2(g) + 3Cl_2(g) ΔH = –460.1 kJ

C. N_2(g) + O_2(g) → 2NO_(g) ΔH = + 180.5 KJ

D. 2Na_(s) + Cl_2(g) → 2NaCl_(s) ΔH = –821.8 kJ

E. C_(s) + 2S_(s) → CS_2(g) ΔH = + 92.0 KJ

B. 2NCl_3(g) → N_2(g) + 3Cl_2(g) ΔH = –460.1 kJ

creation of more gas moles means there is an increase in disorder, an increase in disorder/more disorder is indicative of a positive (+) change in entropy (S)

negative change in enthalpy and a positive change in entropy means the reaction will be spontaneous at ALL temperatures!

Based on the reaction below, which of the following statements is correct?

HClO₃ + H₂O ⇌ H₃O⁺ + ClO₃^-

A. H₂O acts as a base and ClO₃^- is its conj. acid

B. H₂O acts as a base and H₃O⁺ is its conj. base

C. HClO₃ acts as a base and H₃O⁺ is its conj. base

D. H₂O acts as a base and H₃O⁺ is its conj. acid

E. HClO₃ acts as a base and ClO₃^- is its conj. acid

D. H₂O acts as a base and H₃O⁺ is its conj. acid

In the reaction above:

• HClO₃ acts as an acid because it is a proton (H⁺) donor. Therefore, ClO₃^- is the conjugate base. 

• H₂O acts as a base because it is a proton (H⁺) acceptor. Therefore, H₃O⁺ is the conjugate acid. 

Key Takeaway:

• According to the Bronsted-Lowry definition of acids and bases, an acid is a proton (H⁺) donor and a base is a proton (H⁺) acceptor.

Which of the following gases will have the greatest density at STP?

a. Cl₂

b. N₂O

c. Ar

d. SO₃

e. CO₂

d. SO₃

The density, ρ of a gas:

P is the pressure of the gas, M is its molar mass, R is the ideal gas constant(0.082), and T is the absolute temperature. Because all of the gases are at the same temperature and pressure, the density is only dependent on the molar mass. Density increases with molar mass.

SO₃ has the highest mass and the highest density.