Question 1

Highway road crews sometimes spread salt on icy roads during the winter because the solution process generates heat, which melts the ice.

Accepted Answer

Spreading salt on icy roads lowers the freezing point of water, which causes the ice to melt; it does not generate heat during the solution process.

Question 2

The following aqueous solutions, with one mole of each solid in equal volumes of water are prepared.
C₆H₁₂O_6(s) $\rightarrow$ C₆H₁₂O₆₍_aq₎
NaNO_3(s) $\rightarrow$ Na⁺₍_aq₎ + NO₃^-₍_aq₎
CaCl_{2 (}_aq₎ $\rightarrow$ Ca²⁺₍_aq₎ + 2Cl^-₍_aq₎
Which solution would have the lowest freezing point?

A) C₆H₁₂O₆
B) NaNO₃
C) CaCl₂
D) All of the responses would have the same freezing point.

CaCl₂

Accepted Answer

CaCl2 dissociates into three ions (Ca^2+ and 2 Cl^-), resulting in the highest number of particles in solution, which lowers the freezing point the most according to colligative properties.

Question 3

One mole of particles lowers the freezing point of 1,000 g of water by 1.76ºC. What is the freezing point of a solution containing one mole of NaNO₃ in 1,000 g of water? A) 30.24ºC B) 28.48ºC C) ?1.76ºC D) ?3.52ºC

Accepted Answer

The freezing point depression is directly proportional to the molality of the solution and the van't Hoff factor (i), which represents the number of particles the solute dissociates into. NaNO₃ doesn't exist, but assuming a typo for NaNO3 (sodium nitrate), which dissociates into 2 particles (Na+ and NO3-), the van't Hoff factor (i) is 2. Therefore, the depression is 1.76ºC * 2 = 3.52ºC. Since water freezes at 0ºC, the new freezing point is 0ºC - 3.52ºC = -3.52ºC.

Question 4

What is the number of atoms on each side of the equation, CH₄ + 2O₂ $\rightarrow$ CO₂ + 2H₂O? A) 5 B) 6 C) 7 D) 9

Accepted Answer

The equation has 1 carbon, 4 hydrogen, and 4 oxygen atoms on each side, totaling 9 atoms on each side.

Question 5

What is the total mass of products in the methane reaction CH₄ + 2O₂ $\rightarrow$ CO₂ + 2H₂O? A) 80 u B) 64 u C) 62 u D) 48 u

Accepted Answer

The total mass of products in the given reaction is the sum of the masses of CO2 and 2H2O. The molar mass of CO2 is 44 u (C=12, O=16x2=32, 12+32=44) and the molar mass of H2O is 18 u (H=1x2=2, O=16, 2+16=18). Since there are two H2O molecules, their combined mass is 36 u (18x2). Adding the masses of CO2 and 2H2O gives 44 u + 36 u = 80 u.

Question 6

What is the mass percent of sodium in washing soda, Na₂CO₃? A) 43.4% B) 32.5% C) 21.7% D) 62.1%

Accepted Answer

The molar mass of Na2CO3 is 105.99 g/mol. The molar mass of sodium (Na) is 22.99 g/mol. Since there are two sodium atoms, the mass of sodium in Na2CO3 is 2 x 22.99 = 45.98 g/mol. The mass percent of sodium is (45.98/105.99) x 100% = 43.4%.

Question 7

How many molecules are in an 8.0 g sample of oxygen gas, O₂? A) 6.0 × 10²³ B) 3.0 × 10²³ C) 1.5 × 10²³ D) 12.0 × 10²³

Accepted Answer

The answer of How many molecules are in an 8.0...

Deck 3: Chemical Reactions, Water and Solutions