If the temperature of an aqueous solution of NaCl is increased from 20°C to 90°, which one below is true?

NetherCraft 0

A) The density of the solution remains unchanged

B) The molarity of the solution remains unchanged

C) The molality of the solution remains unchanged

D) The mole fraction of the solute decreases

E) The mole fraction of the solute increases

  1. A yellow precipitate forms when 0.5 M NaI(aqueous is added to a 0.5 M solution of which of the following ions?

A) Pb2+(aq)

B) Zn2+(aq)

C) CrO4¯(aq)

D) SO4²¯(aq)

E) OH¯ (aq)

  1. A hot-air balloon rises. Which of the following is the best explanation for this observation?

A. The pressure on the walls of the balloon increases with increasing temp.

B. The difference in temperature between the air inside and outside the balloon produces convection currents.

C. The cooler air outside the balloon pushes in on the walls of the balloon

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D. The rate of diffusion of cooler air is less than that of the warmer air

E. The air density inside the balloon is less than that of the surrounding air.

Please any help and explanation would be great

2 Answers

  • Water expands when heated from 20 to 90 C, so, assuming the solution does not evaporate at all, the volume of the solution will increase. This means that the density will decrease and the molarity (grams solvent per liter of solution) will decrease. Heating (in the absence of evaporation) will not affect the number of moles of water or solute present, so the mole fraction of the solute will not change. So answers A, B, D, and E are all false. Molality is defined as the number of moles of solute per kg of solvent. As noted above, heating does not change the amount of solvent or solute present, so the molality of the solution is constant. Answer C is true.

    Different salts would be produced in each of the scenarios you are given. (A) would produce lead iodide (PbI2), an insoluble yellow salt. (B) could produce zinc iodide (ZnI2), a white soluble salt. (C) could produce sodium chromate NaC4O4, a soluble yellow salt. (D) could produce sodium sulfate Na2SO4, a highly reactive (and soluble) colorless salt. (E) would produce sodium hydroxide (NaOH), a highly soluble colorless salt. You figure out the correct answer.

    The correct answer to #59 is E. The pressure inside and outside the balloon is the same, but the gas inside the baloon is hotter than the outside air. For a given pressure, the density of a gas decreases with increasing pressure.

  • I forget why. It just does? Something about more ions and the Na+ and Cl- have definite charge instead of just partial charge (like in the water molecules), so the salt solution will hold and conduct a current much easier than an ordinary water solution.


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