Study guide for my exam next week. This will not be graded but I need help under
ID: 1015628 • Letter: S
Question
Study guide for my exam next week. This will not be graded but I need help understanding how to do the problems 1-6.
The answers I have my not be correct.
CHEM107 E02 HOMEWORK QUIZ Multiple Choice Identify the choice that best completes the statement or answers the question I. Which of the solutions shown here will have the kowest vapox pressure? White circles indicate solvent molecules, black circles indicate molecules of a monvolatile solute 2 Indicate which aqucous solution has the highest vapor pressure. e. 0.2MMgC c. 0.2MNaCI 3. Indicate which aqueous solution has the lowest vapor pressure. a. 0.1 MKCI b. 0.1 MNa CO c 0.2MNaC d. 0.1 MMgCl e 02MMgCl 4. Indicate which aque us solution has the slowest evaporation rate. d. 0.1 MMgCl c. 0.1 MNaBr a. 0.1 MKC b. 0.2 MNa CO 5. Indicate which aqucous solution has the fastest evaporation rate. d. 0.1 MMgCl a. 0.1 MKC b. 0.2MNa CO c. 0.2 MMgCl 756 mm Hg what is the vapor pressure of water in a 0.500 m d. 2535 mm Hg c 0.2MNaC At 25C, the vapor pressure of pure water is 25 solution of sodium chloride? 6. a. 25.52 mm Hg b. 0.2301 mm Hg c. 0.4602 mm Hg e. 12.88 mm Hg
Explanation / Answer
(1) In all four systems, number of solvent circles (white circles) are same.
Vapour pressure is pressure exerted by the gas or vapour molecules over the liquid.
When a non-volatile solute is added to a solvent, vapour pressure decreases because surface covered by solvent molecules will decrease and they will have less space to pass into gaseous phase.
System d, has highest number of non-volatile solute molecules (black circles) will have least vapour pressure.
Correct option - d
(2) Vapour pressure does not depend on the nature of the non-volatile solute added. It depends on the number of solute particles. Higher the number of solute particles, lower will be the vapour pressure.
0.1 M KCl aqueous solution will have highest vapour pressure as it has lowest number of solute particles.
(Note: All the given solutes are ionic and will produce ions in dissolving in water. KCl and NaCl will give 2 ions each and Na2CO3 and MgCl2 will give 3 ions each
More the number of ions produced, lesser will be vapour pressure)
Correct option - a
(3) 0.2 M MgCl2 will have lowest vapour pressure. MgCl2 will furnish one Mg2+ ion and two Cl- ion for each molecule.
Correct option - e
(4) Evaporation means vapourization of any liquid.
Correct option - b (0.2 M Na2CO3)
More the number of solute, less space for solvent molecules to escape to gaseous or vapour phase, therefore slow rate of evaporation.