# States of Matter, Solids, Liquids, Gases, Colloids and Solutions

142. (Colligative properties, boiling point elevation, freezing point depression, phase changes) Demonstrations: A digital thermometer is used to monitor temperature in each of these experiments.
What will the boiling point do when lots of salt is dissolved in the water?

increase, decrease, stay the same

What will the freezing point do when lots of salt is dissolved in the water?

increase, decrease, stay the same

143. (Concentration, moles) To a solution of 10 mL of 6 M NaOH is added enough water to make 100 mL of solution. The number of moles of NaOH present is

increased by a factor of 10, decreased by a factor of 10, unchanged

The concentration of NaOH is

increased by a factor of 10, decreased by a factor of 10, unchanged

144. (Concentration, moles) Demonstration: A mass of 0.02 moles of copper sulfate is to be dissolved in 200 mL of water to make solution A. A mass of 0.04 moles of copper sulfate is to be dissolved in 400 mL of water to make solution B. Will the two solutions have the same concentration?

yes no

Will they have the same intensity of color in a given pathlength?

yes no

146. (Ions) Solutions of NaNO3 and K2SO4 are dissolved in water and the water then allowed to evaporate. How many possible salts could be recovered?

2, 3, 4

158. (Solid solutions; Ch. 3 "Companion") The following trio of metals all form the BCC structure.

Which two metals are most likely to form a solid solution?

V and Mo, V and Na, Mo and Na

Additional example:

Which two elements are most likely to form a solid solution?

C and Si, C and Ge, Si and Ge

179. A beaker contains 10 mL or 0.1 M HCl. How much water do you need to add to obtain a pH of 2?

~10 mL, ~100 mL

How much water would need to be added to raise the pH to 3?

~10 mL, ~100 mL, ~1000 mL

Could you get a pH of 10 by continuing to add more water?

yes, no

180. A beaker contains 100 mL of salt water. If 100 mL of distilled water is added to the beaker, the number of moles of NaCl

increases by 50%, decreases by 50%, doesn't change

181. The pressure of oxygen Ph as a function of height h from the earth's surface was calculated, assuming a particular value of temperature T in the atmosphere, using the expression Ph = Poexp(-Mgh/RT); Po is the pressure at the earth's surface; g is the acceleration due to
gravity; M is the molecular weight of oxygen; R is the universal gas constant.

What effect will increasing the temperature have on the slope of the line plotted above?

increase slope, decrease slope, the slope will stay the same

182. In the so-called "free electron gas" model, the electrons in a semiconductor can be regarded as a gas with properties described by the kinetic molecular theory. The mass of an electron is about 1/1800 of an amu.

Shown below is the distribution of speeds for helium gas and for the free electron gas, both at the same temperature. Which curve represents the free electron gas?

A, B

The kinetic molecular theory assumes negligible volume for the gaseous species and no interactions among them. Comparing helium to a free electron gas in a semiconductor, which seems better matched to the assumption that the gas takes up no volume?

free electron gas, helium

183. It has been predicted that if we could put the element hydrogen, normally an invisible gas of diatomic molecules at room temperature and pressure, under sufficiently high pressure - millions of atmospheres - it can become a metal!

Which of the above three band diagrams represents solid hydrogen?

A, B, C

To conduct the experiment, the gas is compressed in a so-called anvil. The anvil must be made of a material that is 1) strong enough to withstand high pressures and 2) transparent, so that the sample can be viewed while it is being squeezed. Which of the following materials is the best choice for the anvil material?

diamond, NaCl, graphite

If you could conduct a diffraction experiment on the hydrogen sample while it was being squeezed, what do you predict would happen to the spacing between diffraction spots as the atoms are placed under increasing pressure?

the spacing would increase
the spacing would decrease
the spacing would stay the same

184. When the solid solution CdS0.5Se0.5 is reacted with excess strong acid, H+, the gases H2S and H2Se are released.

Which of the following plots represents the mass of each of the gases vs. mL of acid added, and which represents the volume of each of the gases vs. mL of acid added?

plot A represents the volumes of the two gases (H2S and H2Se) and plot B represents the masses of the two gases

plot A represents masses of the two gases and plot B represents volume of the two gases

Which of the two curves in plot B represents the mass of H2S?

1, 2

In which part of either plot is the acid the limiting reagent?

flat part
rising part

219. (Ideal Gas Law) The following volume-temperature plots were made at different constant pressures (and constant number of moles of gas). Which plot represents the higher pressure?

A, B

221. (Ideal Gas Law) Which of the following pV curves obtained at different constant temperatures ("isotherms") represents the lower temperature?

A, B

240. DEMONSTRATION Two samples of liquid Br2 are placed in each of two ampules that are then sealed. One ampule will be dropped so as to break in a transparent tube filled with air. The other will be dropped so as to break in an evacuated tube. Compare the relative rates of diffusion, which are made visible as the red-brown Br2 vapor fills each tube. The rate of diffusion will be:

The same in both tubes

Faster in the air-filled tube

Faster in the evacuated tube

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