Special Sub-Topic: Properties of Solutions
|What class of matter is a solution?|
Homogeneous mixture. All solutions are composed of one substance uniformly dispersed in another, which is a property of homogeneous mixtures. Heterogeneous mixtures consist of a substance not uniformly dispersed through another substance, like sand in water. A compound is a combination of elements that is uniform throughout, while an element is only made up of atoms having the same atomic number or number of protons.
|Why will salt dissolve in water, but not oil?|
Salt and water are both polar while oil is nonpolar.. The rule for solubility is "like dissolves like". On the molecular level, salt is composed of sodium and chloride ions, which are positively and negatively charged. This causes them to be polarized. The water molecule is asymmetrical, which means it is also polarized. Oil, on the other hand, consists of carbon to hydrogen bonds, which are neither charged nor polar. Therefore, the polar salt dissolves in the polar water but not the non-polar oil.
|Which of these solutions is capable of dissolving gold?|
Aqua regia. Aqua regia, known as king's water, is a corrosive mixture of very concentrated hydrochloric acid and nitric acid. When gold is dissolved, it is oxidized and loses electrons to the nitrate ion from nitric acid. The nitrogen in the nitrate ion is reduced and receives electrons. This causes it to form a brown gas called nitrogen dioxide. Acetone is an organic solvent found in nail polish remover. Battery acid is very concentrated sulfuric acid.
|While on a camping trip, you shine your flashlight through a thick fog. Because of the fog, you can see the beam of light from your flashlight. Is fog a solution?|
No, it is a colloid.. Fog is a colloid, not a solution. Colloids, like solutions, are homogeneous mixtures, but they contain slightly larger molecules dissolved in another substance. This larger size gives the dissolved particles in fog the ability to absorb and diffract light, which is why fog is not transparent and also why you can see the beam of light. Being able to see the beam of light is known as the Tyndall Effect, and distinguishes solutions from colloids. If you shine a light through a glass of salt water, you cannot see the beam of light. However, if you shine a light through gelatin, you can see the beam of light. (Gelatin is another colloid)
|Which of these is a solution?|
Steel. Normally, when we think of solutions, we think of a gas or solid dissolved in a liquid, but solutions can be composed of anything as long as a substance is uniformly dispersed through another substance. Steel is a type of solution known as an interstitial alloy. It is a solution of large iron atoms with holes filled by smaller carbon atoms (hole filling is interstitial). Other types of alloys include substitutional alloys, where one element replaces some of the atoms of a similar sized element in the alloy. Many metal alloys are substitutional alloys. Muddy water is not a solution because the mud particles are not uniformly dispersed throughout the water; it settles and the remaining liquid after settling is a colloid because the mud particles are too large and will exhibit the Tyndall Effect. Diamonds consist of a network of bonded carbon atoms. Since it is made up of only one type of substance, a diamond cannot be a solution. Oil and vinegar do not mix, so it is impossible for them to be a solution.
|Which of these is a solution?|
Air. Solutions do not have to be a solid or gas dissolved in a liquid. Air is a solution because it is one substance uniformly dispersed throughout another substance. Air consists of uniformly dispersed nitrogen, oxygen, argon, methane, carbon dioxide, and other gases. Gelatin is a colloid since the dissolved particles in gelatin are too big to form a solution, even though they are uniformly dispersed. (Unlike a solution, you can see a beam of light in gelatin if you shine a light through). Shampoo is either a suspension, which contains even larger dissolved molecules than a colloid, or a heterogeneous mixture, depending on what type you use. Water vapor is uniform throughout, but it only consists of one substance: a compound.
|Which of these is not considered part of hydration when dissolving a substance in water? Solute is the substance dissolved, solvent is the substance dissolving the solute.|
Separating particles of the solute. When we dissolve a substance, three things must occur. First the particles of the solute (substance being dissolved) must be separated. This is so it can be surrounded by water molecules in solution. Second, the molecules of solvent (substance that dissolves the solute) must be separated in order to surround the solute particles. Finally, the solute and solvent particles interact with one another. The solvent particles (water) use their polarity to pull away solute particles from the solute. For example, to dissolve sugar, the sugar molecules must separate from one another, the water molecules must create space for sugar between them, and the water molecules have to rip away individual sugar molecules from the crystals. The last two steps are considered hydration, so separating particles of the solute is not hydration (it has nothing to do with water).
|If a solution is supersaturated with a substance, what happens when I add a tiny crystal of the substance?|
The substance quickly crystallizes and precipitates out of solution.. A supersaturated solution is a solution where the amount of substance dissolved exceeds the theoretical amount that should dissolve. For instance, if 100 g of salt are supposed to dissolve in 100 g of substance X, then a solution with 200 g of salt dissolved in 100 g of substance X is supersaturated. Adding a crystal causes the molecules in solution to crystallize onto the crystal added. This happens rather quickly, and after crystallization, the solution usually becomes just saturated. The crystallization means that the solute particles no longer remain dispersed throughout the solvent, so they precipitate. Supersaturated solutions are usually prepared by strongly heating a solution, adding enough solute to make it saturated, and then cooling it quickly(the amount of solute needed for saturation decreases usually with temperature).
|Which of these will lower the freezing point of water the most?|
Salt (Calcium Chloride, CaCl2). The boiling point and freezing point of a solution are influenced only by the amount of a substance dissolved, not the identity of the substance. This is known as a colligative property. However, dissolving certain substances releases more ions. Since the solution doesn't care about the identity of the substance, the ions are considered separate substances. Table salt releases the sodium and chloride ion, releasing two ions. Hydrochloric acid releases the hydrogen ion and the chloride ion, so it releases two ions. Chalk is insoluble in water, so it releases no ions. Finally, road salt, calcium chloride, breaks up into three ions: calcium and two chloride ions. Since three ions are more than two, there is more substance dissolved in a solution of calcium chloride than the others.
|Two solutions are set up so that they are in the same beaker, but are separated by a membrane that only water can pass through. One solution contains 4% sugar while the other contains 5% sugar. How will the water levels of the solutions change if left undisturbed for three days?|
The level of the 5% solution will get higher.. In the two solutions the 5% solution is more concentrated than the 4% solution. The solutions will try to achieve equilibrium by having the same concentration of solute. Since only water can move through the membrane, the sugar molecules are not free to move between solutions. The water molecules will move from the less concentrated to the more concentrated solution of sugar so that there is more solvent in the 5% solution, causing it to be more dilute. The net movement of water from the 4 to 5% solution will stop when both solutions have the same concentration due to the dilution that arises from water molecules moving. The net effect of adding water molecules is increasing the volume of the solution and a rise in the level of the 5% solution.
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