Why Solutions Form

We start this stage of our exploration of the nature of solutions by looking at some of the reasons why certain substances mix to form solutions and why others do not. When you are finished reading this section, you will have the necessary tools for predicting the solubility of substances in liquids. 

122 possible arrangements produce a more dispersed, gas-like state. 

4 possible arrangements of the red produce a less dispersed, solid-like 

If the four particles had 16 possible positions, there would be 1820 possible combinations. Nine of these would be in solid-like states, and the other 1811 would be in gas-like states. Thus over 99.5% of the possible arrangements would represent gaslike states, as opposed to 96% for the system with 9 possible positions. This shows that an increase in the number of possible positions leads to an increase in the probability that the system will be in a more dispersed, gas-like state. In real systems, which provide a huge number of possible positions for particles, there is an extremely high probability that substances will shift from the less dispersed, solid form, which has fewer ways of arranging the particles, to the more dispersed, gas form, which has more ways of arranging particles. 

Fewer ways to arrange particles More ways to arrange particles 

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Although much of the explanation for why certain substances mix and form solutions and why others do not is beyond the scope of this text, we can get a glimpse at why solutions form by taking a look at the process by which ethanol, C2Fi50H, dissolves in water. Ethanol is actually miscible in water, which means that the two liquids can be mixed in any proportion without any limit to their solubility. Much of what we now know about the tendency of particles to become more dispersed can be used to understand this kind of change as well. 

On the basis of atomic properties, explain why copper forms solid solutions that can have the following percent of lattice sites containing the following atoms Ni 100%, A1 17%, and Cr <1%. 

In this section, you learned why solutions of different salts have different pH values. You learned how to analyze the composition of a salt to predict whether the salt forms an acidic, basic, or neutral solution. Finally, you learned how to apply your understanding of the properties of salts to calculate the pH at the equivalence point of a titration. You used the pH to determine a suitable indicator for the titration. In section 9.2, you will further investigate the equilibria of solutions and learn how to predict the solubility of ionic compounds in solution. 

The question must be asked Why are solid solutions formed in some cases and not in others A common denominator in the successful films and their difference from the unsuccessful ones (success being defined as formation of a solid solution) is the higher temperature used in the former (80-95°C). Higher temperature will facilitate intermixing of the codeposited CdS and ZnS. 

Rhombic Sulphur. Pour 4-5 ml of chloroform into a dry test tube in a fume cupboard ) and spill in a sulphur powder in small portions, shaking the contents of the tube, until a saturated solution forms. Filter the solution into a porcelain bowl (do not wet the filter with water, why ), cover it with a glass, and let it stand in the fume cupboard for slow evaporation. Put a drop of the solution on a slide, cover it with a cover glass, and observe under a microscope how the crystals grow. Draw the sulphur crystals. 

Explain why precipitates form only in some of the solutions. What substances form when hydrogen sulphide reacts with solutions of iron(II) salts Classify the studied metal sulphides according to their olubility in water and acids. 

Put a few crystals of mercury (I) nitrate into a test tube and add 2 ml of distilled water. Why does a turbid solution form Write the equation of the reaction. Run a similar experiment with mercury(II) nitrate. Under what conditions can a transparent solution of these salts be obtained ... 

Using a Bom-Haber cycle employing the various energies contributing to the formation of M+, e(NHj)J species in ammonia solutions, explain why such solutions form only with the most active metals. 

To understand why solution experiments sometimes fail to produce cocrystal products, and why solvent-drop grinding experiments can work when performed on the same system, the 1 1 cocrystal formed by nicotinamide and frans-cinnamic acid (frans-(2E)-3-phenylacrylic acid) has been studied [56]. In this work ternary isothermal phase diagrams of the cocrystal system was used to understand the crystallization phenomena, and to deduce methodologies and for the experimental design of cocrystal preparation. Cocrystals are most likely to form from solutions in which the two reactants have similar degrees of solubility, and the success of solvent-drop grinding was explained in that crystallization took place in the region of low solvent mole fractions where the cocrystal would be more stable relative to the separated reactants. 

We have discussed the problems concerning association and complex formation separately. There is no reason why species formed by association and by complex formation should not be present in the same solution. The methods used in the thermodynamic treatment of such systems, no matter how complicated, would be the same as those discussed here. 

Explain why beads formed when drops of alginate solution are added to a divalent metal ion solution, but long strands form when a continuous stream is introduced into the same solution. What would happen if you cut one of the strands into short segments ... 

Water is a good solvent for many substances. You may have noticed, however, that grease-stained clothing cannot be cleaned by water alone. Grease is one substance that does not dissolve in water. Why doesn t it dissolve In this chapter, you will find out why. You will learn how solutions form. You will explore factors that affect a substance s ability to dissolve. You will find out more about the concentration of solutions, and you will have a chance to prepare your own solutions as well. 

The reasons why a solute may or may not dissolve in a solvent are related to the forces of attraction between the solute and solvent particles. These forces include the attractions between two solute particles, the attractions between two solvent particles, and the attractions between a solute particle and a solvent particle. When the forces of attraction between different particles in a mixture are stronger than the forces of attraction between like particles in the mixture, a solution forms. The strength of each attraction influences the solubility, or the amount of a solute that dissolves in a solvent. 

The higher the temperature of the solvent, the more easily solutions form, and also the greater is the proportion of solute that actually dissolves. This is why sugar dissolves better in hot tea than in iced tea. 

The smaller the particles of the solute, the more easily a solution forms. This is why finely ground sugar is used in iced tea. 

In this chapter, we discuss the types of solutions, why they form, the different concentration units that describe them, and how their properties differ from those of pure substances. 

If it takes energy (AHso n > 0) for NaCl and NH4NO3 to dissolve, why do they It turns out that the heat of solution is only one of two factors that determine whether a solution forms. The other concerns the natural tendency of any system to distribute its energy in as many ways as possible. A thermodynamic variable called entropy (5) is directly related to the number of ways that a system can distribute its energy, which in turn is closely related to the freedom of motion of the particles and the number of ways they can be arranged. 

What happens when you put a teaspoon of sugar in your iced tea and stir it, or when you add salt to water for cooking vegetables Why do the sugar and salt "disappear" into the water What does it mean when something dissolves—that is, when a solution forms ... 

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