Pure water dissolved substances found

Every substance has a definite set of properties. Properties are the characteristics by which we can identify something. For example, we know that pure water is a colorless, odorless, tasteless substance that is a liquid under the conditions usually found in an ordinary room. Water puts out fires, and it dissolves sugar and salt. Liquid water can be changed into a gas (called water vapor or steam) by heating it, or into a solid (ice) by cooling it. Salt has a different set of properties from water sugar has yet another set. 

According to Chapter 11, an acid is a substance that upon dissolving in water increases the concentration of hydronium (H30 ) ions above the value found in pure water, and a base is a substance that increases the concentration of hydroxide (OH ) ions above its value in pure water. Despite the careful language, it is commonplace to view acids and bases as substances that dissociate to give protons (which upon hydration become hydronium ions) and hydroxide ions, respectively. If the dissociation is complete, we can easily calculate the concentration of hydronium and hydroxide ions in the solution and then calculate the yield of acid-base neutralization reactions, and acid-base titrations, by the methods of stoichiometry in solution. But experience shows that many acid-base reactions do not go to completion. So, to predict the amount (or concentration) of... 

We have seen that the matter found in nature is typically a mixture of pure substances. For example, seawater is water containing dissolved minerals. We can separate the water from the minerals by boiling, which changes the water to steam (gaseous water) and leaves the minerals behind as solids. If we collect and cool the steam, it condenses to pure water. This separation process, called distillation, is shown in Figure 2.15. 

Conduction of electric current in conductors can be electronic or ionic, depending on the type of charges involved. Electronic conduction is found in all metals and also in certain other nonmetals. Ionic conductors are also known as electrolytes. Substances that ordinarily are not conducting can produce ionic conduction after being dissolved in water or another solvent (e.g., electrolyte solution and weak electrolyte ). The relative amount of substance present in a solution or a mixture is known as its concentration. The different concentration units used mostly are molarity, molality, normality, and mole fraction. The acidity or basicity of a solution is measured by a relative measurement called the pH of solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions (H" "). Pure water is said to be neutral. The pH for pure water at 25 °C (77 °F) is close to 7.0. Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are said to be basic or alkaline. 

Water (H2O) is the most abundant compound on Earth s surface, covering about 70%. In nature, it exists in liquid, solid, and gaseous states. It is in dynamic equilibrium between the liquid and gas states at standard temperature and pressure. At room temperature, it is a tasteless and odorless liquid, nearly colorless with a hint of blue. Many substances dissolve in water and it is commonly referred to as the universal solvent. Because of this, water in nature and in use is rarely pure and some of its properties may vary slightly from those of the pure substance. However, there are also many compounds that are essentially, if not completely, insoluble in water. Water is the only common substance found naturally in all three common states of matter and it is essential for all life on Earth. Water usually makes up 55% to 78% of the human body. 

For example, some compounds will dissolve in water and others in fat (called a lipid). One of their 20 questions was, "Does the poisoning agent dissolve in water or fat To get an answer, they shook one mussel sample with a mixture of water and another mussel sample with a mixture of fat and injected the water and fat parts into different mice.The part of the mussel that dissolved in the water still caused the mice to scratch themselves, but the part that dissolved in fat didn t. So they knew they were looking for a chemical that dissolves in water. They divided the mussel over and over using many different methods, including chromatography, which is similar to the project at the end of this chapter. Finally, after four days of continuous work, the scientists had separated out of the mixture a pure substance that was the toxic compound.They compared all of its properties to compounds they already knew about and found a match a neurotoxic compound called "domoic acid. ... 

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