Mixtures+and+Solutions+2012

=Mixtures and Solutions Overview= toc Chemistry is the study of the structure of matter and the changes or transformations that take place in it. Learning about the makeup of substances gives us knowledge about how things go together and how they can be taken apart. Learning about changes in substances is important for several reasons: changes can be controlled to produce new materials; changes can be used to give off energy to run machines. The **Mixtures and Solutions Module** has four investigations that introduce students to these fundamental ideas in chemistry. = =



Vocabulary Games Audio stories for mixtures and solutions

=Big Ideas=
 * Investigation 1** • A mixture combines two or more materials that retain their own properties. • A solution forms when a material dissolves in a liquid (solvent) and cannot be retrieved with a filter. • Evaporation can separate a liquid from a solid in a solution. • The solid material separated by evaporation from a solution forms distinctive patterns.


 * Investigation 2** • Solubility is the property that substances have of dissolving in solvents. Solubility is different for different materials and can change with temperature and different solvents. • A solution is saturated when as much solid material as possible has dissolved in the liquid. • When equal volumes of two solutions made from the same ingredients are compared, the heavier one is the more concentrated solution.

=Physical Properties of Matter= Physical proprieties of matter are properties that can be measured or observed without changing the chemical makeup of the matter. Examples include size, shape, color and texture.

Remember all objects take up space and have mass. You use your sense of taste and smell to tell the difference between spinach and an orange. Physical properties- The measurement of mass and other characteristics that can be seen without changing how that object looks are its physical properties. When you look at oranges, you know that they are oranges because of their color, shape, and smell. Mass, color, shape, volume, and density are some physical properties. The answers to the question about the present are physical properties.

[|Density] is an important physical property. Density is the mass of a substance per unit volume. [|Volume] is the amount of space an object occupies. Chemical properties- These are properties that can only be observed by changing the identity of the substance. A piece of paper burns and turns to a black substance. After the flame goes out you can no longer burn the new substance. The chemical properties have been changed.

**Properties are constantly changing...** Matter is constantly changing. Ice in your soda melts, glass breaks, paper is ripped. When ice in your soda melts where does it go? What does it become? If you remember, ice is water in the solid state. If you don't remember this or don't know it, you should go back and review [|states of water]. When you drop the ice cube into the liquid, it begins to melt because the temperature is higher than that of the ice cube. It's like putting a snowman on your front lawn in July. The ice cube becomes liquid water. This is an example of a **physical change**. The solid water turned to liquid water. It doesn't turn into soil or macaroni. It remains water. If it did change into soil or macaroni, your drink would taste terrible and you would have an example of a **chemical change**.

Chemical changes are changing substances into other substances. If it could happen, ice changing into macaroni would be an example of a chemical change. A real example of a chemical change is spoiling milk or burning toast. Milk needs to be in the refrigerator or else it will go bad. If you've ever seen or smelled spoiled milk, it is not a pretty sight. The milk gets a sour odor and becomes lumpy. Unlike physical changes, you cannot reverse chemical changes. You can melt ice to get water and freeze that water to get ice again. You cannot make milk unspoiled.

Phase Changes
One way to separate two substances from one another in a physical mixture is to take advantage of differences in their boiling points. Distillation is the technique used for this kind of separation. However sometimes one of the substances to be separated will chemically decompose before it reaches its boiling point. One way to remedy this problem is to reduce the pressure within the distilling flask sufficiently to lower the boiling point of the substance below it decomposition point. This is called reduced pressure distillation and is a common technique used among Organic Chemists.

= Mixtures = **Mixtures** are physical combinations of two or more pure substances (elements or compounds). As a physical combination one should be able to separate these substances from the mixture by physical methods so that no chemical change can take place during the separation. Substances can be separated from the mixture by taking advantage of any differences the substances have in physical properties. For example, most pure substances have different boiling points (temperature at which a substance will boil). If we can heat a mixture so that the lowest boiling substance will boil off before any other substance begins to boil, we will effectively be able to separate that substance from the mixture. One such laboratory resolution method is known as distillation. Other separation techniques include chromatography, settling out, filtering, evaporation, and centrifuging.
 * **Properties of Elements, Compounds, and Mixtures** ||
 * **Elements** || **Compounds** || **Mixtures** ||
 * made up of only one kind of atom || made up of more than one kind of atom || made up of more than one kind of molecule ||
 * can not be broken down by chemical means || can not be broken down by physical means || can be broken down by physical means ||
 * has same properties as atoms making it up || has different properties from elements making it up || has same properties as substances making it up ||
 * has same properties throughout || has same properties throughout || has different properties throughout ||

Mixtures can be classified according to how well they are mixed together. There are two kinds of mixtures: **heterogeneous** and **homogeneous.**

Heterogeneous Mixtures
The matter in most mixtures is heterogeneous. The substances in a heterogeneous mixture are not chemically combined and the individual substances are still visible. Each substance keeps its own identity and most of its own properties. No new substances are formed because the chemical composition of the substances have not changed. A substance in a mixture can be present in any amount and can be separated by physical means. The substances that make up a mixture determine the mixture's properties.

Homogeneous Mixtures
In a homogeneous mixture, the parts look the same throughout because their components are uniformly mixed together. Homogeneous mixtures are uniform in their distribution. If we took a sampling anywhere in the mixture, and then analyzed it as to its composition for each component we would find that the distribution was the same throughout the mixture. All solutions are said to be homogeneous mixtures.

= Separation Techniques = Most materials in our world are mixtures. Very few materials are pure substances. The art of separating mixtures is important because it enables us to isolate pure substances. Mixtures are either homogeneous or heterogeneous. Homogeneous mixtures are uniform in composition. Heterogeneous mixtures are not. Salt water is a mixture of water and NaCl and is homogeneous if thoroughly mixed, with all the salt dissolved. Oil in water is a heterogeneous mixture. Both types of mixtures can be separated into their component parts by physical means. A salt water mixture can be separated by distilling or evaporating the water and collecting the salt residue. An oil and water mixture will separate into an oil layer and a water layer because the materials are not attracted to one another and gravity "pulls" the denser water beneath the less dense oil. Settling, magnetic attraction, distillation, decantation, solubility, evaporation, filtration, chromatography, and manual methods are all means of separating the components of a mixture. Choice of method depends on the type of mixture and the characteristics of its components.

A heterogeneous mixture of solid and liquid or solid and gas is usually fairly easy to separate because of the 2 different physical phases. The solid may settle out, allowing you to pour off the liquid. This is called ** //decantation// **. Or, maybe the liquid can be evaporated, leaving the solid behind. Or the mixture can be poured through a filter, catching the solid on the filter and allowing the liquid or gas to pass through. We use filtration frequently--in our coffee makers, automobile fuel lines, automobile air cleaners to name only a few examples.

A mixture of two or more solids is usually separated by utilizing the different chemical or physical properties of the substances. For example, a heterogeneous mixture of red M&M's and yellow jellybeans can be separated using the different colors or the different shapes of the solids. The parts of the mixture are large enough to be separated manually. A mixture of black peppercorns and white table salt might be separated this way as well. But what could be done with a mixture of sand and sugar? True, you could get a magnifying glass and tweezers and try picking out the grains of sand, but is there an easier way? Is there some property that sugar has that sand does not (or vice versa)? Could this be used to separate sand and sugar? If you said that sugar dissolves in water and sand does not, you are on the right track.

Homogeneous mixtures of a solvent and one or more solutes (dissolved substances) are often separated by chromatography. Chromatography works to separate a mixture because the components of a mixture distribute themselves differently. Food colorings are one example, a homogeneous mixture of a solvent and a single dye or combination of selected dyes that produce the desired color.

= Solutions = A **solution** is a homogeneous mixture in which one substance is dissolved in another substance. In a solution, two or more substances are uniformly mixed. The solution formed is the same in all parts. In a sugar-water solution, molecules of sugar are evenly spread throughout the molecules of water. Solutions consist of two parts: the solute and the solvent. The **solute** is the substance being dissolved. The **solvent** is the substance in which a solute is dissolved. The the sugar-water solution, sugar is the solute and the water is the solvent. The substance present in the largest amount is usually called the solvent. The most common solutions are those in which the solvent is a liquid. The solute can be a solid, gas or liquid. A solution with water as the solvent is called an **aqueous solution**. Water is considered to be a **universal solvent**. Another common solvent is alcohol. A solution with alcohol as the solvent is called a **tincture**. However, other types of solutions can be formed.
 * **Types of Solutions** ||
 * **Solvent** || **Solute** || **Example** ||
 * liquid || liquid || antifreeze ||
 * ^  || solid || sugar water ||
 * ^  || gas || soft drink ||
 * gas || liquid || humidity ||
 * ^  || solid || mothballs ||
 * ^  || gas || air ||
 * solid || liquid || dental fillings ||
 * ^  || solid || steel ||
 * ^  || gas || gas stove lighter ||

The Solution Process
When sugar is added to water, a solution forms. The dissolving action takes place on the surface of the crystal. Water molecules surround the surface molecules of sugar. The sugar molecules are held together only by weak bonding forces. The sugar molecules are attracted more to the water molecules than to each other. surround by water molecules, surface sugar molecules are carried away from the crystal surface. the process of diffusion causes the sugar molecules to distribute evenly within the water molecules. As the outer layer of molecules dissolves, the next layer is exposed to the water molecules. This process continues until all the sugar molecules are separated from each other and mixed evenly throughout the solution. Check out this animation to see how salt dissolves in water.

You can classify solutions as saturated, unsaturated, or supersaturated.

A **saturated solution** is a solution that contains all the solute it can possible hold at a given temperature. If additional solute is added to a saturated solution, it will settle undissolved to the bottom of the solution. Saturation is dependent on temperature. A solution that contains less solute than this amount is called **unsaturated**. An unsaturated solution can range from dilute to concentrated. A dilute solution contains very little solute. A concentrated solution contains a large amount of solute. Because these terms are not precise, you can refer to a wide range of actual concentrations.

In some cases you can make a **supersaturated** solution. This is a solution in which the solvent can hold more solute than normal. You make a supersaturated solution at a high temperature and then cool it very slowly. At room temperature, it will contain more solute than could normally dissolve at that temperature. This type of solution is very unstable. If the solution is not disturbed, all the solute will stay dissolved. If the smallest amount of solute is added to the supersaturated solution, the excess solute comes out of the solution and settles to the bottom. Only enough solute to make the solution saturated remains dissolved.

Rate of Solution
1. When a solution is stirred, particles of the solute move away form the crystal surface at a higher rate. This exposes more particles to the solvent sooner. Thus the solute dissolves at a faster rate. 2. Solution action occurs only at the surface of the solid solute. So if the surface area of the solute is increased, the rate of solution is increased. More solute molecules are in contact with the solvent when the solid solute is ground into a find powder. 3. If heat is applied to a solution, the molecules move faster and farther apart. As a result, the dissolving action is speeded up. Water is the most common substance on the earth. Water plays an important role in dissolving a great variety of substances. Because thousands of substances are soluble in water, water is sometimes called the universal solvent. However, you should also remember, that there are certain substances that will not dissolve in water. These substances are described as insoluble.

Solubility Factors
The solubility of a solute is a measure of how much of that solute can be dissolved a given amount of solvent under certain conditions. Two main factors that affect the solubility of a solute are temperature and pressure. Generally, an increase in the temperature of a solution increases the solubility of a solid in a liquid. The solubility of most solids is increased by raising the temperature of the solution. Raising the temperature of a gas-in-liquid solution decreases the solubility of the gaseous solute. Thus, the solubility of a gas is decreases as the temperature of the solution increases. For solid and liquid solutes, increases and decreases in pressure have practically no effect on solubility. For gases dissolved in liquids, an increase in pressure increases solubility and a decrease in pressure decreases solubility.