Solutions and Dissolving

Solutions and Dissolving

What is a solution? 

A solution is a specific type of mixture where one substance is dissolved into another. A solution is the same, or uniform, throughout which makes it a homogeneous mixture . Go here to learn more about mixtures. 

A solution has certain characteristics:

• It is uniform, or homogeneous, throughout the mixture
• It is stable and doesn't change over time or settle
• The solute particles are so small they cannot be separated by filtering
• The solute and solvent molecules cannot be distinguished by the naked eye
• It does not scatter a beam of light

Example of a Solution 

One example of a solution is salt water which is a mixture of water and salt. You cannot see the salt and the salt and water will stay a solution if left alone. 

Parts of a Solution

• Solute - The solute is the substance that is being dissolved by another substance. In the example above, the salt is the solute.
• Solvent - The solvent is the substance that dissolves the other substance. In the example above, the water is the solvent.

 
A solution is a type of homogeneous mixture

Dissolving 

A solution is made when one substance called the solute "dissolves" into another substance called the solvent. Dissolving is when the solute breaks up from a larger crystal of molecules into much smaller groups or individual molecules. This break up is caused by coming into contact with the solvent. 

In the case of salt water, the water molecules break off salt molecules from the larger crystal lattice. They do this by pulling away the ions and then surrounding the salt molecules. Each salt molecule still exists. It is just now surrounded by water molecules instead of fixed to a crystal of salt. 

Solubility 

Solubility is a measure of how much solute can be dissolved into a liter of solvent. Think of the example of water and salt. If you keep pouring salt into water, at some point the water isn't going to be able to dissolve the salt. 

Saturated 

When a solution reaches the point where it cannot dissolve any more solute it is considered "saturated." If a saturated solution loses some solvent, then solid crystals of the solute will start to form. This is what happens when water evaporates and salt crystals begin to form. 

Concentration 

The concentration of a solution is the proportion of the solute to solvent. If there is a lot of solute in a solution, then it is "concentrated". If there is a low amount of solute, then the solution is said to be "diluted." 

Miscible and immiscible 

When two liquids can be mixed to form a solution they are called "miscible." If two liquids cannot be mixed to form a solution they are called "immiscible." An example of miscible liquids is alcohol and water. An example of immiscible liquids is oil and water. Have you ever heard the saying "oil and water don't mix"? This is because they are immiscible. 

Interesting Facts about Solutions

• There is a solvent called aqua regia which can dissolve the noble metals including gold and platinum.
• You can't see a beam of light when shining it through a true solution. This means fog is not a solution. It is a colloid.
• Solutions can be liquid, solid, or gas. An example of a solid solution is steel.
• Solids are generally more soluble at higher temperatures.
• Carbonated beverages are made by dissolving carbon dioxide gas into liquid at high pressure.

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Separating Mixtures

Separating Mixtures

Many of the substances we use everyday were actually once part of a mixture. Someone somewhere separated that substance from the mixture so we could use it. It turns out that many compounds and elements aren't found in nature in their pure form, but are found as parts of mixtures. Separating substances from mixtures is an important part of chemistry and modern industry. 

Some important chemistry terms are used in this section including mixtures, suspensions, andsolutions. You can click on the links to learn more about each of them. 

Why do we want to separate mixtures? 

All the way back to Ancient History, industrious humans have separated mixtures in order to obtain the specific substances that they need. One example of this is extracting metal from ore in order to make tools and weapons. We'll discuss some other examples of separation below. 

Separation Processes 

The way in which different substances in a mixture are separated is called a process. There are a number of different processes used for separation. Many of them are very complex and involve dangerous chemicals or high temperatures. A lot of important industries in the world today are based on separation processes. 

Filtration 

One common method of separation is filtration. Filters are used everywhere. We use them in our houses to filter dust and mites out of the air we breathe. We use them to filter impurities from our water. We even have filters in our bodies such as our kidneys which act as filters to get bad stuff out of our blood. 

The filtration process is generally used to separate a suspension mixture where small solid particles are suspended in liquid or air. In the case of filtering water, the water is forced through a paper that is made up of a very fine mesh of fibers. The water that has been run through the filter is called the filtrate. The particles that are removed from the water by the filter are called the residue. 

Distillation 

Another common separation process is called distillation. Distillation uses boiling to separate mixtures of liquid solutions. It takes into account that different substances in the mixture will have different boiling points. 

For example, if you heat salt water the water in the solution will boil before the salt. The water will then evaporate leaving the salt behind. If the steam from the water is collected it will turn back into liquid as it cools. This cooled water will be pure water without any salt. 

Centrifuge  In some cases, there are suspension mixtures where the solid particles are too fine to be separated with a filter. In these cases, sometimes a centrifuge is used. Centrifuges are mechanical devices that spin at very high speeds. These high speeds allow the solid particles in suspensions to settle very quickly. For example, rather than wait for sand to slowly settle to the bottom of water, a centrifuge can cause the sand to settle in a matter of seconds.  Some examples of how centrifuges are used include separating blood into plasma and red cells, separating cream from milk, and separating uranium isotopes for nuclear power plants.

The heavier particles move to the outside of the cylinder as the centrifuge spins allowing the mixture to be separated.

Other Processes 

There are many other separation processes such as sublimation, adsorption, crystallization, and chromatography. Sometimes it takes many stages of processes to get to the final result. One example of this is the processing of crude oil. Crude oil uses many levels of fractional distillation to produce a number of different products including gasoline, jet fuel, propane gas, and heating oil. 

Interesting Facts about Separating Mixtures

• To separate liquid solutions where the substances have similar boiling points, a more complex version of distillation is used called fractional distillation.
• Painting uses the separation process of evaporation. The wet paint is a mixture of color pigment and a solvent. When the solvent dries and evaporates, only the color pigment is left.
• The separation process of winnowing was used in ancient cultures to separate the grain from the chaff. They would throw the mixture into the air and the wind would blow away the lighter chaff, leaving the heavier grain.
• High speed centrifuges can spin up to 30,000 times a minute.
• Many separation processes are occurring constantly in nature.

Chemical Mixtures

Chemical Mixtures

One of the main aspects of chemistry is combining different substances. Sometimes combining substances can cause a chemical reaction and bonding which creates an entirely new substance called a compound. However, sometimes there is no chemical reaction or bonding. In this case, a mixture is formed from the combined substances. 

Mixture 

A mixture is made when two or more substances are combined, but they are not combined chemically. 

General properties of a mixture:

• The components of a mixture can be easily separated
• The components each keep their original properties
• The proportion of the components is variable

Types of Mixtures 

There are two main categories of mixtures: homogeneous mixtures and heterogeneous mixtures. In a homogenous mixture all the substances are evenly distributed throughout the mixture (salt water, air, blood). In a heterogeneous mixture the substances are not evenly distributed (chocolate chip cookies, pizza, rocks) 

Within the categories of homogeneous and heterogeneous mixtures there are more specific types of mixtures including solutions, alloys, suspensions, and colloids. 

Solutions (homogeneous) 

A solution is a mixture where one of the substances dissolves in the other. The substance that dissolves is called the solute. The substance that does not dissolve is called the solvent. 

An example of a solution is salt water. These components can be easily separated through evaporation and they each retain their original properties. However, the salt is dissolved into the water to where you can't see it and it is evenly distributed in the water. In this example the water is the solvent and the salt is the solute. 

What is the difference between a solution and a mixture? 

In chemistry a solution is actually a type of mixture. A solution is a mixture that is the same or uniform throughout. Think of the example of salt water. This is also called a "homogenous mixture." A mixture that is not a solution is not uniform throughout. Think of the example of sand in water. This is also called a "heterogeneous mixture." 

Alloys (homogeneous) 

An alloy is a mixture of elements that has the characteristic of a metal. At least one of the elements mixed is a metal. One example of an alloy is steel which is made from a mixture of iron and carbon. 

Suspensions (heterogeneous) 

A suspension is a mixture between a liquid and particles of a solid. In this case the particles do not dissolve. The particles and the liquid are mixed up so that the particles are dispersed throughout the liquid. They are "suspended" in the liquid. A key characteristic of a suspension is that the solid particles will settle and separate over time if left alone. 

An example of a suspension is a mixture of water and sand. When mixed up, the sand will disperse throughout the water. If left alone, the sand will settle to the bottom. 

Colloids (heterogeneous) 

A colloid is a mixture where very small particles of one substance are evenly distributed throughout another substance. They appear very similar to solutions, but the particles are suspended in the solution rather than fully dissolved. The difference between a colloid and a suspension is that the particles will not settle to the bottom over a period of time, they will stay suspended or float. 

An example of a colloid is milk. Milk is a mixture of liquid butterfat globules dispersed and suspended in water. 

Colloids are generally considered heterogeneous mixtures, but have some qualities of homogeneous mixtures as well. 

Interesting Facts about Mixtures

• Smoke is a mixture of particles that are suspended in the air.
• Tap water is a mixture of water and other particles. Pure water or H2O is generally referred to as distilled water.
• Many of the substances we come into contact with every day are mixtures including the air we breathe which is a mixture of gases like oxygen and nitrogen.
• Blood is a mixture that can be separated by a machine called a centrifuge into its two main parts: plasma and red blood cells.
• Mixtures can be liquids, gases, and solids.

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Naming Chemical Compounds

Naming Chemical Compounds

Chemical compounds are formed when elements are joined by chemical bonds. These bonds are so strong that the compound behaves like a single substance. Compounds have their own properties that are unique from the elements they are made of. A compound is a type of molecule with more than one element. You can go here to learn more about molecules and compounds. 

How Compounds are Named 

Chemists have a specific way of naming compounds. It is a standard method of naming compounds that is used by scientists around the world. The name is built from the elements and the construction of the molecule. 

Basic Naming Convention 

First we'll cover how to name molecules with two elements (binary compounds). The name of a compound with two elements has two words. 

To get the first word we use the name of the first element, or the element to the left of the formula. To get the second word we use the name of the second element and change the suffix to "ide" at the end of the word. 

Some examples of adding the "ide": 

O = oxygen = oxide
Cl = chlorine = chloride
Br = bromine = bromide
F = fluorine = fluoride 

Examples of binary compounds: 

NaCl - sodium chloride
MgS - magnesium sulfide
InP = indium phosphide 

What if there is more than one atom? 

In cases where there is more than one atom (for example there are two oxygen atoms in CO₂) you add a prefix to the start of the element based on the number of atoms. Here is a list of the prefixes used: 

# Atoms 1 2 3 4 5 6 7 8 9 10

Prefix mono- di- tri- tetra- penta- hexa- hepta- octa- nona- deca-

** note: the "mono" prefix is not used on the first element. For example CO = carbon monoxide. 

Examples: 

CO₂ = carbon dioxide
N₂O = dinitrogen monoxide
CCL₄ = carbon tetrachloride
S₃N₂ = trisulfur dinitride 

How is the order of the elements determined? 

When there are two elements in a compound, which element goes first in the name? 

If the compound is made of a metal element and a nonmetal element, then the metal element is first. If there are two nonmetal elements, then the first name is the element to the left side of the periodic table. 

Examples:

• In a compound that contains iron and fluoride, the metal (iron) would go first.
• In a compound that contains carbon and oxygen the element to the left on the periodic table (carbon) would go first.

More Complex Naming Rules 

See below for some of the more complex naming rules. 

Naming Metal-Nonmetal Compounds 

If one of the two compounds is a metal, then the naming convention changes a bit. Using the stock method, a roman numeral is used after the metal to indicate which ion is using the charge. 

Examples: 

Ag₂Cl₂ = silver (II) dichloride
FeF₃ = iron (III) fluoride 

Naming Polyatomic Compounds 

Polyatomic compounds use a different suffix. Most of them end in "-ate" or "-ite". There are a few exceptions that end in "-ide" including hydroxide, peroxide, and cyanide. 

Examples: 

Na₂SO₄ = sodium sulfate
Na₃PO₄ = sodium phosphate
Na₂SO₃ = sodium sulfite 

Naming Acids 

Hydro acids use the prefix "hydro-" and the suffix "-ic". 

HF = hydrofluoric acid
HCl - hydrochloric acid 

Oxoacids containing oxygen use the "-ous" or the "-ic" suffix. The "-ic" suffix is used for the acid that has more oxygen atoms. 

H₂SO₄ = sulfuric acid
HNO₂ = nitrous acid
HNO₃ = nitric acid 

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