### Accuracy and Precision

Precision is how reproducible a measurement is compared to other similar measurements.
Accuracy is how close the measurement (or average measurement) comes to the accepted or real measurement.
Uncertainty is the margin of error and there are two types of uncertainty, absolute and relative.

There are 2 methods of finding absolute uncertainty

Method 1: Discard any unreasonable information.  Then find the average of the 3 numbers and find the largest difference between the average and either the lowest or highest reasonable measurement.

Trial 1 - 29.86 g (this would be discarded because the other numbers include numbers from 0.90-0.96)
Trial 2 - 29.97 g
Trial 3 - 29.93 g
Trial 4 - 29.94 g
Trial 5 - 29.96 g
Average of the numbers: 29.95 g

Difference between average and lowest number =  29.95g - 29.93g = 0.02g
Difference between average and highest number = 29.97g - 29.95g = 0.02g
Absolute certainty based on average: 29.95 ± 0.2 g

Method 2: Measure to the most precise measurement then estimate to the 0.1 of the smallest measurement on a measuring instrument.

For example, if the measuring instrument is a ruler, the smallest measurement is 0.1mm.  The data recorded for a measurement of a ruler would end up looking  like  ________(best precise measurement) ±0.1mm
For relative uncertainty, it is the ratio of absolute uncertainty to the estimated measurement. For example, if the absolute uncertainty is 29.95 ± 0.2 g, the relative uncertainty would be 0.2 / 29.95.  It can be expressed as a percentage or in significant figures.
Significant Digits
The last digit in a measurement is always the uncertain digit(it could be one digit higher or lower, we don't know). The significant figure in the measurement includes all of the certain digits and the uncertain digits.

Significant Figure Rules
1. Leading zeros are not counted
Example: 0.01 = 1 SF
2. Trailing zeros after the decimal point are counted
Example 10.050 = 5 SF
3. Trailing zeros in front of the decimal point are not counted
Example  1200000000000 = 2 SF
4. Zeros between significant figures are counted
Example  123000.000123 = 12 SF

Rounding Rules
To start off, rounding just almost like we do it in math
1.Look at the digit to the right the the digit you are rounding (The uncertain digit)
2. If that digit > 5 then you round up
3. If that digit < 5 then you keep it the same
4. If that digit = 5 and it has more non-zero digits following behind it, round up
5. If that digit = 5 and ends at that 5, round to make digit your rounding even (2,4,6,8)

Math "+" & "-" Rules
When you add or subtract, round to the number with the fewest DECIMAL places
For Example
222.123123
+    1.1
223.223123
Which becomes 223.2 because the 1.1 had the lowest decimal point

Math "X" & "÷" Rules
When you multiply or divide, round to the number with the fewest number of significant figures
For Example
(123)(1)  =  123
Which becomes 100 because the number with the lowest significant figures (that 1) only had 1 SF.

### Separation of a Mixture by Paper Chromatography

Before this lab, 3 tables from the text book were to be copied down onto paper.  This lab had 6 objectives:
To assemble and operate a paper chromatography apparatus
To study the meaning and significance of Rf values
To test various food colorings and to calculate their Rf values
To compare measured Rf values with standard Rf values
To separate mixture of food colorings into their components
To identify the components of mixtures by means of their Rf values

The supplies were:
5 stirring rods
scissors
3 large test tubes
Ruler
Chromatography paper strips
Food colorings (assigned either yellow, green, blue, or red)
Unknown mixture of food colorings

Part I: Setting Up
Obtain 3 Erlenmeyer flasks and 3 pieces of chromatography paper.  Draw a line at 4 cm into the paper and then cut the edges to make it into a arrow shape. Then place 2 cm of solvent into the flasks.

Part II: Rf Values of Individual Food Colorings
One food coloring was assigned either red yellow or blue.  On the center of the line that was drawn on the chromatography paper, the color that was assigned was to be spotted onto the center of the line. Next the strip was to be inserted into the test tube.  Once that was placed, observe the sample spot and make any observations in the next 20 minutes.  While that was happening, move onto the next part of the lab, the green and unknown food colorings.  Observe any changes with those two colorings as well.  After the solvent and food coloring sample have moved up and no longer moved, take them out and using the ruler measure how much cm the solvent and food coloring sample moved.  Record these on the tables that were drawn before the start of the lab.  Then clean up and continue onto the lab report.
Naming Acids
Acids are formed when a compund of Hydrogen Ions and a negitively charged ion are dissolved in water(aqueous). Ions separate when they are dissolved in water.

For Example:
H + Cl  ->  HCl(g)
HCl(g) + H2O(l) ->  H3O(aq) + Cl(aq)

Naming Acid Guidlines
1. Use "hydro" as the beginning
2. Last syllable of the non-metal is dropped and replaced with "-ic"
3. Add "acid" at the end
*                ide ->  hydro                ic  acid*
For Example:
HF        becomes      hydro flouric acid

Naming Complex Acids
1. -ate is replaced with -ic
-ite is replaced with -ous
2. "acid" at the end of the name
For Example:
HCH3COO    becomes Acetic Acid

Try This Video, It should help

### Heating and Cooling of a Pure Substance experiment

Last class was when we did the heating and cooling of a pure substance.  The materials used were a pair of safety goggles, a test tube with the pure substance, a beaker with warm water, 2 thermometers, a mini stove like device, and a device that held the test tube that could also adjust to move the test tube up or down.

The Cooling Process

The test tube was adjusted on the device and lowed into a beaker of room temperature water.  In every 30 seconds, the thermometer would either drop quickly or slowly.  The original temperature of the pure substance was 45 degrees.  The purpose was to see how long it would take for the substance to have a temperature of 25 degrees.  The whole process was to be recorded on the pre drawn table.  Next was the heating process.

The Heating Process

By now the pure substance should be a solid from the cooling process.  The next step was to bring out the mini stove like device and place a beaker of water on top of it.  The mini stove like device has a nob which was turned to 200 for the amount of heat used.  By now the substance's test tube is 25 degrees.  Place it in the beaker that is sitting on top of the mini stove like device.  The result should be a increase of temperature.  The temperature may move rapidly or slowly depending on how cold the water of the beaker is.  The temperature was to be recorded every 30 seconds until the temperature of the pure substance reached 50 degrees.  When the temperature reaches close to 50 degrees, the pure substance should start to change state.  By 50 degrees, the pure substance would be completely dissolved.  By the end of the heating process, your table should have the amount of time it took to reach the required temperature of both the heating and cooling processes.  When you have both of them, clean up the station and move onto the lab report.
Law of Definite Composition
Compunds will have a definite composition
Ex. H2O will be H2O anywhere (It will always have 2 H's and 1 O)

Law of Multiple Preportions
When 2 or more compunds with different proportions of the same element can be made
Ex.  CO2   ->   C2O4  -> C4O6

The Heating/ Cooling Curve of a Pure Substance

A: It is now in a solid state ( any temperature below melting point ). The particles are packed very close and neatly together and the forces between the particles are very strong. The particles can only vibrate at a fixed position.

A-B: As the particles are heated, the heat energy is converted to kinetic energy. The Kinetic energy increases and the molocules vibrate faster around their fixed position. This also increases the temperature

B: By here the solid will change into a liquid or a liquid turned into a solid (Frozen)

B-C: In Both solid and liquid states ( Ice and water ), the temperature remains constant because the heat supplied is used to overcome the forces of atractiong between particles. This constant temperature is called the melting point.

C: All melted, solid has now become liquid

C-D: It is still a liquid, as it is heated the molocules hgain more heat energy and the temperature increases. The particles move faster as the kinetic energy increases.

D: It still exists in a liquid state. The molocules have recieved enough energy to overcome forces of attraction between particles and they start moving freely. The liquid starts becoming gas.

D-E: The liquid is changing into a gas (Is both a liquid and gas at the moment). The temperature remains unchanged which we call the boiling point. The absorbed heat is being used to overcome the forces of atraction instead is raising the temperature.

E: all liquid is now gas
E-F: The gas particles continue to absorb energy and move faster. The temperature increases as the heating continues.

Matter in the Macroscopic World
When you look at anything, you will see that you have used the tools of science to observe and order observations through classification. For example you could say that from what you've seen, people are happy and are preparing to eat. Science uses the same skills as looking except you make much more precise and detailed observations requiring much time and effort to specialize in something. Chemists specialize in matter with questions asking what is it, how does one differ from another, what different things have in common, and how matter can be kept the same?

We've learned a lot about matter as we've grown up like water when cooled turns into ice and the water can be freely poured to fill any solid container. But if you took water from a muddy stream and water from a river you could say their different right? Properties can help us identify things in many ways including touch and taste. Part of the study of science is learning of all the ways you can distinguish one piece of matter from another like the temperature at which liquid changes into gas is which called the Boiling Point

Purifying Matter
There are 2 classifications of matter. Mixtures which are 2 or more kinds of matter that have separate identities or Pure substances which cannot be separated. Understanding which samples can be separated and which samples can be not is something that comes with experience. If you have dirty water then put it in the light, it will scatter the light. If you check with clean water, it won't scatter the light. That means you should be able to separate the mud from the water by how? If you go to a water processing plant, clean the water, and then see if it scatters the light which it doesn't, is it pure water? If we check the water there could be salt or sugar added to the water that do not scatter light which is when we call the water a Solution. This is still a mixture though so you should be able to separate it right? Then if we boil the water so that we still will have the water and a white solid of sugar or salt separate, this procedure is what we call Distillation. After you have boiled the water you can conlude that the water and the sugar or salt is pure. Many mixtures are too difficult to separate thus are considered pure for years until a way is found to separate them.

Characteristics of Pure Substances
An easy way to detect an important difference between mixtures and pure substances is that pure substances have a CONSTANT boiling point unlike mixtures that ordinarily do not. The problem is nature likes to defy our simple definition of saying the mixtures never have a constant boiling point. The reason the mixture of water and grain alchohol cannot be separated is that it has a constant boiling of 78.2 degrees celcius. The temperature when a liquid changes to a solid is call the Freezing Point. The temperature at which a solid becomes a liquid is called the Melting Point.

Chemecal and Physical Changes
Density is the property of matter that describes its mass per volume unit. A chemical change when a new kind of matter with different properties is formed. When a new substance is formed, thats a good way to tell if a chemical change occurred. Decomposition is a chemical change where one kind of matter come apart to for 2 or more kinds of matter. Changes that are easy to reverse or reversable are called Physical Changes. Physical changes do not produce new kinds of matter.

Compunds & ElementsElectrolysis is when a passing electric current throught a substance causes it to decompose into new kinds of matter. Usually electrolysis represents a chemecal change in the form of decomposition. Distillation is a physical change that separates two or more things that already exist like separated components that are still in the original mixture as separate substances. Pure substances that can be decomposed into new kinds of matter are called Compounds. The word comes from the fact that they appear to be "compunded" or put together from simpler substances. Pure substances that cannot be decomposed are called Elements. There are 109 known elements, 85 exist in nature and the others have been made in atomic reactors(they do not exist in nature).

Compunds have a Definite Composition
Not all combinations of elements are compounds. The important difference between mixtures of elements and compunds of elements is that the mixtures can have almost any composition desired but the compounds will have a definite composition which is called The Law of Definite Composition. The fact of 2 or more compunds with different amounts of the same elements is called The Law of Multiple Proportions.