What does it mean to be "uncertain"?

Before we move onto the answer to the question, let us define a few terms to better understand "uncertainty". 

Precision - this is how reproducible a measurement is compared to other similar measurements. In other words, the more decimal places you have, the more precise your number is. 

Accuracy - this is how close your measurement (or average measurement, in some cases) comes to the accepted/real value

Let's say you're shooting arrows at a target. If you shoot 5 arrows, and they all end up close to the bullseye, but all of them are far apart from each other, then the shots were accurate, but not precise.

If you shoot 5 arrows and they are far away from the bullseye, but are very close together, as if you shot all 5 of them at the same time into the same area, then your shots were very precise. 

If your 5 shots were both very close to the bullseye, and very close together (meaning you can hit the same area consistently), then your shots were both very accurate and very precise.

Now: 

Realize that no measurements are exact. Every measurement is just a best estimate, meaning there is room for error and "uncertainty". 

However, when you count a set of objects, it is exact. There are 5 humans. There can't be 4.34 humans.

Now that we know the background, what is uncertainty? 

A: Uncertainty is the margin of error, usually stated by giving a range of values that contains the real or true value.

There are 2 types of uncertainty: Absolute and Relative.

In absolute uncertainty, there are 2 methods. 

Method 1: First, discard any unreasonable data first. You must have at least 3 reasonable measurements  in order to use this method. Then, take the average of the measurements. Then, find the largest difference between the average and either the lowest or highest reasonable measurement. 

For example:

Trial 1 - 15.3 g

Trial 2 - 15.5 g

Trial 3 - 15.2 g 

Trial 4 - 11.9 g (remove it, because it looks very different from the rest of the data)

Average of the reasonable measurements: 15.3g

Difference between average and lowest number = 15.3g - 15.2 g = 0.1 g

Difference between average and highest number = 15.5g - 15.3g = 0.2 g

Absolute certainty based on average: 15.3 ± 0.2 g

Method 2: By using the uncertainty of each instrument

Measure to the best precision, then estimate to 0.1 of the smallest segment on instrument scale. 

For example, a ruler's smallest segment is 1 mm. The uncertainty would be the tenth of 1 mm, which is 0.1 mm. So the data recorded for a measurement with a ruler would be: 

 _____(measured value to the best precision) ± 0.1 mm

In relative uncertainty, it is the ratio of absolute uncertainty to the estimated measurement.

So for example, if the data was 39.3 ± 0.1 g, then the relative uncertainty would be 0.1 / 39.3 

This can be expressed in percentage, or in Significant Figures. 

The number of significant figures is the relative uncertainty. Refer to the previous blog post for info on Significant Figures.

Here's a video 

                                                                                                                                  

SIG FIGS .....its hard.. ='(

Why are Significant Figures important?...

Well, they help make the number more precise. Numbers which have more significant digits are more precise. The last number in the measurement are usually uncertain.

There are some rules that are associated with making significant figures as precise as possible.

Rules on how to count the number of significant figures:

1) All number's that are not zero are always SIGNIFCANT

  

ex. 35322 , this number has 5 significant digits

2) Zeros that are in front of the non-zero numbers are NOT SIGNIFICANT 

ex. 0.0065 , this number has 2 significant digits

3) Zero's that come after a decimal point ARE COUNTED

ex. 50.601 , this number has 5 significant digits

4) Zero's that come after numbers, but are NOT after a decimal point, are NOT COUNTED

ex. 340000000 , this number only has 2 significant digits

                                                            Both Number's have 2 Significant Figures

Some numbers require rounding, however, there are "exact numbers" that require no rounding at all. For example, you cannot say that there are 2.4 numbers of deers. Or say that there are 5.6 jackets.

So now that you know how to count significant numbers, let's learn how to round!!

Here are some rules for rounding:

1) Always look at the number to the right of the digit you want to round

 

2) If the digit is greater than 5, round up, and if the digit is less than 5,the number stays the same.

3)If the digit is the number 5, and there are more non-zero digits after the 5, round up

4)If that digit ends in the number 5, round the digit to make it an even number, (0,2,4,6,8)

In addition to rounding rules, there are also math rules.

When you add or subtract, remember to round to the number that has the fewest number of decimal places. You determine this by the number's position. 

For example,

  11.34 L                                            

+ 13.4 L 
___________                   

  24.74 L ----> 24.7 L        

For this equation, you round to the nearest tenth, because that number has the fewest number of decimal places.

Multiplying and Dividing is a bit different from adding and subtracting significant digits. When you multiply and divide you round to the fewest number of significant digits. 

For example, 

12.3 Km                       

x1.2 Km                       

_______                       

14.76Km ---->  14.8Km         

For this equation, the number with the fewest number of significant digits is 1.2, which has 2 significant figures. So the new number has to have only two significant figures too.

ANDDD... THAT IS ALL :) 

But... for more practice, visit this site:

http://www.fordhamprep.org/gcurran/sho/sho/worksheets/workshtindex2.htm

Also, watch this funnish video to reinforce your understanding:

Lab 3B: Paper Chromatography

Last class we had a lab. In this lab we experimented with paper chromatography. This particular type of paper is used to separate mixtures, which is one of the techniques that can be used to separate mixures.

So first, we cut 3 thin strips of chromatography paper with a pointy end (like a pencil). On these strips we draw a line 4 cm from the point and place 3 different food colourings on each strip. Later, we test these strips and dip them in test tubes filled with water. The results should be a separation of the food colouring components.
For example we had the green dye. The dye later broke from a yellow color to a blue color. Of course everyone knows blue + yellow =green.

The lab was a success, and it was interesting to see the colors seperate. Well thats a wrap then.
Study hard for the test next class!!!!




PH

Techniques for Separating Mixtures

Today we will be teaching you several techniques that are used to separate mixtures.
The result after the separation of the mixtures should be different components with different properties.

To do this, you must first realize how to differentiate between components and properties.
For instance, do you want materials to be separated by high density vs. low density, or do you want something reactive vs something inert?

The first method: Hand Separation (solids and solids)
This is the method to use if you want to separate mechanical mixtures or heterogeneous mixtures by using a magnet or some kind of sifting tool.

Second: Evaporation (solids dissolved in a liquid solution)
In this method, you would boil away the liquid, so only the solid would remain.


Third: Filtration (not dissolved solids and liquids)
First, you would pour the mixture containing solid particles through a porous filter.
The result should be solid particles staying on the filter and the liquid compounds passing through.


Fourth: Crystallization (solid in liquid)
Precipitation is the conversion of a solute to solid by chemical or physical change. First, the solids should be separated by filtration or floatation. Then, you need a supersaturated solution of the desired solid and cool it. The result should be pure crystals.


Fifth: Gravity Separation (solids based on density)
In this method, you would use a machine called a centrifuge. This machine would whirl the test tube around at very high speeds, causing the denser materials to move to the bottom.


Sixth: Solvent Extraction 
Here, the component moves into a solvent shaken with the mixture.
In a mechanical mixture (a solid with a solid), use a liquid to dissolve one solid, but not the other. This would result in the desired solid becoming left behind.
In a solution, the solvent is insoluble with the solvent that is already present. This solvent dissolves 1 or more substances, leaving the unwanted substances behind.

Seventh: Distillation (liquids in liquids) 
If you heat the mixture, the liquid with the lowest boiling point will vaporize first. Then, the vapour moves into the distillation flask and enters the condenser. As the gas cools, it condenses into a liquid, dropping the distillate as a purified liquid.


Eighth: Chromatography
In this method, you move a mixture over material that will retain some components more than others.
The components are distributed between 2 phases. A mixture dissolves in a mobile phase through a stationary phase.
This method can be used to separate very complex mixtures, such as plastics, drugs, and foods; it will also produce highly accurate analyses. There are 2 types of chromatography:

Paper Chromatography:
The stationary phase is a liquid soaked onto a strip of paper.
The mobile phase is the liquid solvent.
Some components tend to spend more time in the stationary phase than others. On the strip of paper, the components should appear as separate spots after drying or developing.


Thin Layer Chromatography:
The stationary phase is a thin layer of absorbent coating a sheet of plastic or gas.
Some of the components will attract to the absorbent strongly. As a result, the components will appear as spots on the sheet.


Here's a video on chromatography:


For more information on separation methods:
http://www.docbrown.info/page01/ElCpdMix/EleCmdMix2.htm

Naming Acids

First of all, how are acids formed?
An acid is formed when a compound composed of Hydrogen ions and a negativley charged ion are dissloved in water, meaning they are aqueous (aq). Once the ions are dissolved in water, they seperate.

Some Guidelines
For acids we add "hydro" at the begining. Then get rid of the last syllable of the non-metal and replace it with (ic). Then you can proceed and add acid at the end.

HCI(aq) -----> Hydrochloric acid

For complex acids replace the last syllables with new ones. Such as.... ___ate ----> ___ic and ____ite -----> ____ous
You dont' need the "hydro" for these complex acids.

H2SO4(aq) ----> Sulphuric acid





PH

Writing and Naming Ionic and Covalent Compounds

Hi everybody! In today's Chemistry class, we reviewed how to write and name ionic and covalent compounds.

An ionic compound is a compound of a 2 or more particles that are oppositely charged. So for example, a metal ion and a non-metal ion.

If we have a K⁺ and a N^3-
then what is the compound? 


First we look at the charges. K has a positive 1 charge, and N has a negative 3 charge. 
How can we make the charges equal 0? 
+1-3=-2, so what we could do is increase the number of K ions to 3. This would give us a positive 3 charge and a negative 3 charge of N, AND +3-3=0 :) 
So now we know the ionic compound of K⁺ and N^3- is K₃N. 
If we want to name it, it would be Potassium Nitride. Note that the metal is always first.



Now try to write or name these formulas with the Periodic Table:
1) Copper(I) oxide
2) FeO
3) SnCl_{4
There are also ions called complex anions. Anion indicates that it is a negative ion, and complex just means that it is a group of atoms that behave as one atom.}


For example, if we have
Na₂SO₄ Treat SO₄ as basically any other ion. We wouldn't call this sodium sulphur oxide. Instead, there is a specific name for the ion SO₄ and that is sulphate. So this compound is called sodium sulphate.

It gets easier with covalent compounds. Covalent compounds are compounds of a non-metal and another non-metal. They share electrons rather than transferring like ionic compounds.

To name covalent compounds, we use the Greek prefixes:

If we want to name CO₂, we don't say monocarbon dioxide. We never say mono for the first non-metal. If it was N₂O₃, then we would put dinitrogen trioxide, but never monocarbon or mononitrogen.



There are also diatomic molecules. These can be memorized by the acroynm HOFBrINCl. These are a special group of molecules composed of 2 identical atoms.

Here is a video on naming ionic compounds:


And here is the covalent compound:


Here are the answers to the practice questions above:
Cu₂
Iron(II) oxide
Tin(IV) chloride

2B: Heating and Cooling Curves of a Pure Substance

Today, we conducted a lab on the heating and cooling curves of a pure substance. For this lab, our objective was to determine, while comparing the melting and freezing points of a pure substance; dodecanoic acid.

First of all, we read through the lab and made sure we knew what we were doing. Then, in the beginning of the lab, we put on some safety equipment to prevent the impossible from being possible. The chemical’s that we worked was not a very strong acid, so it wasn’t a big threat to our safety. 

We started the cooling process of the dodecanoic acid before starting the heating process. The cooling process took a bit of time, but the process was simple. First, we filled a beaker that had room temperature water. Then, we clamped a test tube that contained the acid. We attached it to the ring stand, placing the test tube inside the room temperature water. After doing so, we observed the temperature of the acid. Every 30 seconds, we used a thermometer to record the temperature of the acid, until it is near 25 degrees Celsius. Also, note when solidification beings and ends, and any other observations you see.

This picture includes a ring stand, clamp, test tube and thermometer.

Right after finishing the cooling process, we began the heating process! WOOO!! Similarly, we put the test tube (with the solidified acid inside) in water, and kept it hot with a hot plate. Until a temperature of 50 degree Celsius (or above) is achieved, you record the temperature every 30 seconds; while noting down any other observations. When the acid melts, you mix the solid and liquid together, then record when the melting began and ended.

This is a hot plate! Be Careful! Don't burn yourself!!

After, you put away the equipment and return the test tube to your instructor. After, you wash your hands thoroughly with soap! Last but not least, you do a lab report, and after completing it, you would have already compared the melting and cooling curves of a pure substance. 

For further information on melting/cooling curves a pure substance, visit these links:
http://www.dillpickletheater.com/REMSL/index.htm
http://www.enotes.com/earth-science/freezing-melting

This video may also somewhat assist you with your understanding of melting and freezing points:

Laws and More Matter

We began this class with distinguishing Laws for Definite Composition and Multiple Proportions.

The Law of Definite Composition states that compounds will have a definite composition. Ex. H2O will always remain as H2O anywhere. The compound will always have 2 Hydrogens and 1 Oxygen.

The Law of Multiple Proportions is when 2 or more compounds that contain different proportions of the same element can be made. EX. CO2 x2= C2O4.


Matter

Pages 25-34 and 36-39 of the Heath Chemistry Textbook allows us to refresh our brains on matter.

2.1 What we know about matter
Basically matter is anything that takes up space. We know that matter can take any shape or form, in the three states known as liquid, gas, and solid. Physical/Chemical chnages occur to change the substance's form. We can also identify matter through color, taste, and boiling or melting points. A prime example is water. Water can be different. If we compare distilled water to muddy water, we will see huge differences.



2.2 Purifying Matter
There are two types of matter. Pure substances only have one set of properties while mixtures have more than one set of properties and a substance. We can purify substances to separate the mixture and the substance. E.g. alum and lime can trap impurites. Salt and sugar will change the taste but will blend in with the substance. These are called substances. Distillation is the process where the components are seprated from the mixture; however, some solutions cannot be seperated. When there is no way to seperate matter into components, it means that the substance is pure.

2.3 Characteristics of Pure Substances
The freezing point and melting points of both pure substances and mixtures are quite similar. However pure substances have a constant boiling point, while mixtures do not, but some do have a constant boiling point. For example Grain Alcohol is comprised of 95.6% of ethanol and 4.4% of water. Together they have a constant boiling point of 78.2 degrees C. Any other mixture of ethanol and water will not have a constant boiling point. The freezing point and melting points of both pure substances and mixtures are quite similar. Electrolysis is when matter decomposes to form new kinds of matter. Decomposition is the process when a pure substance are seperated into components.


2.4 Physical and Chemical Changes.
Physical changes do not produce a new substance . That being said, chemical composition does not change and is reversible. Chemical changes on the other hand produce a new substance and are irreversible.

2.5 Compounds and Elements
Elements are pure substances that cannot be broken down by decomposition. Elements can change to different states, from liquid to solid and to gas. The increase and decrease of temperatures is what makes the elements change form. Compounds on the other hand can be decomposed into new kinds of matter. Compunds are formed together by simpler substances, they are also comprised of 2 or more atoms.

2.7 Atoms
Atoms happen to be the smallest part of an element.Atoms are closely packed in thier solid state. In liquid form, atoms are some what close together. When they are in the gas state, the atoms are far apart.

The Heating/Cooling Curve



Point A - Solid State, Paticles packed together

Point A-B - Molecules vibrate faster

Point B - Molecules start to melt or remain frozen

Point B-C - Temperature remains contant, exist in both liquid and solid states.

Boint C - Everything is melted, liquid form

Point C-D - Particles are heated and they move faster and faster, due to the kinectic energy increasing. In Liquid state

Point D - Still exists in liquid state, molecules start to move freely

Point D-E - Liquid turns into gas. Temperature remains the same.

Point E - All liquid is now gas

Point E-F - Gas absorbs energy, molecules move freely . Temperature increases.

For more information on matter, here is a Youtube video from the Discovery Channel.