Oct. 28, 2010 Relative + Absolute Uncertainty

PRECISION is how many times a certain measurement figure appears compared to other measurements taken. (e.g. how many times 2.3 is the result)

ACCURACY is how close your measurement is to the real or accepted number or figure. ( 2.3 ---real value is 2.4)

ABSOLUTE UNCERTAINTY:

-measured in the units, not expressed as a ratio

-2 methods of calculation
-1. Find the average of your measurements(take at least 3). The greatest difference between the measurement amounts is the absolute uncertainty.
****Discard the value that is either much larger or smaller than others.

Ex. Values: 12.2, 12.4, 12.4, 12.2, 11.7

1. Discard 11.7.
2. Find the average (12.2+ 12.4 + 12.4 +12.2/4 = 12.3
3. Find largest difference ( 12.4-12.2 = 0.2)
4. Absolute uncertainty is 12.3 +-0.2

-2. The uncertainty of instruments of measurement
Find the smallest unit/segment of measurement and estimate to fraction of 0.1.
(e.g. 1 mL = 0.1 mL)

RELATIVE UNCERTAINTY

absolute uncertainty / estimated measurement

Absolute uncertainty can be expressed as %

The number of significant figures reveals the relative uncertainty

Significant Figures

Significant Figures are important to help find out which numbers are precise, and how to make number's more accurate. In every measurement, the last digit are usually uncertain. 

However, some quantities do not require you to round. For example, you cannot determine that there are 4.1 pairs of jeans, or 2.3 pencils.

There are some rules which you will have to remember in order to make the significant figures precise.

Keep in mind these rules on how to count significant figures:

1) Numbers that are greater than zero are ALWAYS counted as a sig dig. 

For example: 456793 . For this number here, there are 6 sig digs.

2) Zeros that come before a number>0 ARE NOT counted

For example: 0.000087 --> Although there are so many zeros before 87,  those zero's are not counted, therefore there are only 2 sig digs.

3) Zeros that go after the decimal points ARE counted


For example: 56.09  --> This number has 4 sig digs

4) Zeros that go after numbers>0, but ARE NOT before or after a decimal, ARE NOT counted

For example: 4120000000 --> This number has so many zeros, but there are only 3 sig digs

Go to this site for practice on counting sig figs, and see what you get! 

http://science.widener.edu/svb/tutorial/sigfigures.html 

Now on to rounding...

Memorize the following rules:

1) Look to the the number on the right of the digit in which you wish to round

2) If the number>5 round the number up

3) If the number<5 the number stays the same

4) If the number = 5 and there are number>0 after it, then round the number up

5) If the number IS 5 and ends in 5, make sure you round to make the last digit even, (0,2,4,6,8).

Here are some MATH RULES WHEN ADDING AND SUBTRACTING TO REMEMBER:

When you add or subtract you always look at the number that has the fewest number of decimal places, then you round the new number according to that.

For this equation you see that 1.6 has the fewest decimal places, so that means the new answer has to have only one decimal place as well. thus, instead of 23.934m, the answer is 23.9m

 
When you are multiplying or dividing, you find the number that has the fewest number of significant digits. Then you round by the fewest number of significant digits.

 

For more practice on rounding, adding, subtracting, multiplying, and dividing significant figures, visit this site:

 http://www.teacherbridge.org/public/bhs/teachers/Dana/SigFigOperations.html

Lab 3B: Separation of a mixture by paper chromatography

Lab 3B was performed in class on October 19. The objective of the lab was to identify the components of mixtures by means of there Rf values. It was fun to see how the food dyes separated into many colours.

Equipment:

3 Large test tubes
3 Erlenmeyer flasks
Ruler
3 pieces of chromatography paper
Food colouring ( yellow, red, or blue)
Green food colouring
Unknown mixture of food colouring
Water
Glass stirring rod


Procedure:


Part 1:


Students in groups of two, acquired 3 Erlenmeyer's flasks, and 3 Large test tubes. The test tubes were placed in the Erlenmeyer's flasks with two centimeters of water in each. A line was drawn across the chromatography paper, four centimeters from the end. The paper was then cut into a point from the pencil line.



Part 2:

 Students received food colouring on there chromatography paper. One, of there choice, (red, yellow, or blue) one green, and one unknown mixture. The food colouring was placed on each paper via glass stirring rod, in spots. The first paper, the colour of your choice, was lowered into the first test tube so that about two centimeters were submerged. As the water climbed the chromatography paper, students made observations on the change in colour, the solute front, and the solvent front. After twenty minutes had elapsed, the paper was taken out, and a line was quickly drawn where the water had stopped climbing. After recording the solvent and solute fronts, the Rf values were recorded, and written on the board. All students copied down this information.

Part 3:

The unknown and the green food colouring was also placed in the test tubes. The same procedures as part 2 were then carried out up until the recording of the Rf values. Data was copied into table three in our notebooks.

 Results:

Acids and Bases Oct.13 2010

An acid is a substance that tastes sour, has a pH of less than 7 and reacts with metals.  They are formed when a compound made up of hydrogen ions and a negatively charged ions(anions) are dissolved in water(aqueous)
A base is the chemical opposite of an acid, and can be oxides or hydroxides of metals. They are aqueous solutions that can take hydronium ions.

Naming  Simple Acids

1. Use prefix "hydro" at beginning
2 The last syllable of the non-metal is dropped and replace with -ic
3. Add the word acid at the end

ex. HCl


Hydrogen Chloride---------- hydrochloride which then becomes hydrochloric because you drop the ending. Then simply add the word acid at the end

HCl= hydrochloric acid

Naming Complex Acids

If the compound ends with -ate you replace it with -ic
If the compound ends with-ite you replace it with -ous

Then add the word acid at the end

ex. 1
hydrogen nitrite (HNO2) =
1. drop the word hydrogen
2. nitrate= ends with -ite so you replace -ite with -ous
3. then add word "acid".

= nitrous acid


 ex.2

Hydrogen Phosphate(H3PO4)

1. drop the word "hydrogen"
2. Phosphate ends with-ate so you replace it -ate with -ic
3. =Phosphoric
4. Add the word "acid"

= Phosphoric Acid


***** For most acids you would drop the ending completely (e.g. chlorate=chloric and nitrate=nitric) This is not the case for sulphur and phosphorus.

Phosphate becomes phosphoric (not phosphic)
Sulphate becomes sulphuric ( not sulphic)

Ionic and Covalent Compounds

Ionic compounds consist of two or more ions which are held together by ionic bonds. These particles are oppositely charged; the particles which are positively charged are including metal cations, and the particles that are negatively charged are includes anions, or the polyatomic ion. Through the oppositely charged particles, they stick together by electrostatic force. The transfer of electrons always occurs between a metal to a non-metal. Generally, ionic compounds have similar properties; a high melting and boiling point, and being hard and brittle.

Ex. W (+6) & F (-1)
The charges of the positive and negative ion have to be able to cancel out. Therefore, you need 6 F’s in order to satisfy the equation. So the result is:

Ex. WF₆ (Tungsten fluoride)

Also, when you name an ionic compound, the metal always comes before the non-metal.

Ex. Cu (+2 or +1) & S (-2)

Cu2S (Copper (I) Sulphide)

Sometimes there are more than one charge on the ion, and depending on the formula given and the situation, (I), (II) etc… show us what the charge is on the ion.

What are complex anions? Complex anions actually aren’t complex at all; they are just a group of atom that are already combined, which acts as one atom. They are negative particles that are made up of combined gases. For example, chlorate (Clo3-).

Ex. Combine Potassium and Acetate

K(+1) is potassium and CH3COO (-) is Acetate, and since the charges will cancel, the result is simply:

KCH3COO

Now, on to covalent compounds; covalent compounds are essentially the opposite of an ionic compound, instead of transferring electrons, they share them. The two elements in the covalent compound should be both non-metal’s.

To name or to write formula’s of covalent compounds, you need to know your diatomic molecules. They consist of two atoms, and to name it you need to know your prefixes.

The diatomic molecules are: H2, 02, F2, Br2, I2, N2, and Cl2. An easier way to memorize this is to remember the HOFBrINCl, or the Magnificent Seven (the elements are in a shape of a 7 on the periodic table).

The prefixes you should have memorized are :

mono- 1 tetra- 4 hepta- 7 deca- 10
di- 2 penta- 5 octa- 8
tri- 3 hexa- 6 nona- 9

When you name covalent compounds, the first element stays the same. However, with the second element, you add the prefix to the beginning, then change the last part of the element to "ide". Also, if the prefix and the element both have a vowel, cancel out the vowel from the prefix. For example, instead of it being tetraoxide, it'd be tetroxide.

Ex. NI3

N being Nitrogen, and I is Iodide. The prefix for 3 is tri, therefore the result would be:

Nitrogen triodide

For more information on this , go to these links :
http://misterguch.brinkster.net/ionic.html
http://misterguch.brinkster.net/covalentcompounds.html
http://en.wikipedia.org/wiki/Diatomic_molecule

Lab 2B: Heating and Cooling Curves of a Pure Substance

Lab 2B was was done in class on October the 4th. It involved the measuring of the freezing and melting points of Dodecanoic cid. It was interesting to see how quickly change of state occurred during the experiment.

Equipment:

Ring stand
Buret clamp
Hot plate
beaker with water (hot and cold)
2 Thermometers
Safety goggles
1 Test Tube
Dodecanoic Acid
Paper to record observations

Procedure:

(Part 2 was done first)

Part 2:
We started off by putting on saftey goggles. Followed by gathering materials needed to conduct the experiment. Students in groups of 2, were given liquid Dodecanoic acid in a test tube. A thermometer was placed in both the acid and the water beaker. The test tube was then suspended inside a beaker filled with cold water by a buret clamp attached to the ring stand. Students then observed the acid as it slowly reached its freezing point. Temperature change was recorded in 30 second intervals, along with observations. Once the acid reached 25 Degrees Celsius, observations and recordings of time intervals were stopped, and students moved on to part 1.

Part 1:
Once the acid had reached 25 Degrees Celsius, students turned on there hot plates. The hot plate's temperature was turned to 2. The cold water from the beaker was replaced by hot water, and placed on the hot plate. The acid was once again suspended inside the beaker of water. Time intervals of 30 seconds were recorded along with observations while the acid reached its melting point. Once the acid had reached 50 Degrees Celsius, observations were stopped and the experiment was complete.

Result:

After preforming the experiment, the melting and freezing points were recorded. The melting point was recorded at 40 - 45 Degrees Celsius, and the Freezing point at 30 - 35 Degrees Celsius. The recording of the temperatures came out very unexpectedly. There were some time intervals where there was no change in temperature, this is because all the energy being transferred from the water to the acid was changed into kinetic energy and used to help break the attractions between the molecules in the acid instead of raising the temperature. Thus creating plateaus in the temperature change graphs made. It was interesting to do this experiment. What made it interesting was knowing that the temperature in which Dodecanoic acid melts and freezes is so close together, and can be changed very quickly.

October 1st Class was one to remember.

Friday's class was full of fun and learning! Now my job on this Sunday evening is to re-word my knowledge from last class onto this blog. I love blogs, they are a hobby of mine, that is for sure!

Anyway, last class we learned about a few basic laws, including the Law of Multiple Proportion and the Law of Definite Composition. The Law of Multiple Proportion is when at least 2 compounds with different amounts of the same element can be created. The example from the class was Co2->C2O4->C3O6... and so on. The Law of Definite Composition is when a compound will always remain a compound, no matter what the circumstances are. The class example was H2O, it will always be H2O no matter if it is a solid, liquid, or gas.

Moving on, we learned about the heating/cooling curve of a pure substance. Now I could be fancy, and make a chart or grid of some sorts, but lets go old school here, and use our imagination. Now imagine a grid, with the X Axis as Time/Minute, and the Y Axis as Temperature in Celsius. Now picture the letters A to F, resembling points in a stair like fashion, towards the top right corner of the grid. Got it? Great. Now point A is on the Y Axis, and it is a solid state at any temperature below the melting point. A solid is packed very tightly together and does not move a whole lot. Now between points A and B is a line, and that line shows how the Kinetic energy increases, the molecules move faster, and the temperature increases. At point B, the substance remains a solid, but is beginning to melt. The line B-C is a mixture of both a solid and a liquid. It can be either Freezing or Melting, depending on whether the substance is being heated or freezing. The temperature remains constant but it is melting into a liquid at the same time. The substance's particles are becoming more spread out and moving at a faster rate. Now point C. Point C is officially what humans call, a liquid. If it is H2O, then it is water. Cool stuff eh? I thought so. Moving on, C-D is the liquid being heated and the molecules again acquire more heat and speed via Kinetic Energy. Point D exists in a Liquid State. The particles in the substance have enough Kinetic Energy to man up and overcome the adversity of the attraction of particles, so it is not a solid. In fact it is on its way towards being a gas. Now line D-E can either be Evaporation (liquid into gas), or Condensation (Gas to Liquid). Even though the line is in between a liquid and a gas, the temperature remains unchanged. In fact the heat energy is absorbed is not to change the temp, but rather the speed of the molecules. This consistent temperature is known as the boiling point. Now point E is strictly a Gas. Plain and simple. Finallllllllllly, is the line E-F. E-F shows that the gas particles continue to absorb energy and move faster, leading to another increase in temperature. After that, the gas may transform into a solid (Sublimation). If it were Solid to Gas, it would be Deposition. Now for you uncool, mindless, unimaginative people, here is a graph to show all that I explained beautifully.




Textbook Pages 25-34

-The temperature at which matter changes from a liquid to gas is called its boiling point
- A mixture is two or more kinds of matter that have separate identities. They can be divided into different components that are different from each other.
-By classifying matter, you develop a better understanding of it
-Mixtures that are uniform(the same) throughout are called solutions.
Distillation is a procedure used to separate solutions into separate components.
-Changes that produce new substances with different properties are called chemical changes
-Physical changes are changes that can be reversed to obtain the original substance easily. They don't produce new substances.
-Decomposition is the type of change when one kind of matter splits into two or more kinds of matter.
-Electrolysis is a procedure where an electric current is passed through a substance, causing it to decompose into new substances.
-Decomposition and distillation appear similar, but study reveals that they are actually fundamentally different processes.
-Pure substances that can be broken down into new matter are called compounds.
- Compounds are composed of pure substances called elements which cannot be broken down.
-109 known elements
-All matter on Earth made up of 85 elements
-Just 8 of these make up 99% of earth's crust
Law of Definite Composition:
Mixtures can have almost any composition that is desired but compounds will have a definite composition.
e.g. The volume of H2 obtained from water is always twice the volume of O2 obtained.

Law of Multiple Proportions:
Two or more compounds with different proportions of the same elements can be made.
- A particular compound = not more than 1 proportion like a mixture; same elements can form different compounds though, that have different make up but having different composition from the others.

Pg 36-39

-Matter is made up of atoms
-Macroscopic observations are observations you can make by seeing, feeling or smelling.
-The word atom means "smallest piece of something"
- Temperature increases- movement becomes faster and stronger and breaks forces that hold them together as a solid, and become a liquid, and the particles then flow past each other.
-Temp. of a liquid reaches boiling point, the liquid becomes a gas b/c particles move with such energy and force they break forces of attraction and move freely
- Compounds can be solids, liquids or gases
- One atom of an element*----One molecule of a compound
-Molecules are two or more kinds of atoms combined.
-Ions are particles that have an electric charge