Accuracy & Precision

Accuracy : how close the measurement comes to the accepted/real value

Precision : how reproducible a measurement is compared to similar measurements

No measurement is exact. Its just a estimation. It may still has some degree of uncertainty

~Absolute uncertainty = largest difference between the average and the lowest/highest measurement

Method 1 : Calculate the average(at least 3)

For example : 8.3, 8.5 & 8.1

Average = 8.3
Absolute uncertainty = 8.5 - 8.3 = 0.2
It will recorded as 8.3+/-  0.2

Method 2 : Determine the uncertainty

Measure the best precision that you can. You should estimate to a fraction 0.1 of the smallest segment on the instrument scale.

For example :
Thermometer  Smallest : 1degree,   Best precision : 0.1degree,   uncertainty+/- : 0.1degree

~Relative Uncertainty = Absolute uncertainty/Estimated measurement

                                    

SIGNIFICANT FIGURES

So last class we learned about sig figs, the last digit is always uncertain, there're 3 rules in sig figs, they're: leading zeros aren't counted (0.01); trailing zeros after the decimal point are counted (10.050); trailing zeros without a decimal point ARE NOT counted (12000). we also learned about exact numbers, some quantities, they have certain amount with no rounding and they have definite sig figs.

We also have different rules for rounding (1. look at digit after position of rounding; 2. >5, round up; 3. <5, same value; 4. =5, if more non zero digits after 5, round up; =5, ends with 5, round it "even")

GOLDEN RULE: (aka differences between adding and subtracting with multiplying and dividing)

1. Adding and subtrating------------> round to fewest number of DECIMAL PLACES.
2. Multiplying and dividing----------> round to fewest number of SIG FIGS.




After studying about the sig figs, I found it not that difficult because I have done some of that in my physics class. Maybe that is why I have some basics with this material.

SEPARATING MIXTURES~

Why we separate?
Because we want to find what different components and properties do the mixtures have.

We base on these strategy to find :
high/low density                reactive/inreactive
volatile/non volatile           magnetic/non magnetic
slouble/insoluble               pol;ar/non polar

Also, the teachniques are also very important.
We have.......
1. Hand separation & Evaporation
~by hands....by a magnet or sieve....by boiling away the liquid to get solid remains
2. Filtration
~by using filter paper to filter the solid particles in order to get the filtrate
3. Crystallizatiuon
~by evaporating/cooling so that the solid comes out as pure crystal
4.Gravity separation
~by using a centrifage that can force the denser materials to the bottom of the test tube
5.Solvent extraction
~by using liquid/separatory funnel in order to remove the unwanted material.
6.Distillation (liquid in liquid solution)
~by heating a mixture....the liquid with the lowest b.p. boils first...the vapour ascents to distillation flask and enters condenser, finally the gas cools and condenses back to liquid dropping the distillate as a purified liquid
7.Chromotography
a. paper chromotography
~by using a sheet or strip....components appear as separating spots spread out on the paper after dying or 'developing'
b. Thin layer chromotography
~by using a thin layer of absorbet(Al2O3 / SiO2)....components appear as spots on the sheet.

Oct 19, Lab 3B

lab 3B: Separation of a Mixture by Paper Chromatography
we use 3 color dyes (unknown, green and either red, blue, and yellow).
-And drop those color on each piece of chromatography paper
-Put the paper into the teststube, which have already contained a small amount of water
-Wait for 20mins

Then the result may seem like the picture from below

Conclusion: Chromatography is one of the seperation that can seperate complex mixture, such as food colour from above. They are both combined with different colour and get the new one, and originally each color have different solubility, through the chromatography paper, different will stop according to their component's solubility.

ACIDS

    So today we learned about naming acids, acids are formed when a compound composed of HYDROGEN ions and a negatively charged ion are dissolved in water { Aqueous (aq) }. We also learned about the guidelines, like use "hydro" as the beginning; last syllable of the non metal is dropped and replaced with "-ic"; add "acid" at the end, so its basically like ____ide -----> hydro____ acid

We also learned about naming complex acids, its like we replace -ate with -ic, and -ite with -ous.

Ex. HC1(aq) + H20(l) -----> H30 (aq) + C1(aq)

Writing + Naming Ionic and Covalent Compounds

Ionic Compounds-Composed of 2 or more particles(oppsitely charged), which is Metal and NON- Metal
Ex.
K+1  ,   N3-   >   K3N , as three more Potassium get 3 positive charge to held with Nitrogen 3- and get the balance- 0.

Copper (I) Oxide > Cu2O 
Copper has two different charge as we see in the periodic table, that's why we have to notice that which charge do we use it.   If it's +2, we use Roman number notice it by (II).

Covalent Compound
-Share electrons
-Compose with NON- Metal and NON- Metal

Diatomic molecules: H2, O2, F2, Br2, N2, Cl2, I2
-Use GREEK prefixes to Indicade the number of atoms.

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

Ex.
N2O4 >  dinitrogen tetroxide

Heating And Cooling~

THE HEATING PROCESS ~

1. Put on your safety equipment.

2. One partner will as observer, the other will act as recorder. Recorder is responsible for stating the 3os intervals when temp. readings are to be taken. Prepare the table for experimental result.

3. Obtain a test tube assembly consisting of a thermometer endedded in solid dodecanotic acid and remove the cotton plug and save it for the end of experiment.

4. Put 300mL of tap water in a 400mL beaker and place the beaker on a hot plate. Turn it on to high heat and raise the temp. of water bath between 55 and 60. Monitor the water temp. with thermometer. While the water is heating, set up a ring stand withg a buret clamp to hold the test tube.

5. When the water bath reached 55, turn the hot plate to low heat. Lower the test tube into the water line. Record the temp. of dodecanoic acid and every 30s after that. During the heating process, the temp. of water bath should be monitored with its thermometer to make certain that the water temp. remains above 55.

6. Continue temp. recording until the temp. above 50. As the dodecanoic melts, stir it gently to mix the solid and liquid. Record the times when melting begins and ends, as well as observations.

7. Turn off the hot plate.

THE COOLING PROCESS~

1. Require teamwork, table 1 will be continued to read.

2. Raise the test tube out of the hot water bath and clamp it in position in room temp.. Just replace the hot water in beaker with room temp.

3. Immediately start monitoring the cooling process. Record the temp. of liquid dodecanoic acid

4. Record the temp. of dodecanoic acid every 30s until the temp. is near 25. Record when solidification begins and ends , as well as observations.

5. When the temp. at or near 25, stop recording temp. readings.

6. Reset the test tube with cotton plug. Return the test tube to your instructor and put away all your equipment.
7. Wash your hand with soap and water.