Accuracy and Precision

Today, we have learnt the accuracy and precision of practises of measuring.
The following is the textbook definition:
Precision
It is how reproducible a measurement is compare to other similar measurements.

Accuracy
It is how close the measurement (or average measurement) comes to the accepted or real value.

Measurement and Uncertainty

- There are no measurment that is excact because every measurement is a best estimation with margins of error.

- Despite of have the best estimation, for example, there are 39 cars in a parking lot is an exact number because it's a set of objects.

Absolute Uncertainty

A measurement of the uncertainty which is expressed in units. There are 2 methods to find it:

Method 1: Make at least 3 measurements and calculate the average. In the other hand, the absolute uncertanty is the largest difference between the average and the lowest or highest reasonable measurement.

               - For example: when calculating the avery of a few data eliminate the unreasonable data first:

1. 59                          The average is 59
2. 60                          I have eliminated 53 because it is a absolute uncertainty.
3. 58
4. 53
5. 59

 Method 2: Determine the uncertainty of each instrument

• When you are making a measurement, make sure you measure the best estimation you can (precision). In some real practices, you should estimate whatever the smallest segment that is possible on a instrument scale.
• For exmple, our rulers have the smallest scale as 1 mm, so that the best precision should break down to 0.1 mm. When you are measuring a thing, you need to see more carefully and precisely to be certain of the 0.1 mm differences.

Relative Uncertainty and Significant Figures

Relative          Absolute uncertainty

uncertainty =--------------------------------------

                        Estimated measurement

That's about what we have learnt today.

Kevin Wang

Chapter 3:Sig Figs

Today in class, we begin our new unit on Sig figs. So what are Sig figs and why do we need them?


Sig figs
-They are meaningful values that are accurate.

- They can also be precise if there are many of them

-We need them to get precise accurate measurements and not just approximating

Eg.24.37, 24.5, 35.3

"Watch this video if you did not listen in class. It is very helpful trust me"

More Practice problems go to:http://science.widener.edu/svb/tutorial/sigfigures.html

Rules to Significant Numbers

-Non-zero digits are always significant eg.23490.33

-All final zeros after the decimal point are significant eg 95.000

-Zeros between two other significant digits are significant. eg 1.00009

-Zeros used solely for spacing the decimal point are not significant. eg.0.00009

Rounding Rules For Sig Figs

"When Adding Sig figs you always round to the nearest Decimal"



"When dividing and multiplying Sig Figs you always round to the fewest Sig figs in this case 2"



Exact Numbers

Today we also learn about exact numbers which are numbers that cannot be round up because it is exact.

Eg.
-1 km will always=1000 meters
-2 cats will always be 2 cats. There cannot be 1.9 cats
-1 human will always be 1 human. Not 0.99

Two cats will always be 2 cats not 1.999!!!!!!!!!!!!!!!

• Look for numbers to the right of the digit to round up
• If the digit is less than 5, the number does not change
• If the digit is more than 5, the number rounds up
• If the digit is exactly 5, than round the digit to make it an even number like 4,6,8,2.
• If the digit is the number 5 and there are more no zero digits after five than round the number up. 

Lab Experiment: Separation of a Mixture by Paper Chromatography

Paper Chromatography:
- technique for separating and identifying mixtures that are or can be colored.

In this experiment, we've became acquainted with paper chromatography.  There are 3 parts in this lab experiment, in part 1, we assemble a paper chromatography apparatus, which  tells us how to set up a paper chromatography.  In part 2, we examined chromatography results for a variety of food colorings.  In part 3, we separated two mixtures of these colorings and study the significance of the Rf (ratio of fronts) values.

Please referred to videos on youtube about paper chromatography  below.

 Leif Tung

Separation Techniques

Separating Mixture

To separate into different component & different properties.

Separation:
It is a process to reveal the identities of the components in a mixture. However, it is hard to separate them, the properties, in which they have the similar properties.

Basic techniques

- Filtration: select components by particle size( undissolved solids and liquid)

 Cystallization(Solid and Liquid)

The resultant which we want is a solid state formed by a chemical or physical change.

Distillation collects and condenses volatilized (vaporized) components. In other words, it is a process of boiling the liquid and vaporizing it and then condenses it back to purified liquid.

Chromatography is the purpose of separating complex components by flowing the mixture over a material that retains components more than others, so different components flow with different speeds on the material.

Paper Chromatography(PC)

A highly accurate component separation material. The paper is liquid soaked with the sheet or strip of paper. The components appear as separated spots on the paper chomatography after drying.

(Videos from Youtube)

Kevin Wang

Naming Simple Acids and Complex Acids

Today in class we learnt how to name and identify both simple and complex acids.  First of all acids are form when composed of hydrogen ion and composed of a negatively charged ion.

 

Almost all acids starts with H and is negatively charged.



Simple Acids

• Uses hydro in the begining
• Ends in ide when form with hydrogen. However you will need to change the ide to ic
• Ends with writing acids

Eg. HF-hydrogen flouride turns into hydrofluoric acid.

Complex Acids

• Does not begin with hydro
• They end in ate or ite when combines with hydrogen.
• However you change the ate to ic and ite to ous and wrtie acid at the end

Eg. H2SO4-hydrogensulphate turns into sulphuric acid.

Eg. HNO2-hydrogennitrite turns into nitrous acid.

That concludes all we learnt today!!!!!!

Test Next Thurs On What we learn so far which is Chap1 and 2

Writing & Naming Ionic and Covalent Compounds

Ionic Compound:
-composed of two or more particles  (oppositely charged)
                                                 (ions)
-held together by electrostatic forces.
-electrons are transferred from a metal→non metal.
 
             Physical Properties                     Ionic Compound
              -States                                          - Solid
              -Electrical conductivity                    - Solid:No Liquid:Yes
              -Boiling point and Melting Point       - High
              -Solubility in water                          - Often high
              -Thermal conductivity                      - Low

← example: Sodium Chloride
                           NaCl

Resource: Wikipedia







Covalent Compound:
   To start off covalent compound, let's look at the prefixes first:
mono-1     tetra-4     hepta-7     deca-10           triskaideca-13
di-2           penta-5    octa-8       hendeca-11    tetrakaideca-14
tri-3           hexa-6     nona-9      dodeca-12      pentakaideca-15

-share electrons
-non metal with non metal
※ Diatomic molecules: Hydrogen, Oxygen, Florine, Nitrogen, Chlorine, Bromine, Iodine

  
             Physical Properties                    Covalent Compund                          
                 -States                                        -Can be a solid, liquid, or gas
                 -Electrical conductivity                  -No
                 -Boiling point and Melting Point      -Low
                 -Solubility in water                        -Variable
                 -Thermal conductivity                    - Usually low

←example.


Resource: Yahoo! Image









                                                                                                                                   Leif Tung

Experiment!

Heating and Cooling Curves of a Pure Substance

(Wikipedia.com)

Today, we have done a fascinating lab which we cooling down the pure substance of dodecanoic acid(C₁₂H₂₄O₂ ). It is a white powder when the temperature is about 25 degree centigrade. When the process of cooling the substance is done for about 13 minutes. We started to go down to the heating process. The process that will melt the dodecanoic acid from solid state into the state of liquid again. The process of heat it up into liquid took about 9 minutes. The whole purpose of the experiment is to investigate the heating and the cooling process of liquid/solid dodecanoic acid and to determine and compare the melting and freezing points of dodecanoic acid.

Kevin Wang

Chapter 2 Intro



The Heat/Cooling Curve of a Pure Substance



Description of the diagram

A                                                                      A-B



The particles are closely packed together and
can only vibrate at a fixed position. 

It stays solid anywhere below its meling point.

B



The particles in the solide are being heated

and the heat enrgy is converted to kinetic enrgy.

Thus the particles vibrate faster and move further apart.

B-C

 

Solid has begun melting but the

temperature remains the same

C



At solid at its melting point. it is in

both solid and liquid state. The temperature

remins constant becuase it is used to

over come forces between the particles

C-D



Turn to full liquid state.

D

Liquid is heated and molecules begans to move faster

due to the kinetic energy in the increase of temperature

                           D-E

Molecules recieves enough energy to

to overcome forces between particle. Some liquid

molecules begin to change into gas

E

Evaporation begins.

E-F



Liquid has turn all into gas

 Temperature increases as heating continue.Gas particles are moving much fast do to much bigges space





 Text Book Summary