Accuracy, Precision, and a whole lot of Uncertainty

Accuracy & Precision

What is Accuracy?

• Accuracy is how close a measured value is to the actual (real) value.

What is Precision?

• Precision is how close the measured values are to each other.

For example:

Big black circle: Low Precision

Small Black circle: High Precision

Farther away from Bull's Eye: Low Accuracy

Close to Bull's Eye: High Accuracy



High Accuracy, High Precison



High Accuracy, Low Precision



Low Accuracy, High Precision





Measurement and Uncertainty

No measurement is exact. It is only a best estimate, which has some degree of uncertainty. We only get an exact number when we count a set of objects.

• e.g. there are 23 books on the bookshelf

Absolute Uncertainty

Uncertainty is expressed in the units of measurement, not as a ratio.

To determine absolute uncertainty:

Method 1:

• Discard unreasonable data. Calculate the average of at least 3 measurements. The absolute uncertainty is the largest difference between the average of the highest and the lowest reasonable measurement.

Method 2:

• Determine the uncertainty of each instrument used. Make sure the measurement(s) is as precise as possible. Estimate to 0.1 of the smallest segment on the instrument scale.

e.g. if the smallest measurement on a ruler is in centimetres (cm), measure to 0.1cm, or 1 millimetre (mm)

Relative

Uncertainty  = absolute uncertainty / estimated measurement

the ratio can be expressed:

                                        (1) in percent (%)

                                        (2) using significant figures

Here are some videos to help clearify anything you do not understand.

Accuracy and Precision



Measurement and Uncertainty



FUN FACT OF THE DAY:
DID YOU KNOW... each cell in your body has more molecules that there are stars in the Milky Way Galaxy?

By: JZ

SIGnificant FIGures

Significant figures, or significant digits, establish the value of a number.  They are measured and exact.


Significant Digits

• The last significant figure on the right is uncertain
• The significant digits include all of the certain digits plus the only first uncertain digit on the right.
• To find the number of significant figures in a given number
1. count all the digits starting at the first non-zero digit on the left
2. for a number written in scientific notation count only the digits in the coefficient

Significant Figures

• Zeros shown merely to locate a decimal point are NOT significant figures
• Ex: 0.56 (2 sig figs)
• Zeros located to the right of another number after a decimal point ARE significant
• Ex: 12.00980 (7 sig figs)
• Zeros without a decimal point are NOT counted
• Ex: 530000000 (2 sig figs)

http://www.youtube.com/watch?v=7b60RZqut0U&feature=related

http://www.youtube.com/watch?v=ExETL3IiRSw&feature=related

Exact Numbers

• Exact numbers are defined as a specific amount
• Since it is a whole number ALL numbers ARE significant
• No rounding required!
• Like the number of objects counted
• Ex: 1m = 100m

Rounding Rules

• If the first after the position of rounding is less than 5, then the least significant digit remains unchanged.
• If the first digit after the position of rounding is greater than 5, round up.
• If the first digit after the position of rounding is 5 and the 5 is followed by zeros, round up
• If the first digit after the position of rounding is 5 and the 5 is followed by a 5, round to make the last digit "even"(2, 4, 6, 8)

Adding and Subtracting Significant Figures

Great video on explaining.

http://www.youtube.com/watch?v=2eXC6s9X6Wc&feature=related

Multiplying and Dividing Significant Figures

Great video on explaining.

http://www.youtube.com/watch?v=5UjwJ9PIUvE&feature=fvw (intro)

http://www.youtube.com/watch?v=PNH7_nDE6SQ&feature=related 

http://www.youtube.com/watch?v=o5BmoMDJLRY&feature=related

*All the videos are really helpful.

By: Hikari Hoshika

Lab #3: Experiment 3B, Separation of a Mixture by Paper Chromatography

The purpose of this lab was to identify and calculate the Ratio of Fronts for 3 given solutions. The solvent and solutions in this case are water and food colouring respectively.

Using paper chromatography, we identified which base colours were in each of the dye.

First, we cut out 3 strips of paper measuring 22cm x 2.5cm.

Then, we measure 4cm from one end and draw a line in pencil, and then trim that part into a point. The sample spot goes on the pencil line.

After, we put the labelled strips of paper with the food colouring into the test tube, with water only reaching up to about half of the point. Check on it after 10 min.

Finally, after 20 min since we put them in, we take the strips of paper out of the test tubes and identify the solute front and the solvent front. Draw a pencil line to show the solvent front.

Experiment 1 resulted in a single colour, and the others in multiple colours.

To solve for the ratio of fronts:

Rf   =  d1 / d2

Where:

Rf is the ratio of fronts

d1 is the distance traveled by solute

d2 is the distance traveled by solvent

For example:

If the solution traveled 7.3cm from the sample line, and the solvent traveled 7.5cm from the sample line:

Rf = 7.3 / 7.5

Rf = 0.97

0.97 is close to Blue #1 on the Table for Some of the Dyes Approved for Food Colouring

By: Jason Zhang

More Separation Techniques

Gravity separation

centrifuge

• Uses the force of gravity to separate mixtures
• Solid is based on density
• Centrifuge whirls the test tube at high speeds so the solids or heavy fluids would sink to the bottom and lighter liquids would stay at the top

o A centrifuge is a device that spins test tubes in a circle

   (see picture)

Solvent Extraction

• Component moves into a solvent shaken with the mixture
• mechanical mixture: solid—solid: uses liquid to dissolve one solid, leaving the other behind
• solution: insoluble with the solvent already present, leaving unwanted substance(s) behind

example of distillation

Distillation (liquid in liquid)

• heating mixture cause low-boiling components to vaporize
• distillation is collected and condensed
• liquid(s) with low boiling points boils first, which is collected in another flask and condensed

 

By: Jason Zhang

CHROMATOGRAPHY, not photography.

Chromatography

• It is a physical method of separation.
• the components separated are distributed between 2 phases
• "mobile phase" and a stationary phase
• It involves a mixture dissolving in a "mobile phase" though a stationary phase.
• It is a method of separating and analyzing mixtures of chemicals.
• The separation process, especially of closely related compounds, by allowing a solution or mixture to seep through an absorbent (such as clay, gel, or paper).
• so each compound becomes absorbed into a separate, often colored, layer.
• Different components travel at different rates.

Sheet Chromatography

Paper Chromatography (PC):

• Is a technique that involves placing a small dot or line of sample solution onto a strip of chromatography paper.
• The paper is placed in a jar containing a shallow layer of solvent and sealed. As the solvent rises through the paper, it meets the sample mixture which starts to travel up the paper with the solvent.
• The stationary phase is very uniform absorbent paper.
• The mobile phase is a suitable liquid solvent of mixture of solvents.
• It is inexpensive and provides graphic, clear results.
• Is a rapid and reproducible procedure - as long as all conditions are controlled and maintained.
• Accurate for the separation and identification of many important organic and inorganic compounds.

Thin Layer Chromatography (TLC):

• It involves a stationary phase of a thin layer of adsorbent like silica gel, alumina, or cellulose.
• Advantage of faster runs, better separations, and the choice between different adsorbents
• Is a procedure of chemistry that can identify over 700 types of biochemicals, including significant medical drugs of legal importance.
  
• Reliable, rapid and easy procedure.
• Relatively inexpensive.
• Able to detect upward of 700 different types of drugs and medications.

By: Hikari Hoshika

NO MORE POSTS AFTER THIS!

We are learning how to separate mixtures.
The basis for separation is that different components, different properties.
Strategy: to create a process that divides the components with different properties
            
Separation
Properties that are more similar to each other are more difficult to separate.

Some separating techniques:
filtration: select components by their particle size
floatation: ''       '' by density
crystallization+extraction: ''           ''  by solubility
distillation: ''            '' by boiling point
chromatography: "             " by affinity to a 'stationary phase'

Hand separation + Evaporation
-Handpicking(solids+solids)
     -mechanical/heterogeneous mixture can be separated by magnet/sieve
-Evaporation(solid dissolved in liquid)
     -boil away the liquid allowing the solid to remain


Filtration
(solids not dissolved)
-use filter paper


Crystallization
(solid in liquid)
-solids are sepatarted by filtration
-comes out as pure crystals
-then filtered again

Gravity Separation
(solids based on density)
-a centrifuge whirls the test tube around at a high speed causing the denser materials to the bottom, works for small volumes

Naming ACIDS

Acids taste sour, are corrosive to metals, change litmus (a dye extracted from lichens) red, and become less acidic when mixed with bases.  They are formed when a compound made out of HYDROGEN ions and a negatively charged ion are dissolved in water (aqueous (aq) ).

NAMING ACIDS GUIDELINES (SIMPLE ACIDS)

*simple acids are acids formed from the elements on the periodic table.

1. "Hydro" is the beginning of the name.
2. The last syllable of the non metal is dropped and replaced with "-ic"
3. The last step is to add "acid" at the end and your done naming your acid:)

Ex:

 ♥  HCL    ⇒   Hydrochloric acid

 ♥  H₂S     ⇒   Hydrosulphuric acid **

NAMING COMPLEX ACIDS

*complex acids are acids formed with polyatomic anions

1. ♥"- ate" if the anion name ends in "- ic"

♥"- ous" if the anion name ends in "- ite"

     2.  Then add acid at the end of the name.


Ex.

♥  H₂SO₄    ⇒   sulphuric acid

          ♥  HNO2       ⇒   nitrous acid


☺Joke☺:
A physicist, biologist and a chemist were going to the ocean for the first time.
The physicist saw the ocean and was fascinated by the waves. He said he wanted to do some research on the fluid dynamics of the waves and walked into the ocean. Obviously he was drowned and never returned.
The biologist said he wanted to do research on the flora and fauna inside the ocean and walked inside the ocean. He too, never returned.
The chemist waited for a long time and afterwards, wrote the observation, "The physicist and the biologist are soluble in ocean water".

By:  Hikari Hoshika

do-dodec--ca-ca-----n-o-o-....screw it, I'll have some lauric acid please :D

Sorry for the late lab post, we did a lab on heating and cooling curves of pure substances.(we used lauric acid). The point of this lab is to determine the freezing and melting points of pure substances.

To start, we got our goggles and the appropriate equipment needed. We began with cooling our substance. We lowered a test tube with a thermometer into a beaker filled with cool water and observed and recorded the temperature at each 30 s interval until the temperature reached 25 degrees Celsius. 

For the heating process, we placed the beaker on a hot plate and lowered the test tube into it. We observed and recorded the temperature in 30 s intervals until it reached around 55 degrees Celsius.   Once we're finished, we cleaned up everything and started our lab reports. 

again..sorry for the latelate late latelatelate lab day post.

(unrelated photo post achieved)

Naming Ionic and Covalent Compounds

­Ionic Compounds

• Composed of 2 or more particles (ions) that are oppositely charged
• Held together by electrostatic forces
• Electrons are transferred from a metal → non-metal

Ex.         Na⁺   +   Cl^-

      =   NaCl            Sodium Chloride

         Li⁺   +    N^3-       

                                   Lithium      Nitrogen     charges

                                       ↓                  ↓

                                 3 ( + 1 ) + 1 ( - 3 ) = 0

                                 ↑                 ↑

                               Balanced to equal zero

      =   Li3N             Lithium Nitride

• If an ion has more than one charge, we use Roman Numerals to express that charge in writing

I	-   +/- 1	V	-   +/- 5
II	-   +/- 2	VI	-   +/- 6
III	-   +/- 3	VII	-   +/- 7
IV	-   +/- 4	VIII	-   +/- 8

Ex.         Palladium has either a +2 or a +4 charge

If:   Pd²⁺  +    F^-

= PdF2                Palladium (II) Fluoride

If:   Pd⁴⁺  +    P^3-

= Pd3P4            Palladium (IV) Phosphide

• Complex ions are a group of atoms that behave as one atom

Ex.     Na2SO4       Sodium Sulphate

          Cu(NO2)2    Copper (II) Nitrite

Covalent compounds

• Shares electrons
• Non-metal with non-metal
• Uses Greek prefixes

Mono*	-    1	Hexa	-    6
Di	-    2	Hepta	-    7
Tri	-    3	Octa	-    8
Tetra	-    4	Nona	-    9
penta	-    5	Deca	-    10

*if there’s only one in the first ion, then you don’t have to write Mono

Ex.    CO2    Carbon Dioxide

         S3B2    Trisulphur Diboride

         CCl4    Carbon Tetrachloride

Diatomic Compounds on the Periodic Table

o       There are 7 diatomic molecules, which are 2 atoms of the same element

o       They make a “7” shape on the Periodic Table, with the exception of Hydrogen



H2	Hydrogen
Br2	Bromine
I2	Iodine
O2	Oxygen
N2	Nitrogen
F2	Fluorine
Cl2	Chlorine

An easy way of remembering the 7 diatomic molecules is by remembering this name:

HOF BrINCl   (pronounced:  Hoff Brinkle)

Fun Fact of the Day

DID YOU KNOW... if an octopus is hungry enough, it will eat its own arms??

By: Jason Zhang