Measurement & Uncertainty

Today we learned about Measurement and Uncertainty! Yayyy ...

Measurement and Uncertainty

Okay, sooo when you make a measurement the results usaully specify in a range of values. To show the range of values of a measurement is......

measurement = best estimate ± uncertainty

- Every estimate has some degree of uncertainty because it is only the "best" estimate, no estimate is exact

For example!
For a measurement of 6.07g  ± 0.02g, it means that the "true value" is between the range of 6.05g and 6.09g.

- We can only get an exact number if we count

For example, you can see and count two test tubes in the above image. You can't have 1.75 of a test tube (unless it's broken of course, but you don't use broken test tubes!) so therefore 2 test tubes is an exact number.




Absolute Uncertainty

Absolute uncertainty is the uncertainty in a measurement which is expressed in the units of measurements.

If a measurement is 2.12 and the "true value" is 2.00, the absolute uncertainty would be 2.12 - 2.00 = 0.12.
If the mass of something is measured like 3 times with the values of 1.00g, 0.95g, and 1.05g, the absolute uncertainty would be ± 0.05g.

Method 1

When you make atleast 3 measurements, you can calculate the average. The greatest defference between the average and the highest or lowest reasonable value is the absolute uncertainty.

Method 2

When finding the uncertainty of instruments, always measure to the best precision. Estimate to a fraction of 1/10 of the smallest segment on scale of whatever instrument you're using.

For example, a ruler's smallest segment is millimeter which is 0.1cm. The uncertainty of the ruler would be 0.01 because 1/10th of 0.1 is 0.01.













Relative Uncertainty and Sig Figs

Relative Uncertainty = absolute uncertainty/estimated measurement

- It can be expressed in percentage.
- Using sig figs indicate the relative uncertanty, the last digit is uncertain.


~ ~






Hope this helped you at least a little bit!
- Melody L. =)

Precision, Accuracy & Significant Figures

Today in class, we learned about precision, accuracy, but mostly significant figures.
Here are some definitions...


Precision - how reproducible measurement is compared to other similar measurements.
Accuracy - how close the (average) measurement  comes to the accepted or real value.
Significant Figures - measured in meaningful digits and the more precise means the more significant digits.


A - Significant Digits
- the last digit in a measure is uncertain as it could be one digit higher or lower. 
[ example: 3.24L. The 3 & 2 are certain whereas the 4 is uncertain ]
- significant digits in the measurement include ALL of the certain and first uncertain digit.
[ example: 3.24 = 3 sig figs ]


B - Significant Figures: Digits
- leading zero are not counted.
[ example: 0.04 = 1 sig fig ]
- trailing zeros after the decimal point are counted.
[ example: 10.0230 = 6 sig figs ]
- trailing zeros without a decimal point are not counted.
[ example: 15100 = 3 sig figs ]


C - Exact Numbers
- some quantities are defined as exactly a certain amount and no rounding is required.
- have an infinite number of sig figs.
[example: 4 dogs can be expressed as 4.000 dogs]
[example: a "pair" of shoes = 2 shoes (not 1.853892 shoes rounded up to 2) ]


D - Rounding Rules
1. look at the digit after the position of rounding.
2. if the digit is <5, round down.
3. if the digit is >5, round up.
4. if the digit is =5, and there are more non-zero digits after the 5, round up.
5. if that digit is =5 and it ends at the 5, round to make the last digit an even number.


Here are some practice rounding questions: round to the nearest tenth.
a) 26.73 =
b) 26.79 =
c) 15.31 =
d) 83.298634 =
e) 62.4585 =


Answers:
a) 26.7
b) 26.8
c) 15.3
d) 83.3
e) 62.5


E - Math Rules: Adding & Subtracting
- when adding and subtracting, round to the fewest number of decimal places (least precise).
[example: 12.544g + 1.3g = 13.844 ---> 13.8 (1.3 only has one decimal place) ]
here's a visual example:













F - Math Rules: Multiplying & Dividing
- when multiplying and dividing, round to the fewest sig figs.
[example: 12.27g x 3.8g = 46.626 ---> 47g(squared) ]
[example: 24.845g(squared) / 1.3g = 19.11 ---> 19g ]
visual example:

















hope this helped!
submitted by Kimberly Leung:)

Lab 3B & Naming Non-Acids and Acids

Today, we did a lab on separating mixtures on chromatography strips. The purpose of this lab was to calculate the Rf (ratio of fronts) values and identify each component. This is to help us identify components of a mixture based on their invidivual Rf values.

Well, how do you calculate the Rf value?


Rf: d1 / 21
d1: distance traveled by solute
d2: distance traveled by solvent

eg. Solute traveled 9.0 cm and solvent traveled 12.0 cm. Find the Rf value.
Rf = 9.0/12.0
    =  0.75 cm

Based on this, we identified the Rf values of three primary food colorings: red, yellow and blue.
There were two mixtures, one green and the other was unknown. We could identify the different components based on observing the chromatography strips. The green food coloring was composed of yellow and blue, while the unknown was composed of all three primary colors. We confirmed it by comparing the Rf values and the average Rf values of the components. :)




Now, I will go over how to name non-acids & acids!


Naming Non-Acids


IONIC COMPOUNDS

• composed of a metal (positive ion) and a non-metal (negative ion)
• when naming ionic compounds, make sure the ions always equal to zero
• change the ending of the non-metal with the suffix "ide" unless it is a polyatomic atom (keep it as it is)
• some metals form more than one ion, so indicate the charge using Roman Numerals
  
  eg. CaCl2 > Calcium Chloride
        MnO2 >  Manganese (IV) Oxide
        Pb(NO3)2 > Lead (II) Nitrate

COVALENT COMPOUNDS

• non-metal + non-metal
• make sure the ions equal to zero
• use Greek prefixes to identify if there is more than one atom
• do not use "mono" for the first element
• the last non-metal should end in "ide"
  
  Greek Prefix                Corresponding Number
  mono                                         1
  di                                              2
  tri                                              3
  tetra                                          4
  penta                                         5
  hexa                                          6
  hepta                                         7
  octa                                           8
  nona                                           9
  deca                                          10
  
  
  eg. SF3 > Sulphur Trifluoride
        H2S > Dihydrogen Monosulphide

Naming Simple Acids (Hydrogen + Another Element)

• use the prefix "hydro"
• drop the "ide" on the non-metal element and end with the suffix "ic"
• add the word "acid" at the end
  
  eg. hydrogen chloride >> hydrochloric acid

Naming Complex Acids (Hydrogen Ion + Polyatomic Ion)

• drop the "hydrogen"
• if the polyatomic ion ends with "ate" replace it with "ic"
• if the polyatomic ion ends with "ite" repliace it with "ous"
• add "acid" at the end
  
  eg. hydrogen chlorate >> chloric acid
       hydrogen hypochlorite >> chlorous acid

Good news for you, there is an easy way to remember the rules!
* We ate-ic-y sushi and got appendic-ite-ous   :)

Law of Definite Composition (Proust's Law)

• a chemical compound always contains exactly the same proportion of elements by mass (so nothing will be left over)
  
  eg. H2O (water) has two atoms of hydrogen (2g) and one atom of oxygen (16g)
  Total mass: 18g

Law of Multiple Proportion (Dalton's Law)

• same elements can combine in more than one proportion to form different compounds
• one element with the same mass combine with the different masses of another element are in the ratio of small whole numbers
  
  eg. CO (one oxide) and CO2 (two times the number of oxide)
  or FeO and Fe2O3

entry by grace

Separation Techniques + Curves..

So last class, I'm not going to lie, I don't think my brain absorbed anything.  I was too busy focussing on copying down the notes as quickly as I could.  The good news is, I got almost everything.  The bad news - I can barely read my own writing.  Cool story bro.

So WHY do we separate...

Well really, because we want the good grade.  But don't write that on a test.

We separate substances because we want to view the individual components/properties of each chemical.

So since you remember the basic separation techniques (ha), I don't really need to remind you.   But since repetition is supposedly the most effective (and annoying) method of education, I'll list the main techniques out for you.  How nice am I.

- Hand Separation (eg using a magnet)

- Filtration (separation by particle size)

- Floatation (separating by density)

- Crystallization (separating... by crystallizing a substance)
- Extraction (separating by solubility)

- Distillation (separating by boiling point)

- Chromatography (stationary phase)

To start it off, here is a video of some guy (who clearly has no life) separating iron from sand.  FYI, this is Hand Separation.

http://www.youtube.com/watch?v=n3Usa6mOkhM

Another way to hand separate is to boil away a liquid, leaving the solid remaining.

Filtration

Filtration is a relatively easy method of separation.  It is useful when you have a (non-dissolved) solid and a liquid, and some fancy-schmancy paper.  You would pour the mixture into the porous paper, and while the liquid would go right through, the solid would leave a residue on the paper. Magic.

Crystallization

This is a useful procedure when you have a solid in a liquid.  The precipitate is 'crysallized,' and then floats because of the change in density.  The crystals can then be filtered out.

Floatation (Gravity Separation)

This method is used to separate materials based on their densities.  This is done by putting the mixture in a container (most likely test tube) and then swirling it around.  IN A CONTROLLED MANNER.  You could have an acid in that container, and unless you really dislike your partner and want to splash acid on them, or on yourself (to get away from them, duh), you want to keep the mixture in the container.  Plus, you want to see the awesomeness of the separation of densities - while you swirl, gravity will pull the denser substance to the bottom.

Solvent Extraction

Solvent extraction, or just extraction, is the term used for separating two materials based on their solubility (ability to be dissolved) in different solvents.

Distillation

Distillation is a method you could use if you were given two different liquids. You would heat the liquids up, and the liquid with the lower boiling point would vaporize.  That leaves you with the other component of the mixture (thank you, captain obvious), and you would be able to collect the volatized (that's a fancy word for vaporized) component later.

Chromatography

We talked about this technique probably more than any other one technique last class.  You know, the whole "bees and hornets flying over a flower bed, bees stop, hornets keep going" thingy? Supposedly that's going to help us remember that chromatography is a method where a mixture is flowed over a material that can retain some components of the material.  For example, if you mixed honey and water together, theoretically, the honey, which has a higher viscosity than water, would stick to the paper more.  Meanwhile, the water would flow right on by.  Like I said, that is my hypothesis.  I'm not wasting any perfectly good honey to test that out.

Heating Curve


A: Solid; closely packed in an orderly manner, strong bonds and vibrates at a fixed position
A→B: Still a solid; heat is converted to kinetic energy, vibrates a bit faster, KE and temperature increases
B: Same or similar to "A"
B→C: Melting point (solid -> liquid); heat absorbed is called latent heat of fusion, temp stays the same because heat is used to overcome forces of attraction that hold particles together
C: Liquid; solid has melted
C→D: Temperature and KE increases, particles move faster
D: Still liquid but starts changing from liquid state to gas; some molecules start to move freely
D →E: Boiling point (liquid -> gas); temperature stays the same since heat is used to overcome the forces of attraction that hold the particles together
E: Gas state
E→F: Heating continues so KE and temp increases; particles move faster

Cooling Curve


P: Gas; particles have more high energy and moves quickly
P→Q: Temperature and KE decreases; particles are getting closer together
Q: Still a gas; start to form intermolecular bonds, condensation begins, starts to form a liquid
Q→R: Boiling point (gas to liquid); condensation, temperature is constant, heat energy is released called latent heat of vaporization
R: Liquid state
R→S: Temperature and KE decreases; molecules lose energy, vibrate slower and moves closer to each other
S: Starts to freeze into a solid
S→T: Freezing point (liquid to solid); particles arrange in an ordered manner
T: Solid state
T→U: Temperature decreases until room temperature
U: Substances has reached room temperature:
U→V: Remains as a solid in room temp.

Well, thanks for not reading this.  I'm just gonna remind myself that I better go do that Pre-Lab homework. Can I get a whoot whoot?

Nope. Didn't think so.

XOXO BerylliumChemists

(written by Heather LeWonderful)

Chemical & Physical Changes

Physical and Chemical Changes

Hey people, so last class we did many experiments on physical and chemical changes and you guys got to see how matter of different substances can change when it’s influenced by other substances. You guys already know the basics of physical and chemical changes but if you don’t…I hope this blog will help you! J

Physical Changes:

Physical changes are changes that DO NOT result in the production of new substances. Physical changes affect size, shape, or state but it does not alter its composition. For example, if you melt a block of ice, you would still have water at the end of the change but the state changes, therefore, it is a physical change. You can change that water back into its solid form, by freezing it. Another good example would be bending a piece of copper wire. You can change the form or shape of the wire, however in the end it is still composed of the same material. Other common examples of physical changes are; melting, freezing, condensing, breaking, cutting and bending.

Chemical Changes:

Chemical changes are changes that result in a NEW production of another substance. Chemical changes undergo chemical reactions where substances react with each other to form new substances. You can notice the chemical change if the substance changes colour, or when two substances mix together. Dissolving and heavily reactive materials are also chemical changes. Bonds are broken and formed between different atoms. For instance when you burn a piece of wood, the burning will create carbon gas. When hydrogen is burned with oxygen, water is formed and heat will also be released.  When you light a Bunsen burner, it will produce water and carbon dioxide.  Some common examples of chemical changes are; burning, decomposition, photosynthesis and etc. Bottom line is, in the end, its original composition is altered into a new substance.

  

How can you tell physical and chemical changes apart?

Well first, chemical changes makes a new substance that wasn’t there before. There may be clues that a chemical reaction took place, for example light is emitted, heat is produced, colour changes, gas is produced, temperature changes and odor is produced. Second, the starting and ending of substances of physical changes are the same, even though they may look different.

Here is a little song that can hopefully help you understand chemical and physical change better!
(Entry by Melody Lu)

All About Matter!

In class we learned a matter chart:

MATTER

- has mass & occupies space

MIXTURE
Homogeneous

- uniform throughout
- appears to have only 1 component but actually more than one component that's spread throughout the substance

• solution
• colloid (ex. milk)
• eg. sugar in coffee (unable to see the sugar)

Heterogeneous
- non-uniform, different properties do not blend together
-appears to have more than 1 component
- all the components are visibly seen

• suspension
• mechanical mixture
• eg. trail mix

PURE SUBSTANCES

- one set of properties 

- one type or particles
-classified as either element or a compound

Element 

- made of atoms

- matter in its simplest form

- cannot be decomposed

• metal (eg. copper)

• metalloids (eg. silicon)

• non-metals (eg. sulphur)

Compound

- made up of elements chemically combined (more than one atom)

- smallest particle is a molecule

• ionic - salt / base / acid
• covalent
• eg. water 

Posted by Kimberly:)