Precision, Accuracy and Uncertainity

Precision: is a reproducible a measurement is compared to other similar measurements.

Accuracy: is how close the measurement comes to the accepted value

Low accuracy
High Precision

High accuracy
Low precision

High accuracy
High precision

Uncertainty
No measurement is exact; it is an estimate. Only when a set of whole objects are counted can we get an exact number ie. There are 25 cars in the parking lot.

Absolute Uncertainty
Is expressed in the units of a measurement instead of a ratio.

Method 1
The average of three measurements is calculates. (Remove unreasonable data)
The absolute uncertainty is the largest difference between the average and the largest or smallest reasonable measurement.
The answer is written as: The average plus or minus the biggest differnce
ie. 76.5 +- .2g

Method 2
Determind the uncertainty of of the innstruments used.
estimate to 0.1 of the smallest fraction of the measurment. ie. rulers smallest fraction is 1mm therefore we estimate to 0.1mm


Relative Uncertainty= absolute uncertainty/ estimated measurement
This ratio can be expressed as a percent

Significant figures tell us the relative uncertainty, since the last digit is uncertain!

http://www.mathsisfun.com/accuracy-precision.html

KP

Significant Numbers

Greetings Significant People! 

Happy Independence Day for Turkmenistan from the USSR!
!warning! excessive links ahead

When creating measurements, there is always uncertainty. To minimize the importance or meaning of the error; we write down digits of a measurement that will be meaningful. 

To better understand the meaning of significant digits/figures, we'll look at some examples:

• We'll use 3.29 grams as an example
• 3 and 2 are certain digits
• when measuring we are sure that these digits are correct
• 9 is uncertain
• the last digit of any measurement is always uncertain as it is the last number that is measured

Significant digits in the measurement include all of the certain digits plus the first uncertain digit for a given measurement. To further understand these important figures of significance, let us look at how we figure out significant figures! 

• leading zeros are not counted
• 0.000004
• there is only one sig fig
• trailing zeros are counted
• 50.0540
• there are six sig figs
• trailing zeros without a decimal point are not counted
• 1 000 000 000
• there is only one sig fig

Exact Numbers

Some quantities are defined as a certain amount.

There is no need for rounding and have an infinite amount of significant figures.

Objects that are counted are exact numbers.

Rounding Rules

When writing answers, we must round to the appropriate number

• if the number is > than 5; round up
• if the number is < than 5; round down
• if the number is 5 with non-zero digits following it; round up
• if the number is 5; make the last digit 'even'
• even numbers to be exact (2, 4, 6, 8)

http://www.youtube.com/watch?v=5UjwJ9PIUvE


Adding and Subtracting Significant Digits
When adding or subtracting, we round to the fewest number of decimal places, as well as the first uncertain digit.
http://www.youtube.com/watch?v=U6k7VpdW_rQ
http://www.youtube.com/watch?v=cEMSHsIeKMM&feature=related


Multiplying and Dividing Significant Digits
When multiplying or dividing, we round to the fewest number of significant digits.
http://www.youtube.com/watch?v=qm2bY8tcNQ0
http://www.youtube.com/watch?v=oxqW1LFm7aw&feature=related

and for those who enjoy awkward music videos

http://www.youtube.com/watch?v=ZuVPkBb-z2I

-JY

Lab 3B: Separation Of A Mixture By Paper Chromatography

So todays class we had a lab involving one of the separation techniques we learned from the previous. The separation technique we used for todays lab was paper chromatography. We used the paper strips to make separations between various food colorings. The was very successful with mild problems. Some of the groups results were very low, but as an over all average everything was pretty up to scale. The video below is an example of paper chromatography, so a basic summary of todays lab, enjoy :)

http://www.youtube.com/watch?v=IRZ4lHEe1DI&feature=related

P.S., STUDY FOR THE TEST!

Separation Techniques

The basis of separation is that everything is made up of different components or properties. These components can be separated and then individually analysed.

Strategy: Devise a process that will separated the substance best. Use properties such as

Low/High density

(non) volatile

(non) soluble 

(un) reactive

(non) magnetic

(non) polar

Properties of Separation:

The components stay the same

The more similar the components are, they harder it is to separate them.

Examples of separation methods:

Hard Separation (two solids): mechanical or heterogeneous mixture separated by a magnet sieve, etc.

Evaporation (Solid dissolved in a liquid): Boil away the liquid to leave the solid. 

Filtration ( solid (not dissolved) in a liquid): Pour through a porous filter, solids stay behind because they are larger than the pores in the filter.

Crystallization (solid in a liquid): A precipitate is formed by a chemical or physical reaction. The solution is then filtered. Then it is evaporated to form crystals which is then filtered again to produce the remaining solvent.

Gravity (solids): A centrifuge whirls a test tube around, pushing the more denser objects to the bottom. (Works best for small volumes)

Solvent Extraction: Solvent is used to dissolve one component of the mixture. Only works when the solvent dissolves one component.

     Liquid: dissolves one solid, leaves the other behind.

     Solution: Solvent is insoluble with solvent present. The solvent dissolves one or more of the substances and leaves behind the unwanted substances. Then it is shaken in a separatory funnel which forms layers in the solution. Some of these layers can be drained to leave you with the wanted material.

Distillation(Two Liquids): Mixture is heated, one substance has a lower boiling point than the other. It evaporates up a tube and then condenses on the other side. 

                                            

Chromatography: Used to separate very complex mixtures. A mobile phase is swept over a stationary phase. Components move over stationary phase at different speeds, allowing each components to be collected individually, producing very precise and accurate information.

    Sheet Chromatography

      Paper Chromatography: The stionary phase is paper soaked in a liquid. The mobile phase is a solvent. The results appear as dots on the paper.

      Thin Layer Chromatography: The stationary phase is Al 2 O3 or Si O2 which is an absorbent on glass. The mobile phase is poured over, some components bond with the absorbent, appearing as dots on the sheet.

Here is a very good video explaining many of the above mentioned separation techniques

http://www.youtube.com/watch?v=jWdu_RVy5_A&feature=related

Law of Multiple Prportions

Elements can combine in different ratios to form compounds

Such as NO2, NO, N2O or N2O5

Naming Acids

Alright wonderful people! If you haven't guessed, we're going to be learning about how to name acids!

Now because this is chemistry, and not computer virus class; I will not be teaching you how to corrupt files from 1992. BAD READERS.  BAD.

Acids are formed when a compound made of hydrogen ions and a negatively charged ion are dissolved in water. We call this state aqueous.

When acids are placed in water:

• Hydrogen combines with water
• Negatively charged ions dissolve in the water; separating them
• Hydrogen joins with water to form H₃o (an hydronium ion)

Here are basic guidelines to naming acids

meaning not EVERY acid is named this way, every rule has an exception

Simple Acids (group 16&17 of periodic table)

• use 'hydro' as your prefix
• this indicates that hydrogen is present
• last syllable of the non-metal is dropped
• the suffix 'ic' is used in it's place
• add the word 'acid' at the end
• _______ide --> hydro_______ic acid
• insert your ion into both blanks

Complex Acids 

• you do not use 'hydrogen' while naming complex acids
• your negative ion suffix will change according do its name
• ___ate is replaced with ____ic
• ___ite is replaced with ____ous
• add the word 'acid' at the end

-acids that end with 'ide' are considered simple-

Helpful Hint Honouring Hamish

Acronyms are extremely helpful when memorizing anything.

Here is one courtesy of a teacher:

we ate ic-y sushi and got appendic ite-ous.

chortle, chortle, it's so clever!

• the endings are together in this acronym, so it's pretty self explanatory.

If this post isn't clear enough; here is a website that can explain, and even has interactive excercises!

JY

Review: Naming and Writing Ionic and Covalent Compounds

In todays class we had a review for writing and naming ionic compounds. Listed below is a summary of the class :)!
Ionic Compound
-composed of two or more particles that must be oppositely charged
-electorstatic forces hold them together
-metal-->non-metal transfer

Example: Na^+ P^3-
=Na3P  (criss cross)
=Sodium Phosphide

Example: Fe^2+ S^2-                **use roman numerals when an element has more than one charge**
=FeO
=Iron(II)Oxide

Complex Anions
-group of atoms that act as one atom

Example:
a)zinc phosphate-->Zn3PO4
b)tin(II) permanganate--> Sn(MnO4)2
c)Pb(CO3)2--> lead(II) carbonate

Covalent Compounds
-share electrons
-non-metal with non-metal
**Diatomic molecules: H2, O2, F2, Br2, N2, Cl2, I2**
-use greek prefixes to indicate the nuber of atoms


Example:
a)CO2--> carbon dioxide
b)sulphur trioxide--> SO3

DONT FORGET TO DO YOUR HOMEWORK! ENJOY THE LONG WEEKEND! HAPPY THANKSGIVING :)!

Heating and Cooling Curves of a Pure Substance Lab 2B

Today in class we preformed an experiment in which we studied the properties of cooling and heating dodecanoic acid (C11H23COOH)

I would write down the answers to our investigations but my work in currently in the classroom, since Ms. Chen collected it after the lab. However here is a video explaining heating and cooling curves.

http://www.youtube.com/watch?v=DhZ3r9qp7Ik

Dodecanoic acid

KP

Concepts of Matter (warning: teal deer crossing)

Hello fellow chemists! To segway out of an awkward introduction and into the nitty gritty stuff; I present you a warning!

an online phrase commonly used in discussion forums as a response to previous posts that are deemed unnecessarily long and extensive; it’s short for Too Long; Didn’t Read.


Alright! So with our previous knowledge of matter, we are going to explore different concepts around matter. 

HEATH CHEMISTRY: pg 25-34, pg 36-39

Macroscopic changes in matter

• are changes we are able to see with our naked eye

Mixtures and Pure Substances

Mixtures are two (or more) kinds of matter that have visible components, they are also called impure
Solutions are substances that look uniform but are made of two (or more) different kinds of matter

• mixtures scatter light since it contains different visible components.



-insert irrelevant picture and caption here!- 

• this would mean we are able to separate the mixture into it's component parts
• With muddy water; we are able to use alum or lime to produce that a jelly-like substance that can be filtered out. This separates the substance into its component parts
• BUT, what if we described solutions like salt water as a mixture?
• we than imply that we can separate it into different components.

Distillation is the process of heating a liquid until it boils, capturing and cooling the resultant hot vapors, and collecting the condensed vapors.

•  distillation gives us a clue about how solutions can be separated
• With salt water, we are able to boil away the water. This leaves the salt behind, therefore, separating the components.

Only when we can no longer separate substances can we call it pure, however, sometimes it is extremely difficult to separate some substances. This could mean it could take years to discover impure properties of a substance (Say hello to the future advancements in science!)

Pure Substances are matter that are made out of the same particle

• pure substances have a constant boiling point and freezing point
• with water: 0° (freezing point) and 100° (boiling point)
• mixtures usually do not have constant boiling/freezing points

Heating/Cooling Curve

The curve shows the process in which a pure substance changes from solid to gas

The cooling curve is the opposite of the heating curve; going from top left to bottom right.

• Point A
• particles are closely pack together
• Point A-B
• heat is converted to kinetic energy
• substance starts to melt
• Point B
• point where it will either melt or freeze
• Point B-C
• exists in both solid and liquid state
• temperature remains constant
• melting/freezing point
• Point C
• substance is liquid
• Point C-D
• still in liquid state
• kinetic energy increases as particles move faster
• Point D
• begins to change into gas
• Point D-E
• exists in both liquid and gas state
• boiling point
• Point E
• all liquid is now gas
• Point E-F
• gas particles continue to absorb energy and move faster
• temperature increases as heating continues

Chemical and Physical Change

Density is a property of matter that describes volume

Chemical Changes are irreversible 

• produce new matter with different properties than the original matter
• When sugar is heated, it bubbles and turns black as well as a colourless liquid forming. When the black matter and liquid are mixed together it does not change back to the original sugar
• electrolysis
• matter decomposes to form new kinds of matter
• decomposition 
• of a pure substance in which they are separated into components

Physical Change is easily reversed

• it is a change of state 
• it does not appear to create a new kind of matter
• we are able to get the original matter back again
• When moth flakes are heated, the solid material disappears and a liquid is in it's place. If we allow the liquid to cool it changes into a solid. This solid has the same properties as the moth flakes.
• distillation
• of a pure substance in which they are separated into components that already exists

Compounds

Compounds are pure substances that can be decomposed into new kinds of matter

• They appear to be put together from simpler substances
• must be made out of 2 more kinds of atoms
• separated if there is enough energy supplied to separate the components
• not all compounds are made out of molecules; some are made out of elements

Ions are particles that have an electrical charge 

• to know which compounds are ionic and which compounds are molecular is to check them for conductivity

Law of Definite Composition

Law of definite composition is an experimental fact that defines that all compounds have a definite composition

• water is always made out of 2 hydrogens and 1 oxygen
• however, mixtures can have almost any composition desired

Law of Multiple Proportions

Law of Multiple Proportions explains that two or more compounds with different proportions of the same element can be made

• they do not represent the same compound
• they are just multiples of each other
• do not have the same proportions as mixtures

Elements

Microscopic Model is a smaller representation of matter, rather than macroscopic(which is seeing, smelling, touching)

Elements are pure substances that cannot be decomposed into simpler substances

• we assume elements are made out of only one kind of atom
• each element contains a different kind of atom
• elements can exist in solid, liquid, or gaseous state
• elements change state through changes in temperature

Molecules are particles made of more than one atom

• some elements exist in larger units
• have definite shapes and composition

Atoms are the smallest unit of an element

• are usually represented in spheres, spheres are used to suggest the relative size of the atom
• atoms in solid state are closely packed together in an orderly,organized pattern
• atoms in liquid state are still close together but; are no longer in an organized pattern
• atoms in gaseous state move very far apart and move into a straight line until it collides with another atom/container

Still alive and kicking everyone? Don't worry, if you've stayed to the end you get a cookie. But don't lie. I don't give cookies to people who tl;dr. People who tl;dr make me sad.

enjoy your weekend!

-JY