Joke of the day :D

A neutron walks into a bar. He asks the bartender, "How much for a beer?" The bartender offers him a warm smile and says, "For you, no charge"

Significant Figures!

One of the great things about science is that nobody's perfect (for some of you, that may take a little getting used to!)No measuring device can measure any quantity exactly, so one must remember the uncertainty in every measurement when using them in calculations.

Digits in a measurement that are important for it are called significant figures (or significant digits). Using them keeps us honest, because we are prevented from seeming overly precise in our work.

In order to present results with the proper precision, we need to know how many significant figures are present in each number we use in a calculation. There are four basic rules:

1. Zeroes in the beginning of a number never count.
2. Zeroes at the end of a number count only if there is a written decimal point.
3. The digits 1 - 9 always count.
4. Zeroes between the digits 1 - 9 always count.

So how many significant digits are present in the following numbers: 5, 51, 55, 510, 501, 5010, 5010.0, 5.0, 0.00501
(the answers are 1, 2, 2, 2, 3, 3, 5, 2, 3).

When adding or subtracting, the answer can only be as precise as the least precise number used. For example, a 250 pound person who has a hair pulled out (say, 0.001 pounds) still weighs 250 pounds. That's because the last significant digit is the 5 (in the tens place), and everything after that is not even estimated. So you have no idea how many ones of pounds the guy weighs, or how many tenths, or hundredths, or thousandths. Therefore, you have no idea what from to subtract 0.001 pounds. So he still weighs 250 pounds.

When multiplying or dividing, the answer has the same number of significant digits as the number used with the least. For instance, there is a quick estimation of pi (p) as 22¸7. On a calculator, that gives 3.1428571423, which is pretty close. But if you had measured a circle as 22 feet around and 7 feet across, the answer must be rounded to "3" to match the least number of significant digits.

*remember*
when multiplying/dividing, round it to the fewest number significant digits.


VIDEOS! :) .. on significant figures

Lab 3B Summary

Today, we did a lab, Separation of a Mixture by Paper Chromatography.  

Paper chromatography is a modern method used separate mixtures. Paper chromatography uses paper as the stationary phase and a liquid solvent as the mobile phase.

The purposes of this lab were to separate mixture of food colorings into their components and to identify the components of mixtures by means of their Rf values.

Materials we need: 3 large testtubes, 3 Erlenmyer flasks, 3 strips of 22 chromatography papers, food colourings,  a pencil, a ruler and a calculator

The procedures of this lab would be:

Part I

1. draw a line across each strips of chromatography paper 4.0 cm from one end, then trim the end of the strip
2. place 2.0  cm deep water in each testtube
3. spot one strip with the color, label, and insert the strip in test tube A
4. observe what happens
5. identify two front on the paper after the next 10 min
6. start part II as the movement slow down
7. after 20 min, remove the strip and immediately draw a pencil line across the top edge
8. measure d2 and d1 and record in Table 1 and 2
9. clean up

Part II

1. spot the second strip of CP with a sample of green food coloring, and spot the third CP with an unknown mixture
2. insert the strips and follow the same procedures in part 1
3. record data

So, Here's a great video about color chromatography. Watch it and you would know more about this lab!!

Separation Techniques

So Last class we did a notes from Miss Chen Notes. Here's all the info .
*Basis for separation : Different components , Different properties.
*Strategy: Devise a process that discriminates between components with different properties..

High Density/Low Density

Volatile/nonvolatile

Soluble/Insoluble

...

Separation

*Components in a mixture retain their identities: mixtures components have different porperties

Some Basic Technic:

-Filtration: Select component by particle size.

-Floatation: Select component by density

-Crystallization & Extraction: Select component by Solubility

-Distillation: Select component by boiling point.

Hand Separation & Evaporation

-Hand separation (solids and solids)

*mechanical mix or heterogeneous mix can be separate by using magnet or sleeve

-Evaporation (solid dissolved in liquid solution)

-Boil away the liquid and the solid remains.

Filtration: (solids(not dissolved)and liquids)

-Pass a mix that contains solid particles through a porous filter.

-If pores are smaller than particles,solid particles stay on filter and liquid/gaseous components pass through often used after separate by precipitation

-Use filter paper- residue left in

Crystallization (solid in liquid)

-Precipitation: Converse solute to solid form by chemical or physical change.

-Solids are separated by filtration or floatation.

-Evaporate or cool - solid comes out as pure crystal.

Gravity Separation: (solids based on gravity)

A centrifuge whirls the test tube around at high speeds forcing the denser materials to the bottom. Workds best for small volumes.

Solvent Extraction
-Component moves in a solvent shaken with mixture.
-Mechanical Mixture (solid and Solid) use liquid to dissolve one solid and the other one dissolved.
-Solution: Solvent is insoluble with solvent already present. Solvent dissolves one or more substances and leaves unwanted substances behind.

Distillation (Liquid in Liquid Solution)
-heating a mixture can cause low-boiling components to volatilize (vaporize)
-Distillation is collecting and condensing volatilized component.
-Liquid lowest boiling temperature , always boils first.

Chromatography
-Flow the mixtures over a materials that retains some components more than others
-Mobile phase sweeps the sample over a stationary phase (as the wind sweeps the swarm over the flower bed)
-Separate very complex mixtures

Sheet Chromatography
-Paper chromatography (PC)
Liquid soaked into a sheet in stationary phase ,some take longer than others
-Thin layer chromatography (TLC)
Stationary phase is a thin layer of absorbent (Al2O3 or SiO2) coating a sheet of plastic bond the absorbant strongly and other weakly.

Naming Acids

Last class we learnt about Acids and their formulas. You may not know how to determine an acid if you just saw their formula, but that's what these notes are for. Once you're done reading these notes, (hopefully) you'll be an expert at naming acids and writing their formulas. If not, just ask Ms. Chen for help :p

First of all, we need to know how an acid is formed.

Acids

An ACID is formed when a compound composed of HYDROGEN ions and a negatively charged ion are dissolved in water. (Aqueous -aq-)

- Ions separate when dissolved in water

- H ion joins with H2O (water) to form H3O (Hydronium Ion)

Ex. H + Cl --> HCl(g)

      HCl(g) + H2O(l) --> H3O(aq) + Cl(aq)

Naming Acids Guidelines (Simple Acids)

1. Use "hydro" as the beginning

2. Last syllable of the non metal is dropped and replaced with "-ic."

3. Add "acid" at the end.

* ____ide -> hydro____ic acid

Example. Name the SimpleAcids:

1. HF(aq) - Hydrofluoric acid

2. HCl(aq) - Hydrochloric acid

3. Hbr(aq) - Hydrobromic acid

4. HI(aq) - Hydroiodic acid

Naming Complex Acids

1. -ate replace with -ic

    -ite replace with -ous

2. "Acid"at the end of the name.

Example. Name the Complex acids

1. HCH3COO(aq) - Acetic Acid

2. HClO3(aq) - Chloric Acid

3. HNO2(aq) - Nitrous Acid

4. HClO4(aq) - Perchloric Acid

Here's a website for you to practice what you've learned. 

http://faculty.msugf.edu/wenz/CHMY%20121/Handouts/Naming%20Acids%20Practice.pdf

Have fun :)

Writing and Naming Ionic and Covalent Compounds

Okay, so today we did a review on Ionic and Covalent compounds which we all learned from last year. If you dont recall any of the terms. Well then here it is.

Ionic Compounds

• contain electrically charged particles called ions
• ions can be positive or negative
• they attract each other strongly because of their opposite charges
• the number of positive charges must equal the number of negative charges in a compound

For example: 

iron (III) sulfide

Example: 

Covalent Compounds

• share electrons
• non-metal with non-metal
• all covalent compounds have two word names
• the first word correspond to the first element in the formula and the second corresponds to the second element in the formula except it ends with "ide"

For example:

Name: Carbon Dioxide

For Example: HF

Name: Hydrogen Fluoride

If there is more than one atom of an element in a molecule, we need to add prefixes to these words to tell us how many are present.  Here are the prefixes you'll need to remember:

*NEED TO KNOW*
Diatomic molecules [highlighted in pink]

VIDEOS! 

 Covalent Bonding ... Or not! 

( Examples of ionic and covalent bonding)

Lab 2B

Today, we had a lab.  It's on heating and cooling processing.  The purpose of this lab is to investigate the heating and cooling process, and to determine and compare two of them.  We did the cooling process first and here is the procedure:

1. put on safety equipment
2. decide the roll (observer or recorder), prepare table 1
3. obtain a test tube consisting of a themometer, remove the cotton plug and save it
4. put 300mL 30-35'C water in a 400 mL beaker
5. set up a ring stand, a buret clamp to hold the test tube
6. put the testube assembly into cold water
7. record the temperature every 30s
8. record when the solidification begins and ends and other observations
9. stop when the temperature reach 25'C

then, we started the heating process immediately, and the procedure is

1. change the roll
2. turn the plate on and raise the temperature to 55'C and 60'C
3. turn the hot plate to low heat when it reaches 55'C
4. record the temperature in table 1 and every 30s after that
5. readings should continue until it reaches 50'C
6. record the times when melting beings and ends. 
7. reseal the test tube assembly with the cotton plug and return all the equipment
8. qash your hands with soap and water before leaving

After the lab, we got to draw a heating and cooling curve.  The graph should probably look like this:

Joke of the day

Two atoms are walking down the street.

Says one atom to the other, "Hey! I think I lost an electron!"

The other says, "Are you sure??"

"Yes, I'm positive!"

hahaa .. (ya i know. its not that funny) 

Summary of 2.3, 2.4, and 2.7

Finally! It's the weekend now we can relax and do our science review!! Oh ya..science review. Anyways, here's a short summary of the pages assigned by Ms.Chen to read and take notes on. Enjoy.


2.3 Characteristics of Pure Substances p.28
- Pure substances have a constant boiling point
- Mixtures ordinarily don't have a constant boiling point (however, a few do)
- Freezing Point: The temperature a liquid changes to solid
- Melting Point: Temperature a solid turns into a liquid

2.4 Chemical and Physical Changes p.30
- Density: Property of matter that describes its mass per unit volume
- Sugar and Baking powder do not have a melting/freezing point because a new substance is formed when                    
   heated or cooled.
- Chemical Change: Changes that produce a new kind of matter and cannot be reversed. (ex.Cooking an Egg)

- Decomposition: One kind of matter decomposes to form 2 or more kinds of matter.
- Melting: Change of a solid to a liquid without the formation of a new kind of matter. (Ex. Melting ice.)

- Physical Changes: Changes that are easily reversed to get the original material back again.

2.7 Atoms p.36

- Atom: The smallest possible piece of something

- Not visible

- Idea of atoms in matter began in the 1800s

Thanks for reading. :)

Compounds and Elements 2.5 +2.8 summary

Now we all know that pure substances is made up of only one kind of matter and has a unique set of properties, such as; color, hardness, boiling point and melting point.

So, for example: If you were to add sand with water then its no longer a pure substance. The property changes and so does the mixture.

A pure substance is

• either an element or a compound.

Example:  Carbon [ C ] is an element and sugar [ NaCl ] is a compound.

Electrolysis is the production of a chemical reaction by means of an electric current.

Here's a video showing the electrolysis of water.

MORE facts about elements.

• it cannot broken down / decompose
• there are 109 elements
• it can exist as a solid, liquid, or gas
• can exist as an individual or as larger units
• have different melting and boiling points

Molecules 

• made of more than one atom

Finding Out about Matter (Summary of page 25-28)

Matter in the Miscroscopic World
How do you observe when you just look at the picture
How can you describe what you see so that others can understand results of careful observation?
These are the questions you will explore in taking a closer look at matter!
Science applies the same skills you use to interpret the picture to make increasingly presice observationand detailed interences.  Detailed observation takes so much time and effort that it is necessary to speciallize.
Chemists specialize in matter; what it is, how one kind differs from another, what differencekinds have in common, how one kind can be changed to another, and even how mateer can be kept the same.

2-1 What You Know about Matter
By living in a world of matter, you have learned a tremendous amout about the subject.  (ex. water normally exists as a liquid)  A variety changes can be understood using a few powrful ideas may be even more amazing to you now.  To see how a few ideas can explain a lots of observation, you will learn to specialize, you will look carefully at a few familiar substances , classify them, and make generalizations about them based on the reqularities you see.


Property

• characteristic of matter
• describe matter specifically and can be used to identify matter
• ex. colour, tast, boiling point
• part of the study of science is the accumulation of such information
• another part is using the information you have to make sense of the world by decribing it with increasingly greater precision

2-2 Purify Matter 
Mixture - Matter that is easily separated into component parts. It is impure.
Classifying matter into pure forms and mixtures is one step toward understanding matter and developing a language to describe that understanding.  It is based on experience.  Chemists derive the idea of mixture and pure substance to describe matter.

People purify water by adding alum and lime to the water, and a gelatinous material is produced.  As this gelatinous material settles out or is removed by filtering through  beds of sand, small particles suspended in the water stick to the gelatinous material and are removed.

Scattering cannot be used as a test of whether a material is pure.  Mixtures like salt water or sugar water that look unifrom throughout and do scatter light are called solutions.

Salt water cna sugar water can be separated into their component parts using a procedure called destillation.

Although most mistures containing water can be separated by distillation, some cannot.
ex. household ammonia, whisky

Many mistures are difficult to separate .  Such mixtures may be considered pure for many years until someone invents a new procedure or a better instrument for analyzing and separation.  Many environmental conerns have come about because new and better techniques have been found to detect thier impurities.

Video: Classifying Matter and Pure Substances

 

Video:  Solution and Classifying Matter

Summary of pg 34(2.6),36,38(2.9)

p.34 (2.6)
Compounds have a definite composition: Elements can't decomposed,compounds are the elements together. However ,not all combination of elements are combination. Hydrogen and oxygen gases produced when water is decomposed can be mixed together in any proportion, the result will be colorless,odorless gas like air. The difference between mixture of elements and compounds of elements: mixture of elements can have almost any composition desired and compounds will have definite composition, the experimental fact is called the Law of definite composition. Every compound has a definite composition, it is possible to make several compounds from the same elements. The fact that two or more compounds with different proportions of the same elements can be made is known as the Law of multiple proportions.

p.36
Macroscopic observations(macro means large;scopic means viewing or observing) is what you see,feel or smell .
Macroscopic properties are melting point, boiling point,heat of fusion ,temperature, and mass are all properties of large chunks of matter .
Atoms: the word atom means this smallest possible piece of something., they are normally spheres of various size and colors.

p.38(2.9)
Compounds: All compounds must be made of two or more kinds of atoms. Since compounds are made of two or more kinds of atoms,the different atoms can be separated if enough energy is supplied to break the compound apart. Heat and electricity are forms of energy ,and both heating and electrolysis can supply the energy to decompose the compound . Like elements ,compounds exist in 3 forms: Solid,Gas,Liquid. For example: when ice melts or water boils, the molecules come unstuck, but the atoms do not.

Here is a video of how atoms are made
http://www.youtube.com/watch?v=qmgE0w6E6ZI

The Heating/Cooling Curve of a Pure Substance

State A 

• solid
• closely packed particles
• forces between particles are strong 
• only vibrate at a fixed position   

State A-B

• heat is converted to kinetic energy
• energy increases
• vibrate faster
• temperature increases

State B

• solid starts to melt or freeze

State B-C

• solid & liquid states
• constant temperature = melting point

State C

• completely melted
• solid turns to liquid

State C-D

• in liquid state
• molecules gain heat energy + temperature continue to increase
• particles move faster and faster ( because kinetic energy is increasing)

State D

• still in liquid state
• molecules starts to move freely

State D-E

• exist in liquid - gaseous states
• temperature is unchanged
• constant temperature = boiling point

State E

• liquid to gas

State E-F

• moves faster ( as gas particles absorbs energy)
• temperature increases

 So that's basically what we did in class last friday. We took some notes and did some reading about  MATTER, which you will find out more later on after we "summarize" what's in the textbook.

Now here's  the song of the day for your own pleasure.
Its called the "Atom Rap"
Enjoy!