Percent Composition

Hello!!

We are going to talk about Percent Compositions!!!

(Isn't that what we use to calculate our marks?? you ask.)

Well... Kind of :)

It is actually: percentage by mass of a species in a chemical formula

Imagine a fruit pie that consists of strawberries, blueberries and blackberries.

and try to figure out how much of the pie is strawberry, blueberry or blackberry.

So back to chemistry.

Eg. What is the percentage composition of H^20?

Always assume you have 1 mole.

Total molar mass is 18g/mol

Molar mass of H^2 is 2g

                      O      is 16g

H^2 =  2g/ 18g  *  100%  =  11.1%

0      = 16/18g  * 100% = 88.9%

The results should  add up to 100%.

This is basically percent compositions!

see ya later!

More Mole Conversions

So we learned that there are 6 main mole conversions. So far we have learned only 4.

So what's the other 2?

Mole Conversion type 5:

Atoms to mass:

     # of atoms           x           1 mole               x         Mass of atom        
                                    6.022 x10^23atom               1    mole

Mole Conversion type 6: (it's the last one =D)

Mass to atoms

         Mass # (in the question)      x              1 mole            x        6.022 x 10^23atoms      
                                                             Mass of atom                       1 mole

This is the finale of types of mole conversion.

To make these kinds of questions "easier", you have to make a plan.

Always try to find the number of moles


See you next time

Mole Conversions

(Yup, there IS such a thing!!)

1) From particles <----> moles

• From particles ---> moles  

 Ex, 3.01 x 10^24  particles of C --->  mole

 3.01 x 10^24 particles   X       1 mole         =  5.00 moles

                                              6.022 x 10^23 particles

PS, Don't forget sig figs & units..

• From moles ---> particles/ molecules/ formula units

Ex, 0.75 moles  of CO2 ---> molecules

0.75 moles  X  6.022 x 10^23 molecules  = 4.5 x 10^23  molecules

                                   moles

Now, 0.75 moles of CO2 ---> atoms of O2

              4.5 x 10^23  molecules X  2 atoms of  O  = 9.0 x 10^23 atoms



2) From grams <----> moles
 

• From moles ---> grams

Ex, 2.04 moles of Carbon ---> grams

                 molar mass of Carbon = 12 g / mol
            
                 2.04 moles  x  12 grams  =  24.5 grams of Carbon
                                      1 mole

Ex, 0.341 moles of NO2 --->  grams 

       molar mass of NO2 = 46.0 g / mol

       0.341 moles  x  46.0 grams   =  15.6 grams of NO2  

                                         1 mole

• From grams ---> moles 

Ex,, 3.45 grams of Carbon ---> moles

        atomic mass of carbon = 12 grams

                  3.45 grams  x    1 mole   =  0.288 moles
                                       12 grams

Ex,, 6.2 grams of MgCl2 ---> moles

        molecular mass of MgCl2 = 95.3  grams

        6.2 grams  x    1 mole    =  0.065  moles

                                     95.3 grams

This is what we took so far.. Explain the rest next class!!! :D:D

THE MOLE

NO!   Not the animal, or the TV series, or the body thing!!!!

Soo, What is it then ???

Interesting question!

A MOLE is the amount of pure substance containing the same number of chemical units as there are atoms in exactly 12 grams of carbon-12 (i.e., 6.023 X 10^23). 

This involves the acceptance of two dictates -- the scale of atomic masses and the magnitude of the gram. 

Its a very huge number used as a relative comparison between substance. So 1 mole of a substance could weight more that 1 mole of a different chemical substance.

 

Equal volumes of different gases have a constant ratio..

ex,,   O2 : H   ---> 16 : 1        (16 & 1 are the atomic mass of the 2 elements)

          CO2 : H ---> 22 : 1

 It gets more interesting..

Avogadro's Number 

(Again, the scientific "Avogadro")

Equal volumes of different gases at the same temperature & pressure have the same number of particles. Since they have the same number of particles, the mass ratio is due to the mass of particles. 

Avogadro's number indicates that the amount of particles in 1 mole of any substance is 

6.022 x 10^23   particles / mole

By the way, relative masses of all atoms is measured in Atomic Mass Unit (aka, AMU)..  

Formula Mass

IONIC compounds >> Add AMUs

Ex,  Potassium Fluoride

atomic mass of Potassium is 39.1

atomic mass of Fluorine is 19

Therefore, 39.1 + 19 = 58.1 amu

Molecular Mass

COVALENT compounds >> Add Masses

 Ex, Carbon Dioxide (CO2)

atomic mass of Carbon is 12

atomic mass of Oxygen is 16

There are 2 atoms of oxygen..

Therefore, 12 + 16 + 16 = 44 amu

Molar Mass

Mass of 1 mole of an element.. 

Unit >> grams per mole  ( g/mol ) 

Ex, 1 mole of oxygen = 16.0 g/mol

I bet you are saying to yourself,, " myself,, what is the whole point of this??"

I'll tell you what.. IT ALLOWS CHEMISTS TO COUNT ATOMS AND MOLECULES EASIER (yes, it is a big deal!!)..


You've all heard of Mole Day,, (no, not really)...
Well it is on Oct 23rd from 6.02 am till 6.02 pm ..

Check out this Song ::

Thanks for stopping by.. ;)

Ch.3 Review

Last class, we had a review of chapter 3.


Things to know:

Significant Figures

Measurement and Uncertainty

Scientific Notation

Density

Graphing

Unit Conversion


Good luck on the Test

Density Graphs

Last class, we went to the computer lab to make a density graph of cold water and hot water.

LAB 2E!!

Hey

Last class, we did a lab from Essential Experiments for Chemistry!!

We are going to go over what we did.

Our Purpose was to use scienticfic notation and significant figures after determining both volume & density  
                            of an Aluminum sheet.

We measured the length and the width and the mass of the sheet. Then we figured out the density.

Follow up Questions

1. A rectangular metal tray (22.55cm by 15.33cm) plated with thin layerof gold (density: 19.32g/cm3).
Gold plating mass : 0.0538g. Calculate the thinkness using scientific notation and number of sig. figs.

First, write the general formula of density.

                          D =     m   
                                     V

Then plug in numbers.

                  19.32g/cm3 =   0.0538g   
                                              V
                   
                               V    =   0.0538g     
                                           19.32g/cm3

                                 V  =   2.78 x 10-3cm3

Calculate thickness or height

                         V = LWH
                 
                 2.78 x 10-3 = 22.55(15.33)H

                          H =   2.78 x 10-3
                                   22.55(15.33)

                       H = 8.06 x 10-6cm

2. 1000.0cm3 of oil. Surface area = 850.0m2. Density: 0.850g/cm3
    How thick was the oil?

Ok, first there is some irrelevant info here.

Density info is not need because we need to find height or thickness

Therefore, write equation for volume.

                   V = LWH

Dont forget to convert m to cm

                1000.0 = 8.50 x 106(H)

                    H =  8.50 x 106  
                             1000.0

                   H = 1.76 x 10-6cm

Thats it for today!

Good nite!

Written by JK Nov 4,2010

Density!!

Hi everyone!

We are going to teach you about density.

DENSITY is just mass contained in a given volume of a substance.

Before we go on, enjoy this cartoon.



Hahaha I hope you are laughing!!

Back to chemistry.

Density is represented by the formula :

                              Mass(g)      

                            Volume(cm3)

Basically, if density of an object is greater than the density of the liquid then it will sink

If the density of an object is less than the density of the liquid then it will float.

Written by JK (Nov2,2010)

Measurement and Uncertainty

Hello

We are going to cover measurement and different types of uncertainty.

There are some rules that you need to know regarding Measurement and Uncertainty

• no measurement is exact
• every measurement is a best estimate which has some degree of uncertainty
• only when we count a set of objects, we get an exact number

Absolute Uncertainty

This is expressed in units of measurement; not ratio

In order to express uncertainty:

• Make at least 3 measurements
• Calculate average
• Absolute uncertainty is the largest difference between the average and lowest or highest reasonable measurement
• Discard unreasonable data

Eg.1  47cm, 48cm, 45cm, 46cm
          
Calculate the average of these numbers ((47+48+45+46)/4)) = 46.5

Then calculate the difference 46.5- 45 = 1.5 or 48 - 46.5 = 1.5 (does not matter because the result is the same)

Therefore + 1.50cm is the absolute uncertainty.

Absolute uncertainty:

This is determined by uncertainty of each instrument

• Always measure to the best precision
• Estimate to 1/10 or 0.1 of the smallest segment of the instrument scale

Eg.
Take a ruler

The smallest scale is 0.1cm
0.1 of the scale is 0.01 cm
Therefore the absolute uncertainty is 0.01cm

This is how you express it: (the average value) + (absolute uncertainty)

 Eg. 15.6 + 0.03cm

Don't forget the units.

Relative Uncertainty

Relative Uncertainty is absolute uncertainty/estimated measurement
It is expressed in percent or significant figures(the number of significant figures indicates relative uncertainty; the last digit is uncertain)

Written by JK (Oct 31,2010)

Accuracy and Precision

Hello

We are going to explain what accuracy and precision is.

The Textbook says that:

ACCURACY is how close the measurement (or average measurement) comes to real value

PRECISION is how reproducible a measurement is compared to other similar measurements


Written by JK (Oct 31, 2010)

Significant Figures

Hello how are you doing?

Ready to learn more new stuff about chemistry.

We are going to teach you about "Significant Figures" or for a lack of a better expression: How to write you math answers correctly.

I know that right now you people are going to be like "Why are we learning math?", "Isn't this physics or something?" and yapping about how this isn't chemistry.

This part is about units and writing them properly.

Significant Figures are not very big or small numbers, it is MEANINGFUL NUMBERS

There are some rules that you need to know:

• Last digit of a number is uncertain
• That number can be either one digit higher or lower

Eg: Take 2.56g ; numbers 2 and 5 are certain however 6 is uncertain therefore it can either be one digit higher(7) or lower(5)

• Significant Figures  includes all certain digits plus one uncertain digits

There are some exceptions

• Leading zeros DON'T count (eg. 0.01 has 1 sig. digit because 0.0 are leading zeros)
• Trailing Zeros COUNT (eg. 10.050 has 5 sig digits because 0 after 5 is trailing and 0's before 1 and 5 are between certain numbers)
• Trailing zeros without decimal point DON'T count (eg. 12000 has 2 sig. digit because 0's after 12 is not stopped by a decimal)

NOTE:

Some quantities are exact meaning no decimal mubers

Eg. pair of shoes are always 2 shoes

       1 dog not 0.75 dog

       1m = 100cm

These numbers are decided so think carefully.

                                                                                  

Rounding:

Rounding numbers are basically the same as what you would do in math class

However with one set of EXCEPTIONS:

1. Look at the digit after the number you have to round
2. If that digit is greater than 5, round up
3. If that digit is less than 5, keep the same
4. If that digit is equal to 5 and there are more digits after, round up
5. If that digit is equal to 5 and it ends at the 5, make the last number even (eg. 0,2,4,6,8) 

                                                                          

Adding, Subtracting, Multiplying and Dividing:

When adding or subtracting round to the fewest number of decimal places

Eg.  12.544g
       + 1.3g    
         13.844g

In this case you have to round to 1 decimal place because 1.3 has fewer number of decimals than 12.544 so the answer becomes 13. 8g

Eg.  12500mL
       + 6000mL
         18500mL

In this case, you have to round to the thousands because that is fewer digits than 12500 so the answer becomes 18000mL 

When multiplying or dividing, round to the fewest number of significant digits:

Eg.  12.54m
       x  1.3 m
        3762
    +12540
       16.302square meters

In this case, you should round the answer so that there are 2 significant digits so the answer becomes 16meters squared

                            9.646m
Eg.   1.3m |  12.54m
                      117      
                           84
                           78
                             60
                             52
                               8

In this case, the answer is 9.6m because 1.3 has 2 sig. digits and 12.54 has 4 sig digits.

REMEMBER:

Always use the rule: round to the fewest sig. figs for multiplying and dividing

Thank you for tuning in. We will see you next time

Ciao!

Written by JK (Oct 27,2010)

Summary of Textbook (p25-34, 36-39)

Hello

Today we are going to explain CH.2 of the Chemistry textbook.

From the previous posts, we explained to you that matter is everything around us.

However to understand matter fully, we must look at it on a macroscopic level.

This is like look at the sand on a beach.

If we see this sand from far away, all we see is a blob of light brown.

However, if we look closely, we can see the individual grains of sand.

In our world, matter can be in a form of a mixture, which is formed with 2 or more kinds of matter that have separate identities.

Classifying matter into either a pure form or a mixture is a big step in unders
tanding matter.

You can make a mixture by simply adding stuff to your water maybe Kool-Aid or sweetners.
Sometimes, you can find a mixture that does not scatter light and looks uniform throughout. These mixtures are called solutions.

Mixtures can be separated by using different procedures(eg. distillation).

There are few characteristics that you should know about Pure Substances:
actually you need to know this fact: the melting point and the freezing point of a pure substance is the same!!

(Info of chemical and physical changes: refer to "Changes in Matter" article)

There are few rules that you need to know (in general)

Law of Definite Composition: The compounds will have a definite composition.

Law of Multiple Proportions: The fact that two or more compounds with different proportions of the same elements.

(For summary of p36-39) refer to "All about Matter!!" article.

Thanks for tuning in.

Written by JK (Oct4,2010)

PS been edited a few times

More Details in Separation (Hehehe...)

Helloo!! We are back.

We are going to tell you more about different separation techniques.

Hand Separation:

• Used usually for mechanical mixture or heterogeneous mixtures
• separation by a hand, magnet or a sieve
• Evaporation which is solid dissolved in liquid solution or boil away the liquid and solid remains

Filtration:

• deals with solids(not dissolved) and liquids
• passing a mixture that contains solid particles through a porous filter
• the liquid pass through the filter and residue is left on the filter
• separation by using filter paper

Crystallization:

• solids in liquids
• Precipitation: conversion of a solute to solid form by chemical or physical change
• after, solids are separated by filteration or floatation
• saturated solution of a desired solid evaporate or cool - solid come out as crystals

Gravitiy Separation:

• solids based on gravity
• centrifuge whirls the test tube around at high speed forcing the denser materials to the bottom
• Works best for small volumes

Solvent Extraction:

• a component moves into a solvent shaken with the mixture
• works best with solvents that dissolve only one component
• For mechanical mixtures: use liquid to dissolve one solid but not the other so that the desired solid is left behind or dissolved
• Solution: solvent is insoluble with solvent already present

Distillation:

• Heating a mixture creates vapour
• collecting and condensing vollatillized components
• liquid with lowest boiling point boils first
• vapour ascents to distillation flask and enters condenser
• gas cools and condenses > back to liquid and distillates as a purified liquid

Chromatography:

•  Flow mixture over a material and different components goes in different speeds and stops
• mobile phase sweeps the sample over a stationary phase
• can separate complex mixtures
• very small sample sizes; analysis is highly accurate and precise
• separated components can be collected individually

Paper Chromatography:

•  Stationary Phase: liquid soaked into sheet of paper
• Mobile Phase: liquid solvent some components spend more time in the stationary phase than others after drying; spots appear on the paper

Thin layer Chromatography (TLC):

• Stationary Phase: thin layer of absorbent (Al203 or SiO3) coating a sheet of plastic or glass
• some components bond to the absorbent strongly; others more weakly
• appear as spots

Written by JK (Oct 18, 2010)

Separation Techniques

Hello everyone, we are back again.

Today we will talk to you about basics of separating different components and properties.

Separations are all about mixtures and distinguishing the different components and properties in them.

 Before we learn the different techniques to separate mixtures, we need know a few things. :D

• Components in a mixture do not lose their identities

• Components have different properties

• More similar the properties are, more difficult it is to separate.

Also one more thing, when you want to separate a mixture, you need to have a strategy which is to devise a plan with the different techniques to discriminate between components with different properties.

Now onto the different types of separation:

Filtration: This method separates the components by particle size.

Filtration

Floatation: This method separates the components by density.

Crystallization: This method separates the components by solubility(ability to dissolve).

                                 

 Extraction: This method separates the components by solubility.

                                  

Distillation: This method separates by boiling point.

                               

Chromatography: This method separate components by affinity for a stationary phrase.

                                         

Now you have learned the different types of separation.

Tune in soon to learn more about separation in detail.

Written by JK(Oct, 18/2010)

How to Name Complex Acids

Hello we are back with more acids!! (AHHH!! It's burning my face!!)

Here are the rules:

1. any polyatomic atoms(that are negatively charged) that end with --ate replace with --ic
    any polyatomic atoms(that are negatively charged) that end with --ite replace with --ous

2. Put "acid" at the end

Examples:

HCH3C00 - acetic acid (CH3C00 is acetate which you need to replace with --ic)

HClO3      - chloric acid (ClO3 is chlorate which you need to replace with --ic)

HClO2      - chlorous acid (ClO2 is chlorite which you need to replace with --ous)

H2SO3      - sulphurous acid (SO3 is sulphite which you need to replace with --ous)

So this is basically how you name acids!!! :D

Thanks for tuning in!! Bye!


Written by JK (Oct 14,2010)

How to Name Acids

Acids are formed when a compound compsed of hydorogen ions and negatively charged ions become an aqueous or dissolved in water.

*Note: all numbers underlined are subscripts.

In water, these ions separate when dissoved. Also hydrogen ions join with H20(water) to form H30 (hydroniums)



Eg. H+ Cl - => HCl

       HCl (g) +H20 => H30 (aq)  + Cl (aq)

Guidelines in Naming Acids:

For columns 16 and 17, use simple acid formulas.

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

Eg.

1. HF(aq)  -  hydrofluoric acid

2. HCl(aq) -  hydrochloric acid

3. HBr(aq) - hydrobromic acid

4. HI (aq)  -  hydroiodic acid

5. H20 (aq)  - water  :D

6. H2S (aq) - hydrosulphic acid

7. H2Se (aq) - hydroselenic acid

Written by : JK (Oct 14, 2010)

Answers from the changes in matter questions

Here are the answers:

a) physical change because fog is water vapour that is condensed into droplets of moisture

b)chemical change because new substances are formed: smoke and cancer cells-causing chemicals)

c)chemical change because the growth involves chemicals being produces and used up

d)chemical change because rust is a new substance formed by combination of iron, air and water)

e)physical change because no reaction has occurred to make new substances

f) physical change because we are only separating substances, not producing new ones

If you got perfect, you are ready to go but if you got less than 4 you need to study... :(

Written by JK

Changes in Matter

There are 2 main changes in Matter : Physical and Chemical

In a Physical Change:

no new substance is formed

the chemical composition does not change

it is reversible (you can drink water(liquid) if you melt ice :)

Eg. boiling point, melting point

In a Chemical change:

it is irreversible (you can't undo a salad dressing)

new substances are produced

Eg. burning, cooking

So these are the basic changes in matter

Here are some questions that you can answer.

Classify each of the following as either chemical or a physical change

a) formation of a fog
b)burning a cigarette
c)sprouting of a seed
d)rusting of iron
e) mixing yellow and blue paint to make green paint
f) separating an alcohol- water mixture into water and alcohol

The answers will be up shortly!

Written by JK

All About Matter!!

Do you guys know what matter is??

(you say: NO, what is it??)

Matter is anything that has mass and volume a.k.a everything around us

MATTER can be broken down into 2 categories:



Calcium

PURE SUBSTANCE:  only one set and kind of properties

MIXTURES: more than one set of property and substance

                       physically combined

These categories can be broken down further.

PURE SUBSTANCES can be broken down to 2 more categories

ELEMENTS: simplest form (cannot be decomposed) and made up of atoms

                         ie. metals, metalloids, non-metal

COMPOUNDS: made up of elements

                              chemically combined

                             smallest particle (molecule)

     

                         ie. ionic, covalent

MIXTURES can be broken down to 2 more categories.

HOMOGENEOUS MIXTURES:

uniform throughout

appears to have only one component

ie. solution

HETEROGENEOUS MIXTURES:

not uniform

appears to have more than one component

ie. water and oil, salad dressing

can be broken down further to : SUSPENSION, MECHANICAL MIXTURE

In conclusion,

I hope that you guys unders

How to Do Unit Conversions (PART II)

Hello, we are back again.

Few days ago, we introduced the concept of unit conversions and showed you a simple example.

Today we are going to show you how to do complicated examples

Lets take this example.

Convert 50km/h to m/min

First, look at the question to find what needs to be converted.

You can see that the km and the h needs to be converted.

Before you make an equation, lets write out the conversions

10^3m = 1km  ;      60min = 1hr

Now lets make an equation.

50km x  10^3m x     1hr     =      
  1hr          1km      60min   

From here you need to cancel the units

50km x  10^3m x     1hr     =      
  1hr          1km      60min   

After you do multiplication:

                 50x10^3
                      60
and the result is 833.33 or 8.33x10^2m/min.

This is basically what unit conversions are about.

Written by Jk

Brief Review of Scientific Notation

Yesterday, we taught you the basics of unit conversion.

Today, we will guide you through more questions that are complicated but not so hard if you follow our way.

First, before we do any questions, we need to review SCIENTIFIC NOTATION.

Scientific notations are used to express really big and really small numbers such as 500billion or 0.000000000000003333 using powers of 10.

One thing to note here is that the number that is constant is bigger or equal to 1 but less than 10.

Example:

Express 25,100,000,000 in scientific notation.

First we need to make a constant number that is more than 1 but less than 10.

As you can see, I made a constant number from the original number.

In this case, the number we need is 2.51

The Next step is to count the zeros from the original decimal to the decimal of 2.51




              

 







On the above, I moved the original decimal point to the new decimal point.

As I did that I counted how many digits until the decimal of 2.51. In this case there are 10 digits.

Now you put all of it together.

Take the constant number and multiply it at the 8th power of 10

The result would be 2.51 x 10^8

I hope that you will have an easier time with scientific notations and hopefully with unit conversions.

See you next time!

Written by: JK (Sept 21,2010)

How to Do Unit Conversions (PART I)

Before we start doing any crazy chem labs and experiments, we need to learn how to do Unit conversions.

This will be fairly easy for those who are adept at math.. to those who aren't... deal with it.

First, unit conversion is simply converting the original numbers into the same number with different units.

NOTE: CONVERSION FACTOR: fractional expression relating or connecting 2 different units

I am sure that you know how many cents are in a dollar or how many minutes are in a hour.

When you change certain amount of cents into dollars (ie. 25cents →$0.25), you are also converting units.

Also, take a good look at the unit conversion table that Miss Chen gave us.

Now on to some basics:

Incredibly, vitally important NOTE:

You must ALWAYS include the UNITS. or else you will get confused and get the wrong answer.

Example 1:

If a car can go 80km in 1 hr, how far can it go in 8.5hrs?

In this question, simply do a math ratio, it is the easiest way.

                                       80km      (x)km
                                          1hr         8.5hr

From this do cross multiplication:

                                  (80km)(8.5hr) = (x)km
                                           
After you multiply you get this number 680km

This is the basics of unit conversions, part 2 coming soon

Check out this video from Youtube which gives a different but effective way of doing unit conversions:

http://www.youtube.com/watch?v=ClxIsX9JV-M

Written by: JK