Calculating the Empirical Formula of Organic Compound

Today we've learned how to calculating the empirical formula of organic compound, well, it is sort of complicated, but if you follow step by step you will find out it is not hard at all !!

So, to get started, lets know what is an organic compound.
-An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon.

The empirical formula of an organic compound can be found by:
-Burning the compound
-Collecting and weighing the products
-From the mass of the products, the moles of each element in the original organic compound can be calculated


Ex. What is the empirical formula of a compound that when a 5.00 g sample is burned produces 15.0 g of CO2 and 8.18 g of H2O?

First let the empirical formula of the compound be CxHy
CxHy  +  z  O2  =  x  CO2  + y/2  H2O

We want to find x and y (the simplest ration of the atoms or moles of the elements).
From the equation above, we can see that ALL of the C and the H in CxHy went into making x CO2 and y/2 H2O

mol CO2  = 15.0 g CO2  x 1 mol CO2 / 44.0 g CO2 = 0.341 mol
mol H2O =8.18 g H2O x 1 mol H2O / 18.02 g H2O = 0.454 mol

0.454 moles of water and 0.341 moles of Carbon dioxide were produced

mol C = 0.341 mol CO2 x 1 mol C / 1 mol CO2 = 0.341 mol  C
mol H = 0.454 mol H2O x 2 mol H / 1 mol H2O = 0.908 mol H 

Divide both by the smallest molar amount 

Carbon  0.341 / 0.341 = 1
Hydrogen  0.908 / 0.341 = 2.66


Scale ratio to whole numbers


2.66 x 3 = 8  H
0.341 x 3 = 3  C


   C3H8

Percent Composition

It is a percentage that you can calculate the mass of one of the elements in a chemical formula.

The Questions of the Fives:

1. If a compund contains 394.0g of Au, 96.3g of S and 192.0g of O, calculate the total malar mass and % compostion.

2. What percent of Rutin, which is found in buckwheat and in the fruit of the Fava D'anta tree etc, is C₂₇H₃₀O_x , has a total molar mass of 610g/mol. Find the number of oxygens there are in this compound and the percentage composition.

3. Calculate the percentage of the bold species in each of the following:
       a) CaCl2 + 2H2O

4. If a compund contains 394.0g of Au, 96.3g of S and 192.0g of O, calculate the total malar mass and % compostion.

5. What percent of Rutin, which is found in buckwheat and in the fruit of the Fava D'anta tree etc, is C₂₇H₃₀O_x , has a total molar mass of 610g/mol. Find the number of oxygens there are in this compound and the percentage composition.

5.Determine if the percent compostion of ammonium oxalate (NH4)2C2O4) is accurate
%N=22.6%
%H=6.5%
%C=19.4%
%O=51.6%

Solutions:

3. Total MM= 682.3g/mol

     % of Au= (394.0g/mol)/(682.3g/mol)=57.74%

     % of S= (96.3g/mol)/(682.3g/mol)=14.1%

     % of O=(192.0g/mol)/(682.3g/mol)=28.14%

4. MM oxygen= 610.0-324.0-30.0=256.0g/mol

          (256.0g/mol)/16=16 oxygen atoms

     % of C27=(324.0g/mol)/(610.0g/mol)=52.11%

     % of H=(30.0g/mol)/(610.0g/mol)=4.92%

     % of O=(256.0g/mol)/(610.0g/mol)=41.97%

5.MM ammonuium oxalate=124g/mol
% of N: 28.0g per mol/ 124g/mol x 100= 22.6%
% of H: 8.0 g per mol / 124g/mol x 100 = 6.5%
% of C: 24,0g per mol / 124g/mol x 100 = 19.4%
% of O: 24.0g per mol/ 124g/mol x 100= 51.6%
Thus the Percent Compostion is correct!!

Empirical and Moliecular Formula

Today In Class we learnt about two diffrent formulas.  They were very interesting because they are somewhat related.  The two formula we leart are:

Empirical Formula
-It is the simple formulae expressing the compostion of a compound.  It gives the simples whole number ratio of atoms or ions.

eg. The empirical in this case will be Fe3O4 as they are calculated by dividing the number of grams they have
by the total number of mass of the combining compound which is the molar mass.  After Fe and O is divided by the MM than we can use the lowest ratio in this case 1.29 to divide by the other rations like 1.72.  At the end it resulted 3 Fre and 4 Oxygens.  This shows the lowest number formula of the compound.

Molecular Formula
-Is a multiple of the empirical formula.  If the lowest common denominator of the subscripts is 1, the empirical and molecular foulae for the compoud are the same.

eg. Molecular Formula

An organic compound is analyzed and found to be 69.5% carbon, 7.3% hydrogen, and 23.2% oxygen
by mass.  The molar mass of this compound is 276.0g/mol. If the EF is found to be C4H5O than what is its Molecular Formula

Easy!
If we know the the most simple formula of the compound and we were given the molar mass of the original compound which is 276.0g/mol than we can find the MF.

1. We first Find the MM of C4H5O the EF of the compound=69.0g/mol
2. Than we will devid the MM of the EF by the MM of MF which will be 276.0g/mol/69.0g/mol
3. You will than receive the number 4
4. Than you will need to multiply the number 4 to the original EF which will be 4(C4H50)
5. You will than get the MF C16H20O4

Mole Conversion Quiz!

                      Today we had a easy quiz on Mole Conversions.  It was easy because the quetions are based on the following:

1. find the molar mass of a compound
2. convert molecules, atoms, to grams
3. convert grams, atoms molecules to mole

Map that helped me prepare for the quiz

                   After the quiz we spend 10min working on another work sheet on Mole Convertions again.  How fun!!

Harder Mole Conversion

At the previous class of the mole conversion, we've learnt:
-From particles → moles.
-From moles → particles/molecules/formula units/atoms
-From moles → grams
-From grams → moles

The previous sections showed how to perform single-step conversions between moles and any of mass, volume, or number of particles.  This section shows how to convert between mass and volume, number of particles and mass, and so on.  The box table below summarizes the conversion factors needed.


                            Conversion                    |              Conversion Factor       
          
                                                                        6.022x10^23 particles
                 -mole → particles                     |               1 mole
                ______________________________________________________       
               
                  -mole → mass                        |      molar mass g                                  
                                                                             1mol
                ______________________________________________________

                -mole → volume                       |           22.4 L
                                                                           1 mol
                ______________________________________________________

               -molecules → atoms                |           # atoms      
                                                                         1 molecule

Mole Conversions

There are two main types of mole conversions:

1. Gram to Mole Conversion
2. Mole to Gram Conversion
3. Particles to moles Conversion
4. Moles to Particles Conversion

First of all,
Let's see some Grams to Moles Conversion

Moles to Grams Conversions:



Conversions between particles and moles:

More information about Mole Conversions:



Chapter 4 Moles

Chapter 4 Moles



Avogradro and his mole number!

 

                                    What is a mole?

         A mole is a number, just like a dozen is the number 12.  However the mole number is called the Advagadro's number which is about 6.022*10^23.

Why do is mole so important in Chemistry?
-Acording to Avogadro's Hypotheses, Gas with equal volume at same temperature and pressure will have the same number of particles.


Equal volumes of gas, at the same temperature and pressure, contain the same number of molecules.-This means each of these gas will contain 1 mole and 1 mole more=6.022*10^23  partciles,unites or molecules



Review: Chapter 3

Significant Figures:
-measured or meaningful digits.
-can be precisedif there are many of them.
e.g 24.37  24.6

Accuracy:
-It is how close the measurement (or average measurement) comes to the accepted or real value.

Precision:
-It is how reproducible a measurement is compare to other similar measurements.

Absolute Uncertainty:
-the uncertainty expressed in the units of measurement, not as a ratio.

Relative Uncertainty:


-Relative Uncertainty =         Absolute Uncertainty
                                       ———————————
                                        Estimated Measurement


Density:
-defined as its mass per unit volume.

-formula of density:             Mass
                         D    =     ————
                                       Volume

Lab 2E Quiz and Graphing

Today we have just done a quiz on Lab 2E.

The quiz was just all about calculating the thickness of a certain object, such as alunminum foil.

Equation:

Density=Mass/Volume

If you want to calculation the thickness based on the information of an object:
Density=2.70g/cm^3
Mass=5.0g
The object Area=15cm by 16cm
And calculation the thickness:
It goes,
Volume=(2.70g/cm^3)/5.0g=0.54m^3
Thickness=0.54cm^3/15cm/16cm=2.25*10^-3cm

Next, we went to lab room and learnt how to graph base on the information of mass and volume.

 

Lab 2 E

               Today in class, we had an exciting lab on determining the thickness(height) of the aluminum foil.The lab was to help us get more familiar with sig figs, accuracy, precision, uncertainties and the formula of density.  Thus we all enjoy this super amazing lab!!!

Purpose: Find accurate and precise measurement of the thickness of the aluminnum foil expressed using correct number of sig figs.

Procedure

1. We start off by measureing all measuring the length and width of foil that is at least 15 cm on each side

2. Than we use the centigram to measure the mass of each foil.

3. After we calculated the Mass we than use the density formula to calculate the volume of the foil.

4. When we finished calculating the volume of the aluminum foil, we than use the lengh and width to calculate

the height because LxWxH=V

eg.V=0.36cm^3

L=15.60cm

W=15.35cm

Hight=0.36cm^3

--------------

15.60cm*15.35cm

=1.5*10^-3(Remember  round you sig figs till the very end!!)

5.  The final step is for us to calculate the experimental error when it comes to the accepted value for thickness of the aluminum foil which Mr.Chen gave us was 1.55*10^-3.

Formula Expremental error:

Experimental error=Your measurement-Accepted value

---------------------------------------------

accepted value *100

6.At the end of the experiment we wrote a conclusion on how accurate and precise

our messurement was.  Our measurement was precise because our experimental error

was only 3.2%. It was also precise because we got almost the same value each

time when we calcute the thickness of the foil for 3 trials.

Need more help go to:   http://www.mefeedia.com/watch/29045208

Note:Quiz next class on everything we done today on the lab !!!!

Density

Density:
-defined as its mass per unit volume.
-or, its weight per unit volume.
-Osmium is the most densest known substance at standard conditions for temperature and pressure.
-less dense fluids float on more dense fluids if THE FLUIDS DO NOT MIX.

 Here is an example of density between fluids.















-formula of density:             Mass
                         D    =     ————
                                       Volume


Example: An iron bar has a mass of 12.00 g and a volume of 1.25 L.  What is the iron bars density?

    As we know D=M/G, we could simply plug in the number, D=12.00g/1.25L which equals to 960 but don't forget the units! Its 960 g/L.

Leif Tung

Accuracy and Precision

Today, we have learnt the accuracy and precision of practises of measuring.
The following is the textbook definition:
Precision
It is how reproducible a measurement is compare to other similar measurements.

Accuracy
It is how close the measurement (or average measurement) comes to the accepted or real value.

Measurement and Uncertainty

- There are no measurment that is excact because every measurement is a best estimation with margins of error.

- Despite of have the best estimation, for example, there are 39 cars in a parking lot is an exact number because it's a set of objects.

Absolute Uncertainty

A measurement of the uncertainty which is expressed in units. There are 2 methods to find it:

Method 1: Make at least 3 measurements and calculate the average. In the other hand, the absolute uncertanty is the largest difference between the average and the lowest or highest reasonable measurement.

               - For example: when calculating the avery of a few data eliminate the unreasonable data first:

1. 59                          The average is 59
2. 60                          I have eliminated 53 because it is a absolute uncertainty.
3. 58
4. 53
5. 59

 Method 2: Determine the uncertainty of each instrument

• When you are making a measurement, make sure you measure the best estimation you can (precision). In some real practices, you should estimate whatever the smallest segment that is possible on a instrument scale.
• For exmple, our rulers have the smallest scale as 1 mm, so that the best precision should break down to 0.1 mm. When you are measuring a thing, you need to see more carefully and precisely to be certain of the 0.1 mm differences.

Relative Uncertainty and Significant Figures

Relative          Absolute uncertainty

uncertainty =--------------------------------------

                        Estimated measurement

That's about what we have learnt today.

Kevin Wang

Chapter 3:Sig Figs

Today in class, we begin our new unit on Sig figs. So what are Sig figs and why do we need them?


Sig figs
-They are meaningful values that are accurate.

- They can also be precise if there are many of them

-We need them to get precise accurate measurements and not just approximating

Eg.24.37, 24.5, 35.3

"Watch this video if you did not listen in class. It is very helpful trust me"

More Practice problems go to:http://science.widener.edu/svb/tutorial/sigfigures.html

Rules to Significant Numbers

-Non-zero digits are always significant eg.23490.33

-All final zeros after the decimal point are significant eg 95.000

-Zeros between two other significant digits are significant. eg 1.00009

-Zeros used solely for spacing the decimal point are not significant. eg.0.00009

Rounding Rules For Sig Figs

"When Adding Sig figs you always round to the nearest Decimal"



"When dividing and multiplying Sig Figs you always round to the fewest Sig figs in this case 2"



Exact Numbers

Today we also learn about exact numbers which are numbers that cannot be round up because it is exact.

Eg.
-1 km will always=1000 meters
-2 cats will always be 2 cats. There cannot be 1.9 cats
-1 human will always be 1 human. Not 0.99

Two cats will always be 2 cats not 1.999!!!!!!!!!!!!!!!

• Look for numbers to the right of the digit to round up
• If the digit is less than 5, the number does not change
• If the digit is more than 5, the number rounds up
• If the digit is exactly 5, than round the digit to make it an even number like 4,6,8,2.
• If the digit is the number 5 and there are more no zero digits after five than round the number up. 

Lab Experiment: Separation of a Mixture by Paper Chromatography

Paper Chromatography:
- technique for separating and identifying mixtures that are or can be colored.

In this experiment, we've became acquainted with paper chromatography.  There are 3 parts in this lab experiment, in part 1, we assemble a paper chromatography apparatus, which  tells us how to set up a paper chromatography.  In part 2, we examined chromatography results for a variety of food colorings.  In part 3, we separated two mixtures of these colorings and study the significance of the Rf (ratio of fronts) values.

Please referred to videos on youtube about paper chromatography  below.

 Leif Tung

Separation Techniques

Separating Mixture

To separate into different component & different properties.

Separation:
It is a process to reveal the identities of the components in a mixture. However, it is hard to separate them, the properties, in which they have the similar properties.

Basic techniques

- Filtration: select components by particle size( undissolved solids and liquid)

 Cystallization(Solid and Liquid)

The resultant which we want is a solid state formed by a chemical or physical change.

Distillation collects and condenses volatilized (vaporized) components. In other words, it is a process of boiling the liquid and vaporizing it and then condenses it back to purified liquid.

Chromatography is the purpose of separating complex components by flowing the mixture over a material that retains components more than others, so different components flow with different speeds on the material.

Paper Chromatography(PC)

A highly accurate component separation material. The paper is liquid soaked with the sheet or strip of paper. The components appear as separated spots on the paper chomatography after drying.

(Videos from Youtube)

Kevin Wang

Naming Simple Acids and Complex Acids

Today in class we learnt how to name and identify both simple and complex acids.  First of all acids are form when composed of hydrogen ion and composed of a negatively charged ion.

 

Almost all acids starts with H and is negatively charged.



Simple Acids

• Uses hydro in the begining
• Ends in ide when form with hydrogen. However you will need to change the ide to ic
• Ends with writing acids

Eg. HF-hydrogen flouride turns into hydrofluoric acid.

Complex Acids

• Does not begin with hydro
• They end in ate or ite when combines with hydrogen.
• However you change the ate to ic and ite to ous and wrtie acid at the end

Eg. H2SO4-hydrogensulphate turns into sulphuric acid.

Eg. HNO2-hydrogennitrite turns into nitrous acid.

That concludes all we learnt today!!!!!!

Test Next Thurs On What we learn so far which is Chap1 and 2

Writing & Naming Ionic and Covalent Compounds

Ionic Compound:
-composed of two or more particles  (oppositely charged)
                                                 (ions)
-held together by electrostatic forces.
-electrons are transferred from a metal→non metal.
 
             Physical Properties                     Ionic Compound
              -States                                          - Solid
              -Electrical conductivity                    - Solid:No Liquid:Yes
              -Boiling point and Melting Point       - High
              -Solubility in water                          - Often high
              -Thermal conductivity                      - Low

← example: Sodium Chloride
                           NaCl

Resource: Wikipedia







Covalent Compound:
   To start off covalent compound, let's look at the prefixes first:
mono-1     tetra-4     hepta-7     deca-10           triskaideca-13
di-2           penta-5    octa-8       hendeca-11    tetrakaideca-14
tri-3           hexa-6     nona-9      dodeca-12      pentakaideca-15

-share electrons
-non metal with non metal
※ Diatomic molecules: Hydrogen, Oxygen, Florine, Nitrogen, Chlorine, Bromine, Iodine

  
             Physical Properties                    Covalent Compund                          
                 -States                                        -Can be a solid, liquid, or gas
                 -Electrical conductivity                  -No
                 -Boiling point and Melting Point      -Low
                 -Solubility in water                        -Variable
                 -Thermal conductivity                    - Usually low

←example.


Resource: Yahoo! Image









                                                                                                                                   Leif Tung

Experiment!

Heating and Cooling Curves of a Pure Substance

(Wikipedia.com)

Today, we have done a fascinating lab which we cooling down the pure substance of dodecanoic acid(C₁₂H₂₄O₂ ). It is a white powder when the temperature is about 25 degree centigrade. When the process of cooling the substance is done for about 13 minutes. We started to go down to the heating process. The process that will melt the dodecanoic acid from solid state into the state of liquid again. The process of heat it up into liquid took about 9 minutes. The whole purpose of the experiment is to investigate the heating and the cooling process of liquid/solid dodecanoic acid and to determine and compare the melting and freezing points of dodecanoic acid.

Kevin Wang

Chapter 2 Intro



The Heat/Cooling Curve of a Pure Substance



Description of the diagram

A                                                                      A-B



The particles are closely packed together and
can only vibrate at a fixed position. 

It stays solid anywhere below its meling point.

B



The particles in the solide are being heated

and the heat enrgy is converted to kinetic enrgy.

Thus the particles vibrate faster and move further apart.

B-C

 

Solid has begun melting but the

temperature remains the same

C



At solid at its melting point. it is in

both solid and liquid state. The temperature

remins constant becuase it is used to

over come forces between the particles

C-D



Turn to full liquid state.

D

Liquid is heated and molecules begans to move faster

due to the kinetic energy in the increase of temperature

                           D-E

Molecules recieves enough energy to

to overcome forces between particle. Some liquid

molecules begin to change into gas

E

Evaporation begins.

E-F



Liquid has turn all into gas

 Temperature increases as heating continue.Gas particles are moving much fast do to much bigges space





 Text Book Summary



Lab Experiment: Physical and Chemical Change

Today in chemistry we did a lab experiment on physical and chemical changes.

Physical changes:
-any change not involving a change in the substance's chemical identity
-occur when objects undergo a change that does not change their chemical nature
-involves a change in physical properties (i.e texture, shape, size, color, volume, mass, weight,
and density)
-REVERSIBLE
-an example of a physical change:
                                          formation of ice.
 

Resource: www.flickr.com

Chemical changes:

- bonds are broken and new bonds are formed between different atoms.

                            　　　　　　　　　　　↑

This breaking and forming of bonds takes place when particles of the original materials collide with one another

-when chemical change occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products are generated.

-IRREVERSIBLE

-an example of chemical change:

                                        burning wood.

                                                        Resource: Yahoo! Image.

Leif Tung

Unit Conversion prepartion

              Schedule for the day :)

 


1. Start off correcting our homework on overhead.

2.Had  a practice quiz on unit conversion. 

3. Ms. Chen gave us precious time to study for the rest of the class.
 








How to prepared for an A+
      
       -Warm up by watching this video on Unit Conversion
       -Go over corrections on previous homework
       -Memorize the SI Prefixes table
       -Finish the last home on Unit Conversion
       -Try more practice quiz questions on this website              

Do last homework on Unit Conversion





Memorize this table

 
 Watch fun video on Unite Conversion




More Practice Quizes