Lab 4C "Formula of hydrate"

Hydrate:  A compound that contains water. Written in the formula: AB x C(H20)

Anhydrous:  Without water.

Here is the procedure for our lab:

We found the mass of the water by subtracting the mass of the anhydrous salt after heating from the original hydrate. Then, by dividing the mass of the water by the mass of the hydrate and multiplying by 100, we got a percent of the water in the hydrate. We then determined the number of moles in the salt by dividing the mass of the salt by the molar mass of the hydrate (120.4g). By dividing the mass of the water by the molar mass of the water, we determined the number of moles present in the hydrate.


By:  JZ

Calculating the Empirical Formula of a ORGANIC Compound

C_xH_2y =(burned in O₂)=> x CO₂ + y H₂O

• From the weight of CO₂ and H₂O produced by burning a definite amount of the substance, you can figure out the percent of C and H in the compound.
• Percentage of O is usually obtained by subtracting all percentages of C, H, and N, if the compound does not contain any other element.

Review Empirical Formula:

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

For example:

Calculate the empirical formula of a compound that is 45.99 % C, 5.38% H and the rest is O.

1. Find the moles of the compound

C:  45.99g x  1 mol / 12 g  =  3.8325 moles

H:  5.38g x 1 mol  /  1.0 g  =  5.38 moles

O:   

• 45.99 + 5.38 = 51.37
• 100 - 51.37 = 48.63  -->  O

48.63 x 1 mol  /  16 g  =  3.039375 moles

2. Divide each answer with the lowest number, which is the oxygen.

C:  3.8325 / 3.039375 = 1.260950031 -->  1.27 x 4 = 5
H:  5.38 / 3.039375 = 1.770100761-->  1.77 x 4 = 7
O:  3.03975 / 3.03975  =  1-->  1 x 4 = 4

ANS:  C₅H₇O₄

By: Hikari Hoshika

Empirical & Molecular Formulas!!!

Empirical Formula :  help state the lowest ratio of atoms(or moles) inside a formula

*ALL IONIC COMPOUNDS ARE EMPIRICAL FORMULAS*

For example: C₁₂H_{10 Acnaphthene's empirical formula would be C6H5}

To convert molecular formulas to empirical formulas, use this :

1. Convert grams to moles

2. Divide each mole by the lowest molar amount

3. Scale the ratios to whole numbers

An example would be like this:

Calculate the empirical formula of a compound that contains 65% nitrogen and 35% fluorine.

*assume that it adds up to 100 grams*

Step 1: N:  65g x 1 mol    = 4.643

                                     14 g

            _{F: 35g x 1 mol     = 1.842}

                           _19g

_{Step 2:              4.643   = 2.52}

                         1.842

                          1.842   = 1

                          1.842

Step 3: Since 2.52 isn't a whole number, we need to scale it. Multiply each number by a whole number until 2.52 is a whole number .

In this case, 2.52 x 2 = 5.04<----since it's so close you can round down to 5.

Don't forget to multiply 2 to the other number as well . 2 x 1 =2

N5F2 is the empirical formula.

Tip: if the numbers are already whole, just use them as the empirical formula.

Molecular Formula (MF): is the multiple of an empirical formula that shows the actual # of atoms combined to form a molecule.

Formula :   n=      molar mass of compound 

                         molar mass of empirical formula 

Which means that MF= empirical formula x n

Example: A compound contains a empirical formula of C2H3 with a molar mass of 54 g /mol. Find the molecular formular.

Molar mass of C2H3= 27 g/mol

n=   54g/mol  =2

       27g/mol

MF= 2(C2H3) = C4H6


By : JN

Percent Composition

Percent Composition:
The percent composition of a compound is a relative measure of the mass of each different element present in the compound.



To calculate the percent composition (percentage composition) of a compound

1. Calculate the molar mass, MM, of the compound
2. Calculate the total mass of each element present in the formula of the compound
3. Calculate the percent composition: % by weight (mass) of element = total mass of element present ÷ molar mass x 100

Examples:

Calculate the percent by weight of sodium (Na) and chlorine (Cl) in sodium chloride (NaCl)

• Calculate the molecular mass (MM):

MM = 22.99 + 35.45 = 58.44

• Calculate the total mass of Na present:

1 Na is present in the formula, mass = 22.99

• Calculate the percent by weight of Na in NaCl:

%Na = (mass Na ÷ MM) x 100 = (22.99 ÷ 58.44) x 100 = 39.34%

• Calculate the total mass of Cl present:

1 Cl is present in the formula, mass = 35.45

• Calculate the percent by weight of Cl in NaCl:

%Cl = (mass Cl ÷ MM) x 100 = (35.45 ÷ 58.44) x 100 = 60.66%

    The answers above are probably correct if %Na + %Cl = 100, that is,  39.34 + 60.66 = 100.

http://www.youtube.com/watch?v=xbEeyT8nK84

By: Hikari Hoshika

HARDER Mole Conversions



(click to enlarge)



Conversions between: PARTICLES → MASS

E.g. WHAT IS THE MASS OF:  1.34x10²² Zn atoms?   

           

     1.34x10²² atoms  X  .  1 mole      . X      65.4g  .  =   1.46g  of Zn

                                                 6.022x10²³          1 mole

Conversions between: GRAMS → PARTICLES

E.g.  HOW MANY ATOMS WOUD YOU HAVE IF YOU HAVE 10.0g OF COBALT?

            10.0g   X     1 mole  .  X   6.022x10²³   =   1.02x10²³  atoms of  Co

                                      58.9g               1 mole

By: JZ

Mole Conversions

Refer to the mole map:

Particles ----> Moles

Ex.  How many moles of hydrogen molecules (H₂) are present in 9 x 10²³ molecules of hydrogen?

                                                                                  1 mole

9.0 x 10²³ molecules of hydrogen X  --------------------------------  =  1.5 moles

                                                                     6.022x10²³ molecules

*** Round to the correct significant figure!

Moles ---> Particles/Molecules/Formula units/atoms

Ex.  How many molecules are contained in 3 moles of water molecules, H₂O?

                           6.022x10²³ molecules

3.0 moles X  --------------------------------  =  1.8x10²⁴ molecules

                                       1 mole 

Moles ---> Grams

Ex.  Determine the mass in grams of 3.60 mole of H₂SO₄.

1. Find the molar mass of H₂SO₄.

H --> 1.0(2) =      2

S --> 32.1   =     32.1 +

O --> 16.0(4)=   64

                       ---------

                        98.1 g

     2.  Solve.

                           98.1 g

3.60 moles X  ------------  =  353g of H₂SO₄

                           1 mole 

♥  http://www.youtube.com/watch?v=NMdN1LtHuDA&feature

Grams ---> Moles

Ex.  How many moles of methane molecules, CH₄, are in 80 grams of methane?

C --> 12.0 =     12

H --> 1.0(4) =   4 +

                       ------

                        16 g

             

                 1 mole

80g X  ------------  =  5.0 moles

                  16g 

♥  http://www.youtube.com/watch?v=ehepBBtSbDc

By: Hikari Hoshika

Who wants some guacamole?

Unfortunately, I was kidding about the title


The mole = volumes of different gases, has a constant ratio.

 Amedeo Avogadro

His law states that equal volume of different gases at the same temperature and pressure have the same number of particles

So if the particles are the same then the mass ratio is the mass of the particles.

MOLAR MASS:

- molar mass can be used for atomic/molecular/formula mass and are written in the form of grams per mole (g/mol)

       ex. 1 mol of sodium = 23.0

Avogadro's number: 6.022× 10^{23  PARTICLES} 

                                                                                                           ^MOLE

^{Since Ms. Chen mentioned something about a mole day...}

^{http://www.youtube.com/watch?v=ReMe348Im2w}

not very original don't you think??

Post : JN

To Excel in Excel

Title basically means: to Exceed in Microsoft Excel
(If you didn't get it, it's fine. Not many people understood Kariodisonium-119 either)

Today, we went to the computer lab to learn(?) how to make a graph using Microsoft Excel.

Click here to see what we had to put on the graphs
So here's a video on how to make a graph using Microsoft Excel



By: JZ

LAB day. Measuring Thickness of Aluminum Foil

HOW TO FIND THE THICKNESS OF ALUMINUM FOIL

Remember the formula, 

                    

density = mass/volume

Also remember the formula, volume = length x width x height.  Thickness will substitute height, therefore making the formula, volume = length x width x thickness.  Since length x width = area, we could rewrite the density formula to: 

density of Al = mass of Al / area of Al x thickness of Al

The formula can be rearranged into:

thickness of Al = mass of Al / area of Al x density of Al

Information needed:

• length and width of aluminum square
• mass measured by a centigram measure

Exponential Error 

It expresses the future growth a very small error can become.

Formula:

Exponential error = your measurement - Accepted value / Accepted value x 100 --> %

 *It is written as a %

Accepted Value

A value of a substance accepted and approved by many

*given by instructor


By: Hikari H.

the knowledge of density can give oneself more knowledge

 formula for density is.. Density =Mass

                                                  volume

OR

V = m       OR     m = DV

       D

TIPS TO REMEMBER:
solid is g/cm3
liquid is g/mL
1 cm3 of water = 1mL

Density of water is 1000 g/L or 1.0 g/mL

If d of object is < than the d of liquid..then it should be floating on top

otherwise, it would be sinking!

Below is a colourful experiment involving density!

http://www.youtube.com/watch?v=7HNMiUH1Xkk

JN

Accuracy, Precision, and a whole lot of Uncertainty

Accuracy & Precision

What is Accuracy?

• Accuracy is how close a measured value is to the actual (real) value.

What is Precision?

• Precision is how close the measured values are to each other.

For example:

Big black circle: Low Precision

Small Black circle: High Precision

Farther away from Bull's Eye: Low Accuracy

Close to Bull's Eye: High Accuracy



High Accuracy, High Precison



High Accuracy, Low Precision



Low Accuracy, High Precision





Measurement and Uncertainty

No measurement is exact. It is only a best estimate, which has some degree of uncertainty. We only get an exact number when we count a set of objects.

• e.g. there are 23 books on the bookshelf

Absolute Uncertainty

Uncertainty is expressed in the units of measurement, not as a ratio.

To determine absolute uncertainty:

Method 1:

• Discard unreasonable data. Calculate the average of at least 3 measurements. The absolute uncertainty is the largest difference between the average of the highest and the lowest reasonable measurement.

Method 2:

• Determine the uncertainty of each instrument used. Make sure the measurement(s) is as precise as possible. Estimate to 0.1 of the smallest segment on the instrument scale.

e.g. if the smallest measurement on a ruler is in centimetres (cm), measure to 0.1cm, or 1 millimetre (mm)

Relative

Uncertainty  = absolute uncertainty / estimated measurement

the ratio can be expressed:

                                        (1) in percent (%)

                                        (2) using significant figures

Here are some videos to help clearify anything you do not understand.

Accuracy and Precision



Measurement and Uncertainty



FUN FACT OF THE DAY:
DID YOU KNOW... each cell in your body has more molecules that there are stars in the Milky Way Galaxy?

By: JZ