Translating Word Equations & Balancing Equations

Hello,

I am just going to go over some basics in how to translate word equations and balance equations.

Translating word equations:

This is a review from last year's science classes, but we'll go over it again.

Ex. aqueous aluminum oxide and sulphuric acid produce water and aqueous aluminum sulphate.

First,

Find all the elements in the periodic table.

Then,

Put the right charges and balance equation.

Note, in word equations like these "and" means "+" sign, "produce" means "→"
Balancing equations

First, make sure the number of atoms are equal in both sides of the equation.

Eg.  MgBr2  + Cl2  →  MgCl2  +  Br2 

You can see in this equation that there are:

 2 atoms of Br

2 atoms of Cl  &

1 atom of Mg

This is important because if it is different for each side, then it goes against the law of conservation of Mass.

In order to do this efficiently, follow these guidelines:

1. Try to balance metal ions. They are easier to deal with.

2. Balance the non-metals.

3. Balance Oxygen, Hydrogen and Carbon last.

 Try some examples on this site:

http://www.cartage.org.lb/en/themes/sciences/chemistry/inorganicchemistry/chemicslformula/Equation/BalancingWorksheet/BalancingWorksheet.htm

I will put up answers next time.

See you later.

Last Mole Conversion... for now

Molar Volume of Gases at STP

(btw, STP = Standard Temperature & Pressure)

Gases expand and contract based on the temperature, therefore, the volume changes.

Basically, the whole lesson talks about how 1 mole of gas at STP occupies 22.4 L  ..

Sooo, let's try an example >>

                        Calculate the volume occupied by 3.4 grams of ammonia ( NH3 ) at STP..

                        Molar Mass = 17 g 

                        3.4 g  x  1 mole    =  0.2 moles

                                      17 g 

                        0.2 moles  x  22.4 L  =  4.5 L of NH3 

Simple, eh ?!!

DILUTION OF SOLUTION

In the previous lesson, we talked about Molarity, now... We are talking about the Dilution of Solution.. ( Super!! ) 

Chemicals are usually shipped in a concentrated mode. So to make it less concentrated, water is usually added!!

In this lesson, we are going to learn to make solutions of any concnetration from a more concentrated source. 

You guys remember the law of conservation of mass, right?? ..... Yeah I didn't think so either..

Basically, the amount of mass enterring a reaction is equal to the amount of mass coming out!! How is this relevant, you may ask? Well , one answer... Moles of a solute are constant, and do not change..

The simple equation for this is derived from the previous lesson 

M1(L1) = M2(L2)

I have ...                                    I need...

         2.00 L    of HCl                          0.8 L

         16.0 M                                      2.0 M

Here comes the magic...

        16 x L1 = 2 x 0.8 

              L1 = 0.100 L

So you add 0.800 - 0.100 = 0.700 L of water to get the concentration you needed ..

THAT'S IT!!
see you next class !!!

MOLARITY OF SOLUTIONS!!

WELCOME BACK..

The first lesson we took on the first day we started school again, was MOLARITY, or Molar Concentration, of solutions.

A solution is a homogenous mixture that normally consists of 

•  a Solute, which is the smaller quantity, and 

•  a Solvent, which is, well, the bigger quantity

Concentration, is the amount of solute in a solution.

Molarity, is the number of moles of solute in one litre of solution. 

The unit for Molarity is the number of moles per

litre, and can be extremely abbreviated (like the 

case of "mole") to   mol / L ..

It can also be an "M"

( must be capitalized )

So basically, the formula for Molarity is this ::

MOLARITY =  moles of solute (mol)  

                volume (L)

So what do you think of this statement? 

A 5 M solution is more concentrated than a 4 M solution.

hmmmmmmm

Take a minute to think about this, and give it the amount of thinkin git deserves... okay, DONE. 

WELL, YEAH OBVIOUSLY.. 

( You get the point now )

So,, let's try some examples then>>

• Eg1--

                   Sea water contains 28.0 grams of NaCl per Litre, 

                   what is the molarity?

                   

                   First, you might want to convert grams to moles. This is the

                   equation now:

                   # of moles =  28.0 g X   1 mole      =    0.479 moles

                                                    58.5 g

                   You already know you have a Litre, so you divide 0.479 by 1 

                   and another minute or two to try to solve this.. Then you will

                   realize you got   0.479 M.

• Eg2--

                   What weight, in grams, of KCl is there in 2.50 Litres 

                   of 0.50 M ??

                   

                   First, get the number of moles by multiplying 0.50 M 

                   & 2.50 L..

                   You will get 1.25 moles

                   Then convert moles to grams through this>>

                   mass = 1.25 moles  X      74.6 g       =   79.2 g

                                                   1 mole

                 

This lesson is actually easy, those two examples is the hardest it can get..

NEVER FORGET YOUR UNITS.. AND ALWAYS SHOW WORK!!! ;)

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