## Thursday, January 27, 2011

### Reaction or No reaction?

Reactions, reactions, reactions...
That's all there is.
Let's start off by reviewing some really basis reactions.

1. Synthesis: A+B-->C
In synthesis reactions, reactants combine to form a single product.
eg. _8_Fe+_1_S8-->_8_FeS

2. Decomposition: A-->B+C
In decomposition, the product "decomposes" into the reactants.
eg. _2_H20--> _2_H2+_2_O

So far so good, right?
Now, the new stuff comes in.
When we did single replacement reactions before, we assumed a reaction would result.
Little did we know that this isn't always the case.

We are introduced to an important chart called the "Activity Series".
This sheet is not boyfriend material, and my first impression of it made me cringe.

The Activity Series ranks the elements in order of reactivity. An element higher up on series is able to replace the ion below the chart. Let's see how it's done.

Single Replacement Review:
if A (metal), then A+BC-->AC+B;
if A (non-metal), then A+BC-->BA+C

So, look at the activity series and consider this equation:

Cu + Fe(OH)3-->

1. Predict the products.

Cu + Fe(OH)3--> Fe + CuOH

2. Look at the activity series. Ask yourself "Is copper placed higher iron?"

The answer is no. Iron is placed higher than copper, so NO REACTION WILL OCCUR.

3. Balance the equation.

3Cu + Fe(OH)3--> Fe + 3CuOH

YAY. We're done!!

**Some things to remember:
Whatever element that is replacing the original element has to be higher than the original, or else a reaction will NOT occur.
If the replacement element is higher, rest assured. A reaction will occur.

Time for a song that is really educational. I mean, look at the title!!

"Chemicals React-Aly&AJ"

Good luck with the new material! (:

Written by Jialynn.

## Tuesday, January 25, 2011

### Translating Word Equations + Review of Naming Compounds + Balancing Equations! by Bev & Jialynn

What does a chemical equation tell you?

-the chemicals that are reacting together
-the number of particles involved
-the type of particles involved (ie. atoms, ions, molecules)
-the number of moles per substance
-the reactants & the products
-the state of the substance (ie. solid, liquid, gas, or aqueous)

How do you write a chemical equation?

ex. solid sodium metal burns in chlorine gas to form solid sodium chloride

Sodium chloride = Na +1  +  Cl -1  =  NaCl
Chlorine gas = Cl2 (one of the 7 diatomics*)

Na + Cl2 --> NaCl

# of atoms on each side:

right:              left:
Na - 1           Na - 1
Cl - 1            Cl - 2

To balance the right side of the equation, there needs to be 2 chloride atoms.

Na + Cl2 --> 2NaCl

Count the atoms again:

right:               left:
Na - 2            Na - 1
Cl - 2             Cl - 2

Now add 2 in front of the sodium metal; therefore, the balance equation is:

2Na + 1Cl2 --> 2NaCl

And the coefficients cannot be reduced!

What are diatomics?

The diatomics are 7 special non-metals that always form a molecule of 2 when alone.  They are:

Hydrogen, oxygen, fluoride, bromide, iodide, nitrogen, chloride

The diatomics are in gas form & are expressed as H2, O2, F2, Br2, I2, N2, & Cl2 in word equations.

~~Here is a trick to remember the diatomics~~

HOFBrINCl ("Hoffbrinkle")

or

I Bring Clay For Our New House

and they form a "7" shape in the periodic table! :D

another note: When sulphur & phosphorous are by itself, it is expressed as

S8            and              P4

Some tips for balancing equations:
-treat chemicals that come in groups (NO3, PO4) like a whole (make sure to balance these first!)
-balance everything else before balancing H and O
**remember, the coefficients have to be a whole number!!

Try these on your own (and balance them):

1. __Pb+__O2-->__PbO2
2. Lithium + Magnesium chloride-->
3. Water+hydrogen-->
4. Hydrogen + nitrogen-->ammonia
5. Potassium+water-->potassium hydroxide+hydrogen

## Sunday, January 16, 2011

### Molar VLOUME of a Gas at Standard Temperature and Pressure

what is STP?

it stands for Standard Temperature and Pressure.

equals to 1 atmosphere of pressure and a temperature at 0C or 273.15k.

At STP 1mole of gas pccupies 22.4L
therefore, 22.4L of gas/1 mole of gas OR 1 mole of gas/ 22.4L of gas

now lets take a look at some examples:

What is the volume occupied by 0.350 mol of SO2(g) at STP?
# of litres = 0.350mol x 22.4L/ 1mol =7.84L

How many moles of gas are contained in a balloon with a volume of 10.0L at STP?
# of moles = 10.0L x 1mol/ 22.4L =0.446 mol

Have fun with Molar Vloume!
Mandy

## Friday, January 14, 2011

### Molar Volume of a Gas at STP (by Bev)

Review: Recall that Avogadro's Hypothesis states that at the same pressure & temperature, equal volumes of different gases have the same number of particles.
Also, gases will change volume (contract or expand) with changes in pressure in temperature

So what is molar volume??!
The molar volume of a gas is the volume occupied by 1 mole of gas at Standard Temperature & Pressure (STP), which is 0 degrees Celsius and 1 atmosphere of pressure.

ANY gas at STP has a volume of 22.4 litres.
Therefore, the converstion factor is mol/22.4L or 22.4L/mol

ex. What is the volume at STP occupied by 12.4 mol of NH3 (g)?
12.5 mol x 22.4 L/mol = 278 L (3 sig figs!)

ex. How many moles are in 85.9 L of H2 at STP?
85.9L x mol/22.4 L = 3.83 mol

ex. How many moles are in 201.6dm^3 of HCl (g) at STP?
1 dm^3 = 1 L
--> 201.6 L x mol/22.4L = 9.000 mol

ex. What volume at STP is occupied by 16.5 g of AsH3 (g)?
MM AsH3 = 77.9
g-->mol-->L (it's incredible how grams, a unit of mass, can be converted into litres, a unit of volume!)
16.5 g x mol/77.9 g x 22.4 L/mol = 4.74 L

## Saturday, January 8, 2011

### How Do Chemists PREPARE SOLUTIONS Without Blowing the Lab Up?!

Fact: Chemicals are shipped in their most CONCENTRATED form.

This is pretty much common sense, right? I mean, if they were shipped already diluted, it'll cost more.

Diluted Chemicals=More Chance of Spillage=More Shipping/Packages=More Money=More Greenhouse Gases (due to shipping)

So, chemists and chemistry students like yourself  need to learn how to dilute these concentrated substances.
But before you learn how to do that, burn this concept into your mind:

MOLES OF SOLUTE IS CONSTANT
ie. moles in the solute before=moles in the solute after dilution

Let's break down a question:
Concentrated HCl is 55.6mole/L. How can we make 250 mL of 0.500 mole/L HCl?
1. Write down the formula.
M1L1=M2L2
2. Plus in the numbers.
(55.6M)(L1)=(0.500M)(0.250L)
3. Solve for L1.
(55.6M)(L1)=(0.500M)(0.250L)
55.6L1=0.125
55.6       55.6
L1=0.002248L
4. Put answers to the appropriate number of sig. figs.
L1=2.25mL
5. Don't forget to include UNITS!!

More Practice Problems:
1. 150.0mL of 0.025M KOH solution is added to 150.0mL of water. Calculate the new molarity.

2. A 0.225M solution is concentrated by evaporation to reduce the final volume of 75.0mL and a molarity of 0.275M. Calculate the original volume.

VIDEO TIME! -insert applause-

Good luck in mastering this relatively new concept!

Written by Jialynn.

## Wednesday, January 5, 2011

### Molarity - Isabelle Cheng January 5, 2011

Isabelle Cheng
January 5, 2011
Block 2-2 Chem 11
Ms. Chen

# Molarity

Molarity is the number of moles of the substance contained in 1 Liter of solution. This is based on a substance in a solution. Also the other name for Molarity is called Molar Concentration.

There is a difference between concentration, concentrated, and dilute. The concentration of a substance in a solution is the quantity of the substance, which is in a given volume of the solution. The concentrated solution has a high concentration. This means that a lot of the substance is dissolved in the solution. Dilute solution has a low concentration which means that very little of the substance is dissolved.

Here is the Formula:

Molarity/ Molar Concentration = moles
Volume

Or this way might be easier to remember:

M = mol
L

That means if you want to solve for L it would be:

L = mol
M

That means if you want to solve for mol it would be:

## Mol = M X L

Here is an example:

If 3.0 L of solution contain 5.0 mol of CaCl, what is the molarity of the CaCl?

Molarity = 5.0 mol  = 1.666666667
3.0 L

= 1.6 mol
L

Let’s try something harder now! ~

## This time you have to convert mL into Liters for the equation to work!

Example

40.0 mL of a solution contains 0.060 mole of CaCl?

40.0mL   X    1 L
1                           10^3

= 0.0400 L

Molarity = 0.060
0.0400
= 1.5 M CaCl

The next example is determining the number of moles:

What is the mass of NaCl is contained in 4.00L of 0.300 M NaCl?

Moles of NaCl = 0.300 X 4.00 = 1.2 mol

Mass of NaCl = 1.2mol X 58.5g = 70.2 g

The next example is determining the volume.

What is the volume of 2.40 M HCl can be made from 100.0 g of HCl?

Moles HCl = 100.0 g X 1mol  = 2.74 mol
36.5 g

V = 3.57 X10^-3 mol = 1.14 L
2.40 mol/L