Miercoles 24 de febrero del 2010

Topic: Converting Moles and Grams

Today we had this VERY short topic. We learned to convert moles to grams and grams to moles. It's very easy, first we need a question: How many moles of water will you get if you react 1kg of H with excess O?

As we know, the chemical equation of water is this : 2H2 + O2 → 2H2O

We have 1kg of H but we need to convert it to grams that is equal to 1000 g.

Before resolving a rule of three, we convert the 1000g to moles:

1H2 --- 2g

x --- 1000g

(if 1 mole of H weights 2g, how mant moles weight 1000g?)

1 x 1000 = 1000 / 2 = 500 moles of H weight 1000 g

Now we resolve the rule of three:

2H2 --- 2H2O

500 moles --- x

500 x 2 = 1000 / 2 = 500 moles of H2O

And that's how you convert grams to moles.

Michelle Torrero

Viernes 19 de febrero del 2010

Miercoles 17 de febrero del 2010

oday was our first real class, and we saw a new subject: STOICHIOMETRY. Technically speaking, stoichiometry is the part of chemistry that deals with amounts and quantities, and we can use it to calculate masses, moles, and percents within a quemical equiation (In short words, stoichiometry is the math behind chemistry).

We also saw the Chemical Yield (or Reaction Yield) is the ammount of product obtained in a chemical reaction; in a chemical reaction it would be like this:

2H2 + O2 (Reactants) ------> 2H2O (Products)


The reason of the recipes (short and easy) was to explain with easier words the stoichiometry; the example we used was the Chocolate Milkshake recipe, and in that part i learned that the quantity of ingredients depended on the amount that was going to be used for all (at least that's what i understood).

Homar Hurtado

Monday, November 9th, 2009

Today we saw the topic “Chemical Balancing". Chemical Balancing is a way to balance an equation, and there are 3 methods but today we saw the Trial and error method also known as Inspection method.

We can ask first of all why we need to do it, well we need to follow the rule “matter can’t be created nor destroyed just transformed”.

To make a chemical balance first you need an equation:

Na + Cl → NaCl (It’s not balanced)

Then you need to write the amount of molecules of each element:

Na + Cl2 → NaCl

Na 1 Na 1

Cl 2 Cl 1

If you notice, the amount of Chlorine is not the same and we need to apply the rule of “matter can’t be created nor destroyed just transformed”. So we need to aggregate numbers to balance the equation:

Na + Cl2 → 2NaCl

Na 1 Na 2

Cl 2 Cl 2

Now we balanced Chlorine but now Sodium is not balanced, so we need to aggregate another number:

2Na + Cl2 → 2NaCl

Na 2 Na 2

Cl 2 Cl 2

Now the equation is balanced with the same amount of molecules before and after the arrow.

Michelle Torrero

Friday, November 6th, 2009

Today the class started with awful news: The test is on November 20^th!

So if anyone else was planning to go to the New Moon´s premier you need to come early to school, even if you´re sleepless.

So...

Today´s theme was Chemical formulas and equations

An equation can tell you the elements that you have, the cuantity and, in some cases, the state or compatibility.

A chemical formula is a concize way of expresiing information about the atom that constitute a particular chemical compound.

Every compund that exists has an specific formula.

There are some elements that don´t come alone. They come in pairs:

H2

O2

N2

F2

CL2

BR2

I2

There was another theme today: Types of chemical reactions.

All chemical reactions involve a change in substances and a change in energy. Neither matter or energy is created or destroyed in a chemical reaction, only changed.

There are four types:

SYNTHESIS REACTION
In a synthesis reaction two or more simple substances combine to form a more complex substance.

DECOMPOSITION REACTION
In a decomposition reaction a more complex substance breaks down into simpler parts. Synthesis and decomposition reactions are opposites.

SINGLE REPLACEMENT REACTION
In a single replacement reaction a single uncombined element replaces another in a compound.

DOUBLE REPLACEMENT REACTION
In a double replacement reaction parts of two compounds switch places to form two new compounds.

Erin Alice Gil

The homework was:

Find 3 examples of each type of reaction.

Friday October 30th 2009

On Friday's class we learned about Covalent Bonds.
A Covalent Bond its when atoms share a pair of electrons. The difference between this one and a Ionic Bond its that an ionic bond needs to lose or gain electrons and become positive or negative and covalent bonds just share (both have and use the electrons if they need it).
For example: H= that has 1 valence electron and needs just one to be stable -----> Both can form H2O by a covalent bond.
O= which has 6 valence electrons and needs 2 to be stable
A characteristic of covalent bonds its that are "Polar Molecules", that means that the atoms has more positive charge in one side and negative charge in the other. We can use water (H2O) as an example in this too.




It has positive charge in the Hydrogen side and and negative charge in tho Oxygen side because of the excess of electrons.
(the red one is Oxygen and the whites are Hydrogen.)















When all the class understood this we made an activity outside, we made a covalent and a ionic bond simulating to be atoms (neutrons, protons and electrons).

Laura Carrillo

Monday October 26th 2009

Today we talked about ionic bonds, but class started with a review of what makes up an atom. Which is the proton (positive), electron (negative), and neutron (neutral). Then he went on to tell us that each atom has the same number of neutrons, protons, and electrons, but that the mass is different; For this one is in a way the sum of the neutrons and protons (it is also the electrons but they barely make a difference so it is not very noticeable). Then we got to the actual subject IONIC BONDS.
To know what that is we need to understand what ions are: The elements that have charges, there are two types: Cations (positive) and Anions (negative).
Now to get there we need to discuss metals and nonmetals.
"Atoms of metals tend to lose their electron valances leaving a complete octect in the next energy level."
Which basically tells you that metals tend to give up electrons.
Example: Na (z=11) configuration= 1s²2s²2p⁶3s¹which means it has 1 valance electron, and in order to be like a noble gas it has to lose one electron by doing this the atom goes from neutral to positive because now it has more protons than electrons. So it becomes a cation of sodium, because when they become cations they don't change the name.
-When you look at the periodic table: the number in the top right corner with the negative and positive charge tells you how many electrons ot gives or takes away and whether it becomes a positive or negative charge.
You can also look at he columns (1a, 2a, 3a, etc.) to know how many it loses.

Once an atom becomes a cation or anion it becomes different than the original even if it's a small different it can cause a lot of changes.


"Atoms of nonmetals tend to gain electrons or to share electrons with another nonmetal to achive an octet."

(most not all)

example:Cl (z=17) configuration= 1s²2s²2p⁶3s²3p⁵so it needs one more electron to become a noble gas, and by gaining an electron it emds up having more electrons than protonsand is negative instead of neutral. There are some that become pseudo noble gas because they're not exactly a noble gas but they are stable.
When an atom becomes an anion you change the name by replacing the last syllable with -ide.
ex: Chlorine -> Chloride.

Now the best way to know if it loses or gains electrons is by looking at it's valance number:
if it's 1-3 it loses
if it's 5-7 it gains
if it's 4 then it's a metalloid and it can do either, lose or gain.

If you've paid attention you've realized that despite me saying we were going to talk about ionic bonds I have yet to say anything about them, that's because you need to know evrything I've just said before you understand what's next.
Ionic Bond is held together by electrostatic forces.
Metal cation + Nonmetal anion = Neutral compound
(+) (-) (±)

Ex:
Na (+1) + Cl (-1) = NaCl

(P.S. Cations always go first it would never be written ClNa)

That was the whole class, and there was no homework.

Victoria Bracamontes