Saturday, November 20, 2010

Converting THE MOLE

Mole conversions. They may seem hard, but they're just like unit conversions.

 Things to remember:
-Avogadro's number (SUPER IMPORTANT!!)
-how to calculate molar mass
-the "magic 1" rule

OK. Let's start converting!!

*For these conversions, we'll need to use Avogadro's number: 6.022x10^23*
1. particles-->moles
4.24x10^24 C particle-->moles

4.24x10^24particles               1 mole         = 7.04 moles of C
                                   6.022x10^23 particles

2. moles-->particles
1.34 moles moles CO2-->molecules

1.34moles x 6.022x10^23 molecules = 8.07x10^23 molecules of CO2
                               1 mole

These conversions do not require Avogadro's number. They instead, require a periodic table. Remember how to calculate molar mass!
3. moles-->grams
6.5 moles of C-->grams                                        *Use molar mass of C=12.0g/mol

6.5 moles x 12.0g/mol = 78 grams of C
                      1 mole

4. grams-->moles
8.2 grams of MgCl2-->moles                                *Use molar mass of MgCl2=95.3g/mol

8.2 grams x 1 mole = 0.086 moles of MgCl2
                   95.3 g

YAY!! So now, you should know how to convert from moles<->particles and moles<-> grams.
Just for some extra practice, here are a few questions:

1. How many moles of O2 are in 5.53x10^41 molecules of Ag?

2. How many atoms are in 2 moles of C?

3. How many moles are in 94.0g of Pb?

4. Calculate the mass (g) of 7.42x10^12 atoms of C.

And, lastly, here's a video to summarize the converting stuffs. Don't get distracted by the music!


Written by Jialynn.

Thursday, November 18, 2010

Chapter 4 - Atomic Mass and Avogadro's number - Isabelle Cheng - November 17, 2010

Isabelle Cheng
November 17, 2010
Block 2-2 Chemistry 11
Ms. Chen
Chapter 4 - Avogadro’s Theory and Atomic Masses
The mole is the amount of carbon atoms in 12 grams of carbon. On the other hand, a molar mass is the mass of one mole. For example, a dozen means 12 and so, a mole means 12 grams. Using the periodic table is very necessary for solving these problems. Some examples from using the periodic table is that Iron has an atomic mass of 55.8. Then right away you know that the molar mass of the element is also 55.8g. 
Another example:
AgNO3 - 1 Ag = 1 x 107.9 = 107.9, 1 N = 1 x 14.0, and 3 O = 3 X 16.0 = 48.0 and all of it together is 169.9 grams which means that the molar mass is 169.9 grams.
We also need to include unit conversions in these problems. 
For example, we need to use this equation:
1mol___     molar mass of X
molar mass of X           1mol

Avogadro’s number:
- 6.022 X 10 ^ 23
- large number 

Sunday, November 14, 2010

Experiment 2E: Determining Aluminum Foil Thickness by: Mandy

Lab 2E : Determining Aluminum Foil Thickness
Today, we did experiment 2E. This lab is an indirect measurement of the thickness of a piece of aluminum foil.
There were two formulas involved in this experiment:
Volume of a rectangular solid = length X width X height
Density of a substance = mass / volume
We first took three aluminum foils (15 X15)cm. since the measurement of those square aluminum foils might be off by a little bit, we need to measure the length of two widths and take their average; same as the lengths. Then, we took each aluminum foil to the centigram balance for the measurement of mass.  Now that we knew the lengths, widths, mass, and density (2.70 g/cm^3), the height can be calculated.
In this experiment, accuracy and precision are very important.
An ACCURATE measurement is a measurement that is close to the accepted values.
A PRECISE measurement id a reproducible measurement, thus, more precise the measurement is, the more significant digits it has.
Take the average thickness of those three aluminum foils, and calculate experimental error.
Experimental Error is calculated using this formula:
Experimental Error = abs( your measurement – accepted value) /( accepted value) X 100%
In this case, the accepted value is: 1.55*10^-6 cm

household aluminum foil

a little extra information about aluminum foil :) 
        The shiny side is slightly better reflector of heat. To keep things cold, put the shiny side on the outside [that will reflect incoming heat]. To keep things warm, face the shiny side inward toward the hot food [to reflect the heat that is trying to escape back into the food].

THANK YOU for checking out our blog :D

Tuesday, November 2, 2010

So Like, How Much More "Dense" Can You Get?

Things to remember:
1cm^3 of water=1mL
Density of water=1.0g/mL OR 1000g/L

The formula for density is Density=mass/volume

Density Units

for solids--> g/cm^3
for liquids--> g/mL

Some concepts to think about:

If the density of an object is greater than the density of a liquid, the object will sink
If the density of an object is less than the density of a liquid, the object will float.

Try applying the formula to these practice problems. Remember, D=m/v.

1. An iron bar has a mass of 1225g and a volume of 1.2L. What is the iron bar's density?

2. In a balloon, helium occupies 3.8L with a mass of 4.0g. What is the density of helium?

3. An iron bar has a mass of 250g. If iron's density is 7.86x10^3 g/L, what volume does the bar occupy?

4. A block of beeswax has a volume of 210.0mL and a density of 961g/L. What is the mass of the block?

Fun Fact!!
The density of one brain tissue is 1.05g/mL, which is almost equivalent to the density of water!
How "dense" is that??!?! xD

Written by Jialynn