The Mole

• Scientists in early days found masses for hydrogen, oxygen and carbon dioxide.
• Discovered that equal volumes of different gases have a constant ratio. For example, oxygen : hydrogen 16:1

Relative Mass

• Is expressed by comparing it mathematically to the mass of another thing.
• Hydrogen and oxygen were used as standard for comparison.
• Now, carbon is used as standard. Assigned "12" amu therefore the mass of 1 atom = 1/12 the mass of carbon.

Avogadro's Hypothesis

• Equal volumes of different gases at the same temperature and pressure have the same number of particles. Which means that their mass ratio is due to mass of the particles.

Formula Mass

• All atoms of a formula is ionic (in amu)

Molecular Mass

• All atoms of formula in a covalent compound (in amu)

Molar Mass

• Mass of one mole of each element (in g/mol)
• The atomic/ molecular/ formula mass of any pure substance
• Eg. 1 mole of oxygen = 16.0g/mol ALL OF THESE HAVE THE SAME NUMBER OF PARTICLES.

Avogadro's Number

• The number of particles in a mole of any amount of substance
• 6.022 x 10^23 particles/ mole
• Is a counting unit like a dozen.
• Eg. A mole of atoms equals 6.022 x 10^23 atoms.

Lab 2E Determining Aluminum Foil Thickness

  During this lab. We learn how to get the value of some tiny measurements. For example, it's hard to measure the thickness of a Aluminum Foil's thickness. Therefore, we use the density and volume formula to calculate it. The density of aluminum is 2.70g/cm^3

     1. measure the length and width of each piece of foil. Record the measurements in th table we made.
     2.use a centigram balance to find the mass of each piece, record the mass.
     3.use the density fomula d=m/v, change it to v=m/d to get the volume of the foils
     4.use height=volume/width·length to get the thickness.

Here is an example of our calculation.

v=m/v=0.98g/2.70g/cm^3=0.363 cm^3
h=v/wl=0.363cm^3/15.47cm x 15.14cm=1.55 x 10^-3 cm


In this lab, we learn that not all the measurements need to be measured directly. We can use formula and other things to calculate it. It's easier and more accurate.

Graphing

As we all know : Density = mass/volume
In order to draw a " mass vs volume " graph, we have to consider volume as the dependent variable and mass is the independent one.
So , the x axis contains volume and y contains mass.
The slope of an straight line = rise / run = y / x = volume / mass
If we are to find the density , density will equal to 1/ slope = mass / volume

Here's how to make a graph by Microsoft Excel to save more times.
1. Open Excel then click on INSERT tab

2. Choose Scatter graph ( scatter with only markers )
3. Then the graph panel appears, right click on the graph, choose " Select Data"

4. Click " Add"

5. Enter the value for X and Y then click OK
6. Here we have a graph

7. Click on " Layout " tab then choose trendline --> then choose linear trendline to get the line of best fit

8.If you want to have the computer calculated the line's slope, click on trendline button again --> trendline option --> tick on the " Display Equation on chart " in the bottom of the panel.
9.Now we have finished the mass vs. volume graph! As I mentioned on top, density = 1/slope

Density

Density - The density of a material is defined as its mass per unit of volume.

Equation - mass/volume  (MEMORIZE THIS EQUATION)


Units
-For a solid, the unit is g/cm^3
-For a liquid, the unit is g/mL, Kg/L


1 cm^3 water = 1mL water
The density of water is 1000g/L or 1.0g/mL


Remember--> density of object > density of liquid = sink


density of object < density of liquid = float.

       

Measurement and Uncertainty

• No measurements are exact; there is always some degree of uncertainty. For example, 13.995m.
• The only time when we are "certain" about a measurement is when we count. For example, 31 people.

Absolute Uncertainty

• Expressed in units of measurement.
• Method 1: Make at least three measurements and calculate the average. You should disregard the measurement that is farthest apart from the rest of the other measurements before you calculate average. The absolute uncertainty is the largest difference between the average and the lowest or highest reasonable answer.
• Method 2: Determine the uncertainty of each instrument you're using. Always make the measurement to the best precision that you can. Therefore, you should estimate to fraction 0.1 of the smallest segment on the instrument scale.

On a ruler, the smallest division is 1mm. The best precision is to break this into 10 equal pieces = 0.1mm.

Relative Uncertainty = Absolute Uncertainty/ Estimated measurement

• Can be expressed as a percentage or in sig figs