EXAMPLE: 1.Determine the number of moles for 1 molecule of (NH4)2SO4. Molar mass of (NH4)2SO4 is 132.1g. 1mol(NH4)2SO4 x 1mol/6.022x10^23mol(NH4)2SO4 x132.1g/1mol =2 x (10)^-22
2.Determine the number of grams for 1.5x10^15 molecules of CuCl2. Molar mass of CuCl2 is 134.5g 1.5x10^15mol CuCl2x1moe/6.022x10^23mol CuCl2=2.4x10^-9
3.How many moles are there in 92.0g of Lead? 92.0gx1mol/207.2g=0.44mol
The mole is a unit of measurement used in chemistry to express of a chemical substance.
Avogadro's Hypothesis: Two equal volumes of gas, at the same temperature and pressure, contain the same number of molecules.
Avogadro's Law:
At a constant temperature and pressure, the volume of a gas is directly proportional to the number of moles of that gas.
Avogadro's Number: 6.022*10^23 particles/mole
Atomic Mass: the mass of a specific isotope, expressed in atomic mass unit (amu) Formula Mass: the mass of all atoms of an ionic compound (in amu) Molecular Mass: the mass of all atoms of a covalent compound (in amu)
Example:
What is the relative mass formula of sodium chloride? (Relative atomic masses: Na = 23, Cl = 35.5)
Solution:
Sodium Chloride is an ionic solid with the formula Na+Cl-.
The relative mass formula of sodium chloride is
Example:
What is the relative mass formula of water? (Relative atomic masses: H = 1, O = 16)
Solution:
The formula for water is H2O. Each molecule contains 2 hydrogen atoms and 1 oxygen atom.
The relative mass formula of water is
Today, we learnt how to calculate to thickness of aluminum foil.
Procedure
Use a centigram balance to measure the mass(g) of a rectangular piece of aluminum foil.
Use the metric ruler to measure the length(cm) and width(cm) of the aluminum foil.
Record the measurement in the table.
Repeat the procedure above two more times.
Since we've already known the density of aluminum is 2.7 g/cm3, by using the formula V=M/D, and V=LGH, we can calculate the thickness of aluminum foil!
-The massdensity
or density of a material is
defined as its mass per unit volume.
-We can use these formulas to calculate the density, mass and
the volume.
Density=mass/volume, Mass=density x
volume, Volume =mass/density
-possible units =g/mL, g/L, g/cm², kg/L etc.
-1cm³=1mL
-Density of water=1.0g/mL
Dobject > Dliquid sink
Dobject < Dliquid float
water density
Temp(°c)
Density(kg/m³)
100
958.4
80
971.8
60
983.2
40
992.2
30
995.6502
25
997.0479
22
997.7735
20
998.2071
15
999.1026
10
999.7026
4
999.9720
0
999.8395
-10
998.117
-20
993.547
-30
983.854
-Density problem
1. What is the density of a piece of wood
that has a mass of 25.0 grams and a volume of 29.4 cm3?
Answer:
D=25.0g/29.4cm³=0.850 g/cm3
2. A piece of wood that measures 3.0 cm by 6.0 cm by
4.0 cm has a mass of 80.0
grams. What is the density of the
wood? Would the piece of wood float in water? (Volume = L x W
x H)
Answer: V=3*6*4=72cm³
D=80.0g/72cm³=1.1
g/cm3; No, it would not float on water
3. I threw a plastic ball in the pool for my dog to
fetch. The mass of the ball was 125 grams. What
must the volume be to have a density of 0.500 g/mL.
Measurement and Uncertainty -No measurement is exact. -Only count a set of object can get an exact number.
Absolute Uncertainty Method1:
make at least three measurement
calculate the average
the absolute uncertainty is the largest difference between average and lowest or highest reasonable measurement
Example:
trial# Mass of object(g)
1 20.5
2 20.6
3 20.3
4 19.5 (remove)
5 20.7
(20.5+20.6+20.3+20.7)/4=20.5g
Average:12.5
Difference between average and lowest:20.7-20.5=0.2g
Difference between average and highest:20.5-20.3=0.2g
The mass would be recorded as 20.5±0.2g
Method2: Determine the uncertainty of each instrument Always make the best precision that you can,estimate to a fraction 0.1 of the smallest segment on the instrument scale.
Relative uncertainty=absolute uncertainty/estimated measurement can be expressed in
