Avogadro's Number
Avogadro's number is 6.02x10^23. What this means is that there are exactly 6.02x10^23 particles in a mole of any element / atom.
For example:
Carbon 12
12 being an isotope meaning 12g of carbon is a mole.
IF there were 6g we can predict how many atoms of carbon there are.
( 6.02x10^23 ) x 0.5 = 3.011x10^24
Avogadro's Number There is half a mole of carbon (6/12 = 1/2) Amount of particles in 6g of carbon 12.
For example:
Carbon 12
12 being an isotope meaning 12g of carbon is a mole.
IF there were 6g we can predict how many atoms of carbon there are.
( 6.02x10^23 ) x 0.5 = 3.011x10^24
Avogadro's Number There is half a mole of carbon (6/12 = 1/2) Amount of particles in 6g of carbon 12.
Significant Figures
In chemistry if a specific rule about rounding isn't given in the question, see how many the question uses. Then change your answer according to these simple rules
- Any number that isn't 0 is significant e.g 7 ✓
- A 0 that is between two numbers (not 0) is significant e.g 0.604 / 604.2 ✓
- Any 0 before non-zero digits is not significant e.g 0.0024✘
- Any 0 that is after non-zero digits is only significant.if there is a decimal point e.g 41000 ✘
Molar Mass
Molar mass gives the mass in grams in each mole of the substance. Molar mass in all cases is Relative Atomic Mass.
n = amount of substances
m = mass
M = molar mass
mass (m)
amount (n) = ------------------------
molar mass (M)
Examples:
"Calculate the amount of substance, in moles, in 96.0g of carbon, C."
n = m/M = 96/12 = 8.0 mol
"Calculate the mass, in g, of 0.050 mol of NO2"
m=nxM = 0.050 x 46.0 = 2.3g
"Calculate the molar mass when 2.65g contains 0.025 mol of a substance.
M=m/n = 2.65/0,025 = 106.0g/mol
- Molar mass is the mass per mole of a substance
- The units of molar mass are g mol^-1
n = amount of substances
m = mass
M = molar mass
mass (m)
amount (n) = ------------------------
molar mass (M)
Examples:
"Calculate the amount of substance, in moles, in 96.0g of carbon, C."
n = m/M = 96/12 = 8.0 mol
"Calculate the mass, in g, of 0.050 mol of NO2"
m=nxM = 0.050 x 46.0 = 2.3g
"Calculate the molar mass when 2.65g contains 0.025 mol of a substance.
M=m/n = 2.65/0,025 = 106.0g/mol
Advanced Questions
"Calculate the molar mass of glucose, C6H12O6."
C = 12 H = 1 O = 16
(12 x 6) + (1 x 12) + (16 x 6)
72 + 12 + 96 = 180 gmol^-1
"If the molar mass of glucose weighed out in grams contains 6.02x10^23 molecules of glucose, calculate the number of molecules in 45g of glucose"
If 180g mol^-1 is one mole - 45g is clearly one quarter.
1/4 x (6.02x10^23) = 1.505x10^23
C = 12 H = 1 O = 16
(12 x 6) + (1 x 12) + (16 x 6)
72 + 12 + 96 = 180 gmol^-1
"If the molar mass of glucose weighed out in grams contains 6.02x10^23 molecules of glucose, calculate the number of molecules in 45g of glucose"
If 180g mol^-1 is one mole - 45g is clearly one quarter.
1/4 x (6.02x10^23) = 1.505x10^23