Quantative Chemistry

Question 1

How do you find the percentage of an element?

Answer 1

N x Ar/Mr x 100

Question 2

Calculate the % of sodium in sodium oxide (Na2O)

Answer 2

2 x 23/62 x 100 = 79.19
We need to find the atomic mass of sodium which is 23.
But the Mr of the compound Na2O is 62 since 23x2+16 = 62
Then multiply by a hundred.

Question 3

What is the avogadro number?

Answer 3

6.02x10*23

Question 4

What is the equation for the mole concept (avogadro constant)

Answer 4

Number of molecules/particles
Number of moles Avogadro constant

Question 5

How do you know what to solve for in the questions you will be given

Answer 5

If they’re asking to calculate the number of molecules/ particles: Avogadro constant
If they’re asking you to calculate the concentration of a solution in mol/dm3 and g/dm3: Mass/vol Mass
Conc Vol
If they’re asking you to calculate the maximum/minimum mass of a compound: find the moles, the ratio, then calculate the mass.
If they’re asking you to calculate the volume of gases in a reaction:
Volume
Mole Molar volume