Chemistry - Mole Concept and Stoichiometry

Question 1

What is the formula for no. of moles with the number of particles in a mole?

Answer 1

No. of moles = Quantity (number) / 6.02 x 10^23

Question 2

What is the formula for percentage by mass of an element in a compound?

Answer 2

((no. of atoms of element in formula x Ar of element)/Mr of compound) x 100%

Question 3

What is the formula for no. of moles with mass?

Answer 3

No. of moles = Mass (g) / Molar Mass (g mol^-1)

Question 4

What is the formula for concentration of a solution?

Answer 4

Conc. (mol dm^-3) = No. of moles / Vol of solution (dm^3)

Question 5

What is the formula for volume of gas?

Answer 5

No. of moles = Vol of gas (dm^3) / Molar vol. (22.7 dm^3 at s.t.p.)

Question 6

What is the formula for concentration from mol dm^3 to g dm^3?

Answer 6

Conc. (g dm^-3) = Conc. (mol dm^-3) x Molar Mass (g mol^-1)

Question 7

What are the steps to find the empirical formula?

Answer 7

1. Write the mass/g or the percentage of each element
2. Write down the relative atomic mass
3. Write the number of moles/mol separately (step 1/step 2)
4. Write the mole ratio (divide values by lowest value)
5. Simplest whole number ratio (multiply values until they are a whole number)
6. Find the empirical formula from those values

Question 8

What is the formula for percentage yield and percentage purity?

Answer 8

Percentage yield = actual yield/theoretical maximum yield x 100%

Percentage purity = mass of pure substance in sample/total mass of impure sample x 100%

Question 9

What is the conversion for cubic decimetre?

Answer 9

1m3 = 1000dm3 = 1000000cm3