Formulae, Stoichiometry and the Mole Concept

Question 1

can try to draw the triangles in ur head?

How to calculate relative atomic mass?
(mass)

Answer 1

no.of mol x Mr = relative atomic mass

Mr(molecular mass)

Question 2

How to find no. of mol? using mass and Mr?

Answer 2

mass ÷ Mr

Question 3

How to find vol of a liquid?

Answer 3

no. of mol ÷conc.

Question 4

Hint: conc, is mol/dm^3

How to find the concentration of a sol?

Answer 4

no. of mol ÷ vol(dm^3)

Question 5

How to find vol of gas?

Answer 5

no.of mol x 24dm^3

rmb? violin, number, 24? the triangles

Question 6

how to convert 25cm^3 to dm^3?

Answer 6

25/1000

always divide by 1000 to find dm^3

Question 7

How to calculate percentage of an element in a compound?

Answer 7

(mass of element x Mr ) x 100
what is the percentage composition of H2 in H20?
Chemical formula: H2O
Mr: 2(1)+ 16=18
% of H= (2÷18)x100= 11.2%
% of H2 in H20? = (11.2÷100)=11.2%

Question 8

In 25 cm3 sample of wine, there is 15 g of ethanol. What is the concentration (g/dm3) of ethanol in a bottle of wine?

Answer 8

15÷(25/1000)=600g/dm3

Question 9

A sample of potassium hydroxide is prepared by dissolving 3.36 g of solid potassium hydroxide in 120 cm3 of water. What is the concentration of the
solution in mol/dm3?

Answer 9

Moles of KOH = 3.36 g÷ (39+16+1)
=0.06mol
Concentration = 0.06 mol / 0.120 dm³
= 0.5 mol/dm³

Question 10

define relative atomic mass, Ar

Answer 10

we can define relative molecular mass as
Relative molecular mass =
(Mass of one molecule of a substance)
————————————
(Mass of 1/12 of an atom of carbon-12 atom)

Question 11

how to find limiting reactant in a chemical eqn?

Answer 11

1) find no. of mol of each reactant
2) find mol ratio
3) reactant in excess and reactant that is the LR
4) use LR in subsequent chemical eqns(according to what the qn wants u to find)

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