Stoichiometry

Question 1

stoichiometry?
one mole of water?

Answer 1

the study of the relationships b/w the amounts of reactants & products.
6.023 x 10^23 H2O molecules

Question 2

SI unit for weighing & counting atoms, molecules & ions?
what is it?

Answer 2

mole
a mole is the amount of substance that contains 6.023 x 10^23 representative particles.
This experimentally determined no. is called Avogadro’s number.

Question 3

molar volume?
22.414 dm³ of H₂ gas at STP=?

Answer 3

One mole of any gas at STP occupies a volume of 22.414 dm³.
This volume is called Molar volume.
2g = 6.02 x 10^23 molecules.

(standard temp. & pressure)

Question 4

Determine the volume of 2.5 moles of chlorine molecules at STP.

Answer 4

1 mole of Cl₂ occupies a volume of 22.414 dm³ at STP.
2.5 mole of Cl₂ occupy a volume of 22.414dm³ x 2.5 = 56.035dm³

Question 5

density?
density of a gas is depended on ____________.

Answer 5

mass per unit volume of a substance.
its molar mass.

a gas having higher molar mass will have higher density & vice versa.

Question 6

Calculate the gram molecular mass of a gas which has density of 1.43 g/dm³ at STP.

Answer 6

1 dm³ of gas at STP = 1.43g
22.4 dm³ of gas at STP = 1.43 x 22.4
= 32.032g
As 22.4 dm³ of a gas at STP = molar mass
Therefore, gram molecular mass of gas is 32.032 amu.

Question 7

what does a balanced chemical equation tell us?
2H2(g) + O2 → 2H₂O(g)

Answer 7

pg 82

Question 8

How much MgO formed when 4 moles of magnesium react with excess of O₂. Also calculate
moles of O₂ required?

Answer 8

2 moles of Mg produce MgO = 2 moles
1 moles of Mg produces MgO = 2/2
4 moles of Mg produce MgO =2/2 x4 = 4moles of MgO
So 4 moles of Mg give 4 moles of MgO
4 moles of Mg will require:
pg 84

Question 9

Potassium chlorate is used in making matches and dyes, on decomposition, it produces KCl and
oxygen gas.
If 25 g KCIO3 is decomposed, calculate
a) How many moles of O2 are produced.

Question 10

20g of H,50, on dissolving in water fonizes completely.Calculate
a) No. of H₂SO, molecules
b) No. of H* and so
c) Mass of individual ions

Question 11

what is the most common conc. unit in solutions?

Answer 11

molarity
The molarity of a solution is simply
the numerical value of its conc. in mol/dm³.

Question 12

molarity? formula? units?

Answer 12

Molarity is the conc. unit in which amount of solute is expressed in moles & quantity of solution in dm³
“Molarity is defined as the no. of moles of solute dissolved per dm³ of solution”.
M =mole of solute/dm³ of solution

Question 13

how to find no. of moles?

Answer 13

no. of moles= mass in gm/molar mass

Question 14

what does 12.1M of HCl mean?

Answer 14

12.1 moles of HCI
in each dm³ of solution

Question 15

When 250cm³ of 0.1M AgNO3 solution is added to an excess of NaCl solution. What mass of AgCl
will be formed.

Answer 15

pg 87

Question 16

When two solutions are mixed, we proceed as follows

Answer 16

pg 87
MiV1: M₂V2 = n1: n2

Question 17

LIMITING & NON LIMITING REACTANTS

Answer 17

• the reactant that is completely consumed in the reaction & limits the amounts of product formed is called limiting reactant
• reactant that is left unreacted after the completion of reaction is called non limiting or excess reactant.

Question 18

Theoretical yield?
actual yield?

Answer 18

• The amount of product as calculated from the balanced chemical equation
• Quantity of product produced experimentally in a chemical reaction

Question 19

percent yield?

Answer 19

100 times the ratio of the actual yield to the theoretical yield.
Percent yield = Actual yield/ Theoretical yield x 100

Question 20

Importance of stoichiometry in the production and
dosage of medicine

Answer 20

• In the prep. of antibiotics, the stoichiometry ensures that each dose matches the active ingredient & target bacteria.
• Use of insulin relies on the stoichiometry to precise control of blood sugar levels.
• Stoichiometry determines the conc. of viral antigens in the prep. of vaccine for effective results.

Question 21

relationship b/w molar volume & NA?

Question 22

how to find moles when vol. is given?

Answer 22

moles= volume/ 22.414 dm3

Question 23

find no. of molecules/atoms when moles is given?

Answer 23

no. of molecules=moles x NA

Question 24

how to indentify a limiting reactant?

Answer 24

calculate moles
the one that has least amount is limiting reactant