LLG
Paris–Abu Dhabi
Advanced Math and Science Pilot Class
Academic year 2014-2015
Assignments - Chemistry
Assignments : the mole concept, solution, concentration.
I.
Basics knowledge:
1) A drink is prepared by dissolving fructose and potassium chlorine into water
a- What is the solvent?
b- Which solute is a molecular species?
c- Which solute is a ionic species?
2) Which of this processes is a dissolution:
a- An ice cube “disappearing” when put into a glass full of water.
b- A cube sugar “disappearing” when put in a hot tea.
c- A piece of butter “disappearing” inside the bread when left in the sun.
3) In order to make a 500 mL drink more salted, we add 1.0 g of sodium chloride in it.
a- What is the formula to calculate the mass concentration in sodium chloride of this drink?
b- What is its value?
4) The molar formula of fructose is C6H12O6. What is its molar mass?
5) What is the formula used to calculate the amount of substance of fructose in a sample containing 45g of
it. What is the corresponding value?
II.
Number of entities and amount of substance
Give the amount of substance n corresponding to the following numbers of entities:
a) 12.05 x 1022
c) 3.01 x 1024
III.
b) 6.02 x 1021
d) 1.5 x 1023
Amount of substance and number of entities
Give the number of entities N present in the following amount of substance:
a) 4.5 mol
d) 15 mol
IV.
b) 3.0 mmol
e) 0.0005 mol
c) 60 µmol
Molar mass of molecules or compounds
Calculate the molar mass of the following compounds :
a) dichlorine Cl2
d) chloroform CHCl3
g) talc Mg3(OH)2Si4O10
V.
b) acetone C3H6O
e) lactic acid C3H6O3
h) topaz Al2F2SiO4
c) ammonia NH3
f) potassium permanganate KMnO4
Amount of substance
1) Calculate the amount of substance present in the following samples :
a) 100 g of SiO2
d) 300 mg of C8H9O2N.
b) 10 mg of Au
c) 2.2g of C27H46O
LLG
Paris–Abu Dhabi
Advanced Math and Science Pilot Class
Academic year 2014-2015
Assignments - Chemistry
2) A conical flask contains 68.4 g of octane C8H18. How many molecules of octane are there in the flask? (First
calculate the amount of octane, then the number of molecules).
3) How many ions are there in 20g of magnesium oxide MgO ?
VI.
Relation between mass, number of molecules and number of moles.
Complete the table below:
Substance
Molar mass of
substance
Mass of
substance
present
Number of
moles of
substance
present
Number of
molecules/
formula units
present
Sulphuric acid
3.612  1023
(H2SO4)
Sodium
hydroxide
2.0 g
(NaOH)
Potassium
carbonate
2.4 mol
(K2CO3)
(Molar masses: M (C) = 12.0 g.mol-1, M (H) = 1.0 g.mol-1, M (K) = 39.0 g.mol-1, M (Na) = 23.0 g.mol-1, M (O)
= 16.0 g.mol-1, M (S) = 32.0 g.mol-1).
VII. Characteristics of several solids and liquids.
Complete the table below:
Substance
Ice H2O
Stearic acid C18H36O2
Molecular molar
mass (g.mol-1)
Density (g.mL-1)
0.92
0.94
Amount of substance
1.5
(mol)
Volume (mL)
Octane C8H18
0.70
3.5
120
VIII. Some problems:
1) Caffeine and cola:
Cola drinks usually contain caffeine (molecular formula C8H10O4N2) in
their composition.
A 330 mL can contains a mass m = 35 mg of caffeine.
a) Calculate the molar mass of caffeine.
b) Calculate the amount of substance of caffeine in a can.
c) What is the molar concentration im caffeine?
d) What volume of coffee whose molar concentration in caffeine would be C’ = 6.2×10-3 mol.L-1
would bring the same amount of caffeine as the can of cola drink?
e) How many times should the coffee be diluted so that its concentration in caffeine be the same as the
concentration in the can.
LLG
Paris–Abu Dhabi
Advanced Math and Science Pilot Class
Academic year 2014-2015
Assignments - Chemistry
2) Composition of sweat:
The following table is giving information concerning the composition of sweat. Fill the blanks.
Solute
Molar mass:
M(g.mol-1)
Mass in 200mL of
sweat: m (g)
Amount of
substance in 200mL
of sweat: n (mol)
Mass
concentration: Cm
(g.L-1)
Molar
concentration: C
(mol.L-1)
Sodium ions
Potassium ions
Calcium ions
Vitamin C
(C6H8O6)
0.12
1.5×10-3
8.0×10-4
2.8×10-4
3) Lemonade recipe:
To prepare one liter of lemonade, it is necessary to dissolve 10.0 g of
sucrose (C12H22O11), 22.0 g of glucose (C6H12O6) and 3.5 g of citric acid
(C6H8O7) into water.
a- Give the amount of substance and the molar concentration of
each ingredient in one litre of lemonade.
b- What are the amounts of substance of sucrose, glucose and citric
acid in a 180 mL glass of lemonade?
c- One lump of sugar (5.3 g of sucrose) is added to 180 mL of
lemonade. Assuming negligible the volume variation during the
dissolution, calculate the new concentration of sucrose, glucose
and citric acid in the beverage.
4) Tea with sugar:
To rehydrate after a long training, an athlete prepare a tea and add 3
sugar cubes in a 20 cL cup.
DATA: ● The sugar used is saccharose: C12H22O11
● The mass of a cube sugar is 5.3 g
a- What is the mass concentration in saccharose of the tea?
b- What is the molar mass of saccharose?
c- What is the molar concentration in saccharose?
d- Eventually, the athlete finds its tea too sweet, he pours it into a
500mL flask and add hot water to obtain 500mL of diluted tea.
What is the new molar concentration of the diluted tea?
What is the dilution factor?
5) Orange juice:
Orange juice is an aqueous solution containing a lot of solute among 4.5 mmol.L-1 of ascorbic acid:
C6H8O6.
a- What is the mass of ascorbic acid in a 0.75L bottle of orange juice?
b- What is the mass concentration in the juice?
c- What is the molar concentration in a 0.1L glass of orange juice?
d- What is the molar concentration if the juice is diluted with a volume of water identical to the volume
of juice?