Quiz-Counting Atoms (IGCSE CHEMISTRY)

Quiz-Counting Atoms (IGCSE CHEMISTRY)

quiz   19:40

QUIZ – COUNTING ATOM

NAME/#        : __________________________

DAY, DATE        : __________________________        

1. Calculate the volume of the 3.2 g of sulphur trioxide gas at r.t.p condition and at s.t.p condition

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2.  A sample of carbon monoxide gas, CO, has volume of 6 dm3 at r.t.p.

1. How many moles of the gas are there in the sample?

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2. How many particles are there

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3. What is the mass of the sample?

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3. An unknown compound is analyzed and found to consist of 24.3 % carbon, 4.1 % hydrogen, and 71.6 % chlorine.  If the molecular mass of the compound is 98.8, what is the molecular formula of the compound?

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4. The element boron forms several compounds that contain only boron and hydrogen. A sample of one of these compounds weighing 56 g was found to contain 44 g of boron.

1. Find the ratio of the number of hydrogen atoms to the number of boron atoms in the compound.

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2. The rtelative molecular mass of the compound is 28. Write the chemical formula for this compound of boron and hydrogen.

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5. Hydrated sodium carbonate has the formula Na2CO3.nH2O. on strong heating, Hydrated sodium carbonate decomposes completely into water and anhydrous sodium carbonate, CuSO4. The formula of Hydrated sodium carbonate was found by the following procedure.

                

        A mass of Hydrated sodium carbonate was heated strongly in a crucible until decomposition was complete.

                        

the following result was obtained.

Mass of empty crucible = 11.50 g

Mass of crucible +         hydrated copper(II) sulphate = 17.22 g

Mass of crucible + anhydrous copper(II) sulphate =  13.62 g

1. Suggest how you could find out when the decomposition of Hydrated sodium carbonate is complete                                                                                

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2. Calculate the mass of water evaporated  in the decomposition, and the number of moles of the water.        

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3. Calculate the mass of anhydrous sodium carbonate produced in the decomposition, and the number of moles of Na2CO3                                                                     

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4. Find the value of n in the formula                                                            

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Counting Atoms - Moles (IGCSE CHEMISTRY) slide presentation

Counting Atoms - Moles (IGCSE CHEMISTRY) slide presentation

Quantitative Chemistry   19:37

CH. 9 COUNTING ATOM

KKCS International Program

Chemistry IGCSE

Mr. Markus

MOLE CONCEPT

• The mole is defined as the amount of substance that contains as many particles as the number of carbon atoms, in exactly 12 grams of carbon-12

• The number is equal to 6.0 x 10 23  particles (Avogadro’s number)

• The mole is abbreviated as mol

• The mole is a counting unit used in chemistry to deal with atoms, molecules and ions.

• Example:

1 mole of carbon atoms = 6.0 x 10 23  C atoms

1 mole of ammonia molecules = 6.0 x 10 23  NH3 molecule

1 mole of sodium ions = 6.0 x 10 23 Na+  ions

• To change the number of particles to the number of moles :

number of moles = number of particles

                                       6.0 x 10 23

• To change the number of moles to the number of particles

Number of particles = (number of moles) X (6.0 x 10 23 )

EXERCISE

1. A sample of sodium contains 3.0 x 1020  Calculate the number of moles of sodium.

2. Determine the number of molecules in 0,5 moles of carbon dioxide.

3. How many H atoms are in 0.80 moles of hexane. C6H14?

4. How many NH4+ ions are in 1.5 moles of (NH4)3PO4?

5. How many molecules are there in 0.2 mole of sulphur dioxide, SO2? How many atoms are present?

MASS MOLAR

• The mass in gram of 1 mole of substance is caleed its molar mass

• The molar mass of any substance is always equal to its relative formula mas in gram, :

a. The mass of 1 mole of atom is equal to its relative atomic mass in grams/Ar

b. The mass of 1 molelecules is equal to its relative molecular mass in grams/Mr    

c. The mass of 1 mole of units of ionic compound is wqual to its relative formula mass in grams 

Ex. 1

Relative atomic mass of magnesium, Mg = 24

Hence, mass of 1 mole of Mg atoms = 24 g,

i.e. Molar mass Mg = 24 g/mol

Ex.2

Relative molecular mass of Ammonia,

NH3 = 14 + 3(1) = 17

Hence, mass of 1 mole of NH3 molecules = 17 g

i.e. Molar mass of NH3 = 17 g/mol

Ex.3

Relative formula mass of nitrate ion,

NO3- = 14 + 3(16) = 62

Hence, mass of 1 mole of NO3- ions = 62 g

i.e. Molar mass of No3- = 62 g/mol

• To convert moles to mass, use the following:

mass of substance = 

(number of moles of substance) x molar mass of subst.

• Mass to moles

number of mole of substance

=       mass of substance

    molar mass of substance

Example:

Calculate the mass of 2.50 moles of Al atoms

Solution:

Relative atomic mass of Al (Ar Al) = 27.0

Molar mass of Al = 27 g/mol

Mass of 2.50 moles of Al atoms 

= (moles) x (molar mass)

= 2.50 mol x 27.0 g/mol

= 67.5 g 

1. Calculate the mass of 1.12 moles of sulphur trioxide molecules.

2. Calculate the number of moles of molecus in 66 g of carbon dioxide.

3. Calculate the  number of moles Pb(CH3COO)2 in 250 g of lead(II) ethanoate

4. Calculate the number of moles of each element present in 1 mole of each of these:

a. Sucrose, C12H22O11

b. Calcium phosphate, Ca3(PO4)2

1. Calculate the mass of 1.12 moles of sulphur trioxide molecules.

Answer:

Mr SO3 = 32+3(16) = 80 g/mol

Mass of SO3 = 1.12 mol x 80 g/mol

= 89.6 g

2. Calculate the number of moles of molecus in 66 g of carbon dioxide.

Ans:

Mr CO2 = 12 + 2(16) = 44 g/mol

Moles of CO2 = 66 g = 1.5 mol

  44 g/mol

3. Calculate the  number of moles Pb(CH3COO)2 in 250 g of lead(II) ethanoate

Ans:

Mr Pb(CH3COO)2 = 207 + 4(12) + 6(1) + 4(16)

        = 325 g/mol

Moles of Pb(CH3COO)2 = 250 g       =  0.769 mol

325 g/mol

4.  Calculate the number of moles of each element present in 1 mole of each of these:

a. Sucrose, C12H22O11 

Ans: Carbon = 12 moles, Hydrogen = 22 moles, Oxygen = 11 moles

b. Calcium phosphate, Ca3(PO4)2  

Ans: Calcium 3 moles, Posphate 2 moles, oxygen 8 moles

5. Calculate the number of moles of each element present in 100 g of each of the following:

a. (NH4)2Cr2O7

b. Na2CO3.10H2O