Like this presentation? Why not share!

# Chemical Calculations P

## by Science Café, Science Teacher at Bishops Diocesan College on May 11, 2010

• 3,090 views

A set of slides created to teach Chemicals Calculations P to learners at Bishops Diocesan College in Cape Town.

A set of slides created to teach Chemicals Calculations P to learners at Bishops Diocesan College in Cape Town.

### Views

Total Views
3,090
Views on SlideShare
3,089
Embed Views
1

Likes
0
81
1

### Categories

Uploaded via SlideShare as Microsoft PowerPoint

### Report content

11 of 1 previous next

• A.malik ali thid do help full with my exam for the next week
10x
6 months ago
Are you sure you want to

## Chemical Calculations PPresentation Transcript

• THE NEUTRAL ATOM
The atom consists of a nucleus containing protons and neutrons surrounded by a cloud of electrons.
Atomic NumberZ - Number of protons in the Nucleus = number of electrons in a neutral atom.
Mass numberA = Number of protons + neutrons.
Notation
ZAX
Mass Number (bigger)
symbol
Atomic Number (smaller)
• Relative Mass Atomic
Certain products, such as paper for example, are sold by the ream. A ream is 500 sheets. Since it is impractical to actually count out 500 sheets, the weight (mass) of 500 sheets is determined; then each ream is packaged according to this mass.
Atoms are even smaller than paper, so it is not possible to actually count them. However, it is possible to know the mass of an atom in respect to the mass of another atom. To see how this is done we will used an analogy of oranges and grapefruits.
A given number of oranges have a mass of 3000 grams. An equal number of grapefruits have a mass of 5000 grams. Assuming that all the oranges are the same size, and all the grapefruits are the same size as well, then the oranges have a mass of 3/5 or .60 of the mass of the grapefruits. Since there are an equal number of oranges and grapefruits, the mass of an orange is 0.6 that of a grapefruit. These numbers represent relative mass.
The Relative mass of an object is expressed by comparing it mathematically to the mass of another object. So the relative mass of an orange in relation to a grapefruit is .6. The relative mass of the grapefruit in relation to a grapefruit is 1.0.
• The Mole
The mole is defined as, “the amount of matter with the same number of elementary particles as ….. grams of carbon 12”.
602 300 000 000 000 000 000 000
Six hundred and two thousand, three hundred, billion billion !
6.023x1023 particles
C
Symbol (……)
g
12.00
Number of particles = no of moles x no. particles in a mole
Particles = …….. x …….
• The Mole and Mass
The amount is defined in such a way that the relative atomic mass (MASS NUMBER) of an element is equal to the …………of ……………..of the substance. (in grams) - THE MOLAR MASS
Eg Na = 23g/mol, water(H2O)=18g/mol
Periodic Table Symbol
MOLAR mass
…………
mass(g) of one mole
ZAX
Mass Number (bigger)
protons + neutrons
Atomic Number (smaller)
• The Carbon Standard
Carbon-12 is the standard upon which the relative mass of other atoms is determined. It wasn’t always this way.
At first hydrogen was used and it was assigned the atomic mass of one. If you have equal numbers of nitrogen atoms and hydrogen atoms, the nitrogen atoms are 14 times heavier than the hydrogen atoms. Therefore, nitrogen was assigned the atomic number of 14.
Later oxygen was used as the standard with an atomic mass of 16.
However, carbon-12 proved to be more convenient to ………….. and ……………in pure form, so it became the standard.
However, now even carbon-12 is slowly losing its position as standard, as sophisticated equipment makes it possible to give even more accurate measures of atomic mass.
• Relative Masses
Relative atomic Mass (Ar) - The mass of the atom………....... 1/12 of the mass of a ……… atom. (Number of times heavier than…)
O - 16one atom of oxygen is 16 times heavier than 1/12 of the mass of a C12 atom, Na - 23, H - 1 etc.
Formula mass (Mr) - The ……….of all the atomic masses of the atoms in a molecule.
WaterH2O
One molecule of water has a relative mass of
Mr(H2O) = (2x(…)+….) = …..
• that is the molecular or formula mass of water. One molecule of water is18 times heavier than…)
• Relative Masses - examples
Calculate the Formula masses of:
O2(oxygen gas)
Cl2 (chlorine gas)
NaCl (sodium chloride - table salt)
CaCO3(calcium carbonate)
(NH4)2Cr2O7(ammonium dichromate)
• Isotopes
Isotopes - Atoms of the ………….. element which have different numbers of …………….. Eg: 613C & 612C
Relative atomic mass is (actually) the average mass (of all the isotopes in a random sample) of the atoms of an elementrelative to1/12 of the mass of a carbon-twelve atom.
613C
• ….. protons
• …… electrons
• ……… = ….. neutrons
612C
• ….. protons
• ….. electrons
• …… = … neutrons
• Isotopes
Chlorine has two isotopes 3717Cl & 3517Cl
Cl(35) has 35-17=18neutrons Cl(37) has 20 neutrons!
37Cl (25%) & 35Cl (75%) - exist in the ratio 1:3
Calculate the average mass of a Cl atom. (Two methods)
• Relative Atomic Mass
Periodic Table Symbol
Relative atomic mass
or
mass(g) of one mole
ZAX
Mass Number (bigger)
protons + neutrons
Atomic Number (smaller)
mass of substance = number of moles x mass of 1 mole
Calculate: The mass in grams -
of one mole of copper chloride (CuCl2)
one mole of carbon dioxide (CO2)
One and a half moles of oxygen (O2)
TWO moles of methane (CH4)
Four moles of water.
m = n x Mr
• Relative Atomic Mass
Calculate: The mass in grams -
of one mole of copper chloride (CuCl2)
m(CuCl2) = 63.5 +2(35.5) = 134.5g
2. one mole of carbon dioxide (CO2)
m(CO2) = 12 +2(16) = 44g
3. 1.5 mole of oxygen (O2) m(O2) = 1.5 x 32 = 48g
4. TWO moles of methane (CH4)
m(CH4) = 2x(12 +4(1)) = 2(16) = 32g
5. Four moles of water. m(H2O) = 4 (18) = 72g
• The Mole - moles --> Mass
m = n x Mr
Calculate the mass of
2 moles of copper oxide (CuO)
0.5 moles of copper (II) sulphate (CuSO4)
0.01 moles of calcium carbonate
5 moles of ammonium carbonate
mass = moles x relative mass
• The Mole - Mass --> Moles
n = m/Mr
Eg calculate the number of moles of water that would have a mass of 100g.
n(H2O) = m/Mr = 100/18 = 5.56 mol
Eg Calculate the relative mass of a compound for which 0.001 moles have a mass of 0,0056 g.
Mr (X) = m/n
= 0.0056/0.001 = 5.6 g/mol
• The Mole - Reactions
Sodium reacts with water to form hydrogen and sodium hydroxide according to the equation.
Na + H2O  H2 + NaOH
If 46g of sodium are reacted with excess water what mass of hydrogen would be formed?
Balance the reaction
Work out moles of reactant GIVEN.
Go through the equation to find out the number of moles reacting and being formed. (Molar ratio).
• Reactions – Limiting reagent
The reagent that …………….. first and stops the reaction is known as the …………...REAGENT.
If 46g of sodium are reacted with 50g water what mass of hydrogen would be formed?
Na + H2O  H2 + NaOH
46g 2 moles 50g
n(H2O) = m/Mr = 50/18 = 2.8 mol
Na will run out first
Na is LIMITING REAGENT
What is the minimum amount of water needed to react completely with 46g of sodium??
• Mole Calculations
GIVEN
MASS
MASS
MOLES
MOLAR
RATIO
MOLES
• The Mole - mass calculations
C + O2 CO2
Carbon reacts with oxygen to form carbon dioxide as shown.
If 0.12g of carbon are reacted with excess oxygen what mass of carbon dioxide would be formed?
Balance the reaction
Work out moles of reactant (mass given).
Go through the equation MOLAR RATIO to find out the number of moles beingformed
• Mole examples - B & J p119 21 & p120 22
Na + Cl2 NaCl
Calculate the mass of salt formed if 2.3g of sodium is reacted with XS chlorine.
2. Zn + HCl ZnCl2 + H2
What mass of HCl is needed to produce 100g of hydrogen?
3. KClO3  KCl + O2
What mass of oxygen is produced from 1kg of potassium chlorate?
Fe2O3 + H2  Fe + H2O
What mass of iron is produced if 3g of rust (Fe2O3) is reacted with XS(100g )of hydrogen?
• Percentage Composition
Analysis of a compound by mass makes it possible to work out the % mass of each element.
eg Table salt: NaCl mass analysis:
One mole of NaClwould have a mass of
……..+ ……. = ………… g
The % composition can be found using the formula:
Mass ………….. X 100
………. Mass …………..
%Na = ……………………………………………..
%Cl = ………………………………………………
% Mass Element X =
• Percentage Composition from mass.
Eg2 Calculate the % of oxygen in water.
• Empirical and Molecular Formulae.
A compound consists of carbon, hydrogen and oxygen only. The % by mass are Carbon 52.2% and 13.0% hydrogen. Calculate the formula of the compound.
• Empirical and Molecular Formula.
CH3COOH or C2H4O2
Mr: 2(12)+4(1)+2(16)=60g.mol-1
%C: (24/60)x100 = 40.0%
%H: (4/60)x100 = 6.7%
%O: (32/60)x100 = 53.3%
• Empirical and Molecular Formulae.
Eg3. If a compound consisting of nitrogen and oxygen only - contains 30.4% by mass of nitrogen. What is the molecular formula of the compound? >>
• solute
solute
Concentration - Molarity
The concentration of a solution is defined as the ………………. of ……………………… per ………………. (dm3) of ………………….
Final volume of ……………..
+
500cm3
=
30g of NaCl
Amount of ……… (……….)
Volume of ………………
n
v
Concentration =
C =
• Volume Conversions
1 dm3 (1 litre)
10 cm3
1cm3
10 cm3
10 cm3
1 dm = 10 cm
1 dm3 = 1000 cm3
1 m3 = 1000 dm3 = 1000 000cm3
• Decimal Conversions