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UNASANA COLLEGE MOLE AND CHEMICAL
CALCULATIONS WORKSHEET FOR 2ND GRADES MOLE
NUMBER
n=m/mw or Aw
n=V/22,4 ( at STP, for gases)
n=NA or Nm / 6,02.1023
Ex: Calculate the molecular weights of
a) sodium hydroxide b) calcium carbonate
c) nitric acid
d) water
e) sodium carbonate f) potassium permanganate
g) silver nitrate
h) acetic acid
solution:
a)Mw ( NaOH)= 23+16+1=40g/mol
b) Mw (CaCO3)= 40+12+3.16=100g/mol
c) Mw (HNO3) =1+14+3.16=63 g/mol
d) Mw (H2O) =2.1+16=18 g/mol
e) Mw ( Na2CO3)=23.2+12+3.16=106 g/mol
f) Mw (KMnO4) =39+55+4.16=158 g/mol
g) Mw (AgNO3)=108+14+3.16=170 g/mol
h) Mw (CH3COOH)=2.12+2.16+4=60 g/mol
Ex : Find the mole number of followings…
a) 112 g. of Iron
b) 30 g. of acetic acid
c) 33.6 L of carbondioxide gas at STP
d) 12,04.1022 water molecules
Solution:
a)
b)
c)
d)
n=112/56 = 2 moles
n=30/60 = 0.5 mole
n=33.6/22.4 = 1.5 mole
n= 12,04.1022/6,02.1023 = 0.2 mole
Ex: What is the mass of 11.2 L of sulphur dioxide gas at STP ?
n= 11.2/22.4 = 0.5 mole
0.5= m/64 → m= 32 g.
Ex : How many molecules are there in 72 g of water ?
n= 72/18 = 4 moles 4=Nm/6,02.1023→ Nm = 24,08.1023
Ex : 0.05 mol X2O3 weights 5.1 g calculate the atomic
weights of X ?
0.05 = 5.1/ Mw → Mw = 102 → 2.X+3.16 → X= 27 g/mol
(Al )
Ex: A 0.4 mol mixture of nitrogen monoxide and
nitrogendioxide gases weights 16.8 g what is the mole
percentage of nitrogen monoxide in the mixture
NO
x mol
NO2
UNASANA COLLEGE
y mol
x+y =0.4
30x + 46y = 16.8
16y=4.8
→ y=0.3 ,x=0.1
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Ex: What is the mass percentage of carbon in acetic acid ?
M(CH3COOH)=60 g/mol
mC=24
%(C) =
24/60.100=%4
Ex: If 40% of XO3 is X by weight , what is the molecular
weight of
the compound ?
60% 48
100% X
X=80 g/mol
Reaction Review:
t
Decomposition: CaCO3 → CaO + CO2
t
KClO3 → KCl + 3/2 O2
H2O
HgO
Elect.
→
H 2 + ½ O2
t
→ Hg + ½ O2
Synthesis : 2 Al + 3 Cl 2 → 2AlCl3
4 Na + O2 → 2Na2O
CaO + H2O → Ca(OH)2
SO3 + H2O → H2SO4
Single Displacement: 2KCl + F2 → 2KF + Cl2
KF + Cl2 → no
CuCl2 + Zn → ZnCl2 + Cu
Double Displacement: AgNO3 + HCl → AgCl ↓ + HNO3
BaCl2 + H2SO4→ BaSO4 ↓ + 2 HCl
AgNO3 + KI → AgI ↓ + KNO3
STOICHIOMETRIC CALCULATIONS
Mole calculations related to coefficients of a chemical equation
is called STOICHIOMETRIC CALCULATION.
xA
+
yB
x molecules
→
zC
y molecules
z molecules
x mol of A react with y mol of B produce z mol of C
example:
2H2 + O2  2H20
UNASANA COLLEGE
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Ex: 2C + O2 → 2CO 2 moles of carbon react with 1 mole of
oxygen to form 2 moles of carbon monoxide.
Ex : When 2 moles of sodium are put into water , what volume
of hydrogen will form at STP ?
Na
1 mol
2 mol
+
H2O → NaOH + ½ H2↑
0.5 mol
1 mol =22.4 L
Ex: How many liters of carbon dioxide gas can be obtain from
the decomposition of 50 g calciumcarbonate at STP ?
CaCO3  CaO +CO2
t
CaCO3 → CaO + CO2↑
n =50/100
n = 0.5 = V/22.4 → V= 11.2 L
= 0.5
Ex: Calculate the volume of air needed for the combustion of
23 g ethanol C2H5OH ?
(air contains nearly 20% oxygen by volume ) (C:12 , O:16,
H:1 )
C2H5OH  CO2 + H2O
(unbalanced equation)
C2H5OH + 3O2 → 2CO2 + 3H2O
n = 23/46
1.5 mol
= 0.5
1.5= Vo2/ 22.4 → Vo2 = 33.6 L Vair = 5
. 33,6 = 168.0
Ex : 54 g sample of Aluminum is reacted with hydrochloric
acid ;
a) How many molecules of Aluminum chloride can form
?
b) How many liters of gas can form at STP ?
Al + HCl  AlCl3 + H2 (unbalanced equation)
2Al + 6 HCl → 2AlCl3 + 3H2 ↑
2 moles
UNASANA COLLEGE
2 moles
nAl=54/27=2 mol
3 moles
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1 mol
6,02.1023
2 mol
X
x
x= 12,04.1023 molecules of AlCl3
1 mol
22.4 L
3 mol
x= 67.2 L H2
Note : We can use volume coefficient relationship if
substances are gases.
N2(g) + 3H2(g) → 2 NH3 (g)
1L
3L
2L
1 mol
3 mol
2 mol
Ex:Calculate the volume of hydrogen and nitrogen to
produce 60L of ammonia ?
N2 + 3H2 → 2 NH3
30 L
90 L
60 L
Limiting Reagent
In a chemical reaction, the limiting reagent is
the substance which is totally consumed when the chemical
reaction is complete. The amount of product formed
is limited by this reagent since the reaction cannot proceed
further without it. The other reagents may be present in
excess of the quantities required to react with the limiting
reagent.
4 chairs 5 students ( each can take 1 students)
4 chairs
5 students
limited
excess
excess part does not react
LIMITING & EXCESS PROBLEMS
Ex:
When 2 moles of hydrogen and 2 moles of oxygen are reacted
to give water, which one becomes excess reagent?
How many grams of water can be obtained at most?
2H2
+
initial: 2 moles
reacted:2moles
excess: limit
O2 →
2 moles
1mol
1 mol
excess
2 H2O
----2 moles formed
mH2O=2*18=36 g
Ex:
18 g of carbon and 8 g of oxygen are reacted to form
carbondioxide wwhich element and how many grams remain
behind
UNASANA COLLEGE
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C
+
O →
CO2
nc= 18/12=1.5 mol
nO2=8/32=0.25 mol
1.5 mol
0.25 mol
1.25 mol of carbon is excess
1.25= m/12 →m=15g
Ex:
If 20 L of nitrogen and 15 L of hydrogen gases are reacted,
which gas will be excess? And how many liters?
N2 + 3 H2 → 2NH3
1L N2
3L H2
5L
15L
XL
15 L H2
15L nitrogen excess
X= 5L
Ex:
Equal weights of sodium and chlorine are reacted to give 0.1
mol of sodium chloride. Which element remain behind ?
and how many grams ?
2Na + Cl2 →
/23 →mNa = 2.3g
0.1mol 0.05mol
→mCl2=3.55g
initial
excess
3.55g
mexcess
Na
2 NaCl
0.1mol
0.1= mNa
0.05=mCl2/71
3.55g
= 3.55- 2.3 = 1.25g
CONSECUTIVE
REACTIONS
Some substances can be obtained in a few reactions.
Ex:
can be
steps.
Ex:
the
S + O2 → SO2
2SO2 + O2 → 2SO3
As you see sulphuric acid
SO3 + H2O → H2SO4
obtained from sulphur in 3
How many liters of oxygen at STP will be needed to burn
methane obtained from 14,4 g of aluminum carbide?
Al4C3 + 12H2O → 4 Al(OH)3 + 3 CH4
0.1
0.3 mol
CH4 +
0.3 mol
2O2 → CO2 + 2H2O
0.6 mol
0.6=V/22.4 → V=13.44 L
Ex: Nitric acid can be obtained in three steps from ammonia
nitric
4NH3 + 5O2 → 4NO + 6 H2O
0.5 mol
0.5mol
11.2 L of
2NO + O2 → 2NO2
0.5mol
0.5 mol
4NO2 + O2 → 4HNO3
mol
UNASANA COLLEGE
How many grams of
acid can be from
ammonia at STP
nNH3=11.2/22.4=0.5
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0.5mol
mHNO3=31.5 g
0.5 mol
0.5=m/63 →
Ex : Synthetic alcohol is produced according to the reactions
;
CaC2 + 5H2O → Ca(OH)2 + C2H2
2 moles
2 moles
C2H2 + H2O → CH3CHO
2moles
2 moles
CHJ3CHO + H2 → CH3CH2OH
2moles
2 moles
Ex: How many grams of ethanol that is 92% pure , can be
obtained from
160 g of calcium carbide that is 80% pure ?
mpureCaC2 = 160.80/100=128g
nCaC2 = 128/64=2 moles
m pure alcohol = 2 . 46 =92 g
92% alcohol
100% alcohol
X= 100 g
92 g
X
EMPIRICAL FORMULA DETERMINATION
Empirical = simplest
C6H12O6 ----- molecular formula
CH2O --------- empirical formula
By empirical formula we know the ratios of atoms only
Ex: A 50 g of compound contains 20 g of calcium , 6 g of
carbon and 24 g of oxygen. Find the empirical formula of this
compound.
m
n
CaCO3
n
Ca
20
20/40
0.5/0.5
1
C
6
6/12
O
24
24/16
0.5/0.5
1
1.5/0.5
3
Ex: An oxide of sulphur contains 50% by mass. Find its
empirical formula.
S
m
n
SO2
n
50
50/32
1.56/1.56
UNASANA COLLEGE
O
50
50/16
3.12/1.56
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1
2
Ex: A compound contains 43.40 % sodium, 11.32 % carbon,
45.28 % oxygen by mass. Find the formula of compound and
write its reaction with hydrochloric acid.
Na
C
m
43.4
n
43.4/23
Na2CO3
n
1.88/0.94
2
O
11.32
11.32/12
45.28
45.28/16
0.94/0.94
1
2.82/0.94
3
Na2CO3 + 2HCl → 2NaCl + CO2 + H2O
* 1 molecule water contains 2 atoms of hydrogen and 1 atom
of oxygen
* 1 mole of water contains 2 moles of hydrogen and 1 mole of
oxygen
Ex:16 g of Ca( XO3)2 contain 0.2 mole of X. Whaat is the
atomic weight of X?
nX = 0.2 so
nCa(XO3)2 = 0.1 = 16.4/Mw
Mw= 164 = 40+2x +6.16 ---- x=14 g/mole  N
Ex: A 2.2 g compound containing carbon and hydrogen is
burned and 3.36 L of carbon dioxide at STP are produced .
What is the empirical formula of the compound?
CxHy + O2 → CO2 +
=3.36/22.4= 0.15 mole
2.2 g
6.6 g
0.15*4.4 = 6.6 g
44 g CO2
12g C
6.6 g CO2
0.4
mC = 1.8 g
0.4/1
xg
H
H2O
nCO2
mCO 2 =
C
m
mH = 0.4 g
1.8
n
n
1.8/12
0.15/0.15
0.4/0.15
1
2.6
C3H8
Ex : When a 2.3 g compound containing carbon , hydrogen
and oxygen is burned 4.4 g of carbon dioxide and 2.7 g of
water are produced . Find the formula of the compound?
CxHyOz + O2 → CO2 + H2O
44 g CO2
4.4 g
mC =1.2 g
1.2-0.3=0.8g
C
12 g C
x
H
UNASANA COLLEGE
18 g H2O
2.7 g
m H = 0.3 g
2gH
x
mO=2.3-
O
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1.2
1.2/12
0.1/0.05
2
0.3
0.3/1
0.3/0.05
6
0.8
0.8/16
0.05/0.05
1
C2H6O
Ex : The combustion of 0.25 mole of compound containing
carbon hydrogen and oxygen requires 1.25 mole oxygen and
produces 1mole of carbondioxide and 1 mole of water.What is
the molecular formula compound ?
CxHyOz + 5O2 → 4CO2 + 4 H2O
0.25mol 1.25mol
x=4
y=8
z=2
1mol
1 mol → multiply by 4
C4H8O2
MORE QUESTIONS
1. The fermentation of glucose, C 6H12O6, produces ethyl
alcohol, C2H5OH, and carbon dioxide. C6H12O6 (aq)
2C2H5OH(aq) + 2CO2(g)
How many grams of ethanol can be produced from 10.0 g of
glucose?
2. Silicon carbide, SiC, is commonly known as carborundum.
This hard substance, which is used commercially as an
abrasive, is made by heating SiO2 and C to high temperatures.
SiO2(s) + 3C (s)
SiC (s) + 2CO(g)
How many grams of SiC form when 3.00 g of SiO2 and 4.50 g
of C are allowed to react?
3. What mass of silver chloride can be made from the reaction
of 4.22 g of silver nitrate with 7.73 g of aluminum chloride?
(Be sure to balance the reaction.)
AgNO3 + AlCl3
Al(NO3)3 + AgCl
4. How many grams of iron oxide, Fe2O3 , can be produced
from 2.50 g of oxygen O2 , reacting with solid iron Fe ?
UNASANA COLLEGE
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5. How many moles of H2O are produced when 2.5 mol of O2
react according to the following equation?
C3H8 + 5O2
3CO2 + 4H2O
6. Octane burns according to the following equation.
C8H18 + O2
CO2 + H2O
How many grams of CO2 are produced when 5.00 g of C8H18
are burned?
7. Nitrogen gas reacts with hydrogen gas to produce ammonia
gas.
N2(g) + 3 H2(g)
2 NH3(g)
What volume of H2 is required to react with 3.00 L of N2, and
what volume of NH3 is produced at 200°C?
8. A byproduct of the reaction that inflates automotive airbags
is very reactive sodium, which can ignite in air. Sodium
produced during the inflation process reacts with another
compound added to the airbag contents, KNO 3, via the
reaction
10Na + 2KNO3
K2O + 5Na2O + N2
How many grams of KNO3 are required to remove 5.00 g of
Na?
9. The alcohol in "gasohol" burns according to the following
equation.
C2H5OH + 3O2
2CO2 + 3H2O
How many moles of CO2 are produced when 3.00 mol of
C2H5OH is burned in this way?
10. Automotive airbags inflate when sodium azide, NaN 3,
rapidly decomposes to its component elements via this
reaction.
NaN3
Na + N2
How many grams of sodium azide are required to form 7.00 g
of nitrogen gas?
UNASANA COLLEGE
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11. CO2 exhaled by astronauts is removed from the spaceship
atmosphere by reaction with KOH.
CO2 + 2KOH
K2CO3 + H2O
How many kg of CO2 can be removed with 1.00 kg of KOH?
12. In the reaction 3NO2 + H2O
2HNO3 + NO, how many
grams of HNO3 can form when 1.00 g of NO2 and 2.25 g of
H2O are allowed to react?
13. In making H2O from hydrogen and oxygen, if we start with
4.6 mol of hydrogen and 3.1 mol of oxygen, how many moles
of water can be produced and what remains unreacted?
14. How many grams of H2O are formed from the complete
conversion of 32.00 g O2 in the presence of H2, according to
2H2 + O2
2H2O?
15. A reaction that produces crude iron from iron ore is shown
below.
Fe2O3 (s) + 3CO (g)
2Fe (s) + 3CO2 (g)
How many moles of iron are produced from the reaction of 10
mol Fe2O3 and 25 mol of CO?
16. In the synthesis of ammonia gas from nitrogen and
hydrogen, N2 (g) + 3H2 (g)
2NH3 (g), what is the maximum
volume of NH3 that can be formed from 10.00 L of H2?
17. If 3.00 mol of gaseous SO2 react with oxygen to produce
sulfur trioxide, how many moles of oxygen are needed?
Percent Yield: Write the balanced chemical equation, and
SHOW ALL WORK to determine the percent
yield.
18. In the reaction 2 NH3 (g) → 3 H2 (g) + N2 (g) , if 12.0
g of ammonia produced 1.87 g of hydrogen, what
was the percent yield?
19a) Excess hydrochloric acid was reacted with 8.57 g of
calcium carbonate and produced 3.11 g of CO2. What
was the percent yield?
b) In another experiment, using 9.21 g of calcium
carbonate, 1.90 L of CO2 was collected. What is the percent
UNASANA COLLEGE
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yield?
20. What is the percent yield of precipitate if a solution
containing 33.4 g of sodium phosphate produced 19.6 g of
precipitate when reacted with excess aluminum chloride
in solution?
BT
KEEP SMILING!!!
UNASANA COLLEGE
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