Sunday, February 26, 2012
Friday, February 24, 2012
Chemical Equilibrium XI Year BIEK( Multiple choice questions)
Chapter: Chemical
Equilibrium
Multiple choice questions
i) Which of the following is correct solubility product
expression for Al2(SO4)3
a) Ksp =[Al3+] [SO42-] b)
[Al3+]2 [SO42-]3
c) [2Al3+]2 [3SO42-] 3 d) [2Al3+] [3SO42-]
ii) Which of the following equation that describes
the relationship between the solubility product for MgF2 and the
solubility
a)
Ksp= 2S b)
Ksp= S2
c)
Ksp= S4 d) Ksp= 16S4
iii) Which is more soluble salt
a) Ag2S (Ksp=
6.3x10-50) b)
Pb3 (PO4) 2 (Ksp= 8.0x10-43)
c)
HgS (Ksp= 4x10-53) d)
Ca3 (PO4) 2 (Ksp= 6.3x10-29)
iv) Which salt is less soluble
a) Ag2S (Ksp=
6.3x10-50) b)
Pb3 (PO4) 2 (Ksp= 8.0x10-43)
c)
HgS (Ksp= 4x10-53) d) Ca3 (PO4) 2 (Ksp= 6.3x10-29)
v) Precipitation of salt will
occur when product of ionic
concentration
a) Ksp = product of
ionic concentration
b) Ksp < product of
ionic concentration
c) Ksp≥ product of ionic
concentration
d)Ksp > product of
ionic concentration
vi) The expression of Ksp is [Ca2+][PO43-] the equilibrium state of salt
a) Ca3(PO4)2 ↔
Ca2+ + PO43- b) Ca3(PO4)2 ↔3
Ca2+ + PO43-
c)
Ca3(PO4)2 ↔ Ca2+ + 2PO43- d) Ca3(PO4)2 ↔3
Ca2+ +2 PO43-
vii) What is the
effect of adding a strong acid (HCl) solution that contain
H2S ↔ 2H+ + S2-
a)
the concentration of sulphide ion
increase
b) the concentration of
sulphide ion decrease
c
) No effect of concentration of sulphide
ion
d) dissociation of HCl will increase
viii) The Cation of III-group precipitation
as
a)
Sulphide b) Carbonate
c)
Hydroxide d) Chloride
ix) The Cation of II
and IV precipitate as
a)
Chloride b) Carbonate
c)
Hydroxide d) Sulphide
x)The Cation of I A group
precipitate as
a)
Hydroxide b) Carbonate
c)
Chloride d) Sulphide
Sunday, February 19, 2012
Concentration
Parts per million (ppm)and Parts per billion (ppb)
The only difference in the
calculations of parts per million and parts per billion is factor used to
multiply the ratio. The formulas for these two are:
Parts per million
|
Concentration
|
Amount
of solute
|
|
|
|
=
|
|
|
1,000,000
|
Amount
of solvent
|
Parts per billion
|
Concentration
|
Amount
of solute
|
|
|
|
=
|
|
|
1,000,000,000
|
Amount
of solvent
|
Assignment: Percent, ppm and ppb
1)
Calculate the concentration of salt in a solution of water in percent if 45
grams is dissolved in 1,200 ml of water.
2)
Calculate the mass of solute in a 10% salt solution if the mass of the solvent
is 350 grams.
3)
Calculate the mass of solvent in a 6 ppm solution of a drug if the mass of the
solute is 0.050 milligrams.
4) What
is the concentration in ppm of selenium if 1.3 milligrams is found in 2,500 kg
of soil?
5) What
is the concentration in ppb of PCB's in a chemical spill, if their is 0.060 mg
in 4,600 Kg of soil?
6)
Calculate the mass of solute of hydrogen peroxide in a 35 % solution if 450 ml
of solution is being used.
7)
Calculate the mass of solute PCB's in a 65 Kg person, if the concentration is 4
PPM?
8) What
mass of nickel is in a 2.4 Kg sample of propanol if the concentration is 20
ppb?
9)
Calculate the mass of solvent that would contain 3.0 mg of a drug if the
concentration was 3.5%.
10)
Calculate the concentration in ppm if 8 grams of CaCl2 is dissolved in 250 ml of water.
Wednesday, February 15, 2012
Important constant
Reference : Table 12.1
of General Chemistry
By Robinson-Odom-Holtzclaw(10th
Edition)
|
Solvent
|
Boiling point(oC)
|
kb
oC.
mol.kg-1
|
Freezing point
|
kf
oC
mol.kg-1
|
|
Water
|
100.00
|
0.512
|
0.00
|
1.86
|
|
Acetic Acid
|
118.1
|
3.07
|
16.6
|
3.9
|
|
Benzene
|
80.1
|
2.53
|
5.5
|
5.12
|
|
Chloroform
|
61.26
|
3.63
|
-63.5
|
4.68
|
|
Nitrobenzene
|
210.9
|
5.24
|
5.67
|
8.1
|
Best Questions of Solution
1.
What
is the molarity of HNO3in concentrated nitric acid , a solution with
a density of 1.42g /cm3 that contains 68.0% HNO3 by mass?
2.
The
antifreeze in most automobile radiators is a mixture of equal volumes of ethylene glycol and water with minor
amount of other additives that prevent corrosion . What is the molarity of
ethylene glycol in a solution prepared from 2218 g of ethylene glycol and 1996
g of water
3.
At
25 0C ,25 g of glycine the
simplest amino acid found in proteins, will dissolve in exactly 100 g of water
.Calculate the mole fraction of glycine and water in solution.
4.
Calculate
the mole fraction of solute and solvent in a 3.00 molal solution of sodium
chloride .
5.
A
sulphuric acid solution containing 2.001 g of sulphuric acid in 0.350 liter of
solution at 20 0C has density of 1.3294 g/ml . Calculate (a) the
molarity , (b) the molality, (c) the percent by mass of Sulphuric acid and (d)
the mole fraction of sulphuric acid .
6.
Assume
the solution is the ideal and determine the vapour pressure of a solution of
92.1 g of glycerin in 184.4 g of ethanol at 40 oC . The vapour
pressure of pure ethanol is 0.178 atm at
40 oC. The glycerin is essentially non volatile at this temperature
7.
Find
the Freezing point of a solution of 92.1 g of iodine , in 800g of Chloroform,
assuming that the iodine nonvolatile at that the solution is an ideal. Kf of chloroform is 4.68 oC/mol/kg an
freezing point is -63.5 oC
8.
Find
the boiling point of a solution of 92.1 g of iodine , in 800g of Chloroform,
assuming that the iodine nonvolatile at that the solution is an ideal. Kb of chloroform is 3.63 oC/mol/kg an
freezing point is 61.26 oC
Reference : Table 12.1
of General Chemistry
By Robinson-Odom-Holtzclaw(10th Edition)
By Robinson-Odom-Holtzclaw(10th Edition)
Saturday, February 4, 2012
Chemical Equilibirium (Subjectives and Problems)
Chemical Equilibirium
Subjective Question
Q.1 Discuss the conditions of
concentration , pressure and temperature in the presence of catalyst for
maximum yield of ammonia in the reaction
N2 + 3H2 ↔ 2NH3 ∆H
= Negative
Q.2 How is the equilibrium constant
value used to predict the extent of reaction ?
Q.3 Explain the term “ Solubility
Product” . What is the criterion for the precipitation from a solution?
Q. 4 Explain the following term
i )Reversible
reaction ii) Equilibrium constant
iii) Solubility product iv) Law of Mass Action
v) Le- Chatelier principle
Q.5 State and explain Law of Mass Action.
Q.6 State
and explain Le-Chatlelier principle
Q.7 Discuss the condition to increase
the yield of NH3 in Haber’s process.
Q.8 Differntiate
solubility product with solubility.
Q.9 How is Kc used to
predict the direction of a reversible reaction?
Q.10 Predict the effect of change of temperature and effect pressure on
following equilibrium mixture :
H2 + I2 + Heat
↔ 2HI
Q.11State
and explain Law of Mass Action and derive the
equilibrium constant expression for the general equilibrium reaction :
mA + nB
↔ xC +
yD
Problems
Q.1 In
chemical reaction
PCl5 ↔
PCl3 + Cl2
Calculate the mole of chlorine produce
at equilibrium when 1 mole of PCl5 is heated at 2500c in
a vessel of capacity 10 dm3 (Kc for the reaction is 0 .041)
Q.2 For reaction
N2 + 3H2
↔= 2NH3
The equilibrium mixture contain .25 M nitrogen .15 M
hydrogen gas at 250 c. Calculate the concentration of NH3
gas when Kc =9.6 .The volume of the container is 1dm3.
Q.3 At equilibrium a 12 dm3 falsk
contain 0.21 mole of PCl5 0.32 mole of PCl3 and 0.32 mole
Cl2 at 2500 c find the value of Kc for reaction PCl5 ↔
PCl3 +
Cl2
Q.4 Should AgCl precipitate form a
solution prepared mixing of 400 cm3 0.1M NaCl and 600 cm3
0.03M AgNO3 ?
(Ksp of AgCl=1.6* 10-10 mol2/
dm6 )
Q.5 For
the reaction H2 + I2
↔ 2HI
Kc is
49 . Calculate the concentration of HI at equilibrium when initial one
mole of H2 is mixed with
one more of I2 in one liter
flask .
Q.6 Kc for a reaction is
0.0194 and the calculated ratio of the concentration of the reactants is 0.0116 . Predict the
direction of the reaction.
Q.7 Will PbCrO4 precipitate
from a solution prepared by mixing 200 cm3 of 2.5 x 10-4
M Pb(NO3)2 and 600 cm3 of 1.5 x 10-8
M of K2CrO4? (K(sp) of PbCrO4 = 1.5 x
10-14 )
Q.8 For the reaction 2Hl ↔ H2
+ l2, one mole of Hl is introduced into a vessel at constant temperature. Calculate the number of moles of
l2 when the equilibrium is reached(Kc =0.0156).
Q.9 Define Solubility product (Ksp).
Find the Ksp of CaCO3, the solubility of CaCO3
is 0.001 g / dm3
CaCO3 ↔ Ca2+ + CO32-
Q.10 The equilibrium constant for the
reaction N2 + O2 ↔ 2NO
at 20000C is 0.1. Calculate
the equilibrium concentration of the reactants and product when the initial
concentration of N2 and O2 are 10 mole/dm3
Friday, February 3, 2012
Practice Questions of Stiochiometry
Practice
Questions
XI-AKUEB
Topics:
(Stiochiometry
Q.1
1 When 142 g of calcium fluoride are reacted with an
excess of sodium
bromide,
calculate the mass of calcium bromide formed.
2.
How many grams of sodium
aluminate can be obtained from 7.71 g of
aluminum
chloride according to the reaction:
AlCl3(aq) +
4NaOH(aq) = ¼ NaAlO2(aq) +
3NaCl(aq) + 2H2O(l)
3). How many
grams of carbon dioxide are
obtained when 2.96 g of
cerium(III)
oxalate are formed according to the reaction:
2Ce(IO3)4(aq)
+ 24H2C2O4(aq)= ¼ Ce2(C2O4)3(aq)
+ 4I2(aq) + 42CO2(g) + 24H2O(l)
4). Calculate the mass of sodium permanganate
that can be prepared from
1.27
g of sodium bismuthate according to the reaction:
2Mn(NO3)2
+ 5NaBiO3 + 14HNO3 = ¼ 2NaMnO4 + 5Bi(NO3)3
+ 3 NaNO3 + 7H2O
5). If excess sulfuric acid is reacted with
sodium hydroxide, 15.0 g of water
is
formed. What mass of sodium hydroxide was
used?
6).
50.0 g of calcium carbonate was added to excess phosphoric acid. What
mass
of calcium phosphate was formed?
7). Calculate the
mass of barium nitrate that must decompose in order to
produce
112 g of oxygen.
8).
Calculate the mass of potassium chloride
that is produced when 17.0 g of
potassium
carbonate reacts with hydrochloric acid.
9). When “x” grams of calcium chloride was reacted with an excess of
bromine,
14.0 kg of a gas was formed. Calculate
“x”.
10).
How many grams of zinc oxide are formed when 10.0 g of zinc reacts with
oxygen?
11.
Sodium nitrate decomposes to give 3.00 g of oxygen. Calculate the mass
of
sodium nitrate used.
12.
Potassium metal reacts with 70.0 g of chlorine. Calculate the mass of
product.
13.
Calculate the mass
of magnesium oxide that must be decomposed in
order
to produce 48.0 g of oxygen.
14). Sodium chloride was reacted with an excess
of sulfuric acid to give
hydrochloric
acid and 142 g of a second product. What
is the product,
and
how much sodium chloride was reacted?
15.
What mass of copper(I) sulfide can be produced from 9.90 g of copper(I)
chloride
reacting with an excess of hydrogen sulfide gas?
16.
How many grams of calcium hydroxide will be needed to react completely
with
10.0 g of phosphoric acid?
17.
How many grams of hydrogen can be produced from the reaction of 72.0
g
of sodium with an excess of water?
18.
An excess of nitrogen reacts with 6.57 g of hydrogen. How many grams
of
ammonia are produced?
19.
How many grams of oxygen are required to burn completely 84.9 g of
carbon? C(s)
+ O2(g) = ¼ CO2(g)
20.
In the decomposition of potassium chlorate, 82.6 g of oxygen are formed.
How
many grams of potassium chloride are produced?
21.
The action of carbon monoxide can be expressed by the equation,
Fe2O3(cr) +
3CO(g) = ¼ 2Fe(s) + 3CO2(g)
What
would be the minimum amount of carbon monoxide used if 80.3 g of
iron
were produced?
22.
How many grams of hydrochloric acid are required to react
completely
with
44.7 g of calcium hydroxide?
23.
How many grams of hydrogen are produced when 4.77 g of aluminum react
with
excess hydrochloric acid?
24.
Calculate the mass of lithium carbonate that must decompose to produce
78.0
g of carbon dioxide.
25.
How many grams of oxygen gas are formed when 100.0 g of magnesium
chlorate
are decomposed?
26.
Hydrochloric acid was reacted with zinc
to produce 137 g of hydrogen
gas. What mass of zinc did you begin with?
Q.2
Stoichiometry
- Limiting Reactants
1. Hydrogen gas can be produced in the
laboratory by the reaction of magnesium metal
with
hydrochloric acid.
a) How many grams of hydrogen can be produced
when 4.00 g of hydrochloric acid
are
added to 3.00 g of magnesium?
b) What is the volume of this hydrogen at
standard conditions?
2. Potassium
nitrate is widely used as a
fertilizer because it provides two essential
elements,
potassium and nitrogen. It is made by
mixing potassium chloride and nitric
acid
in the presence of oxygen according to the equation:
4KCl + 4HNO3 + O2 =
4KNO3 + 2Cl2 + 2H2O
How
many kilograms of potassium nitrate will be produced from 50.0 kg of potassium
chloride and 50.0 kg of nitric acid? An important by-product is chlorine. How many
kilograms
of chlorine will be produced?
3. Phosphorus forms a compound similar to
ammonia. The compound has the formula PH3
and
is called phosphine. It can be prepared
by the reaction:
P4 +
3NaOH + 3H2O = ¼
PH3 + 3NaH2PO2
If
20.0 g of phosphorus and 50.0 g of sodium hydroxide are reacted with excess
water,
how
many grams of phosphine will be obtained?
4.
Bromine can be prepared by adding
chlorine to an
aqueous solution of
sodium bromide.
How
many grams of bromine are formed
if 25.0 g of sodium bromide and 25.0 g of
chlorine
are reacted?
5. Silver
tarnishes in the presence of
hydrogen sulfide, a gas that originate from the
decay
of food, because of the reaction:
4Ag + 2H2S + O2
= ¼
2Ag2S + 2H2O
The
black product, silver sulfide, is the
"tarnish". If 25.00 g of silver, 5.00 g of
hydrogen
sulfide, and 4.00 g of oxygen are present in a reaction mixture, which one is
the
limiting reactant, and what mass of silver sulfide is produced?
6. Sulfur dioxide can be produced from the reaction of hydrogen sulfide and oxygen as
shown
by the following reaction: 2H2S + 3O2
= ¼
2SO2 + 2H2O
a) How many grams of sulfur dioxide can be
produced from 70.0 g of hydrogen
sulfide
and 125 g of oxygen.
b) How many grams of excess reactant are left
over after the reaction is complete?
7. What mass of carbon disulfide is produced
when 17.5 g of carbon are reacted with 39.5
g
of sulfur dioxide according to the equation:
5C(s) + 2SO2(g)
= ¼
CS2(s) + 4CO(g)
8. What mass of P4 is
produced when 41.5
g of Ca3(PO4)2,
26.5 g of SiO2 and 7.80 g of C
are
reacted according to the equation:
2Ca3(PO4)2
+ 6SiO2 + 10C= ¼ P4 + 6CaSiO3 + 10CO
9.
What volume of
carbon dioxide, measured
at STP, can
be produced when
15.65 g of
pentane
is reacted with 40.0 L of oxygen, measured at STP, according to the equation:
C5H12(l)
+ 8O2(g) = ¼ 5CO2(g) + 6H2O(l)
10. What mass of hydrogen chloride gas is
produced when 4.50 g of hydrogen and 140.0 g
of
chlorine are reacted. Which reactant is
in excess and how much remains unreacted?
11. The roasting of siderite ore, FeCO3,
produces ferric oxide:
4FeCO3(s)
+ O2(g) ¼ 2Fe2O3(s) + 4CO2(g)
What
mass of ferric oxide is produced when 55.0 g of siderite is reacted with 40.0 L
of
oxygen
gas? Which reactant is in excess and how
much remains unreacted?
12. A manufacturer of bicycles has 5050 wheels,
3013 frames, and 2455 handlebars.
a) How many bicycles can be manufactured using
these parts?
b) How many parts of each kind are left over?
c) Which part is like a limiting reactant in
that it limits the production of bicycles?
13. The fizz produced when an Alka-Seltzer
tablet is dissolved in water is due to the
reaction
between sodium bicarbonate and citric acid:
3NaHCO3(aq)
+ H3C6H5O7(aq) ¼ 3CO2(g)
+ 3H2O(l) + Na3C6H5O7(aq)
In a
certain experiment 1.00 g of
sodium bicarbonate and 1.00 g of citric
acid are
allowed
to react.
a) What volume of carbon dioxide is formed?
b) Which reactant is the limiting reactant?
c) How much of the excess reactant remains after
the limiting reactant is
completely
consumed?
14. One of the steps in the commercial process
for converting ammonia to nitric acid
involves
the conversion of ammonia to nitrogen monoxide:
2NH3(g)
+ 5O2(g) = ¼ 4NO(g) + 6H2O(g)
In
a certain experiment 2.50 g of ammonia reacts with 2.85 g of oxygen.
a) What mass of nitrogen monoxide is formed?
b) Which reactant is the limiting reactant?
c) How much of the excess reactant remains after
the limiting reactant is
completely
consumed?
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