chemistry oct2011
DESCRIPTION
ChemistryTRANSCRIPT
“A WINNER knows how much he has to LEARN,
even when he is considered an EXPERT byothers.
A LOSER wants to be considered an EXPERT by others before he
has learned enough toknow how LITTLE he knows.”
CHEMISTRY
- From egyptian kēme, meaning “earth”- the science concerned with the
composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions.
Hypothesis – A statement or idea that describes or attempts to explain observable information.
Experiment – Is a controlled testing of the properties of a substance or system through carefully recorded measurements.
Theory – The result of thorough testing and confirmation of a hypothesis. A theory predicts the outcome of new testing based on past experimental data.
Law – A hypothesis or theory that is tested time after time with the same resulting data and thought to be without exception
1. Who is said to be the founder of the scientific method?
A. Alexander FlemingB. Joseph PriestlyC. Galileo GalileiD. Antoine Lavoisier
2. In the universe, it is anything that occupies space and has mass.
A. MatterB. IsotopeC. AtomD. Solid
Matter - anything that occupies space and has mass (i.e., anything that has density). It commonly exists in three phases: solid, liquid, and gas.
3. Electron came from the greek word:A. HeliosB. ElektraC. AmberD. Volta
4. Which of the following falls under fluids?
A. gasB. solidC. liquid.D. both a & c.
5. The state of matter which occupies the whole space available is
A. gasB. solidC. liquidD. both a & c.
6. It is a property of matter which can be measured by changing the identity and composition of a substance.
A. ChemicalB. extensiveC. physicalD. extrinsic
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7. Which of the following is not an extensive property?
A. EnergyB. WeightC. Boiling pointD. Length
THE ATOMAtom is the basic building block of
matter. It is the smallest particle of element.
An ELEMENT is a fundamental type of matter in which all of the atoms in the material are the same.
The atomic number of an element is the number of protons that is contained in the nucleus of each of its atoms.
Mass number or atomic weight is the sum of the number of protons and neutrons in the nucleus of the atom.
A compound is a substance with a particular ratio of atoms of particular chemical elements which determines its composition, and a particular organization which determines chemical properties.
The standard nomenclature of chemical substances is set by the International Union of Pure and Applied Chemistry (IUPAC).
8. What do you call chemically identical atoms of the same element but with different numbers of neutrons and different mass numbers.
A. IsotonesB. IsobarsC. IsotopesD. homogenous
9. Tritium hasA. 1 electron and 1 protonB. 1 proton and 1 neutronC. 1 proton and 2 neutronD. 2 proton and 1 neutron
Protium – most common hydrogen isotope
Deuterium – 1 neutron, 1 proton - non radioactive, -“heavy hydrogen”
Tritium – 2 neutrons, 1 protonradioactive
Hydrogen is the only element that has different names for its isotopes in common use today.
10. What is the most abundant element in the universe?
A. nitrogenB. hydrogenC. oxygenD. helium
11. What is the most abundant element in the Earth’s atmosphere?
A. nitrogenB. hydrogenC. oxygenD. helium
12. The net electrical charge of an atom under normal state is:
A. negativeB. positiveC. neutralD. infinite
13. A substance that cannot be decomposed into simpler substances by ordinary chemical reactions
A. CompoundB. MixtureC. ElementD. Homogenous
14. The subdivision of an element that can take part in a chemical reaction
A. ElementB. HydrogenC. ElectronD. Atom
15. The sub-atomic part consisting of neutrons and protons is known as
A. Nuclear fusionB. NucleonsC. NeuronsD. Neutron-proton spatial formation
IV. ATOMIC NUMBER AND MASS NUMBER
The atomic number of an element is the number of protons that is contained in the nucleus of each of its atoms.
Mass number or atomic weight is the sum of the number of protons and neutrons in the nucleus of the atom.
16. The no. of protons in the nucleus on an atom
A. Atomic number B. Mass numberC. Atomic massD. Atomic mass unit
17. The no. of protons and neutrons in the nucleus of an atom
A. Atomic number B. Mass numberC. Atomic massD. Atomic mass unit
18. 1 amu is approximately equal to
A. 6.23 x 10 ^ -27 kg B. 2.36 x 10 ^ -27 kg C. 3.62 x 10 ^ -27 kg D. 1.66 x 10 ^ -27 kg
19. The group of elements that do not normally combine with other elements to form compounds
A. Alkali MetalsB. ChalcogensC. Inert gases or noble gases D. Halogens
20. What do you call the electrons in the outermost orbitals?
A. Valence electrons B. super electronsC. holesD. active electrons
21. Calculate the mass of the product of reaction of 6.54 g of zinc with 3.21 g of sulfur.
A. 21 gB. 3.33 gC. 9.75 gD. 10.15 g
22. Calculate the mass of the oxygen that reacts with 1.24 g of methane (natural gas) to form 3.41 g of carbon dioxide and 2.79 g of water.
A. 7.38 gB. 1.86 gC. 0.62 gD. 4.96 g
ATOMIC MASSThe atomic mass (or atomic weight) of
an element is the average of the element’s isotopic masses.
1 1 2 2 3 3Atomic mass m p m p m p ...
mass of isotopes 1,2,3...
percent abundance of isotopes 1,2,3..n
n
Where m
p
.
23. Calculate the atomic mass of an element if 60.4% of the atoms have a mass of 68.9257 amu and the rest have a mass of 70.9249 amu.
A. 67.9 amuB. 69.7 amuC. 79.6 amuD. 97.6 amu
24. Calculate the atomic mass of an element if 60.4% of the atoms have a mass of 68.9257 amu and the rest have a mass of 70.9249 amu.
A. 79.6 amuB. 67.9 amuC. 96.7 amuD. 69.7 amu
Practice Problem:Calculate the percentage of bromine atoms
that have a mass of 78.9183 amu and the percentage that have a mass of 80.9163 amu. The atomic mass of bromine is 79.909 amu, and theses are the only two naturally occurring isotopes.A. 35.3%, 64.7% C. 50.4%, 49.6%B. 47.5% , 52.5% D. 63.2%, 36.8%
FORMULA MASSThe formula mass (or formula weight) is the sum of the
masses of all atoms in a given formula.
THE MOLE A mole is the amount of pure substance containing the same
number of chemical units, as there are atoms in exactly 12 grams of carbon-12.
AVOGADRO’S NUMBEROne mole refers to Avogadro’s number of particles of
anything:
236 02 10AN .
MOLE – MASS CONVERSIONSThe formula for calculating among mass, gram-
formula mass (also known as molar mass), and the number of moles:
Where: n = number of moles m = mass of the substance in grams
M= molar mass in grams per mole
m
nFM
MOLE – NUMBERS OF PARTICLES CONVERSION
Conversion factor: • EXAMPLE:
How many particles are in 2.00 moles of SO2?
231 6 02 10mole . particles
Ans. 1.2 x 1024 particles
25. Calculate the formula mass of (NH4)2HPO4 (one type of fertilizer).
A. 125 amuB. 132 amuC. 110 amuD. 148 amu
26. Calculate the number of moles of Al atoms in 5.75 x 1024 Al atoms.
A. 19.1 mol Al atomsB. 9.55 mol Al atomsC. 4.77 mol Al atomsD. 14.3 mol Al atoms
27. Calculate the number of moles of H2 molecules in 5.75 x 1024 H2 molecules.
A. 19.1 mol H2 molecules
B. 9.55 mol H2 molecules
C. 4.77 mol H2 molecules
D. 14.3 mol H2 molecules
28. Calculate the number of molecules in 30 g NH3.
A. 1.06 x 1024 moleculesB. 3.08 x 1024 moleculesC. 1.06 x 1023 moleculesD. 3.08 x 1023 molecues
29. In a 5.00-g sample of carbon, how many of the atoms have a mass of 12.01 amu?
A. NoneB. 2.507 x 1023 moleculesC. 2.507 x 1024 moleculesD. 1.44 x 1024 molecules
EMPIRICAL FORMULAAn empirical formula is a formula that gives the simplest whole-
number ratio of atoms in a compound.
Steps for Determining an Empirical FormulaStart with the number of grams of each element, given in the
problem. If percentages are given, assume that the total mass is 100 grams so
that the mass of each element = the percent given.2. Convert the mass of each element to moles using the molar mass
from the periodic table.3. Divide each mole value by the smallest number of moles calculated. Round to the nearest whole number. This is the mole ratio of the
elements and is represented by subscripts in the empirical formula. (If one of the numbers is 1.5, you would multiply each number by 2, and get a whole number of 3).
30. Calculate the empirical formula of “hypo,” used in photographic development, consisting of 29.1% Na, 40.5% S, and 30.4% O.
A. NaS2O2
B. NaS2O3
C. Na2S4O3
D. Na2S2O3
MOLECULAR FORMULAOnce the empirical formula is found, the molecular formula
for a compound can be determined if the molar mass of the compound is known.
Steps for Determining molecular Formula1. Find the empirical formula2. Find the mass of the empirical unit.3. Divide the molecular mass of the compound by the mass
of the empirical formula.4. Multiply all the atoms (subscripts) of the empirical formula
by this ratio to find the molecular formula.
31. Calculate the molecular formula of a compound with molar mass 104 g/mol composed of 92.3% carbon and 7.7% hydrogen.
A. C8H8
B. C7H14
C. C2H3
D. C7H8
CHEMICAL REACTIONA chemical reaction is a process in which
a substance or a combination of substances undergo a change in appearance or properties, and further transform into a different substance or a combination of new substances.
CLASSIFICATION OF CHEMICAL REACTIONS
DIRECT COMBINATION OR SYNTHESIS
A B AB
DECOMPOSITION
AB A B
SINGLE – REPLACEMENT REACTIONS
A BC AC B
Double – Replacement Reactions
AB CD AD CB
32. The reaction Na2O + H2O 2NaOH illustrates a
A. Synthesis ReactionB. Metathesis ReactionC. Single Replacement ReactionD. Decomposition Reaction
33. The reaction Ba(OH)2 + 2CuCNS Ba(CNS)2 + 2CuOH is an example of
A. Synthesis ReactionB. Metathesis ReactionC. Single Replacement ReactionD. Decomposition Reaction
34. The decomposition of a given compound can be carried out
A. by heating the compoundB. by passing the electric current while
heatingC. by passing the electric currentD. either by passing electric current or
heating
I. UNITS OF CONCENTRATION MOLE FRACTIONThe number of moles of solute divided
by the number of moles of solvent and all solutes.
A BA B
A B A B
n nX or X
n n n n
NORMALITYThe number of gram equivalent weights
of solute per liter. A solution is “ normal” if there is exactly one gram equivalent weight per liter.
nORMALITYsolution in liters
Equivalent weight in grams
V
MOLARITYMolarity (M) is defined as the number of
moles of solute dissolved in 1 liter of solution. In other words, molarity is a ratio between number of moles of solute and the number of liters of solution.
( )
solute
solution L
nM
V
FORMALITYThe number of gram formula weights
(i.e., molecular weights in grams) per liter of solution.
FORMALITYsolution in liters
Formula weight in grams
V
MOLALITYMolality (m) is defined as the number of
moles of solute dissolved in 1 kg of solvent. In other words molality is the ratio between the number of moles of solute and the mass of the solvent expressed in kilograms.
solute
solvent solvent
mass soluten MM solute
mkg kg
PERCENT OF VOLUMEPercent of volume refers to the number
of millilitres of solute dissolved in 100 ml of solution.
% 100volume solute
volume xvolume solution
DILUTIONDilution is the process of adding solvent (usually
water) to a concentrated solution to achieve a solution of the desired concentration. When we dilute a solution, we do not change the number of moles of solute present, we simply add more solvent. Thus,
Molesof soluteafterdilution=Molesof solutebeforedilution
after before
after before
n n
MV MV
35. Calculate the molarity of a 250-mL solution containing 80.0 mmol of solute.
A. 0.567 MB. 0.320 MC. 0.118 MD. 0.235 M
36. Calculate the number of moles of solute required to make 50.00 mL of 1.500 M solution
A. 0.025 molB. 0.75 molC. 0.075 molD. 0.25 mol
37. Calculate the molarity of a solution after 1.70 L of 2.06 M solution is diluted to 2.50 L.
A. 1.20 MB. 2.10 MC. 1.50 MD. 1.40 M
38. Calculate the mole fraction of a solution of 0.015 mol of NaCl in 50.0 g of water if the solution has a density of 1.02 g/mL.
A. 0.00536B. 0.0536C. 0.536D. 0.000536
39. Calculate the molality of an alcohol in aqueous solution if the mole fraction of the alcohol is 0.150.
A. 3.60 m alcoholB. 5.40 m alcoholC. 9.80 m alcoholD. 10.12 m alcohol
ACIDS AND BASES
ACIDS Acid is any compound that dissociates H+ ions into water .
Acids with 1,2, and 3 ionizable hydrogen atoms are called monoprotic, diprotic, and triprotic acids, respectively.
Properties of Acids:
1. Acid conducts electricity in aqueous solutions2. Acids have a sour taste3. Acids turn blue litmus paper to red4. Acids have pH between 0 and 75. Acids neutralizes bases6. Acids react with active metals to form hydrogen7. Acids react with oxides and hydroxides to form salts and water
pH Equation:
For a partially ionized compound, X, in a solution of known molarity, M, the ionic concentration is:
1pH log
H
X fraction ionized M
BASESBase is any compound that dissociates OH- ions into water.Bases with 1, 2, and 3 replaceable hydroxide ions are called
monohydroxic, dihydroxic, and trihydroxic bases, respectively. Properties of Basis:
1. Bases conduct electricity in aqueous solutions2. Bases have bitter taste3. Bases turn red litmus paper to blue4. Bases have pH between 7 and 145. Bases neutralize acids, forming salts and water
pOH Equation:
pH and pOH Relationship:
1pOH log
OH
14pH pOH
40. Battery acid is the common name for A. formic acidB. hydrochloric acidC. nitric acidD. sulfuric acid
41. When one element causes the oxidation of another element, it is
A. oxidizedB. an acidC. reducedD. a base
42. According to the Bronsted Theory, an acid is
A. a proton donorB. a proton acceptorC. an electron donorD. an electron acceptor
43. The pH of an acid solution is
A. 3B. 7C. 9D. 10
44. The pH of a solution with a hydrogen ion concentration of 1 x 103 is
A. +3B. -3C. ±3D. +11
45. The pH concentration of a solution that has a hydroxide ion concentration of 1 x 10-4 mol/L is
A. 4B. -4C. 10D. -10
46. A 10-6 M HCl solution is diluted to 100 times. The pH of the diluted solution would be
A. between 6 to 7B. between 7 to 8C. equal to 7D. equal to 10
47. A substance which can act both an acid and a base is:
A. allotropicB. amphotericC. isotopicD. amorphous