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Chemistry
WAEC / WASSCE 2022
Organic Chemistry II: Functional Groups, Polymers & Biomolecules
Solution
The IUPAC name for C\(H_3\)CHC\(H_3\)CHCLCHC\(H_3\)C\(H_2\)C\(H_3\) is
A
2, 4 - dimethyl - 3 - chlorohexane
B
3, 5 - dimethyl - 4 - chlorohexane
C
4 - chloro - 3, 5 - dirnethylhexane
D
3 - chloro - 2, 4 - dimethylhexane
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
- Recognise the functional group in the compound. This will determine the suffix of the name
- Find the longest continuous carbon chain that contains the functional group (it won't always be a straight chain) and count the number of carbon atoms in this chain. This number will determine the prefix (the beginning) of the compound's name
- Number the carbons in the longest carbon chain (Important: If the molecule is not an alkane (i.e. has a functional group) you need to start numbering so that the functional group is on the carbon with the lowest possible number). Start with the carbon at the end closest to the functional group.
- Look for any branched groups:
Name them by counting the number of carbon atoms in the branched group and referring to Table 4.6, these groups will all end in -yl.
Note the position of the group on the main carbon chain. If there is more than one of the same type of branched group then both numbers must be listed (e.g. 2,4 -) and one of the prefixes listed in Table 4.7 must be used. Important: If the molecule is an alkane the branched group must be on the carbon with the lowest possible number.
The branched groups must be listed before the name of the main chain in alphabetical order (ignoring di/tri/tetra).
If there are no branched groups this step can be ignored.
- For the alkyl halides the halogen atom is treated in much the same way as branched groups:
To name them take the name of the halogen atom (e.g. iodine) and replace the -ine with -o (e.g. iodo)
Give the halogen atom a number to show its position on the carbon chain. If there is more than one halogen atom the numbers should be listed and a prefix should be used (e.g. 3,4-diiodo- or 1,2,2-trichloro-). See Table 4.7 for a list of the prefixes.
The halogen atoms must be listed before the name of the main chain in alphabetical order (ignore di/tri/tetra).
If there are no halogen atoms this step can be ignored.
- Combine the elements of the name into a single word in the following order:
branched groups/halogen atoms in alphabetical order (ignoring prefixes)
prefix of main chain
name ending according to the functional group and its position on the longest carbon chain.
Source: Myschool Past Questions Archive (Record #65803)
Chemistry
WAEC / WASSCE 2022
Oxidation, Reduction & Redox Reactions
Solution
A colourless gas with a pungent smell is evolved when dilute hydrochloric acid is added to a sample of a salt. The gas evolved could turn
A
acidified \(K_2\)C\(r_2\)\(O_7\) solution colourless
B
acidified KMn\(O_4\) solution colourless
C
Fe(N\(O_3\))\(_{2}\) solution green
D
Pb(N\(O_3\))\(_{2}\) paper black
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
If the potassium manganate(VII) solution is acidified with dilute sulfuric acid, the purple solution becomes colourless.
The salt that reacts with dilute hydrochloric acid to produce a pungent smelling gas which decolourizes acidified purple potassium tetraoxomanganate (VII) solution is Na\(_2\)SO\(_3\)
Na\(_2\)SO\(_3\)(s) + HCl(aq) → NaCl(aq) + H\(_2\)O(l) + SO\(_2\)(g)
When SO\(_2\) gas which is colourless with a pungent smell, reacts with acidified KMnO\(_4\), it becomes decolorized from purple colour.
Source: Myschool Past Questions Archive (Record #65804)
Chemistry
WAEC / WASSCE 2022
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
If 5.0 g of marble reacts with 25.0 cm3 hydrochloric acid, which of the following combinations has the fastest reaction rate?
A
Marble chips and 2.0 mol dm\(^{-3}\) HCl\(_{(aq)}\)
B
Marble chips and 2.5 mol dm\(^{-3}\) HCl\(_{(aq)}\)
C
Powdered marble and 2.5 mol dm\(^{-3}\) HCl\(_{(aq)}\)
D
Powdered marble and 2.0 mol dm\(^{-3}\) HCl\(_{(aq)}\)
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Powdered marble reacts more rapidly with HCl than the chips of marble because:
Surface area of powdered marble is more that of chips of marble and hence there is more collisions between the molecules of reactants
Number of molecules increases.
Energy of activation decreases
Marble chips will not react with HCl
Source: Myschool Past Questions Archive (Record #65805)
Chemistry
WAEC / WASSCE 2022
Water, Solutions & Solubility
Solution
Increasing the temperature generally
A
decreases the solubility of a solid in a liquid but increases the solubility of a gas in a liquid.
B
increases the solubility of a solid in a liquid but decreases the solubility of a gas in a liquid.
C
increases the solubility of both a solid and a gas in a liquid
D
decreases the solubility of both a solid and a gas in a liquid
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
-The solubility of gases in liquids decreases with increasing temperature. Conversely, adding heat to the solution provides thermal energy that overcomes the attractive forces between the gas and the solvent molecules, thereby decreasing the solubility of the gas
-The solubility of most solid or liquid solutes increases with increasing temperature
Source: Myschool Past Questions Archive (Record #65806)
Chemistry
WAEC / WASSCE 2022
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
A white precipitate was formed when BaCl\(_{2(aq)}\) was added to an aqueous solution
of a salt X. The precipitate dissolved in dilute HCl with rapid effervescence. Salt X is likely to contain
A
S\(O_4\) \(^{2-}\) ions
B
S\(O_3\) \(^{2-}\) ions
C
N\(O_3\)- ions
D
C\(O_3\) \(^{2-}\)- ions
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
A salt that forms a white precipitate (ppt) with BaCl2 and is soluble in HCl is a sulphite (SO3\(^{2-}\)) salt.
A salt that forms a white precipitate with BaCl₂ and is insoluble in HCl is a sulphate (SO₄²⁻), specifically a salt containing the sulfate anion, such as sodium sulfate (Na₂SO₄).
Source: Myschool Past Questions Archive (Record #65807)
Chemistry
WAEC / WASSCE 2022
Reaction Rates & Chemical Equilibrium
Solution
Before a reaction could take place, there should be
A
ionization of reactant particles
B
breakage of bonds of products
C
breakage of bonds of reactants
D
ionization of product particles
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Activation energy must be achieved before reaction begin. This is because in any chemical reaction, chemical bonds in the reactants are broken, and new bonds in the products are formed
Source: Myschool Past Questions Archive (Record #65808)
Chemistry
WAEC / WASSCE 2022
Oxidation, Reduction & Redox Reactions
Solution
Consider the following reaction equation:
CaO + Si\(O_2\) ------> CaSi\(O_3\)
Silicon(IV) oxide is acting as
A
a basic oxide
B
a reducing agent
C
an acidic oxide
D
an oxidizing agent
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
Silicon dioxide is an acidic oxide. It will react with strong bases to form silicate salts, Si\(O_2\) is acidic oxide because Si is non-metal. Oxides of non-metals are acidic in nature.
Source: Myschool Past Questions Archive (Record #65809)
Chemistry
WAEC / WASSCE 2022
Acids, Bases, pH & Salts
Solution
Which of the following acids would form normal salt only?
A
Tetraoxosulphate(VI) acid
B
Trioxonitrate(V) acid
C
Tetraoxophosphate(V) acid
D
Trioxosulphate(IV) acid
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Normal salts are formed when all the replaceable hydrogen ions in the acid have been completely replaced by metallic ions. Trioxonitrate(V) acid, HNO\(_3\) has only one replaceable hydrogen ion(monobasic), that can be replaced by a metallic ion or ammonium ion. Thus, it cannot form an acidic nor basis salt or any other type aside normal salt.
Source: Myschool Past Questions Archive (Record #65810)
Chemistry
WAEC / WASSCE 2022
Non-Metals & Their Compounds
Solution
Graphite is used as a dry lubricant due to the presence of
A
mobile electrons
B
free electrons
C
octahedral structures
D
layered structures
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
Graphite is an excellent dry lubricant. This is because its layered structure allows one layer to slide over another easily. It is non-volatile and not sticky.
Source: Myschool Past Questions Archive (Record #65812)
Chemistry
WAEC / WASSCE 2022
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
Which of the following statements about an equilibrium system is correct?
A
Forward and backward reactions occur
at the same rate
B
The concentrations of reactants must
equal that of the products
C
The concentrations of, reactants and products can be changed by adding a catalyst,
D
The concentrations of reactants and
products are not affected by a change in temperature
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
Equilibrium is a state of a system where there is no observable change in the properties of the system with respect to time
Source: Myschool Past Questions Archive (Record #65814)
Chemistry
WAEC / WASSCE 2022
Reaction Rates & Chemical Equilibrium
Solution
Consider the following reaction equation
\(N_2\)(g) + 3H\(_{2(g)}\) ⇌ 2NH3(g) ∆H = -92kJ
Increasing the temperature of the reaction would
A
shift the equilibrium to the right
B
increase the yield of ammonia
C
decrease the amount of hydrogen
D
decrease the yield of ammonia
medium Difficulty
Verified Correct Answer: Option D
Chemical Principles & Mechanism
In this case, an increase in in temperature will cause the equilibrium position to shift to the left thereby decreasing the yield of ammonia.
Source: Myschool Past Questions Archive (Record #65815)
Chemistry
WAEC / WASSCE 2022
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
When air in a syringe is compressed such that there is no change in temperature, the
A
air liquefies
B
pressure increases
C
intermolecular space increases
D
density decreases
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
Since the temperature of air remain constant.So, it is a isothermal process.
PV=K
This eq. shows that on increasing pressure, the volume gets reduced and vice-versa.
Since the syringe is slowly compressed, volume is decreasing.
Therefore, the pressure inside the syringe will increases because the molecules now hit the syringe walls more frequently.
Source: Myschool Past Questions Archive (Record #65816)
Chemistry
WAEC / WASSCE 2022
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
Which of the following statements about liquids is/are true?
I. Liquids maintain their volume at constant temperature.
II. Liquids have fixed shape
III. Liquids do not diffuse
IV. Change in pressure affects volume of liquids
A
I only
B
IV only
C
I and IV only
D
II and III only
medium Difficulty
Verified Correct Answer: Option A
Chemical Principles & Mechanism
A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure
Source: Myschool Past Questions Archive (Record #65817)
Chemistry
WAEC / WASSCE 2022
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
A hydrogen chloride gas reacted with oxygen gas to yield water and chlorine gas. The mole ratio of the hydrogen chloride gas to water is
A
1:3
B
2:1
C
3:1
D
4:1
medium Difficulty
Verified Correct Answer: Option B
Chemical Principles & Mechanism
4HCl + \(O_2\) -- 2C\(l_2\) + 2\(H_2\)O
4:2 = 4/2
2:1
Source: Myschool Past Questions Archive (Record #65818)
Chemistry
WAEC / WASSCE 2022
Stoichiometry, Mole Concept & Volumetric Analysis
Solution
What number of moles of oxygen would exert a pressure of 10 atm at 320 K in an 8.2 dm\(^{3}\) cylinder?
[R=0.082 atm dm\(^{-3}\) mol\(^{-1}\) K\(^{-1}\)]
A
0.32
B
1.52
C
3.13
D
31.25
medium Difficulty
Verified Correct Answer: Option C
Chemical Principles & Mechanism
P = 10atm, T= 320K, V= 8.2dm\(^{3}\)
PV =nRT
n = P * V/R * T
10 * 8.2/0.082 * 320
= 82/26.24
n = 3.13
Source: Myschool Past Questions Archive (Record #65819)