2023 Waec Gce Chemistry obj and Essay expo Nov Dec second series

 

CHEMISTRY OBJ
1-10: DABBBBABDC
11-20: BADBCCACAC
21-30: BAACBACAAA
31-40: BDADBAACBA
41-50: BACCBBACBC

 

Read more – 2023 Waec gce chemistry practicals Answers available

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2023 WAEC GCE CHEMISTRY THEORY ANSWERS

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(1a)
A solution of ammonia is basic, hence it turns red litmes blue.

(1bi)
Methylmethanoate.

(1bii)
A catalyst, concentrated tetraoxosulphate(vi) acid must be used to speed up the reaction.

(1ci)
CaC₂(s) + H₂0(l) —> C₂H₂(g) + CaO(s)

(1cii)
It is used in the production of oxy-acetylene flame used for welding.

(1d)
(i) Motarity
(ii) Masses
(iii) Saturation level.

(1e)
(i) Rusting requires moisture but burning does not.
(ii) Burning requires heat while rusting does not.

(1fi)
The K₂Cr₂O7 is reduced.

(1fii)
Hydrogen gas is geven off with the formation of iron(11) Chloride (green).

(1gi)
(i) Carbon(1V)Oxide, CO₂
(ii) Steam,
(iii) Heat energy

(1gii)
CxHy + (x + Y/A) —-> xC0₂ + y/₂ H₂0.

CH4 + 20₂ —-> CO₂ + 2H₂0

(1h)
Law of constant composition which states that equal volumes of all gases contain equal quantities of Particles at constant temperature and pressure.

(1i)
The heat of neutralization (ΔH) is the heat evolved when an acid and a base react to form a salt plus water.

(1j)
Increasing the surface area of the solid and also by heating and boiling

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(2a)
M=10g
M of CaCO3 = 40 + 12 + (3×16)
= 40 + 12 + 48
= 100g/Mol

n = Mass / molar mass
n = 10 / 100
n = 0.1 mole

(2bi) C₂H₂ + 2Na2 —> 2NaH + C₂H₂
In this reaction, the sodium Reacts with the hydrogen atom in C₂H₂ to produce sodiumhydride(NaH), which is a
strong base. The resulting product is acidic due to the presence of hydroxide ions which are produced when the alkali metal sodium reacts with the hydrogen atoms C₂H₂

(2bii)
C₂H5OH + Na —-> NaOH + C₂H5
In this reaction the sodium reacts with the hydroxyl group
in C₂H₂OH to produce Sodium hydroxide, which is a strong base the resulting product is acidic due to the presence of hydroxide ion (OH-), which are produced When the alkali metal sodium reacts with the hydroxyl group in C₂H5OH

(2c)
(SEE DIAGRAM ABOVE)

(2di)
Mg —> mg²+ + 2e-
2H+ + 2e- —> H₂(g)

(2dii)
Mg + 2H+ —> Mg²+ + H₂(g)

(2ei)
-TABULATE-
(CHOOSE ONLY TWO)

UNDER MIXTURE
(i) Homogenous in Nature
(ii) Mixed in any proportion
(iii) Components that make up a mixture can be separated by any physical means
(iv) Does not have a chemical Formula

UNDER COMPOUND
(i) May be Homogeneous Or Heterogeneous
(ii) Elements or components are in simple whole number ratio
(iii) Elements that make up a compound cannot be separated by any physical means
(iv) It has a chemical Formula

(2eii)
• An Element : Gold
• A Mixture : Soil
• A Compound : Quick Lime

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(3ai)
Elements was found out buy rutherFord that it can be divisible into sub particles like electrons, protons and
neutrons. (J. I thompson).

(3aii)
Some atoms like Carbon Combine with many other elements, so they are considered to be modified version of the atoms that Compose them. For example, when hydrogen and oxygen atoms Combine to from water the resulting Compound have different Chemical properties

(3aiii)
Some atoms of Same element are not alike, example of Such elements is chlorine. chlorine has an Isotope 35CL, 37CL Isotopes are elements with Same atomic number but different mass number.

(3aiv)
Some atoms can be created and also destroyed, atoms Like Uranum, a radioactive elements which can decay.

(3b)
TABULATE
UNDER K
• 31.84
• 3g
• 0.816
• 0.816
• 1

UNDER CL
• 23.98
• 35.5
• 0.816
• 0.816
• 1

UNDER O
• 39.18
• 16
• 2.449
• 0.816
• 3

X = RCLO3

(3ci)
I = petroleum refining
I = Sugar refining
II = Garring production

(3cii)
I = Magnetism
= Mettalic Solid
II = Size of particles
= Solid at room Temperature
III = Boiling
= Solubility

(3di)
n = Mass / Molar Mass
n = 11/12
n = 0.92Mol

(3dii)
Number of Molecules = No of moles x Avogadro’s number
= 0.92 × 6.02 × 10²³
= 5.54 ×10²⁵ molecules

(3diii)
A mole is 22.4dm³
0.92mole = xdm³
cross multiply
X dm³ = 22.4 × 0.92
= 20.6 dm³

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(4ai)
(i) Carbon: A filter with granular activated carbon is used to remove certain chemical mostly Organic chemicals which gives odor or taste to the water, such as Hydrogen Sulfide.
(ii) Chlorine: This is added to water during treatment in order to kill parasites, bacterias and viruses. This process is called chlorination

(4aii)
(i) Coagulation: Coagulation is often the first step in water treatment. During coagulation, chemicals with a positive charge are added to the water. The positive charge neutralizes the negative charge of dirt and other dissolved particles in the water. When this occurs, the particles bind with the chemicals to form slightly larger particles. Common chemicals used in this step include specific types of salts, aluminum, or iron.

(ii) Flocculation
Flocculation follows the coagulation step. Flocculation is the gentle mixing of the water to form larger, heavier particles called flocs. Often, water treatment plants will add additional chemicals during this step to help the flocs form.

(iii) Sedimentation: Sedimentation is one of the steps water treatment plants use to separate out solids from the water. During sedimentation, flocs settle to the bottom of the water because they are heavier than water.

(4bi)
When humans burn fossil fuels, sulfur dioxide (SO2) and nitrogen oxides (NOx) are released into the atmosphere. Those air pollutants react with water, oxygen, and other substances to form airborne sulfuric and nitric acid. These pollutants causes acid rain

(4bii)
Acid rain can ruin buildings and statues by stripping away the material and corroding metal that makes up these structures.

(4ci)
Allotropy is the existence of a chemical element in two or more forms, which may differ in the arrangement of atoms in crystalline solids or in the occurrence of molecules that contain different numbers of atoms

(4cii)
In a graphite molecule, one valence electron of each carbon atom remains free, Thus making graphite a good conductor of electricity. Whereas In diamond, they have no free mobile electron. That is why diamond are bad conductor electricity.

(4ciii)
Animal Charcoal

(4di)
Water is called a ‘universal solvent’ because water can dissolve much more substances than any other liquid found in nature but water cannot dissolve every substance.

(4dii)
(Pick Any TWO)
(i) Hard water is unfit for washing as it is difficult to form lather with soap.
(ii) Scum may form in a reaction with soap, wasting the soap.
(iii) Furring of tea kettles will take place due to the formation of carbonates of calcium and magnesium.

(4diii)
Due to hydrogen bonding in water which is not in Hydrogen sulphide, water will have the stronger intermolecular force and hence, more temperature will be required to boil it.

(4div)
(Pick Any ONE)
(i) It is used in the production of Ammonia by producing hydrogen.
(ii) It is used in welding and glass making.
(iii) It is used for several organic compound synthesis in industries like the production of several hydrocarbons.
(iv) Water gas helps in the removal of Carbon dioxide from fuel cells.

 

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