2020 - JAMB Chemistry Past Questions and Answers - page 1
The electronic configuration of an element is 1S\(^2\) 2S\(^2\) 2P\(^6\) 3S\(^2\) 3P\(^3\). How many unpaired electrons are there in the element?
5
4
3
2
Based on Hund's rule, there are 3 unpaired electrons in P.
Which of the following can be obtained by fractional distillation?
Nitrogen from liquid air
Sodium Chloride from sea water
Iodine from solution of Iodine in carbon tetrachloride
Sulphur from the solution of sulphur in carbon disulphide
The Fractional Distillation of Liquid Air
An air separation unit is often called an oxygen or nitrogen generator since its purpose is to extract one or both of these elements from the air. In the distillation process, the air is first passed through a filter that absorbs all the water vapour.
An air separation plant separates atmospheric air into its primary components, typically nitrogen and oxygen, and sometimes also argon and other rare inert gases. The most common method for air separation is fractional distillation.
Duralumin consists of aluminum, copper?
Zinc and Gold
Lead and Manganese
Nickel and Silver
Manganese and Magnesium
Duralumin is an alloy made up of 90% aluminium, 4% copper, 0.51% magnesium, and less than 1% manganese.
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An example of a polysaccharide is?
Dextrose
Mannose
Glucose
Starch
A polysaccharide is a large molecule made of many smaller monosaccharides. Monosaccharides are simple sugars, like glucose. Special enzymes bind these small monomers together creating large sugar polymers, or polysaccharides. A polysaccharide is also called a glycan.
8g of CH\(_4\) occupies 11.2 at S.T.P. What volume would 22g of CH\(_3\)CH\(_2\)CH\(_3\) occupy under the same condition?
3.7dm\(^3\)
11.2dm\(^3\)
22.4dm\(^3\)
33dm\(^3\)
Molar mass of methane, CH4 = 16g/mol
At standard conditions, S.T.P., 8g CH4 occupies 11.2
Hence, 16g occupies 22.4 dm\(^3\)
Molar mass of propane = 44g/mol\(^-1\) occupies 22.4dm\(^3\) at S.T.P
Hence,
22g will occupy 11.2dm\(^3\)
The best treatment for a student who accidentally poured conc tetraoxosulphate(vi) on his skin in the laboratory is to wash his skin with?
with cool running water
sodium hydroxide solution
iodine solution
sodium trioxonitrate(v) solution
The treatment: Flushed Sulfuric acid with a mild, soapy solution if the burns are not severe.
Note: Sulfuric acid feels hot when water is added to the acid, but it is better to flush the area and not leave the acid on the skin.
Warning: Don't try to neutralize the burn with acid or alkali. This could cause a chemical reaction that worsens the burn!
Which of the gas laws does this graph illustrate?
Boyle
Charles
Gay-Lussac
Graham
Charles' law states that the volume occupied by a fixed amount of gas is directly proportional to its absolute temperature, if the pressure remains constant.
What are the possible oxidation numbers of an element if its atomic number is 17?
-1 and 7
-1 and 6
-3 and 5
-2 and 6
The element with atomic number 17 is Chlorine which has a valency of -1.
Hence, it needs to receive an electron or lose seven electrons to obey the octet rule which refers to the tendency of atoms to prefer to have eight electrons in the valence shell. When atoms have fewer than eight electrons, they tend to react and form more stable compounds
What process would coal undergo to give coal gas, coal tar, ammoniacal liquor and coke?
Steam distillation
Destructive distillation
Liquefication
Hydrolysis
Destructive distillation is a chemical process in which decomposition of unprocessed material is achieved by heating it to a high temperature; the term generally applies to the processing of organic material in the absence of air or in the presence of limited amounts of oxygen or other reagents, catalysts, or solvents, such as steam or phenols.
Liquid black soap is made by boiling palm oil with liquid extract of ash. The function of the ash is to provide the ?
Acid
Ester of alkanoic acid
Alkali
Alkanol
Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula NaOH. It is a white solid ionic compound consisting of sodium cations Na⁺ and hydroxide anions OH⁻ . Wikipedia