2020 - JAMB Chemistry Past Questions and Answers - page 2
When water drops are added to calcium carbide in a container and the gas produced is passed through a jet and lighted, the resultant flame is called an?
Oxyethene
Oxyhydrocarbon flame
Oxyacetylene flame
Oxymethane flame
The reaction of calcium carbide with water, producing acetylene and calcium hydroxide, was discovered by Friedrich Wöhler in 1862. This reaction was the basis of the industrial manufacture of acetylene and is the major industrial use of calcium carbide.
Which of the following substances is a mixture?
Granulated sugar
Seawater
Sodium chloride
Iron filling
In chemistry, a mixture is a material made up of two or more different substances which are not chemically combined. A mixture is the physical combination of two or more substances in which the identities are retained and are mixed in the form of solutions, suspensions and colloids. Wikipedia
Examples include Air, Soil, Palm oil, Seawater, Blood, Crude oil, etc
If the quantity of oxygen occupying 2.76L container at a pressure of 0.825 atm and 300k is reduced by one-half, what is the pressure exerted by the remaining gas?
1.650atm
0.825atm
0.413atm
0.275atm
By applying the combined gas law formula,
Given:
P\(_1\) = 0.825, V\(_1\) = 2.76 L, V\(_2\) = 1.38 L, P\(_2\) = ?
T1 = T2; we would have P\(_2\) = [ P\(_1\) X V\(_1\) ] ÷ V\(_2\)
[0.825 X 2.76] ÷ 1.38
= 1.650atm
Four elements P, Q, R and S have atomic numbers of 4, 10, 12 and 14 respectively. Which of these elements is noble gas?
P
Q
R
S
They are the most stable because they have the maximum number of valence electrons their outer shell can hold.
Hence, they rarely react with other elements since they are already stable.
The products of the thermal decomposition of ammonium trioxonitrate(v) are?
Nitrogen (I) Oxide and Water
Ammonia and Oxide
Nitrogen and Water
Nitrogen (IV) Oxide and Water
NH\(_4\)NO\(_3\) Ammonium Trioxonitrate(V) decomposes on heating to give nitrogen(i)oxide N\(_2\)O and water, unlike all other metallic trioxonitrates(v).
How many valence electrons are contained in the element \(^{31}_{15}P\)?
3
4
15
31
The element is Phosphorus in group 5 with valencies of 3 and 5. These are contained in the third energy level of the atom. Due to the number of valence electrons, Phosphorus is capable of forming three bonds with other elements.
The number of molecules of Carbon(iv)Oxide produced when 10.0g of CaCO\(_3\) is treated with 0.2dm\(^3\) of 1 Mole of HCL in the equation
CaCO\(_3\) + 2HCL ⇒ CaCl\(_2\) + H\(_2\) O + CO\(_2\) , is ?
1.00 X 10\(^{23}\)
6.02 X 10\(^{23}\)
6.02 X 10\(^{22}\)
6.02 X 10\(^{24}\)
The volume occupied by 1.58g of a gas at S.T.P is 500cm\(^3\). What is the relative molecular mass of the gas? [ G.M.V at S.T.P = 22.4dm\(^{23}\) ]
28
32
44
74
500cm\(^3\) of the gas weighed 1.58
22400cm\(^3\) of the gas weight:
[22400 X 1.58g] ÷ [ 500 ]
= 74
Which of the following gases will rekindle a brightly splint?
B. NO\(_2\)
NO
N\(_2\)O
CL\(_2\)
Nitrogen(I)Oxide rekindles a brightly glowing splinter but extinguishes a feebly glowing one which is not hot enough to decompose the gas to liberate oxygen
The shape of ammonia molecule is?
Trigonal planar
Octahedral
Square planar
Tetrahedral
The ammonia molecule has a trigonal pyramidal shape with three hydrogen atoms and an unshared pair of electrons attached to the nitrogen atom. It is a polar molecule and is highly associated because of strong intermolecular hydrogen bonding.