Chemistry (OBJ And ESSAY) Waec GCE 2016 Free Expo Answers see here>>>>>>>


Chemistry (OBJ And ESSAY) Waec GCE 2016 Free Expo Answers
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Tuesday, 20th September, 2016
Chemistry (obj and essay) 9.30am
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CHEMISTRY OBJ:
1-10: ADCCADAADA
11-20: DCCBADDBCC
21-30: CBAACDDDAB
31-40: CACCBDDADB
41-50: ADBCDADBBA
1a)
i)they are relatively of low cost
ii)They have high heat resistance
1bi)
draw the structure
H H
H-C-C-H
Br Br bromoethane
1bii)
bromoethene
1c)
Because Ethanol is less denser than water
1di)
Le Châtelier’s principle, states that if a system in equilibrium is disturbed by changes in determining factors, such as temperature, pressure, and concentration of components, the system will tend to shift its equilibrium position so as to counteract the effect
1dii)
i)F2+2NaOH—–>NaOF+NaF+H20
ii)Cl2+2NaOH—–>NaOCl+NaCl+H20
1dii)
i)K2SO3 has been oxidized
ii)Ag^2+ has been oxidized
1e)
dynamic equilibrium is a steady state reached when a reversible reaction occurs at the same rate in both directions and has an unchanging ratio of products and reactants.
1f)
diagrams
(k)** (k)** (2) (k)** (k)**
1g)
because it attains equilibrium at very fast rate
1hi)
i)electrovalent bonding.
ii)covalent bonding
1hii)
Aufbau principle states that hypothetically, electrons orbiting one or more atoms fill the lowest available energy levels before filling higher levels (e.g., 1s before 2s). In this way, the electrons of an atom, molecule, or ion harmonize into the most stable electron configuration possible.
1i)
The outer electron in aluminium is in a p sub-level. This is higher in energy than the outer electron in magnesium, which is in an s sub-level, so less energy is needed to remove it.
1j)
i)Substitution
ii)addition
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====================
(2ai)
Vander waal’s force are weak intermolecular gases at room temperature.
(2aii)
-Electronegativity difference
-Ionization energy
(2aiii)
-Ionization energy
-Electron affinity
(2b)
C-F and C-O
C-N and C-H-O and C-N and C-F and C-O
(2ci)
-Be=1S^22S^2
4Mg=1S^22S^22P^63S^2
They both have the same number of electron in the outermost shell
(2cii)
Mg^2+->Na^+->Ne
The size of positive ion is less than that of the neutral atom
(2bii)
C-F>C-O>C-N>C-H(order of polarity).
(2ci)
4Be=1S^2 2S^2
12mg =1S^2 2S^2 2P^6 3S^2.
(2cii)
4Be and 12Mg have similar chemical properties because they belong to the same group in the periodic table. Both 4Be and 12Mg belongs to group II in the periodic table hence they have similar chemical properties.
(2di)
Transition element: Transition elements are those element with partially or incompletely filled d-orbital. Transition metal form coloured ion (or compound), they acts as catalyst,they have variable oxidation stat, they are paramagnetic, they form complex compound or coordination compound
(2dii)
Most transition metals have variable oxidation state because they undergo bonding with the electron in the ns and (n-I) d-orbital .e.g. most of the first series of transition metal from scandium to Zinc have variable oxidation state because they undergo bonding with electron in 4s and 3d- orbital.
(2diii)
(i) Metals are used in electroplating
(ii) Metals are used in making electronic cables and cooking utensils because they are good conductor of heat and electricity.
(2div)
It is used in electroplating and galvanizing to make electrical cable
================================
(3ai)
Crystallisation is a separation technique that is used to separate a solid that has dissolved in a liquid and made a solution. The solution is warmed in an open container, allowing the solvent to evaporate, leaving a saturated solution.
(3aii)
Evaporation is the process of a substance in a liquid state changing to a gaseous state due to an increase in temperature and/or pressure.
(3aiii)
Filtration is any of various mechanical, physical or biological operations that separate solids from fluids (liquids or gases) by adding a medium through which only the fluid can pass.
(3bi)
(i)Their Melting and Boiling Points increases down the group
(ii)Their atomic Radius increases down the group
(iii)Their Ionization Energy: decreases down the group
(3bii)
4NaOH(aq)+2F2(aq)->4NaF(aq)+O2(g)+2H2O(l)
Cl2(g)+2NaOH(aq)->NaOCl(aq)+NaCl(aq)+NaCl(aq)+H2O(l)
(3ci)
Gas is a state of matter while vapour is the gaseous state of substance in equilibrium with its liquid or solid state
(3cii)
Normal temperature and pressure
(3di)
Mg(s)+Cl2(g)->MgCl2(s)
(3dii)
n=mass/molarmass
n=24/35.5
n=1.2/24
n=0.05
number of moles=volume used/molar volume
0.05=V/22.4
V=1.12dm^3
(3e)
-Atomic number is the number of protons present in an atomic nucleus of the element
-Mass number of an element is the sum of the protons and neutrons in the atomic nucleus of the element
(3f)
diagrams
( k )** ( k )** ( 2) ( k )** ( k )**
(3g)
Because it attains equilibrium at very fast rate
========================================
(4ai)
Hard water is water which does not lather readily with soap. Hard water is formed when water percolates through deposits of limestone and chalk which are largely made up of calcium and magnesium carbonates.
(ii)
-Temporary hardness: Ca(HCO3)2
-Permanent hardness: Na2C03
(iii)
-By using chemicals like caustiic soda.
-By using permutot OR zeolite
(4bi)
(i) coagulation
(ii) sedimentation
(iii) filtration
(iv) chlorination/disinfection
(4bii)
(i) Sodium chloride
(ii) Potassium chloride
(iii) Chlorine dioxide
(4ci)
Solubility is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a solid, liquid, or gaseous solvent.
CHEMISTRY OBJ:
1-10: ADCCADAADA
11-20: DCCBADDBCC
21-30: CBAACDDDAB
31-40: CACCBDDADB
41-50: ADBCDADBBA
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