المراجعة النهائية فى مادة الكيمياء لغات - الجزء الخامس

المراجعة النهائية فى مادة الكيمياء لغات - الجزء الخامس



Give reasons for
The line spectra of any element is a specific.
Because each element has certain no of electron so it gives special line spectra
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The electron has a dual nature
Because the electron is a negative particle and it has wave properties
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Electron pairs with another in the orbital rather entering vacant higher energy orbital
Because amount of energy needed to overcome the repulsion is less than energy needed to transfer the electron to higher energy orbital
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It is wrong to consider the electron is a negative particle only.
Because it also has wave properties
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Electron affinity of chlorine is bigger than that of fluorine
Because fluorine has small radius when it gains new electron it will suffer from high repulsion
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Nitrogen has –ve oxidation number in hydrogenated compounds and has +ve oxidation number in oxygenated compounds
Because it has electronegativity more than hydrogen but less than oxygen
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Perchloric acid has more acidity than orthophosphoric acid
Because it has more oxygen not linked to hydrogen
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Bond length in FeO is bigger than that of Fe2O3
Because in Fe2O3 +ve charge of iron increase so attraction increases and radius decreases
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Fluoride ion and sodium ion are isoelectronic.
Fluoride ion = fluorine atom has 9 electrons + electron = 10 electrons
sodium ion = sodium atom has 11 electrons loses 1 electron = 10 electrons
F- = 1s2, 2s2, 2p6 Na+ = 1s2, 2s2, 2p6
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A coordinate bond is formed in ammonium molecule
Because in ammonia gas, nitrogen atom has lone pair of electrons can give it to proton (H+) to form ammonium ion
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Aluminum (Al13) is harder and has higher melting point than sodium (Na11)
Because Aluminum (Al13) has three valence electrons while sodium (Na11) has one ,as the no. of valence electrons increases the metallic bond is harder
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Hydrogen chloride has polar covalent bond while chlorine molecule has pure covalent bond
Because hydrogen chloride is made of two different nonmetals while chlorine molecule is made of two similar nonmetals
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Sodium fire is not extinguish by water
Because sodium reacts with water giving sodium hydroxide, hydrogen and amount of heat enough to burn hydrogen so the fire increases
2Na + 2H2O 2NaOH + H2 + heat
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Elements of group 1A are called alkali metals
Because they dissolve in water forming strong alkalis
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Alkali metals are kept under liquid hydrocarbons
To be away from oxygen and humidity as the are very active elements
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In closed areas exhale gases may be pass through filters containing KO2
Because it reacts with CO2 gives oxygen so it refresh the air
4KO2 + 2CO2 CuCl2 cat. 2K2CO3 + 3O2
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Nitric acid is oxidizing agent
Because it decomposes by heat giving oxygen
4HNO3 ∆ >100 C 2H2O + 4NO2 + O2
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Iron does not react with concentrated nitric acid
Due to passivity (formation of nonporous layer of oxide surround the metal and stop the reaction)
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The abnormal electronic configuration of chromium and copper
Chromium -24 = [Ar18] 4s1, 3d5 half filled sublevel d = more stable
Copper-29 = [Ar18] 4s1, 3d10 completely filled sublevel d = more stable
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The uses of manganese in steel production
To prevent formation of bubbles in steel
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Although chromium is a high reactive element, it resists the effect of atmosphere
Due to formation of non porous layer of oxide surround the element and stop further reaction
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Coinage metals are considered as transition elements
Because they are not completely filled sublevel d in one of their compounds
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The basic solution can't be used to differentiate between litmus indicator and bromothymol blue indicator
Because both has blue colour in basic medium
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Two grams of hydrogen contain the same number of atoms in 32 grams of oxygen at(stp)
Because equals one mole of each gas so both has the same volume and has the same no. of molecules (avogadro's law)
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No free hydrogen ion is present in an aqueous solution of strong acid
Because it combines with water by coordinate bond forming hydroxonium ion
H2O + H+ H3O+
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The law of mass action can be applied in the case of weak electrolyte solution
Because weak electrolyte is not completely ionized, so both reactants and products are found in the medium
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Sodium carbonate has basic effect on litmus
Because sodium carbonate is ionized in water forming strong base and weak acid
Na2CO3 + 2H2O 2Na+ + 2OH- + H2CO3
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Ester formation is a reversible reaction
Because it proceeds in both direction forward and backward
CH3COOH + C2H5OH CH3COOC2H5 + H2O
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The anode is the negative pole of the galvanic cell
Because it is the source of electrons (where oxidation occurs )
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The standard hydrogen potential is not equal zero in some cases
Because the concentration of the acid not equals 1M ,or the pressure of the H2 not equals 1 atmospheric pressure
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Dry cell is a primary galvanic cell
Because it can not be recharged
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The lead-acid battery is a reversible cell
Because it can be recharged
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Using a mixture of fluoride salts of aluminum, sodium and calcium instead of cryolite in preparation of aluminum from bauxite
To decrease the melting point of the mixture and decrease its density
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The organic compounds are abundant.
Due to the ability of carbon to combine with another by different kinds of bonds and methods
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The structural formula is better than the molecular formula.
Due to isomerism - structural formula show the type of bond between atoms
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Vital force theory is destroyed
Wohler prepared organic compound ( urea ) from inorganic compound ( NH4CNO)
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Ethanol and dimethyl ether are isomers.
Because they have the same molecular formula but different in structural ones
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Addition in alkenes takes place in one step where in alkyne it takes place in two steps
Because alkene has one pi bond – alkyne has two pi bond can be broken
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Ethylene glycol is used as antifreeze substance in car radiators
Because it makes hydrogen bond with water molecules and prevent freezing of water