Ok on an assignment I have to tell how something is a strong or weak base/acid?
Answer:
In general, a strong acid is an acid that ionizes 100% in H2O. This means that
HCl(aq) ---> H+(aq) + Cl-(aq)
In water, there is almost no HCl...it is all ionized into H+ and Cl-.
A weak acid will ionize very little in water, often less than 3%. So, when we say:
HF(aq) ---> H+(aq) + F-(aq)
In water, the acid stays as HF rather than H+ and F- because HF is a weak acid.
To determine relative acidity:
For a binary acid such as HI, the larger the size of the atom attached to the Hydrogen, the stronger the ionizability of the hydrogen (ie. the stronger the acid)... This is because the hydrogen is held very loosely in the bond and is "more polarizable"...therefore:
HF < HCl < HBr < HI
Because as you go down the periodic table, the atomic radii/ionic radii increase. When comparing atoms across a row of the periodic table (ie. similar in size), the more electronegative the atom is, the greater the acid strength. So, for C, N, O, F:
CH4 < NH3 < H2O < HF
Now, when Hydrogen is involved in a complex ion (polyatomic ion) and forms an acid, then the more Oxygens attached to the central atom, the stronger the acid:
HOCl < HClO2 < HClO3 < HClO4
HNO2 < HNO3
H2SO3 < H2SO4
For different atoms with the same number of oxygens, the more electronegative atom will make the stronger acid:
HIO2 < HBrO2 < HClO2 ...<HFO2 does not exist!>
Now, the strong acids are a small group:
HNO3, H2SO4, HClO4, HCl, HBr & HI are the typical group given to First year students.
Bases:
Bases are easy. All of the bases of Group IA and Group IIA elements are strong. It is useful to note that some of the Group IIA elements are only partially soluble, BUT what dissolves is ionized (i.e. strong). Nitrogen based bases are all weak. So, NaOH, Ca(OH)2, Ba(OH)2 all strong...NH3, CH3NH2, caffeine, nicotine, etc are all weak.
What makes a strong or weak base is its ability to dissociate into ions while solvating into a solution. You can take an acid dissociation constant and Base to determine if the Acid or base is weak or not. For an acid... H+ x conjugate base/Acid conc
For a base.... OH- x Anion from conjugate acid/Base conc.
:)
the lower the PH the stronger the acid.
Stronger acids are acids that dissolve completely in water.
weaker acids tend to form equilibrium reactions, with
the compound itself present as well as the ions from which it is made.
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