what the state symbol for this equation magnesium chloride
----------------------HCL
( ) plus Mgo
( ) --------MgCl(small 2) plus H(small 2) O
( )
the blank are the state i dont know how to find , can anyone
teach me how to idenify is aqueous,solid ,liquid ? Thank in
advance.
As with all my posts which can be understood to different
extents at different levels, so take from it what you will,
depending on your current level of study (eg. Sec 3, Sec 4,
JC1, JC2, etc). In other words, I write my posts this way so
students from across multiple levels (eg. 'O' levels, 'A'
levels, etc) may benefit.
The more adventurous or
interested, may google/wikipedia any terms they/you might
come across (eg. in my posts) that you might be to
date unfamiliar with.
For secondary school students, you can skip right to the bottom
of my post ("Summary for secondary sch students or 'O' level
students").
The equation required by the question is :
2HCl(aq) + MgO(s) --> MgCl2(aq) + 2H2O(l)
The dinegative oxide anion acts as a Bronsted-Lowry base to
accept two protons H+ (from the hydrochloric acid) to generate two
water molecules. The counter ions left over, constitutes the
so-called salt, MgCl2(aq).
To figure out the state symbols, you must first be familiar with
solubilities, and covalent versus ionic compounds. Oxides
of metals are ionic and hence (ionic compounds by nature of
their giant lattice structure) are usually either solid,
or aqueous (to be precise : ionic compounds are soluble if their
hydrolysis products are soluble; and/or their hydration
enthalpy exceeds their lattice dissociation enthalpy; and/or if the
increase in entropy during lattice dissociation exceeds
the decrease in entropy during hydration) at rtp.
(In contrast, simple covalent molecular compounds have weak
intermolecular interactions and are hence usually gaseous
or liquid at rtp; when mixed with water, some simple covalent
molecules may be aqueous (ie. miscible with water, hence soluble in
water) if they're capable of hydrogen bonding and/or ion-dipole
interactions with water, eg. sugars, alcohols, etc).
Oxides of Group I metals are generally soluble (to be
precise : they undergo hydrolysis to generate soluble products, eg.
O2- + H2O --> 2OH- ) while oxides of Group II metals are
generally insoluble. Hence you may deduce MgO is an insoluble
solid at rtp.
Hydrogen chloride is gaseous at rtp, but dissolves in water as
it dissociates into protons H+ and chloride ions Cl-, because the
heat energy generated from the ion-dipole interactions (a
significant upgrade from permanent dipole - permanent dipole
interactions that undissociated hydrogen chloride would experience
with water) are more than sufficient to compensate for the heat
energy absorbed to dissociate the H-Cl covalent bond.
Hence hydrogen chloride gas HCl(g) dissolves readily
in water to form HCl(aq). It may be represented by either a
proton dissociation equation, or as an hydrolysis equation.
HCl(g) + aq --> HCl(aq)
or
HCl(g) + H2O(l) --> H3O+(aq) + Cl-(aq)
Chloride salts may be soluble or insoluble, depending on the
cation. (The more soluble the salt, the larger its Ksp value or
solubility product, for a given solvent and temperature).
For 'O' levels, all chlorides may be assumed to be soluble
except for silver chloride and lead(II) chloride. For 'A'
levels, if a compound is sparingly soluble, you'll be given either
the Ksp or its molar/mass solubility.
---------------------------------
To Summarize (for secondary sch students or 'O' level
students) :
The equation required by the question is :
2HCl(aq) + MgO(s) --> MgCl2(aq) + 2H2O(l)
As a general rule, acids are aqueous (aq) unless otherwise
specified (eg. some concentrated acids are liquid (l), eg.
concentrated sulfuric(VI) acid H2SO4(l)).
Group I oxides are soluble, and Group II oxides are
insoluble.
For 'O' levels, all chlorides may be assumed to be soluble
except for silver chloride and lead(II)
chloride.
Ionic compounds (including salts) may be soluble or insoluble in
water at rtp; you need to memorize a list of compounds and
their solubilities in water, which should be given in your school
notes or textbook.
Open the following pdf files (see below) which contain the
Chemistry syllabus for 'O' levels and 'A' levels, and look
for the Practical Notes for Qualitative Analysis, which
includes information (if you know how to interpret it) on
solubilities, indeed the basis for identification of cations and
anions, ie. Qualitative Analyais.
'O' Levels :
http://www.seab.gov.sg/oLevel/syllabus/5072_2010.pdf
'A' Levels :
http://www.seab.gov.sg/aLevel/20102011Syllabus/9647_2011.pdf
Note : Interested 'O' level students may wish to check out the
'A' level QA Pract Notes, which give slightly more QA info on a few
additional compounds (that you might encounter at 'O' levels,
depending on your school, even though knowledge of these are
not strictly required at 'O' levels), but are by no means an
exhaustive list even at 'A' levels.