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.
Originally posted by Ffrank.neo: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.
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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.