METALS: SODIUM COMPOUNDS
The commercial applications of sodium compounds in developed countries 
are so numerous that any brief overview has obvious limitations. But,
as a starting point, it does appear appropriate to state that their
extensive use is attributable to the following four aspects. Firstly,
sodium compounds are cheap to manufacture; in part, this reflects the
abundance and accessibility of the raw materials (e.g., sea water and
rock salt both contain sodium chloride). Secondly, sodium compounds are
usually soluble in water and have high thermal stability. Thirdly, in
most applications, it is the chemical properties of the anions which 
are important; the sodium cations are usually mere spectators. And 
fourthly, sodium cations are (relatively) non-toxic.
1. Brine is a concentrated aqueous solution of sodium chloride. Three useful products are obtained from the electrolysis of brine, as this overall symbol equation shows:
The ionic equations for the reactions occurring at the electrodes are:
(a) Label this diagram of a (Diaphragm) electrolytic cell with: Cl2(g);
H2(g); NaOH(aq); Saturated brine; Steel cathode; and, Titanium anode.
(b) A typical electrolytic cell used in industry, which operates 
continuously at 1.5 kA and 4 V, must have at least five hazard symbols 
clearly visible: 'Corrosive' [i.e., NaOH(aq)]; 'Explosive' [H2(g)]; 
'Highly flammable' [H2(g)]; 'Oxidizing' [Cl2(g)]; and 'Toxic' [Cl2(g]. 
State three items of safety clothing necessary for workers or visitors.
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(c) The diaphragm is selectively permeable, allowing hydroxide (but not
chloride) ions to enter the cathodic compartment. Suggest and explain
one advantage in this selectivity. ____________________________________ 
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The diaphragm also prevents mixing of the gaseous electrode products,
dihydrogen and dichlorine, which together react explosively. Construct
the symbol equation for this reaction. ________________________________
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(d) Suggest and explain one reason why electrodes made of iron would be
unsuitable. ___________________________________________________________
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2.  Aqueous sodium carbonate neutralizes aqueous hydrochloric acid:
As this ionic equation shows, it is the carbonate (and hydrogen) ions
which are the reactants: the sodium (and chloride) ions are spectators.
Construct a similar ionic equation for the precipitation reaction
between aqueous solutions of sodium hydroxide and iron(II) sulfate.
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3.  Sodium carbonate is thermally very stable; indeed, it melts before 
it decomposes at temperatures above 1000C:
By contrast, sodium hydrogencarbonate is thermally much less stable;
thus, at temperatures above 90C, it decomposes to give three products.
Construct the symbol equation for this thermal decomposition. _________
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4.  The Table below presents one illustrative application for eight
sodium compounds. Complete this Table by inserting the correct formula 
from this list: [CH3(CH2)16COO]Na ; NaCl ; NaHCO3 ; NaNH2 ; NaOCl ; 
NaOH ; Na2[B2(O2)2(OH)4] ; Na2CO3.
 Formula of compound 
 (Application)
       Property of compound or anion which
      is important in specified application
 
 (Strong base)
 Completely dissociates in water; the hydroxide
 ions neutralize aqueous hydrogen ions.
 
 (Baking powder)
 Partially decomposes when heated; the evolved
 carbon dioxide expands, so dough mixtures rise.
 
 (Fertilizer)
 Hydrolyzes to give ammonia, which is converted
 to ammonium ions in the soil: so crops are
 provided with a usable source of nitrogen.

 (Glass manufacture)
 Completely decomposes when heated at very high
 temperatures; the resulting molten sodium oxide
 fuses with other oxides to form glass.
 
 (Food preservative)
 A concentrated solution, which is non-toxic,
 has a low water potential: so water is removed
 from pathogenic cells by exo-osmosis across the
 semi-permeable membranes.
 
 (Soap)
 Hydrocarbon chain is lipophilic and ions are
 hydrophilic: so has detergent properties, as it
 acts as an emulsifying agent for fats and oils.

 (Bleaching agent)
 Partially decomposes when heated to ca. 80C;
 the evolved hydrogen peroxide acts as a bleach.
 
 (Disinfectant) 
 An aqueous solution slowly photolyzes to give
 'chlorine water', which is a biocide.
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5.  In Man, sodium ions are required principally for osmoregulation and
for conduction of nerve impulses. State briefly how excess sodium ions
are excreted in this species. _________________________________________
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6.  Name the only other metal whose compounds are usually non-toxic,
water-soluble, thermally-stable, and cheap to manufacture. ____________
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