6. Thermal decomposition with medium salts formation:
Ca(HCO3)2 → CaCO3↓ + СO2↑+ H2O.
Double and mixed salts may be considered as the sort of neutral salts. Double salts may be prepared by interaction between any multibasic acid and different bases:
H2SO4 + KOH + NaOH = NaKSO4 + 2H2O.
or during synchronous crystallization of different salts:
K2SO4 + Al2(SO4)3 + 24H2O = 2KAl(SO4)2·24H2O.
Mixed salts may be prepared by interaction of multiacidic bases and different acids. For example, preparation of bleaching powder:
Ca(OH)2 + HCl + HClO = CaCl(ClO) + H2O.
Structural-graphic formulas of chemical compounds
These schemes show the order of atom combination in molecules of substance.
The rules for graphic formula’s compilation are the following:
It may directly connect ions to opposite charges only;
Quantity of chemical bonds for each atom is equal to its charges (modulo) in most cases.
For example:
H2SO4; H+2 S6+ O2-4
A
l(OH)3
; Al3+(O2-H+)3
or H+3Al3+O2-3
CrO3; Cr6+O2-3
Mg(HCO3)2 ; Mg2+ (H+ C4+ O2-3)2
(MgOH)3PO4
FePO4 Na2CO3
PRACTICE PROBLEMS
To determine the oxidation numbers of elements in compounds: Fe2O3, H2S, FeS, HNO2, H4P2O7, Ca3(PO4)2, Fe2(SO4)3, Ni(NO3)3, Na3AlO3, KAlO2, LiFe(SO4)2, CaHAsO4, Na2O2, MnSO3, (NH4)H2PO4.
Which oxides may react with water directly: BaO, Cu2O, P2O5, SO3, SO2, K2O, N2O3, CoO, Cl2O7, ZnO, NO2, SiO2, MnO2, FeO, SrO? To write the corresponding equations of chemical reactions.
Which oxides do correspond to the next compounds: H2SO3, Ca(OH)2, NaOH, Fe(OH)3, HNO3, Co(OH)3, H4P2O7, CuOH, NAOH, CaBeO2, HMnO4, H2CrO4, K2MnO4?
To compile equations for the transformations given below:
Al Al2O3 Al(NO3)3 Al2(SO4)3 Al(OH)3;
Zn ZnO ZnSO4 Zn(OH)2 K2ZnO2 ZnCl2 Zn3(PO4)2 Na2ZnO2.
5. To compile structural-graphic formulas of chemical compounds given below:
Cr2O3, Ni(OH)3, H3PO4, Al2(SO4)3, Ca3(PO4)2.
What oxides may react with each other (by pairs): Na2O, CaO, SO2, H2O, P2O3, ZnO?
To write reactions for conversing of Iron (III) Dihydroxychloride and Calcium Dihydrophosphate in neutral salts.
To write all possible reactions between: a) Aluminium Hydroxide and Orthophosphoric Acid; b) Barium Oxide and Sulfuric Acid (taking into account the possibility of neutral, acidic and basic salts forming).
Example of solution
1. To compile equations for the following transformations:
Al AlCl3 Al(OH)3 Na3AlO3 Al2(SO4)3 AlPO4 Al2O3 .
An initial substance is Aluminium; each next substance is formed in the result of reaction and become itself the initial one for the next transformation. Therefore it will be at least six equations of reactions:
2Al + 6HCl 2AlCl3 + 3H2;
AlCl3 + 3NH4OH Al(OH)3 + 3NH4Cl;
Al(OH)3 + 3NaOH Na3AlO3 + 3H2O;
2Na3AlO3 + 6H2SO4 Al2(SO4)3 + 3Na2SO4 + 6H2O;
Al2(SO4)3 + 2K3PO4 3K2SO4 + 2AlPO4;
2AlPO4
Al2O3
+ P2O5.
2. To compile equations of reactions for the next transformations:
P P2O5 Ca3(PO4)2 Ca(H2PO4)2 H3PO4 (NH4)2HPO4.
4P + 5O2 2P2O5;
P2O5 + 3CaO Ca3(PO4)2;
Ca3(PO4)2 + 4H3PO4 3Ca(H2PO4)2;
Ca3(PO4)2 + 3H2SO4 3CaSO4 + 2H3PO4;
H3PO4 + 2NH3 (NH4)2HPO4.
3. To write all possible reactions between Calcium Hydroxide and Orthophosphoric Acid.
Since Ca(OH)2 is a two-acidic base and H3PO4 – three-basic acid, it is possible to form one neutral salt, two acidic salts and one basic salt:
3Ca(OH)2 + 2H3PO4 Ca3(PO4)2 + 6H2O;
Ca(OH)2 + 2H3PO4 Ca(H2PO4)2 + 2H2O;
Ca(OH)2 + H3PO4 CaHPO4 + 2H2O;
3Ca(OH)2 + H3PO4 3(CaOH)3PO4 + 3H2O.
LABORATORY TRAINING
Experiment 1. Interaction between oxides and water
To add a few grains of solid CaO, CuO, ZnO (total volume of each chemicals - near one match-head) into three tubes. To add 10-20 drops of distillated water into each tube. To mix a tube content. What oxides do directly react with water? To write a corresponding reaction.
Experiment 2. Preparation of insoluble hydroxides
To add separately 1-4 drops of each soluble Iron (III) salts (FeCl3 or Fe2(SO4)3), Copper (CuSO4 or CuCl2 or Cu(NO3)2), Manganese (II) (MnSO4 or MnCl2), and Nickel (NiSO4), Cobalt (II) (CoSO4 or CoCl2) into tubes #1, 2, 3, 4, 5. To add 1-2 drops of any alkali into each tube. What do you observe? To write corresponding reactions. To point out color of precipitate in each tube. To explain why color of Manganese (II) Hydroxide is changed.
Experiment 3. Preparation of amphoteric hydroxides
To add 1 drop of any alkali (NaOH or KOH) into three tubes. To add by drops the solution of Aluminium salt (for example, Al2(SO4)3) into tube # 1 up to the precipitate appearance; into tube # 2 - Zinc salt (for example, ZnSO4) analogously to previous case; into tube # 3 - Chromium (III) salt (for example, Cr2(SO4)3). To divide each prepared precipitate into two tubes. To add solution of any acid (for example, HNO3) to the first part of precipitate, alkali solution up to the whole dissolving of precipitate - to the second one. What do you observe? To write corresponding reactions.
Experiment 4. Interaction of salts solution (metathesis)
To add 2-3 drops of BaCl2 solution into tube # 1 and to drop the same quantity of Sodium Sulfate; 2-3 drops of Lead (II) Nitrate - into tube # 2 and to add 1-2 drops of Potassium Iodide; 2-3 drops of Cobalt (II) Sulfate into tube # 3 and to add 1-2 drops of Sodium HydroPhosphate. What do you observe? To write corresponding reactions.
To prepare a report of laboratory work in the next form:
LABORATORY WORK #1.
Chapter. Classification of inorganic substances
Condition of experiment |
Visual effect |
Equation |
Conclusions |
Experiment 1. Interaction of oxides with water |
|||
To add a few grains of solid CaO, CuO, ZnO into three tubes. To add 10-20 drops of distillated water into each tube. To mix a tube content. |
Solid CuO and ZnO are not dissolved in water. CaO is dissolved in water; content of the first tube become clear. |
CaO + H2O = Ca(OH)2 |
Only oxides of earth-alkaline metals may react with water directly forming the alkalis. |