Sodium hydroxide is corrosive if in contact with the skin. It is particularly dangerous in the eyes, even in the most dilute solutions. Always wear eye protection.
Copper (II) oxide is harmful to the skin, eyes and lungs and toxic. Always wear eye protection.
* Reaction of acids with alkalis (soluble bases)
Measure approximately a 2 cm depth of an acid of your choice into a test tube and add two drops of universal indicator solution. Record the temperature of the solution and note it down. Add the alkali drop-wise until a change in colour of the indicator is seen. Test the temperature of the final solution. Repeat the reaction but with a different acid.
HCl (aq) + NaOH (aq) NaCl (aq) + H2O(l)
H+ + Cl- + Na+ + OH- Na+ + Cl- + H2O
H+(aq) + OH-(aq) H2O
t1= 24 t2= 27 t=3
number of drops: 38
CH3COOH (aq) + NaOH (aq) CH3COONa (aq) + H2O (l)
CH3COO- + H+ + Na+ + OH- CH3COO- + Na+ + H2O
H+(aq) + OH- (aq) H2O
t1= 22 t2= 26 t=4
number of drops: 34
Acid is a substance which contain hydrogen ions (H+). It is a proton donor.
Alkali is a base which is soluble in water and which contains the hydroxide ions (OH-). It is a proton acceptor.
The reaction between acid and the alkali is a specific case of aci-base neutralisation.
It occurs according to the formula:
acid + base salt + water
During this process hydrogen ions (H+) from the proton donor and hydroxide ions (OH-) from the proton acceptor react together forming a water molecule (H2O).
Neutralisation reactions are mostly classified as exothermic, as the heat is released to the surrounding.
* Reaction of acids with insoluble bases
Measure 1 level spatula of copper (II) oxide into a boiling tube and add one of the acids to a depth of 1-2 cm and warm up gently in a blue Bunsen flame. Notice any visible reaction. Repeat the reaction with more acids and copper (II) oxide, noting your observations.
CuO (s) + 2HCl (aq) CuCl2 (aq) + H2O (l)
CuO + 2H + + 2Cl – Cu2+ + 2Cl- + H2O
CuO is a black powder and HCl is colourless solution.
After putting copper (II) oxide in the aqueous solution of hydrochloric acid and warming it up, the change of colour of the solution could be observed. The colour of the solution was green/blue.
CuO (s) + 2CH3COOH (aq) (CH3COO)2Cu(aq) + H2O (l)
CuO + 2CH3COO- + H+ 2CH3COO- + Cu2+ + H2O
CuO is a black powder and CH3COOH is colourless solution.
After putting copper (II) oxide in the aqueous solution of ethanoic acid and warming it up, the change of colour of the solution could be observed. The colour obtained was dark blue.
* Ammonia as a base
Carefully add 1 cm3 of concentrated ammonia solution (corrosive) into a test tube and into another tube add 1 cm3 of concentrated hydrochloric acid (corrosive). Hold the tops of the tubes together and note what you see.
NH3 (g) + HCl (g) NH4Cl (g)
NH3 + H+ + Cl- NH4+ + Cl-
Ammonia is a compound of nitrogen and hydrogen. It is normally encountered as a gas with a characteristic odor. Ammonia combines with acids to form salts.
Completely dry ammonia does not react with dry acid, that is the reason why the solutions had to be made.
After putting the tubes together, the white smoke could be observed.
Hydrochloric acid sample releases fumes which are reacting with ammonia fumes to produce a white smoke of ammonium chloride.
* The presence of water
A dry solution of hydrogen chloride gas dissolved in hexane will have been prepared for you which can be found in the fume cupboard. Add the following substances to the solution, noting down your observations:
Place a 3 cm length of magensium metal and carefully add it to the hydrogen chloride in the hydrocarbon solvent. DO NOT HEAT THIS SOLUTION. Note any changes that you see.
After placing magnesium in the hexane solution, no changes could be observed.
Add two drops of universal indicator solution th the hydrogen chloride solution and note any changes that you see
After using indicator in the hexane solution no changes could be observed.
Anhydrous sodium carbonate
Add 1 level spatula of anhydrous sodium carbonate to the hydrogen chloride solution and note any changes that you see
After placing anhydrous sodium carbonate in the hexane solution, no changes could be observed.
Using the apparatus provided, place two graphite electrodes into the solution of hydrogen chloride in the anhydrous solvent and test for the electrical conductivity. Try to interpret the results in terms of the types of particles that must be present within teh solution.
In hexane solution the hydrogen and chlorine are locked together, a single neutral molecule and no charged ions. Any positive movement of the hydrogen is locked to the negative movement of the chlorine, so any movement balances out to zero charge movement and zero electrical movement
In the given experiments concerning hexane solution no change could be observed as hexane does not dissociate.