In this experiment, you will investigate some of the important chemical properties of acids and bases.

#2 Pass some of the gas produced into limewater.

2. Hydrgencarbnates

#3 Repeat the procedure used above but replace the marble chips with NaHCO3

3. Sulphides

Safety Note

• The hydrogen sulphide gas produced by this reaction is extremely poisonous and should not be breathed in.
• Conduct this part of the experiment in a fume hood.

       #4 Add 2 –3 ml of 2 mol L HCl to a small quantity of solid Na2S. The gas produced has a characteristic odour often likened to that of rotten eggs.

4   Sulfites

Safety Note

• Sulphur dioxide is poisonous and should not be breathed in large quantities.
• Use your hand to waft a small amount of gas to your nose.

       #5 Add 2 –3 ml of 2 mol L HCl to a small quantity of sodium sulfite.                                                                                                                       Warm gently

       #6 Test the gas evolved using moist red and blue litmus paper.

       #7 Carefully sniff the gas by wafting some of it near your nose.

1.  Ethanoates (acetates)

#8 Add 2 – 3ml of 2 mol L HCl to a small quantity of solid sodium ethanoate (sodium acetate), and heat the mixture.

#9 Smell the resulting solution and identify the substance produced. Compare the smell with that of vinegar.

F         Neutralisation of a Strong Acid with a Strong Base

        #1 Place 10 drops of 2 mol L HCl into a test tube and add a small piece of blue litmus paper. Note the colour change of the litmus paper.

        #2 Add 2 mol L NaOH drop wise until the litmus paper changes colour.

G        Reaction of Strong Bases with Cations of weak Bases

Safety Note

• Ammonia has an irritating odour and should not be breathed in large quantities.
• Use your hand to waft a small amount of gas towards your nose.

`        #1 Add 2 – 3 ml of 2 mol L NaOH to a small to a small quantity of solid ammonium chloride and warm the mixture gently until it is almost boiling.

        #2 Test the gas evolved using moist red litmus paper.

        #3 Carefully sniff the gas by wafting some of it towards your nose.

 

Chemical Properties of Acids and Bases

Vivek Salgaocar

Chemistry SL

Ms. Anna

American School of Bombay

39/9/2003

Focus Question:

• To investigate some of the important chemical properties of acids and bases.

Procedure:

• See Teacher’s Instruction Sheet

Materials:

• See Teacher’s Instruction Sheet

Data Collection:

Part A

1. The Blue Litmus Paper turns Red when it reacts with HCl and the Red Litmus remains the same.

2. The Red Litmus Paper turns Blue when it reacts with NaOH and the Blue Litmus remains the same.

Part B

1. Magnesium – it reacts very fast and no heating is required. A gas is released which extinguishes a burning splint with a pop sound.
2. Zinc – reaction proceeds without heating. A gas is released which extinguishes a burning splint with a pop sound.
3. Aluminum – reaction requires heating. A gas is released which extinguishes a burning splint with a pop sound.
4. Copper – reaction does not occur even when heated.

Part D

When HCl is added to CuO and heated, it turns green

Part E

1. CaCO3 – Limewater turns milky, gas evolved

2. NaHCO3 – Limewater turns milky fast, gas evolved

3. Na2S – Exothermic Reaction, gas evolved

4. Na2SO3 – Endothermic, slightly pungent smelling gas evolved

5. CH3COONa – Vinegar smell gas after heating

Part F

1. On adding blue litmus to 10 drops of 2mol L HCL. Blue litmus paper turned pink.
2. On adding 20 drops of 2mol L NaOH and the litmus paper turned back to blue.

Part G

1. Blue Litmus paper turns red when tested with the gas
2. The gas has a pungent odor.

Data analysis:

Part A:

An indicator is a weak acid or base in which the dissociated form is a different color to the undissociated form. Litmus paper contains a vegetable dye and is either blue or red. When litmus paper s made to react with acids or bases, it changes color. For acids, blue litmus paper turns red and red litmus paper shows no color change. For bases, red litmus paper turn blue and blue litmus paper shows no change. In the first part, the blue litmus turns red and the red litmus remains the same because HCl is an acid. However, when the litmus is inserted into the solution of NaOH, the blue litmus paper remains blue and the red litmus paper turns blue because NaOH is a base.

Part B:

When metals above hydrogen in the reactivity series are made to react with acids, they release hydrogen. Sometimes, the reaction does not take place quickly with less reactive metals and so they need to be heated. The gas released can be tested by bringing it near a burning splint. Hydrogen gas extinguishes a burning splint with a pop sound. In the first reaction, magnesium reacts to release hydrogen. Since magnesium is a reactive metal, it does not need to be heated. Similarly, zinc also does not need to be heated. However, aluminum is not as reactive and needs to be heated. In the case of copper, no reaction occurs even when it is heated. This is because copper is below hydrogen in the reactivity series and cannot displace hydrogen from the acid. The reactions all follow the general equation:

Acid + Reactive Metal ➔ Salt + Hydrogen

Mg + 2HCl ➔ MgCl2 + H2

Zn + 2HCl ➔ ZnCl2 + H2

2Al + 6HCl ➔ 2AlCl3 + 3H2

Cu + HCl ➔ No Reaction

Part D:

Acids react with the oxides of metals to form salt and water. This is because these metal oxides act as bases when dissolved. In this part of the experiment, copper oxide was added to hydrochloric acid. This can be seen in the following reaction:

CuO + 2HCl ➔ CuCl2 + H20

The green color imparted to the solution is due to the presence of copper chloride, which is green in color.

Part E:

Acids react with carbonates and bicarbonates of metals to release a salt, water, and carbon dioxide gas. This carbon dioxide gas can be tested by passing it through lime water. It reacts with the lime water to produce insoluble particles of calcium hydroxide which remain suspended in the lime water and give it a milky appearance. In the first part, the acid reacts with calcium carbonate to release carbon dioxide which turns the lime water milky.

CaCO3 + 2HCl ➔ CaCl2+ H2O + CO2

In the second part, sodium bicarbonate reacts with hydrochloric acid to release carbon dioxide which turns lime water milky.

NaHCO3 + HCl ➔ NaCl + H2O + CO2

Sulfides react with acids to produce hydrogen sulfide gas which smells of rotten eggs. In part 3, sodium sulfide is made to react with hydrochloric acid. It releases hydrogen sulfide gas which smells of rotten eggs.

Na2S + 2HCl ➔ 2NaCl + H2S

Sulfites react with acids to release sulfur dioxide. This gas can be identified by its pungent odor. When sodium sulfite is made to react with hydrogen chloride, sulfur dioxide is released which has a pungent odor.

Na2SO3 + HCl ➔ NaCl + H2O + SO2

When ethanoates are made to react with acids, they release methane and carbon dioxide gas. When sodium ethanoate is made to react with hydrochloric acid, a these gases are released.

CH3COONa + HCl ➔ NaCl + CH4 + CO2

Part F:

Acids react with bases to form salt and water. These reactions are called neutralization reactions. When litmus paper is added to the strong acid initially, the blue litmus paper turns red. However, when sodium hydroxide is added, the litmus paper turns back to blue. This is because the sodium hydroxide neutralizes the acid and increases the pH of the solution.

HCl + NaOH ➔ NaCl + H2O

Part G:

When cations of weak bases are made to react with strong bases, the more reactive ions displace the less reactive ones to release a gas. In this reaction, the sodium ions displace the ammonium ions and methane gas is released which has a pungent odor.

NaOH + NH4Cl ➔ NaCl + H2O + NH3

Conclusion:

In this lab, we tested and observed the various chemical properties of acids and bases. We also learnt the ways in which gases release can be tested. The lab helps us understand the chemical properties of acids and bases clearly through practical application.