CBSE Chemistry Experiment Properties of Acids and Bases

Chemistry Experiment - Properties of Acids and Bases

We frequently employ substances that scientists refer to as acids in our daily lives. Citric acid is included in the orange or grapefruit juice you consume for breakfast (also known as vitamin C). Lactic acid is a component of soured milk. Acetic acid can be found in the vinegar used in salad dressing. In accordance with this, an acid-base combination is thought to make up a chemical bond. Thus, by splitting a molecule into its acidic and basic components, its properties can be understood.

Table of content

• Aim

• Reaction with Litmus Solution (Blue/Red)

• Reaction with Zinc Metal

• Reaction with Solid Sodium Carbonate

• Result

Aim

To study the properties of Acids (Hydrochloric Acid) and Bases (Sodium Hydroxide)

Materials Required

1. Test tubes

2. Test tube stand

3. Test tube holder 

4. Cork

5. Droppers

6. Flat bottom flask

7. Beaker

8. Litmus solution/paper (red and blue)

9. Glass rod

10. Zinc granules

11. Freshly prepared lime water

12. Solid sodium carbonate

13. Dil. HCl

14. Dil NaOH

Theory

1. An acid is a chemical like HCl that produces H+ ions when it dissolves in water. Acids do not affect red litmus, but turn blue litmus red. When HCl reacts with zinc metal, zinc chloride (ZnCl2) and hydrogen gas (H2) is released.
   Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g)

2. A pop sound and a blue flame are produced as hydrogen gas burns in the air.

2H2(g)+O2(g)→2H2O(l)

3. Lime water turns milky as a result of the creation of calcium carbonate when HCl combines with sodium carbonate (aqueous/solid). The milkiness vanishes if too much CO2 is added to the solution.

Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g)

Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)

CaCO3(s) + H2O(l) + CO2(g) → Ca(HCO3)2(aq)

4. A base is a substance which gives OH– ions when it is dissolved in water. Sodium hydroxide (NaOH) is a strong base. Its pH is much higher than 7.

5. So, it turns red litmus into blue and does not impact the blue litmus.

6. On reacting with Zn metal, it forms a salt (sodium zincate) and hydrogen gas (H2) is liberated.

Zn(s) + 2NaOH(aq) → Na2ZnO2(aq) + H2(g)

7. Solid Na2CO3 does not react with NaOH because both are basic in nature.

Na2CO3(s) + 2HCl(aq) → No reaction

8. Base (NaOH) neutralises acid (HCl) to give salt (NaCl).

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O

Procedure

1. Litmus Test

1. Place two test tubes in a test tube stand with the labels A and B. Take 5 mL of the blue litmus solution and 5 mL of the red litmus solution, respectively, in test tubes A and B.

2. Add a few drops of HCl using a dropper to each test tube. Each tube is stirred using a different glass rod. Take note if the solutions' colour changes at all.

3. Again, mark two test tubes with the letters C and D. Put three millilitres of blue litmus in test tube C and three millilitres of red litmus in test tube D in a test tube stand.

4. Add a few drops of NaOH to each with a dropper. Take note if the liquids in the test tubes change colour in any way.

Observation

Test with Litmus

1. Reaction with Zinc (Zn) Metal

1. Put a few zinc granules in a test tube that is clean and dry.

2. Add enough HCl to the test tube holding the zinc granules to completely immerse them in the acid.

3. Put a cork with a glass delivery tube in place.

4. After two to three minutes, there will be a strong reaction and the evolution of odourless, colourless gas.

5. When a match is held close to the gas tube's mouth, the gas ignites with a faint blue flame that makes a popping sound.

6. Similarly, fill the test tube with zinc granules with NaOH until they are completely submerged.

7. Heat the test tube and insert a cork with a glass delivery tube.

8. After two to three minutes, there will be a strong reaction and the evolution of odourless, colourless gas.

9. When a match is held close to the gas tube's mouth, the gas ignites with a faint blue flame that makes a popping sound.

Action of NaOH with Zn metal 

Reaction

Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)

Zn(s) + 2NaOH(aq) → Na2ZnO2(aq) + H2(g)

Observation

1. Reaction with Solid Sodium Carbonate(Na2CO3)

1. Take a small amount of solid sodium carbonate in a flat bottom flask and some distilled water in it, shake it well.

2. Take a double bore cork with a thistle funnel and a delivery tube fitted in it, fit it on the open end of the flask.

3. Through the thistle tube, add HCl to the flask.

4. A reaction has occurred, resulting in the development of odourless and colourless gas.

5. Then, using a delivery tube, gas is fed through freshly prepared lime water.

6. The lime water turns milky.

7. Similarly, take a small amount of Na2CO3 in a test tube.

8. Add some drops of dil. NaOH solution in the test tube containing Na2CO3.

Reaction with Solid Sodium Carbonate

Reaction

Na2CO3(s)+2HCl(aq)→2NaCl(aq)+H2O(l)+CO2(g)

Ca(OH)2(aq)+CO2(g)→CaCO3(s)+H2O(l)

CaCO3(s)+H2O(l)+CO2(g)→Ca(HCO3)2(aq)

Observation

Result

From the above experiment, we can conclude that:-

1. Hydrochloric acid turns blue litmus solution/paper to red, but it does not affect red litmus solution/paper. 

2. Sodium hydroxide turns red litmus solution/paper blue, but it does not affect blue litmus solution/paper.

3. HCl reacts with zinc metal to liberate hydrogen gas and also forms zinc chloride as a product.

4. NaOH reacts with zinc metal and liberates hydrogen gas. During this reaction, sodium zincate is also formed.

5. HCl reacts with sodium carbonate to liberate carbon dioxide. Hence, we conclude that hydrochloric acid is acidic in nature.

6. It does not react with sodium carbonate. Hence, we conclude that sodium hydroxide (NaOH) is basic in nature.

Precautions

1. As HCl is corrosive in nature, it should be handled with care.

2. Use small quantities of chemicals.

3. Use small quantities of Zn and HCl, otherwise large amounts of H2 will be formed, which may cause an explosion.

4. Use clean zinc metal, otherwise the reaction will occur very slowly.

5. Add HCl to Na2CO3, when the apparatus is airtight.

6. Observe the milkiness in the lime water soon.

7. In case you allow carbon dioxide to pass for a long time through lime water, the milkiness may be removed due to the formation of soluble calcium bicarbonate as depicted in the reaction as follows:

CaCO3(s) + CO2(g) +  H2O(l) →  Ca(HCO3)2(aq).

8. Shake the solutions and reaction mixtures carefully without spilling.

9. Care must be taken while performing the combustion test with H2.

10.  Since sodium hydroxide is extremely corrosive, it should be handled carefully. Don't bring the zinc and diluted NaOH combination to a boil.

11. To achieve the best results, only a small amount of chemicals should be used to conduct the experiment. Before using, test tubes and droppers should be well cleaned with distilled water.

12. When testing with acids, alkalis, or indicators, never swap droppers.

13. After the experiment is finished, hands need to be carefully washed.

Lab Manual Questions

1. When exposed to a drop of dil. NaOH, what colour would blue litmus paper take on?

Ans. When the blue litmus paper is in contact with a drop of dil NaOH, its colour does not change.

2. What metals, besides Zinc, react with alkalis to create hydrogen gas? What is the name of these metals?

Ans. Aluminium is a metal, besides Zinc, that reacts with alkalis to create hydrogen gas. These metals are called Amphoteric oxides

3. A blue piece of litmus paper was dipped in dilute HCl solution. Which colour do you think you would see on the litmus paper?

Ans. Dilute HCl turns blue litmus paper red.

4. What impact will litmus have on hydrogen gas?

Ans. Hydrogen gas is neutral towards litmus. It is neither acidic nor basic therefore, it neither changes the colour of blue litmus nor red litmus.

Viva Questions

1. When carbon dioxide is passed through lime water, it turns milky. Due to which insoluble substance milkiness is formed?

Ans. Insoluble calcium carbonate (CaCO3) makes the solution milky.

2. What would happen if dilute HCl and dilute NaOH were combined in an equal amount? Also, write the equation.

Ans. Equal volumes of dilute HCl and dilute NaOH cause a neutralisation reaction that results in the production of salt and water. The reaction between an acid and a base is given below: 

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

3. How do acids and bases react with metals?

Ans. Acids react with most metals to form a salt and hydrogen gas. For example, zinc metal reacts with hydrochloric acid, producing zinc chloride and hydrogen gas.

Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)

Bases also react with certain metals, like zinc or aluminium, to produce hydrogen gas. For example, sodium hydroxide reacts with zinc and water to create sodium zincate and hydrogen gas.

Zn(s) + 2NaOH(aq) → Na2ZnO2(aq) + H2(g)

4. What substance is formed from the reaction of aluminium metal with NaOH solution?

Ans. Aluminium metal reacts with NaOH solution to produce sodium meta-aluminate:

2NaOH(aq) + 2H2O(l) + 2Al(s) → 2NaAlO2(aq) + 3H2(g)

5. What are strong bases?

Ans. Bases which dissociate into their ions completely are called strong bases. Example: NaOH, KOH etc.

6. What are strong acids?

Ans. Acids which dissociate into their ions completely are called strong acids. Example: HCl, H2SO4 etc.

7. What do you understand about weak acids?

Ans. A weak acid is an acid that partially dissociates into its ions in an aqueous solution or water. Example: Acetic acid, Citric Acid etc.

8. What are the characteristics of bases

Ans. When dissolved in water, bases:

1. Conduct electricity

2. Change red litmus to blue

3. Have a slippery feeling

4. React with acids to neutralize their properties

9. What are the characteristics of Acids?

Ans. When dissolved in water, acids:

1. Conduct electricity

2. Change blue litmus to red

3. Have a sour taste 

4. React with bases to neutralize their properties

10. What do you understand by weak base?

Ans. Weak Bases are the bases that partially dissociate in water. Example Ammonia, Aluminium Hydroxide etc.

Practical Questions

1. What acids and bases have in common?

1. Conduct electricity in aqueous solution

2. Have same taste

3. Have same ions

4. Have same indication results on reacting with Litmus

Ans. Both acids and bases conduct electricity in aqueous solution

2. Which of the following is not a property shown by acids?

1. Have Sour taste

2. Turns blue litmus red

3. Turns red litmus blue

4. Gives H+ in water

Ans. All acids turn blue litmus red.

3. Which describes the chemical property of acids?

1. Sour taste

2. Acids react with carbonates and hydrogen carbonates to form a salt, water, and carbon dioxide gas.

3. Feel slippery

4. None of the above

Ans. Acids react with carbonates and hydrogen carbonates to form a salt, water, and carbon dioxide gas.

4. Which statement is true about weak acids

1. Completely dissociated in water

2. Partially dissociation in water

3. No reaction observed

4. Very corrosive

Ans. Weak acids are acids that are partially dissociated in water

5. Which statement is true about weak bases

1. Completely dissociated in water

2. Partially dissociation in water

3. No reaction observed

4. Very corrosive

Ans. Weak bases are bases that are partially dissociated in water

6. Which is an example of Strong Acids

1. H2SO4

2. CH3COOH

3. C6H5COOH

4. H3PO4

Ans. H2SO4 is an example of strong acids

7. Which is an example of Weak Bases

1. NaOH

2. KOH

3. LiOH

4. NH3

Ans. NH3 is an example of weak base

8. Which is an example of Weak Acids

1. C6H5COOH

2. H2SO4

3. HCl

4. HNO3

Ans. C6H5COOH is an example of weak acids.

9. Which is an example of Strong Bases

1. NH3

2. Al(OH)3

3. Zn(OH)2

4. KOH

Ans. KOH is an example of Strong Bases

10. Why Acetic Acid is considered as a weak acid 

1. Highly ionised

2. Contains COOH group

3. Partially ionised

4. Aqueous solution is acidic

Ans. Acetic Acid is considered as a weak acid because it is partially ionised

Conclusion

Typically, sour tastes help to identify acidic chemicals. A fundamental definition of an acid is a molecule that has the ability to donate an H+ ion and maintain its energetic favorability even after losing H+. Acids are known to turn blue litmus paper red. On the other hand, bases have a bitter flavour and are slippery to touch. Bases have the ability to donate OH- and can turn red litmus blue.