Chemistry Acids, Bases, and Salts

ACIDS,BASES AND SALTS

LEARNERS ACTIVITIES

Activity 1:  Class experiments

Methodology: Guided discovery and class discussions

Instructional materials

Test tubes, dilute hydrochloric acid (or citric acid from lemon), dilute sodium hydroxide (or solution from ashes from banana peelings), water.

Procedure: (learners in groups of 5 )

• Measure 2cm³ each of a solution of acid, base and water in three separate test-tubes.
• Using a dropper or a straw, add two drops of litmus solution (use litmus papers) to each of the test tubes in (a) above.
• Record the observation made in the table below.
• Now repeat procedure (b) with methyl orange and phenolphthalein indicator. Record your observation in the table below.

Indicator	Colour in
	Acid	Base (alkali)	Water (neutral)
Litmus
Methyl orange
phenolphthalein

Figure 1 Colours of indicators in different solutions

Question: What do you observe?

Activity 2

Extraction of indicators from local materials

Methodology: Group experiment, brain storming and guided discussion.

Instructional materials:

Mortar and pestle, test tubes, measuring cylinder. Glass rod or straw, filter funnel and papers, glass beakers, or plastic cups, red, blue, or yellow flower petals, lemon juice, dilute hydrochloric acid, solution or ashes, (banana peelings).
Soap solution, ethanol, or waragi, red flowers can be got from rose or hibiscus flower and blue petals from sweet potatoes or morning glory flower.

Procedure

1. Place red flowers petals in a mortar and grind them using a pestle.
2. Now add little of a solvent (ethanol or waragi) together with water and continue grinding until the extract is deep in colour as possible.
3. Decant or filter about 10 cm³ of the extract into a test tube.
4. Repeat procedure (a)-(c) with blue and yellow flowers and with other flowers.
5. Using the flowers extracts, (indicators) above test the following solutions, lemon or orange juice, dilute hydrochloric acid soap solutions, dilute sodium hydroxide, solution of ashes.
6. Record your observations in the table below

Plant extract	Colour of solution
	Lemon or orange juice	Hydrochloric acid	Soap solution	Sodium hydroxide	Solution of ashes
1. Red flower
2. Blue flower
3. Yellow flower

Activity 3:   

Use of universal indicator to determine the pH of solutions.

Methodology: demonstration and group experiment.

Instructional materials:

Flowers extract as in activity 2 test tubes, lemon or orange juice, water, milk, soap solution, dilute sulphuric acid, dilute hydroxide, urea, fertilizer, commercial universal indicators.

Procedure

1. Place a bout 2 cm³ each of orange juice, water, milk, soap solution, sulphuric acid, ashes solution, and sodium hydroxide in different test tubes.
2. Using a dropper or straw place about 3 drops each of the universal indicator in each of the test tube in (a).
3. Note the colour shown and record the corresponding pH value in the table below.
4. Prepare a local universal indicator by mixing all the flower extracts.
5. Now place about 1 cm³ of universal indicator in (d) above and repeat procedure (a), (b) and (c).

      (i) Chop red cabbage.
      (ii) Boil the chopped cabbage with  water.
      (iii) Decant the solution formed and add about 2 cm³ of solution into 6 test-tubes.
      (iv) Add the solutions above to each of the test tubes.

Question: what do you observe in each test-tube?

pH	Colour of universal indicator		pH	Colour of indicator
1 – 2	Red		6 – 8	Green
3	Pink		9 – 10	Blue
4	Brown		11 – 12	Indigo
5	Yellow		13 – 14	Violet

Universal indicator	PH value
	Orange juice	Milk	Water	Soap solution	Sulphuric acid	Ashes solution	Sodium hydroxide
Commercial or laboratory
Locally manufactured

Figure 2 universal chart

Activity 4:

Use of indicators to prepare a soluble salt.

Methodology: Demonstration, group experiment, and brain storming.

Instructional materials:    Pipettes, burettes, 2M hydrochloric acid, 2M sodium hydroxide, methyl orange,  evaporating, basin, burner, conical flask, beakers.

Procedure

1. Pipette 25.0 cm³ of 2 M hydrochloric acid into a clean conical flask. Add 2-3 drops methyl orange indicator.
2. Fill the burette with sodium hydroxide solution and adjust the reading to give the initial reading, record the initial reading.
3. Now carefully run the sodium hydroxide solution from the burette until the colour changes from orange to yellow.
4. Note the final reading on the burette and hence determine the volume of sodium hydroxide needed to react with the 25.0 cm³ of the acid pipetted. Let y cm³ = final reading – initial reading.

Table of results for activity 4           

	Burette reading (cm3)
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of base (alkali), y (cm3)

1. Now pipette 25.0 cm³ of the acid and repeat the titration but this time without the indicator. Add exactly the volume of solution hydroxide ‘y’ determined in (d).
2. Place the resulting solution in an evaporating dish and carefully heat the solution until crystals start to form and allow to cool to form crystals.
3. Weigh the salt to determine the mass formed and calculate the mass of the salt expected by mixing 1 dm³ of the acid and the sodium hydroxide solution.

Figure 3 Titration and crystallisation of common salt

Activity 5

Materials: Test-tubes, test-tube racks, water and saliva.

Procedure

1. Learners should go into groups of 5 or 6 and one of them puts some of his/her saliva into a test-tube.
2. A little water should be added to dilute the saliva.
3. Add a drop or two of universal indicator to the solution in (b). Shake the mixture and observe. What is the pH of the saliva from this student?
4. Repeat the activity three or four times.

Follow up activity

1. Biology, agriculture or chemistry department should be encouraged to grow plants which help the teaching of indicators.

1. Learners should prepare universal indicator using flower extract by mixing orange, pink, yellow, green, blue, violet, indigo, flowers and use it to test for the nature of some solutions of salts including water from different sources, (e.g. bore hole, wells, rain water, tap water etc)
2. Learners should also use the universal indicator to test for pH of different types of soils since acidity and alkalinity is very important in determining how well different plants grow.

Learners should be able to relate the knowledge in chemistry to biology in relation to dissection of animals (rats) and insects (cockroaches).

Importance of soil pH to farmers 

The acidity or alkalinity of soil is very important in determining how well plants grow in particular soil. The sample of soil must be taken from about 10 cm below the surface.

1. Plant                                                   Preferred pH range
2. 1 Beans                                                          6.0 – 7.5
3. 2 Cabbage                                                      6.0 – 7.5
4. 3 Onions                                                        6.0 – 7.0
5. 4 Potatoes                                                      5.5 – 7.0
6. 5. Rose Flower                                               5.0 – 6.5
7. 6. Sunflower                                                   6.0 – 7.5      
   
   
   ANSWERS TO LEARNERS ACTIVITIES
   Activity 1
   Litmus in acid and neutral solution is red and in alkaline solution is blue
   Methyl orange shows colours in both acidic and neutral solution but is yellow in alkaline solution
   Phenolphthalein indicator is colourless in both neutral and acidic solution but shows a pink (red) colour in alkaline solution
   Activity 3
   

   Solution	Orange juice	Milk	Water	Soap solution	Sulphuric acid	Ashes solution	Sodium hydroxide
   pH	2	6	7	8	1	11	13

   Answers to activity 5
8. The pH of saliva of a normal person should fall in the range 6.8 – 7.2. If the pH falls far below or above this range spells danger and the learner should be encouraged to see a medical personnel.
9. Answer to question

Solutions containing extracts of red cabbage produce different colours when treated with acidic or alkaline solution depending on the acidic or alkaline nature of the solution, see the illustration, figure 3

(D) ORGANISATION ADVICE

1. Students activities (experiments) should be performed in group of 5-6 students with each group having a leader
2. Prior arrangement should be made to avail some materials which may not be available in school.
3. Try out all the experiments before the students do them
4. Improvise where necessary e.g. use of straws as droppers, mineral water bottle cut to be used as a beaker
5. Safely precaution should be taken care of. The learners must be warned not to drink anything that is colourless even if they think it is water. They could be drinking an acid or alkali.
6.  Should ensure that all members in a group actively participate
7. Learners should be able to make deductions relevant in activity
8. Prepare to answer any questions learners may ask related on the activity.

ACTIVITIES

STUDENTS EXERCISES

Which one of the following is the colour of methyl orange in an alkaline solution?

A. Blue                            

B. Yellow                  

C. Red                       

D. Green

2. Which one of the following indicators shows no colour (colourless) in acidic solution?

A.Universal                  

B. Methyl orange                 

C. Phenolphthalein

D. Litmus

3. Which one of the following salts can be prepared by the use of an indicator?

A.Lead(II) chloride     

B. Copper carbonate                       

C. Silver sulphate

D. Potassium sulphate

4. Which one of the following is a weak acid?

A.Hydrochloric acid   

B. Nitric acid            

C. Ethanoic acid      

D. Sulphuric acid

5. Which one of the following is not an alkali?

A.Sodium hydroxide  

B. Zinc hydroxide   

C. Potassium hydroxide                                    

 D. Ammonium hydroxide

6. Which of the following is most likely to be the pH of lemon juice?

A.4                                 

B. 7                            

C. 9                                        

D. 12

7. Which one of the following hydroxides can be prepared by reacting a soluble salt of the metal with excess sodium hydroxide?

A.Pb (OH)²                   

B. Zn(OH)²               

C. Al(OH)³                

D. Fe(OH)³

UNEB UCE/1 1987 No. 16
8. Ammonium chloride was dissolved in water. The resultant solution

bleached litmus papers                  

B. had no effect on litmus paper

C. changed red litmus paper blue       

D. changed blue litmus paper red

9. Which one of the following method would be suitable for preparing magnesium sulphate?

A.direct combination              

B. double decomposition               

C. Neutralisation

D. displacement of hydrogen by a metal

UNEB UCE 545/1 1988 No.17

10. Lead(II) chloride can be prepared in the laboratory by action of dilute hydrochloric acid on

A. lead metal                             

  B. lead(II) oxide                  

C. lead(II) carbonate   

D lead(II) nitrate

UNEB UCE 545/1 1990 No. 18

11. Which of the following acids can react with a base to produce an acid salt?

A.Ethanoic acid                       

B. Sulphurous acid              

C. Nitric acid

D. Hydrochloric acid

12. Which one of the following equations represents a neutralisation reaction?

A: Fe_(s) + 2HCl_(g)        FeCl_{2 (s)} + H_{2 (g)}

B: NH_{3 (g)} + H₂O _(l)      NH₄OH _(aq)

C: NaOH _(aq) + HNO_3(aq)    NaNO_3(aq) + H₂O _(l)

D: 2H_{2 (g)} + O_{2 (g)}         2H₂O _(l)                         

UNEB UCE 545/1 1995 No. 25

13. To 20.0 cm³ of sodium hydroxide solution in a conical flask was added methyl mange indicator and the mixture titrated with hydrochloric acid until the end point was reached

a) State the colour of solution i) When methyl orange was added before titration
…………………………………………………………………………………………
      (ii) at the end of the titration
      ………………………………………………………………………………………
b)  (i) write the equation of the reaction taking place
      ………………………………………………………………………………………
      (ii) Name the salt formed
      ………………………………………………………………………………………

1. Name one other salt which could be prepared by a similar method

      ………………………………………………............................................................
14. Hydrogen chloride dissolves in water and in dry methylbenzene

 a) State the colour of neutral dry litmus paper

i)               In a solution of hydrogen chloride in water
      ………………………………………………………………………………………
ii)              In a solution of hydrogen chloride in methylbenzene 
      ……………………………………………………………………………………....
b)              Give a reason why litmus behaves differently in (a) (i) and (ii)
      ………………………………………………………………………………………
15. Solutions V, W, X, Y, and Z have the following pH values

Solution	pH value
V	1
W	6
X	7
Y	9
Z	12

Which one of the solutions:

A).is pure water      ………………………………………………………………………………………

b)  is strongly acidic
      …………………………………………………………………………….………..
c)   is strongly alkaline
      ………………………………………………………………………………………
d)  Will give the universal indicator red colour
      ………………………………………………………………………………………

e) Could be a solution of carbon dioxide

           

………………………………………………………………………………………

ANSWERS TO EXERCISE

1. B              2. C              3. D               

4. C              5. B            6.A           

7. D             8. D              9. C            

 10. D              11. B        12. C

13 a)

i) yellow
ii) orangeb) 

b)

i)

ii) sodium chloride

iii) sodium sulphate

14 a)

i) red
                 

ii) no change
       

b) hydrogen chloride dissolves in water to form hydrochloric acid which turns litmus red due to hydrogen ions produced when the acid ionises

Hydrogen chloride gas dissolves in methyl benzene without reacting and therefore does not produce H+. In methylbenzene, solution is neutral

15 a) X                

b) V              

c) Z               

d) V              

e) W