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

Chemistry Nitrogen

NITROGEN AND ITS COMPOUNDS

LABORATORY PREPARATION OF NITROGEN

Apparatus – delivery tubes, furnace, beaker, trough, Bunsen burner, 2 wash bottles
Chemicals – Air, water, sodium hydroxide
Procedure  
Either:
Nitrogen is prepared from the air by removing oxygen and carbon dioxide. Water is used to push air through sodium hydroxide solution (caustic soda solution) which removes carbon dioxide.

2NaOH_(aq) + CO_2(g) Na₂CO₃ + H₂O_(i)

        
The remaining gas is passed over heated copper turnings to remove Oxygen.

2Cu_(s) + O_2(g) 2 CuO_(s)

Nitrogen is collected over water as it is insoluble in water.

OR:
Nitrogen can also be prepared by b heating a mixture of ammonium chloride and sodium nitrite.

NaNO_2(s) + NH₄Cl_(s) NH₄NO_2(s) + NaCl_(s)

Nitrogen is formed by decomposition of ammonium nitrite

NH₄NO_2(s N_2(g) + 2H₂O_(i)

INDUSTRIAL PREPARATION (LARGE SCALE)

Industrially, Nitrogen is prepared by fractional distillation; Oxygen is obtained at the same time. Air is purified by removing gas from it.
Then carbondioxide is removed and lastly water vapour. The remaining air is removed and compressed. The liquidified air is allowed to evaporate. Because Nitrogen has a lower boiling point, it evaporates first leaving liquid oxygen.

PROPERTIES OF NITROGEN

Physical

1. it is colourless gas without smell
2. it is a reactive gas
3. it does not burn / doesn’t support combustion
4. it is neither acidic nor basic

Chemical properties

1. Nitrogen is inert unlike Oxygen, it reacts under special conditions for example

1. It reacts with some metals at very high temperatures forming nitrides e.g. Calcium and magnesium.

3Mg_(s) + N_2(g)MgN_2(s)

3Ca + N_2(g)Ca₃N_2(s)

2. It reacts with hydrogen to form ammonia (Haber’s process)

N_2(g) + 3H_2(g) 2NH_3(g)

NITROGEN AND ITS COMPOUNDS

AMMONIA (NH₃)
Ammonia is a covalent compound. It has a molecular mass of 17.

LABORATORY PREPARATION OF AMMONIA

Apparatus – Round bottomed flask, clump, Bunsen burner, delivery tube, trough, curd board, wire gauze, lime water.

Chemicals – Calcium hydroxide, Ammonium chloride, Calcium oxide.

Procedure

Ammonia is prepared by heating a mixture of calcium hydroxide and ammonium chloride.

Ca(OH)_2(s) + 2NH₄Cl_(s) CaCl_2(s) + 2H₂O_(i) + 2NH_3(g)

The tube in which ammonia is generated is fixed in a slanting position to prevent the water formed from running back and crack the whole tube.

1. Concentrated sulphuric acid and anhydrous calcium chloride are not used to dry ammonia because they react with it. Ammonia is collected by upward delivery as it is lighter than air.

HABER PROCESS (INDUSTRIAL PREPARATION)

Apparatus – Compressing chamber, catalytic chamber, cooling chamber, delivery tube.
Chemicals – Finely divided iron, Alminium Oxide, Water, Hydrogen, Nitrogen.

Procedure:

It is manufactured by reacting Nitrogen and hydrogen in the presence of finely divided iron as a catalyst at temperatures 350ºC - 400ºC at a pressure of about 350 atmospheres.

N_2(g) + 3H_2(g) 2NH_3(g)

Alminium Oxide is added to the catalyst to improve its performance. It makes it more porous and this provides a high surface area to the reaction.
The reaction is reversible hence it is not possible to convert all the reactants into ammonia.
To separate ammonia from the mixture is cooled, only ammonia liquidfies and it is separated.
The uncombined Nitrogen and hydrogen are recycled.
Another way of separation is to pass the mixture into water.
Only ammonia dissolves.

FACTORS AFFECTING THE REACTION (PROCESS)

1. Pressure

High pressure causes a better yield of ammonia because it favours the formation of the smaller products. It also increases the speed of reaction because the reacting molecules collide more often.

2. Temperature

At low temperatures the yield at equilibrium of Ammonia is higher but the reaction is slow. At high temperatures the yield of ammonia is low but the reaction is fast, a temperature of about 500ºC is used. The yield is good but the reaction is still too slow. A catalyst is therefore necessary to speed up the reaction.

3. Catalyst

A catalyst speeds the reaction but does not affect the equilibrium. The catalyst should be finely divided because reaction occurs only at the surface.

Properties of Ammonia

1. Ammonia is a colorless gas with a characteristic pungent smell.
2. It turns dump / wet red litmus paper blue. It is the only common alkaline gas.
3. It forms dense white fumes with hydrogen chloride gas

NH_3(g) + HCl_(g) NH₄Cl_(s)         

Ammonia diffuses faster and white dense fumes will be formed near hydrogen chloride gas – the white dense fume is ammonia chloride.

4. Ammonia is very soluble in water. The great solubility of ammonia can be demonstrated using the fountain experiment.

Procedure:

A largely dry, round bottomed flask with ammonia is used. The mouth of the flask is placed under water and a red litmus paper in a trough of gas jar. It is clamped firmly in position. The spring clip at the end of the long glass tube is opened. Water slowly rises up the tube until one drop is at the jet at the top.
The drop dissolves so much ammonia that there is a partial vaccum in the flask.
Water is sucked rapidly up the tube and enters the flask as a fountain. The litmus paper turns blue.

5. Ammonia burns in a lot of air (oxygen). The flame is yellow green.

4NH_3(g) + 3O_2(g) 6H₂O_(i) + 2N_2(g)

NB: Glass wool is to spread out the oxygen in order to bring it into greater contact with ammonia.

In presence of a catalyst ammonia reacts with oxygen to form nitrogen monoxide. The monoxide is easily oxidized to dioxide hence if a hot platinum or copper wire is suspended in a beaker of concentrated ammonia and oxygen is bubbled through the solution, redish brown fumes are seen. The fumes later turn white. The brown fumes are due to nitrogen dioxide which turn white as ammonium nitrate is formed.

4NH_3(g) + 5O_2(g) 4NO_(g) + 6H₂O_(g)

2NO_(g) + O_2(g) 2NO_2(g)

NO_2(g) + O_2(g) + 2H₂O_(i) 4HNO_3(g)

HNO_3(g) + NH_3(g) NH₄NO_3(s)

6. Ammonia reduces heated copper(II) oxide to copper i.e. copper turns from black to brown.

3 CuO_(s) + 2NH_3(g) 3 Cu_(s) + 3H₂O_(i) + N_2(g)
           

7. Ammonia burns in chlorine forming mist of hydrogen chloride gas. In excess ammonia, dens white fumes of ammonia chloride are formed.

2NH_3(g) + 3Cl_2(g) N_2(g) + 6HCl_(g)

HCl(g) + 3 NH_3(g) NH₄ Cl_(s)

8. Ammonia solution (Ammonium hydroxide) contains hydroxyl ions with metal ions precipitates of the hydroxides are formed. Hence a blue precipitate forms when aqueous ammonia is added to copper II sulphate solution. The precipitate dissolves in excess ammonia forming a deep blue solution.

Cu_(aq)²⁺ + 2OH^-_(aq)Cu(OH)_2(s)

Cu(OH)_2(s)+ 4NH_3(aq) Cu(HN₃)²⁺₄ + 2OH^-_(aq)

Iron(II) is (Fe²⁺) forms a dirty green precipitate with ammonia insoluble in excess Iron(III) is (Fe³⁺) forms a brown precipitate insoluble in excess.

Uses of ammonia

1. It is used in the manufacture of fertilizers e.g. Ammonium sulphate.
2. It is used in softening water.
3. It is used in making nitric acid.
4. It is used in making plastics.
5. Ammonium chloride is used in dry cells.
6. It is used in making explosives.  

Test for Ammonia

1. It is the only common alkaline gas known. It changes the dump / wet litmus paper blue.
2. Ammonia forms dense fumes of ammonium chloride when brought into contact with fumes of hydrogen chloride from concentrated hydrochloric acid.

Chemistry Carbon

CARBON

EXPERIMENT

TEACHING / LEARNING MATERIALS/ACTIVITIES AND GUIDANCE:
(a) The teacher should be able to perform the following experiment on preparation of carbon dioxide.
Apparatus: Flat-bottomed flask, corks, gas jars, water trough, Bee-hive shelve, card boards, dropping funnel or thistle funnel, delivery tube, U-tube.

Chemicals: Concentrated hydrochloric acid, water, marble chips (calcium carbonate lumps), blue litmus papers, calcium hydroxide solution (lime water), wooden splint, candle, anhydrous calcium chloride.

Procedure

1. Place some marble chips in the flat-bottomed flask and add water to just cover the marble chips.
2. Arrange the apparatus as shown in the figure below.

Fig.1  Laboratory preparation of carbon dioxide

1. Run concentrated hydrochloric acid onto the marble chips/water mixture and collect four gas jars full of the gas.

Questions

(a) What was the purpose of adding water to cover the marble chips?

(b) What did you observe when the acid was added to the marble chips?

(c) Explain why carbon dioxide is collected this way.

(d) Write the equation for the reaction taking place.

(e) Explain why sulphuric acid cannot be used in this experiment. Let your learners carry out the following activities.

CARBON

Students’ activities

Activity 1

Chemicals: Gas jar of carbon dioxide, blue litmus paper and water.

Procedure:
Dip the litmus paper in water and insert it in the gas jar containing carbon dioxide.

Question

State what you have observed ?

Write the equation for the reaction that led to what you observed.

What do you conclude from this activity about carbon dioxide?

Activity 2

Apparatus: Empty gas jar and combustion spoon.

Materials: Gas jar full of carbon dioxide, candle and match box.

Procedure:

Firmly fix a candle on the combustion spoon and light it.

Lower the burning candle into the empty gas jar.

Invert the gas jar containing carbon dioxide over the one with a burning candle and observe what happens after some time.

Fig 2 Investigating the property of carbon dioxide

Question

(i) State what you have observed ?

(ii) What do you conclude from this activity about carbon dioxide?

(iii) Mention one area where this property of carbon dioxide is utilised.

Activity 3

Apparatus: Glass rods or transparent drinking straws

Materials: Gas jar full of carbon dioxide and lime water.

Procedure:

Dip the glass rod or transparent drinking straw in lime water

Quickly insert the glass rod or straw with a drop of lime water the gas jar of carbon dioxide.

Note any change on the lime water.

Question

State what you observed ?

What is lime water used for? What do you think would happen if carbon dioxide was bubbled through lime water for a long time?

Write the equation for the reaction that led to what you observed ?

Activity 4

Apparatus: Glass test-tubes, boiling tubes, delivery tubes or transparent drinking straws, beaker, spatula, thistle funnel.

Chemicals: Marble chips, water, concentrated hydrochloric acid, ice-cold water and concentrated sodium hydroxide solution.

Procedure:

Place some marble chips in a flat bottom flask and pour some water to cover the chips.

Set-up the apparatus as shown below.

Figure 3 Laboratory preparation of sodium carbonate

3. Run in the acid from the funnel and bubble the gas through cold sodium hydroxide solution.

Make your observations.

Questions

What did you observe?

Explain your observations.

Write equations for the reactions that took place.

What test could you carry out to find out if the products you suspect to have been formed were actually formed?

Activity 5

Apparatus: Glass test-tubes, spatulas or tea-spoons, plates or saucers or soda bottle tops.

Chemicals: Baking powder, orange/lemon juice and water. (Use an orange that is not very ripe).
Procedure:

Take a little of baking powder and place it on a plate or saucer or soda bottle top.

Pour or squeeze orange juice onto the baking powder and observe what happens.

Questions

What did you observe?

What conclusion can you come up with from this activity?

Suggest an area at home where you can make use of what you observed in this activity?

Make a visit to the nearest bakery and find out how they make either bread or buns or scones. You should specify what raw materials are used in that bakery. Give a brief report to the class.

Would you like to take up the same business in future? If not, which business would you like to start in future? Write a brief report of how you could start a similar business

Activity 6

Read this short passage and answer the questions that follow.
Mrs. Gidudu hails from Bumasifwa village 45 km towards the foot of Mount Elgon in Uganda. She dropped out of school after her S.4. Because of the knowledge she acquired in chemistry she started a small business with 40,000/= she had saved from selling matooke. She invested it in wheat flour, yeast (instant yeast), blue band, sugar, salt and firewood.
A packet of wheat flour cost 3,000/=, yeast is sold at 600/=, a bundle of firewood costs 1,000/= each, 100 g of Salt at 100/= and ¼ kg of Blue Band which is sold at 1,500/=. Mrs. Gidudu built a local oven using abandoned drums that were used in the construction of a basketball court in the nearby village school, called Bumasifwa Primary School. The labour for building her oven was 20,000/=. Mrs Gidudu uses 3 packets of wheat flour daily, 1 packet of yeast, ¼ kg of Blue Band and 2 bundles of firewood to make 150 buns. A small stream runs through the village where she fetches water for her business. She makes the buns and sells each at 100/=.

Questions

Mention what chemical processes are taking place in Mrs. Gidudu’s commercial activity.

What business is Mrs. Gidudu involved in?

Who are her main clients/customers?

Calculate

The amount of money she puts into buying raw materials for her business.

The profit she makes daily, in a week, in a month and in a year.

What would you advise her to do with her profit?

What problems is Mrs. Gidudu’s business likely to face?

Suggest how she can improve and expand her business.

Properties of carbon dioxide

Physical properties

Carbon dioxide is:

• a colourless gas
• sparingly soluble in water
• denser than air

Chemical properties

When bubbled into water it dissolves slightly and some of the carbon dioxide reacts, forming a solution of a weak acid carbonic acid which shows a pH of 5.

H₂O(i) + CO₂(g)   H₂CO₃(aq)

It supports the combustion of only strongly burning substances such as magnesium. Magnesium metal decomposes the carbon dioxide to provide oxygen for its continued burning in the gas.

 2Mg(s) + CO₂(g)   2MgO (s) + C(s)

This reaction is a reduction-oxidation (redox) process in that magnesium is

oxidised as carbon dioxide is reduced

.

The illustration of gas jar with burnt magnesium

 When carbon dioxide is bubbled through lime water (calcium hydroxide solution), a white precipitate (calcium carbonate) is formed. This reaction is used as a test to show that a gas is carbon dioxide.

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

If carbon dioxide is bubbled through the solution continuously then it will eventually become clear. This is because of formation of soluble calcium hydrogen carbonate solution.  
  CaCO₃ (s) + H₂O (l) + CO₂ (g)  Ca(HCO₃)₂ (aq)

Figure 4

Effect of carbon dioxide on lime water

Carbon dioxide reacts with strong alkalis, such as sodium hydroxide, to form carbonates.

A solution of sodium hydroxide can be used to absorb carbon dioxide from the air. If excess carbon dioxide is bubbled through a solution of sodium hydroxide then a white precipitate of sodium hydrogen carbonate may be obtained.

2NaOH (aq) + CO₂ (g)  Na₂CO₃ (aq) + H2O (l)

  Na₂CO₃ (aq) + H₂O (l) + CO₂ (g)  2NaHCO₃ (s)

Figure 5 Laboratory preparation of sodium carbonate

Uses of carbon dioxide

Carbon dioxide has some important uses.

To make ‘fizzy’ (carbonated) drinks like Coca-Cola, Pepsi-Cola etc. Carbon dioxide dissolves in water under pressure. Carbon dioxide gives taste to the soft drink.

Figure 6 Soft drink

As dry ice in refrigerators. Solid carbon dioxide sublimes and so it is used as a refrigerant for ice cream meat and soft fruits. It is used for this purpose because it is colder than ice and it sublimes at -78 oC, and so it does not pass through a potentially damaging liquid state.

 

Figure 7 Dry ice

It is used in fire extinguishers; being denser than air, it blankets the fire and prevents oxygen from reaching it hence putting the fire out.

Figure 8 Fire extinguisher and that of it being used to put out fire

It is produced in situ by baking powder, and also in health salts. Baking powder consists of a dry mixture of sodium hydrogen carbonate and a solid acid such as tartaric or citric acid. Reaction only takes place when water is added, when the acid reacts with the hydrogen carbonate to form carbon dioxide that makes the dough rise. A similar principle is used in health salts like Andrews Liver Salt. In health salts, carbon dioxide evolved helps in relieving indigestion or constipation. See figure 6.

Carbon dioxide gas is used for transferring heat in some nuclear stations in atomic reactors. 

Carbon dioxide is used to create special effects (‘smoke’ effect) you see in pop concerts. Dry ice is placed in boiling water and it forms thick clouds of white ‘smoke’. It stays close to the floor due to the fact that carbon dioxide is denser than air. Excess use of carbon dioxide in pop concerts may lead to global warming.