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.