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CHEMISTRY FORM 1


i Common Chemistry Laboratory Chemicals
ii Common Chemistry Laboratory Apparatus
iii Safety in the Chemistry Laboratory
iv Why we should learn Chemistry
1. INTRODUCTION TO CHEMISTRY
2. SIMPLE CLASSIFICATION OF SUBSTANCES AND SEPERATION OF MIXTURES
3. ACIDS, BASES AND INDICATORS
4. AIR AND COMBUSTION
5. WATER AND HYDROGEN
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Water and Hydrogen: Candle wax and water

5.0 Water and Hydrogen

5.1 Candle wax and water


Did you know that water covers over 70% of the earth's surface, makes up 60% of human body, 79% of our kidneys, and 83% of our lungs? Moreover, many substances such as the solid acid and hydrogencarbonate in liver salt (Topic 4), react only in solutions; so they require water to dissolve them first before they can react.


No wonder, our body mainly consists of water to enable chemical (biochemical) reactions that keep us alive. Water is life; but it also has some important chemical properties.


We have learnt that water takes part in rusting (Section 4.3) and it reacts with sodium peroxide to produce oxygen (Section 4.4). Water itself is produced in reactions between acids and carbonates (Section 3.4), and acids and bases (Section 3.5). What about the burning of a candle?


What are the products of a candle burning in air?


Materials and substances required
  1. Candle stick, glass funnel, delivery tube, match box
  2. Dry test tube, beaker, freezing mixture (ice plus sodium chloride)
  3. Anhydrous copper (II) sulphate or anhydrous cobalt (II) chloride

Set-up

Observe what happens inside the test tube.


Repeat the experiment with anhydrous copper (II) sulphate replaced with lime water as follows.


Set-up

The two set-ups above can be combined as in the video on burning of a candle in air

(Courtesy Youtube - Year 10 Products of Combustion by Susanna Wilkinson). Cobalt (II) chloride paper has been used in place of anhydrous copper (II) sulphate. Open the video, take observations, and answer Questions 5.1.


Questions 5.1

  1. State the function of
    1. the pump ---
    2. freezing mixture
  2. What change occurs inside the
    1. U-tube in the video?
    2. lime water in the test tube (or boiling tube)?
    1. What is the effect on blue cobalt chloride paper of the product collected in the U-tube?
    2. Identify this product.
  3. From your answer to Question 2(b), identify the second (gaseous) product.
  4. Write a word equation for the burning of candle wax in air (oxygen).
  5. Why should the inside of the U-tube be dry at the beginning?
  6. Which substance can be used instead blue cobalt (II) chloride paper?

Answers to questions 5.1


Candle wax is a compound of hydrogen and carbon only. It is therefore called a hydrocarbon. The hydrogen from it combines with oxygen of the air to form water, while carbon burns to form carbon (IV) oxide. The products can be confirmed with blue cobalt (II) chloride paper and calcium hydroxide solution (lime water) respectively.


Other hydrocarbons are kerosene, petrol, diesel, tar, laboratory gas (cooking gas), petroleum jelly and bees wax, among others. They all burn to produce water and carbon (IV) oxide. Water vapour readily condenses on glass surface even at room temperature.