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SS1: CHEMISTRY - 1ST TERM

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  1. Introduction to Chemistry and Laboratory Apparatus | Week 1
    5Topics
    |
    1 Quiz
  2. Nature of Matter | Week 2
    3Topics
    |
    1 Quiz
  3. Separation Techniques I | Week 3
    1Topic
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    1 Quiz
  4. Separation Techniques II | Week 4
    5Topics
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    1 Quiz
  5. Particulate Nature of Matter I | Week 5
    5Topics
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    1 Quiz
  6. Particulate Nature of Matter II | Week 6
    9Topics
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    1 Quiz
  7. Symbols, Formulae & Oxidation Number | Week 7
    7Topics
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    1 Quiz
  8. Laws of Chemical Combination | Week 8
    4Topics
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    1 Quiz
  9. Chemical Equation & Chemical Combination (Chemical Bonding) I | Week 9
    4Topics
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    1 Quiz
  10. Chemical Combination (Chemical Bonding) II | Week 10
    4Topics
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    1 Quiz
  11. Chemical Combination (Chemical Bonding) III & Shapes of Covalent Molecules | Week 11
    3Topics
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    1 Quiz
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Why Atoms Combine:

In our discussion on atomic structure, the atom was described as a neutral particle. The number of positively-charged particles (protons) in the nucleus is balanced by that of negatively charged particles (electrons) revolving around the nucleus.

Atoms are rarely found in nature as free elements apart from the noble (rare) gases: helium, neon, argon, etc.

It is now known that atoms combine when they are in a form whereby they have an attraction for each other. When they combine, bonding takes place which results in chemical bonds being formed within the combining atoms.

Systematic arrangement of Elements in the Periodic Table:

Elements in the Periodic Table are arranged in horizontal and vertical rows. The elements in the Periodic Table fall under eight groups. The elements also fall into periods starting from Hydrogen.

The elements in the same group have the same number of electrons in their outermost shell.

Example: Group 1 elements.

3Li – 2,1

11Na – 2,8,1

19K – 2,8,8,1

Periodic table of the 1st Twenty Elements

Periodic table of the 1st Twenty Elements

The table above shows the Periodic Table of the first 20 Elements.

Elements in the same group have the same number of electrons in their valence shell. They also have similar chemical properties. Example: Beryllium, magnesium, and Calcium have two electrons in their outermost shell. Fluorine and Chlorine have 7 electrons in their outermost shell.

In contrast, elements in the same group have chemical properties which change from metallic (on the left) to non-metallic (on the right). The number of electrons in the outermost shells increases progressively by one from left to right in the periodic table.

In the periodic table, the rare gases are very stable because their outermost shell is filled up. Atoms of other elements are unstable. In order to attain the stable structure of rare gases, elements go into two main combinations electrovalency and covalency combination.

Theory Questions

1.  (a) State the law of (i) definite proportion (ii) conservation of matter.

    (b) Which of these laws govern the balancing of chemical equations?

View Answer

2. Write the balanced equation for each of the following reactions:

       (a)  Zinc + hydrochloric acid → Zinc chloride + hydrogen

        (b) Calcium + water →  Calcium hydroxide + hydrogen

View Answer

3. Balance the following chemical equations

(a) CaCO3 + HCl →   CaCl2 + H2O + CO2

(b)  Na + O2 →  Na2O

(c)  NH3 + O2 → NO + H2O

(d) KClO3 → KCl + O2

(e) C2H6 + O2 → CO2 + H2O

View Answer

4. 2.8g of an oxide of copper gave 2.52g of copper on reduction and 1.90g of another oxide gave 1.52g of copper on reduction. Show that the data illustrate the law of multiple proportions.

5. Two samples of copper (I) oxide were prepared by 

(i) Heating Copper(II) trioxocarbonate(IV) 

(ii) Heating strongly the mixture of copper (II) tetraoxosulphate (VI) and sodium hydroxide. 

Analysis of these two samples shows that:

(i) 4.50g of copper (II) oxide contain 4g of copper

(ii) 5.60g of copper (II0 oxide contain 4.98g of copper. Show that these results illustrate the law of constant composition.

Theory Question 1

(a) State the law of (i) definite proportion (ii) conservation of matter.

Answer:

(i) The law of definite proportion states that all pure samples of the same chemical compound contain the same elements combined in the same proportion by mass.

(ii) The law of conservation of matter states that in an ordinary chemical reaction, matter can neither be created nor destroyed.

(b) Which of these laws govern the balancing of chemical equation?

Answer:

Law of conservation of matter (mass)

Theory Question 2

2. Write the balanced equation for each of the following reactions:

(a)  Zinc + hydrochloric acid → Zinc chloride + hydrogen

Answer:  Zn(s) + HCl(aq)  → ZnCl2 + H2(g)

(b) Calcium + water →  Calcium hydroxide + hydrogen

Answer: 2Ca(s) + 2H2O(aq)  → 2CaOH(s) + H2(g)

Theory Question 3

3. Balance the following chemical equations

(a) CaCO3 + HCl →   CaCl2 + H2O + CO2

Answer: CaCO3 + 2HCl → CaCl2 + H2O + CO2

(b)  Na + O2 →  Na2O

Answer:  4Na + O2 2Na2O

(c)  NH3 + O2 → NO + H2O

Answer: 4NH3 + 3O2 2NO + 6H2O

(d) KClO3 → KCl + O2

Answer: 2KClO3 → 2KCl + 3O2

(e) C2H6 + O2 → CO2 + H2O

Answer:  2C2H6 + 7O2 → 4CO2 + 6H2O

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