Lesson Notes By Weeks and Term - Senior Secondary School 1

SUBJECT: CHEMISTRY

CLASS:  SS 1

DATE:

TERM: 2nd TERM

REFERENCE BOOKS

• New Chemistry for Senior Secondary School by Osei Yaw Ababio; U.T.M.E Past Questions and Answers.
• Practical Chemistry for Senior Secondary Schools by Godwin Ojokuku
• Outline Chemistry for Schools & Colleges by Ojiodu C.C.
• Chemistry Pass Questions for S.S.C.E and UTME.

 
WEEK THREE                                        DATE-------------

TOPIC: STOICHIOMETRY OF REACTIONS

CONTENT

• Calculation of masses of reactants and products
• Calculation of volume of reacting gases

STOICHIOMETRY OF REACTIONS

The calculation of the amounts (generally measured in moles or grams) of reactants and products involved in a chemical reaction is known as stoichiometry of reaction. In other words, the mole ratio in which reactants combine and products are formed gives the stoichiometry of the reactions.

From the stoichiometry of a given balanced chemical equation, the mass or volume of the reactant needed for the reaction or products formed can be calculated.

CALCULATION OF MASSES OF REACTANTS AND PRODUCTS

1. Calculate the mass of solid product obtained when 16.8g of NaHCO3 was heated strongly     until there was no further change.

    Solution:

    The equation for the reaction is:

    2NaHCO3(s) → Na2CO3(s) + H2O(g) CO2(g)

    Molar mass of NaHCO3 = 23 + 12 + 16x3 = 84gmol-1

    Molar mass of Na2CO3 = 23x2 +12+16x3 = 106gmol-1

    From the equation:

    2 moles NaHCO3 produces 1 mole Na2CO3

    2x84g NaHCO3 produces 106g Na2CO3

    16.8g NaHCO3 will produce Xg Na2CO3

     Xg Na2CO3 = 106g x 16.8g    =10.6g

     2x84g

     Mass of solid product obtained = 10.6g

2. Calculate the number of moles of CaCl2 that can be obtained from 25g of limestone [CaCO3] in the presence of excess acid.

     Solution:

      The equation for the reaction is:

       CaCO3(s) + 2HCl → CaCl2(s) + H20(l) + CO2(g)

       Number of moles = Reacting mass

                                     Molar mass

       Molar mass of CaCO3 = 40 + 12 + 16x3 = 100gmol-1

       Number of moles of CaCO3 = 25g           = 0.25 mole

                     100gmol-1

    From the equation of reaction,

    1 mole CaCO3 yields 1 mole CaCl2

    Therefore, 0.25 mole CaCO3 yielded 0.25 mole CaCl2.

EVALUATION

1. What does the term ‘Stoichiometry of reaction’ mean?
2. Ethane [C2H6] burns completely in oxygen. what amount in moles of CO2 will be produced when 6.0g of ethane are completely burnt in oxygen

CALCULATION OF VOLUME OF REACTING GASES

1. In an experiment, 10cm3 of ethene [C2H4] was burnt in 50cm3 of oxygen.
2. Which gas was supplied in excess? Calculate the volume of the excess gas remaining at the end of the reaction.
3. Calculate the volume of CO2 gas produced.

Solution:

The equation for the reaction is:

C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(g)

From the equation,

A.1 mole of ethene reacts with 3mole of oxygen

     1 volume of ethene reacts with 3 volumes of oxygen

    10cm3of ethene will react with 30cm3 of oxygen

    Since 50cm3 of oxygen was supplied, oxygen was in excess

    Hence volume of the excess gas = initial volume – volume used up = 50-30 = 20cm3

B.1 volume of ethene produces 2 volumes of CO2

    10 cm3 of ethene will produce 20cm3 of CO2 

    Therefore, 20cm3 of CO2 was produced

2. 20cm3 of CO was mixed and sparked with 200cm3 of air containing 21% of O2. If all the     volumes are measured at s.t.p, calculate the total volume of the resulting gases.

     Solution:

     In 200cm3 of air,

    Volume of O2 = 21   x 200cm3 = 42cm3

     100

Volume of N2 and rare gases = 200-42 = 158cm3

The equation for the reaction is:

        2CO(g) + O2(g) → 2CO2(g)

Volume ratio            2       :   1     :     2

Before sparking     20cm3   42cm3

Reacting volume     20cm3   10cm3

After sparking                    32cm3   20cm3

Volume of resulting gases = 32 + 20 + 158 = 210cm3

GENERAL EVALUATION/REVISION

1. Find the volume of oxygen produced by 1 mole of KClO3 at s.t.p in the following reaction:      2KClO3(s) → 2KCl(s) + 302(g)
2. Balance the following equations: (a) Cu2S(s) +O2(g) → Cu2O(s) + SO2(g)

                                                     (b) C(s) + H2O(g) → CO(g) + H2(g)       

3. Write the symbols of the following elements: mercury, silver, gold, lead, tin, antimony.
4. Define the term valency

READING ASSIGNMENTNew School Chemistry for Senior Secondary School by

1. Y. Ababio, Pg 156-164

WEEKEND ASSIGNMENT

1. Amount of a substance is expressed in A. mole B. grams C. kilograms D. mass
2. Determine the mass of CO2produced by burning 104g of ethyne [C2H2]A. 256g B.352g C. 416g D. 512g
3. The mole ratio in which reactants combine and products are formed is known as A. rate of reaction 

1. stoichiometry of reaction C. equation of reaction D. chemical reaction

1. The unit for relative molecular mass is A. mole B. gmol-1C. grams D. mass
2. What mass of Pb(NO3) would be required to 9g of PbCl2 on the addition of excess NaCl solution? [Pb=207, Na=23, O=16, N=14] A. 10.7g B. 1.2g C. 6.4g D. 5.2g

THEORY

1. Calculate the number of molecules of CO2produced when 10g of CaCO3 is treated with 100cm3 of 0.20moldm-3 HCl.
2. Calculate the volume of nitrogen that will be producedat s.t.p from the decomposition of 9.60g ammonium dioxonitrate(iii), NH4NO2.