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 TEN                                            DATE-------------

TOPIC: GAS LAWS (CONT.)

CONTENT

• Avogadro’s law
• Gay lussac’s law of combinig volumes
• Graham’s law of diffusion

AVOGADRO’S LAW

This law states that equal volume of all gases at the same temperature and pressure contain the same number of molecules. This means that 1 mole of any gas at s.t.p has a volume of 22.4dm3.

GAY LUSSAC’S LAW OF COMBINING VOLUMES

It states that when gases react they do so in volumes which are simple ratios to one another and to the volumes of the products if gaseous, provided that the temperature and pressure remain constant.

CALCULATION ON THE LAW

Calculate the volume of oxygen required to burn 500cm3 of methane completely.

 Solution:

 The equation for the reaction is:

      2CH4(g) + 3O2(g) → 2CO2(g) + 2H2O(g)

 By Gay Lussac’s law, 

 2 volumes of CH4 requires 3 volumes of O2 for complete combustion

 Therefore, 2cm3 of CH4 requires 3cm3 of O2

      500cm3 of CH4 will require Xcm3 of O2

   Xcm3 of O2 = 500cm3 x 3cm3 = 750cm3

                2cm3

   Thus, 750cm3 of O2 is required

EVALUATION

1. State the Gay Lussac’s law of combining volumes
2. 40cm3 of hydrogen was sparked with 160cm3 of oxygen at 100oC and 1atm. Determine the volume of oxygen left after the reaction.

GRAHAM’S LAW OF DIFFUSION

It states that the rate of diffusion of a gas is inversely proportional to the square root of its density at constant temperature and pressure. 

Mathematically,

            R α 1/√d

            R = k/√d where k is a constant

Comparing the rate of diffusion of two gases:

            R1 = √d2

            R2   √d1

In terms of relative molecular mass, M

            R α 1/√M

For two gases,

            R1 = √M2

            R2   √M1

But rate of diffusion is reciprocal of time, R =1/t

That is,

            R1 = t2

            R2    t1

From the inverse relationship we can deduce that the less dense a gas is, the higher the rate of diffusion and vice versa.

CALCULATION

1. A given volume of SO2 diffuses in 60 seconds. How long will it take the same volume of    CH4 to diffuse under the same condition (SO2 = 64, CH4 = 16)

   Solution:

  Using the expression:  

            t1= √M2

            t2   √M1

                        t2 = √M2 x t1 = √16 x 60seconds = 30seconds

                  √M1        √64

GENERAL EVALUATION/REVISION

1. State Graham’s law of diffusion
2. Under the same condition of temperature and pressure, hydrogen diffuses 8 times as     fast as gas Y. Calculate the relative molecular mass of Y.
3. State the following rule/principle: (a) Hund’s rule of maximum multiplicity (b) Aufbau principle
4. Write the electronic configuration of (a) oxide ion, (b) Aluminium ion,  (c) potassium (d) phosphorus.

READING ASSIGNMENT

New School Chemistry for Senior Secondary School by O.Y. Ababio, Pg 86-92

WEEKENDASSIGNMENT

1. 400cm3 of a gas X diffuses through a porous pot in 2 minutes. Calculate the rate at which X diffuses. A. 6.3cm3s-1B. 20cm3s-1 C. 200cm3s-1D. 3.33cm3s-1#
2. The relationship between the density (d) of a gas and the rate at which the gas diffuses is A. R = kd

1. R= k/√d C. R = k√d D. k/d

1. Calculate the minimum volume of oxygen required for the complete combustion of a mixture of 20cm3 CO and 20cm3 of H2. A. 10cm3B. 20cm3C. 40cm3D. 60cm3
2. If sulphur (iv) oxide and methane (CH4) are released at the same time at opposite ends of a tube, the rate of diffusion will be in the ratio A. 2:1 B. 4:1 C. 1:4 D. 1:2
3. ‘Equal volume of all gases at the same temperature and pressure contain same number of molecules’ is a state of which law A. Avogadro’s law B. Boyle’s lawC. Charles’ law      D. Chemical law

THEORY

1. Arrange the following gases in order of increasing rate of diffusion: CO, SO2, H2S,NO2 and O2.
2. The vapour densities of O2 and Cl2 are 16 and 36 respectively. If 60cm3 of O2 diffuses through a porous partition in 14 seconds, how long will it take 1000cm3 of Cl2 to diffuse through the same partition?