CHEMISTRY LEVEL 3
- 1.1 Boyle's Law
- 1.2 Charles'law
- 1.3 Combined gas law
- 1.4 Standard conditions
- 1.5 Diffusion and Graham's law
- 2.1 Relative Mass
- 2.2 Atoms, Molecules and Moles
- 2.3 Compounds and the mole
- 2.4 Empirical and Molecular formula
- 2.5 Concentration of a solution
- 2.6 Molar solutions
- 2.7 Preparation of molar solutions
- 2.8 Dilution of a solution
- 2.9 Stoichiometry of chemical reactions
- 2.10 Volumetric analysis
- 2.11 Titration
- 2.12 Redox titration
- 2.13 Atomicity and molar gas volume
- 2.14 Combining volumes of gases
- 3.1 Alkanes
- 3.1.1 Formulae of alkanes
- 3.1.2 Cracking of alkanes
- 3.1.3 Nomenclature (systematic naming) of alkanes
- 3.1.4 Isomerism in alkanes
- 3.1.5 Laboratory preparation of alkanes
- 3.1.6 Physical properties of alkanes
- 3.1.7 Chemical properties of alkanes
- 3.1.8 Uses of alkanes
- 3.2 Alkenes
- 3.2.1 Nomenclature of alkenes
- 3.2.2 Isomerism in alkenes
- 3.2.3 Laboratory preparation of ethene
- 3.2.4 Physical properties of alkenes
- 3.2.5 Chemical properties of alkenes
- 3.2.6 Test for alkenes
- 3.2.7 Uses of alkenes
- 3.3 Alkynes
- 3.3.1 Nomenclature of alkynes
- 3.3.2 Isomerism in alkynes
- 3.3.3 Laboratory preparation of ethyne
- 3.3.4 Physical properties of alkynes
- 3.3.5 Chemical properties of alkynes
- 3.3.6 Test for alkynes
- 3.3.7 Uses of alkynes
- 3.4 Recommended practice of topic summary
- 4.1 Extraction of nitrogen from air
- 4.2.1 Laboratory preparation of nitrogen gas from the air
- 4.2.2 Laboratory preparation of nitrogen gas from ammonium nitrite (NH4NO2)
- 4.2.3 Uses of nitrogen
- 4.3 Oxides of nitrogen
- 4.3.1 Nitrogen (I) oxide
- 4.3.2 Nitrogen (II) oxide
- 4.3.3 Nitrogen (IV) oxide
- 4.4.1 Laboratory preparation of ammonia
- 4.4.2 Solubility of ammonia in water
- 4.4.3 Reactions of aqueous ammonia (ammonia solution)
- 4.4.4 Reactions of ammonia gas
- 4.4.5 Industrial manufacture of ammonia: The Haber Process
- 4.4.6 Uses of ammonia
- 4.4.7 Nitrogenous fertilizers
- 4.5.1 Laboratory preparation of nitric (V) acid
- 4.5.2 Industrial manufacture of nitric (V) acid
- 4.5.3 Reactions of dilute nitric (V) acid
- 4.5.4 Reactions of concentrated nitric (V) acid
- 4.5.5 Uses of nitric (V) acid
- 4.6.1 Action of heat on nitrates
- 4.6.2 Test for nitrates (nitrate ions, NO3-)
- 4.6.3 Air pollution by nitrogen compounds
- 4.7 Summary on nitrogen and its compounds
- 5.0 Sulphur and its Compounds
- 5.1.1 Extraction of sulphur
- 5.1.2 Allotropes of sulphur
- 5.1.3 Physical properties of sulphur
- 5.1.4 Chemical properties of sulphur
- 5.2.1 Preparation of sulphur (IV) oxide
- 5.2.2 Physical properties of sulphur (IV) oxide
- 5.2.3 Chemical properties of sulphur (IV) oxide
- 5.2.4 Reducing action of sulphur (IV) oxide
- 5.2.5 Oxidization of SO2 to SO3
- 5.2.6 Oxidizing action of sulphur (IV) oxide
- 5.2.7 Test for sulphite (SO32-) and sulphate (SO42-) ions
- 5.2.8 Uses of sulphur (IV) oxide
- 5.3 Large scale (industrial) manufacture of sulphuric (VI) acid
- 5.3.1 Physical properties of concentrated sulphuric (VI) acid
- 5.3.2 Chemical properties of concentrated sulphuric (VI) acid
- 5.3.3 Reactions of dilute sulphuric (VI) acid
- 5.4 Hydrogen sulphide
- 5.4.1 Chemical properties of hydrogen sulphide
- 5.4.2 Air pollution by compounds of sulphur
- 5.5 Summary on sulphur and its compounds
- 6.1 Occurrence of chlorine
- 6.2 Laboratory preparation of chlorine
- 6.3 Physical properties of chlorine
- 6.4 Chemical properties of chlorine
- 6.5 Oxidizing properties of chlorine
- 6.6 Reaction of chlorine with alkaline solutions
- 6.7 Test for chloride ions
- 6.8 Uses of chlorine and its compounds
- 6.9 Preparation of hydrogen chloride gas
- 6.10 Physical properties of hydrogen chloride
- 6.11 Chemical properties of hydrogen chloride
- 6.12 Industrial manufacture of hydrochloric acid
- 6.13 Uses of hydrochloric acid
Gas Laws: Diffusion and Graham's Law
1.0 Gas Laws
1.5 Diffusion and Graham's Law
A perfume sprayed at one corner finally fills the room. We can detect sweet smell from flowers, and aromatic smell from food. These are possible because matter consists of small particles (molecules), and because of diffusion. Some molecules move faster and therefore diffuse faster than others.
Figure 1.5: Set-up to demonstrate "diffusion" of marble balls
(courtesy Youtube-Diffuion in gases by ormalearn)
The steel balls (glass balls or beads) represent molecules. They all have the same mass except the grey ball, which is lighter.
Observe the video demonstration of movements of steel balls when shaken in a petri dish, to represent diffusion.
Questions 1.5(a): Previous and current experiences
- What is diffusion? (Hint: Primary Science.)
- The balls move fairly fast. But each of them takes long to reach the farthest end. Why?
- Which balls move faster: the lighter or heavier ones?
- From your answer to Question 3, which objects move faster: the denser or less dense objects?
- How does density affect diffusion rate?
- How would an increase in temperature affect diffusion rate? (Hint: Brownian motion, Chemistry Level 2.)
Answers to Questions 1.5(a)
Gas molecules move fairly fast, at typically 600 m/s (over 2 000 km/hr). But they take long to diffuse (or advance) in a given direction because of multiple collisions with other molecules. Collisions aside, rate of diffusion of a gas decreases as its density increases. It is an inverse relationship.
Graham found the relationship to be
Plate 1.5(a) Graham's equation
That is, the rate of diffusion of a gas is inversely proportional to the square root of its density. This is called Graham's law.
Let us play around with Graham's equation to see other possible forms it can take, before we use it to solve problems. Always remember, Density = Mass/Volume. That is, rho = M/V.
Plate 1.5(b) Different forms of Graham's equation
Questions 1.5(b)
- Rewrite the Graham,s equation with an equal (=) sign introduced.
- Rewrite the equation in terms of mass, M, instead of density.
- Rewrite the equation in Question 2 for a gas labelled A.
- Suppose the rate of diffusion of gas A is RA, and of gas B is RB. Write the ratio RA/RB in terms of the densities rho A and rho B of gases A and B respectively.
- Rewrite the equation for RA/RB in terms of Relative Molecular Mass of A (RMMA) and Relative Molecular Mass of B (RMMB).
- Rewrite the equation for RA/RB in terms of volume of A (VA) and of B (VB) diffused.
- Write an equation to relate Relative Molecular Mass of A (RMMA) and Relative Molecular Mass of B (RMMB) with volume of A (VA) and of B (VB) diffused.
- Rewrite the equation for RA/RB in terms of the time taken by A (tA) and B (tB) to diffuse under the same conditions. (Hint: If the rate is high, time taken is short. So if rate is a numerator (up), time is a denominator (down).)
RA/RB = -----
NB: Equal sign comes automatically when we are dealing with ratios. That is, if A is proportional to B, and C is proportional to D, then A/B = C/D.
RA/RB = -----
RA/RB = -----
RA/RB = -----
Answers to Questions 1.5(b)
Questions 1.5(c)
200ml of gas X with a relative molecular mass (RMM) 64 diffuses in 5 minutes. It takes 8 minutes for the same volume of gas Y to diffuse under the same conditions of temperature and pressure.
- Gas P is 4 times less dense than X. How many times does P diffuse faster than X?
- Determine the relative molecular mass of Y.
- How long would it take 200 ml of gas Z, with a relative molecular mass of 2, to diffuse under the same conditions?
- Determine the rate of diffusion of gas Q with a relative molecular mass of 71.0 under the same conditions.
Answers to Questions 1.5(c)
1.6 Project 1
In this topic, we have learnt how volume varies with pressure at constant temperature, and the relationship between volume and absolute temperature of a gas at constant pressure.
- Design an experiment to investigate the relationship between pressure, P, and absolute temperature, T, of air at constant volume. In the design, explain clearly the procedure you would follow, the materials and apparatus you require and how you would use them, the measurements you would take and how you would use them to determine the relationship.
- Carry out the project and prepare a report explaining the method and materials used, measurements and observations made, findings, and any difficulties experienced.
NB: Project work should preferably be done in a group.