Pen ink consists of a mixture of dyes that can dissolve in the solvent and contaminate the chromatogram.
Pencil lead is usually made of insoluble graphite, which made it suitable for drawing the start line in paper chromatography.
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Describe an experiment to determine the centre of gravity of an irregularly shaped thin plastic sheet.
a) Drill 3 small holes on the sheet, as near to the edge as possible, as far away from one another as possible.
b) Hang a plumb line from one of the holes.
c) When the sheet is stationary, trace the vertical line made by the plumb line using a marker.
d) Hang the plumb line from each of the other two holes and repeat the tracing of the lines.
e) The intersection point of the 3 traced lines is the centre of gravity of the plastic sheet.
Describe the test for sulfur dioxide gas.
Bubble the gas into acidified potassium manganate (VII) solution.
KMnO4 solution changes color from purple to colorless in the presence of sulfur dioxide gas.
State Newton’s Laws of Motion
Newton’s First Law of Motion (or Law of Inertia):
Every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it to change its state.
Newton’s Second Law of Motion:
When a resultant force acts on an object of constant mass, the object will accelerate and move in the direction of the resultant force. The product of the mass and acceleration of the object is equal to the resultant force.
Newton’s Third Law of Motion:
For every action, there is an equal and opposite reaction, and these forces act on mutually opposite bodies.
A metal sphere, mass 2kg, and a wooden sphere, mass 1kg, of the same size, are dropped at the same time from the same height of 5m, on Earth. Which sphere would hit the ground first? Explain.
Both spheres would hit the ground at the same time.
The spheres are dropped near to ground, so the effect of air resistance on the spheres’ resultant force is negligible.
The resultant force acting on the sphere will be its downward weight.
The ratio of the weight to mass will be 10 for each sphere, so both spheres will free-fall towards the ground at a constant acceleration of 10m/s2.
What are drying agents and what are the common drying agents?
Drying agents are substances that can be used to obtain a dry sample of a gas by removing its moisture content.
Examples:
* Anhydrous calcium chloride (for any gas except ammonia)
Ammonia will react with calcium chloride.
4NH3 (g) + CaCl2 (s) –> CaCl2.4NH3 (s)
* Concentrated sulfuric acid (for any gas except alkaline gases such as ammonia)
* Calcium oxide
(for any gas except acidic gases such as CO2 and SO2)
What are the 7 base quantities?
| Physical Quantity | SI Unit | Symbol |
| Length | metre | m |
| Mass | kilogram | kg |
| Temperature | Kelvin | K |
| Time | second | s |
| Current | ampere | A |
| Amount of substance | mole | mol |
| Luminous intensity | candela | cd |
Define Kinetic Particle Theory.
Kinetic Particle Theory states that all matter is made up of tiny, discrete particles that are in constant, random motion.
In paper chromatography, why must the start line be above the solvent level?
The start line above the solvent level allows the solvent to move past the start line, carrying the dissolved samples along with it.
With the start line below the solvent level, the samples on the start line will dissolve in the solvent right at the beginning, contaminating the whole solvent, causing the chromatogram to be inaccurate.
Explain the importance of the measurement of the purity of substances that we use in foodstuffs and drugs.
For substances used in preparing food and drugs, it is important to ensure that only permitted substances are being used.
If a substance is impure, and laced with some other substances, these unapproved impurities might not be safe for human consumption, and lead to undesirable effects on human health.