Wednesday, January 14, 2009
WARNING COPY AT YOUR OWN RISKRISK: GOOD LUCK FOR YOUR O level AS U LEART NOTHING!
PURE CHEM ANSWERRedox reactionRespiration, combustion and rusting are similar processes because they all involve
Ans: Oxidation
What happens when a bromine atom is changed into a bromide ion?
Ans: It is reduced
Which element is not a reducing agent?
Ans: Chlorine
Which gas is NOT a reducing agent?
Ans: oxygen
A redox reaction is one which
Ans: a electron are transfer
In which compound is nitrogen in its lowest oxidation state?
Ans: NH3
In a redox reaction, acidified potassium dichromate solution will turn from orange to green.
Ans: true
A substance that is reduced has ___________ .
Ans: gain electron
Which substance is most easily reduced on a charcoal block?
Ans: Copper Oxide
Which one of the following oxide is most easily reduced on a charcoal block?
Ans: Copper(II)Oxide
When copper(II) oxide changes to copper(I) oxide, copper(II) oxide is said to be oxidised.
Ans: False
Which reaction is an example of reduction?
Ans: Copper(II)Oxide to copper
Which metal is a stronger reducing agent than magnesium?
Ans: Sodium
Which statement is true about oxidising agents?
Ans: They are readily accept electron
When iron(II)oxide is heated strongly with carbon
Ans: Iron ion gain 2 electron
An oxidising agent __________ .
Ans: Readily accept electron
A reducing agent is a chemical which ____ .
Ans: Donate electron
What happens to magnesium when it is oxidised to MgCl2?
Ans: It’s oxidation state increase
An oxidised substance is one that has __________ .
Ans: Gain oxygen
Which reaction is not an example of reduction?
Ans: iron to iron(II) ions
METALSMetals have a dull appearance
Ans: False
Lead reacts with water to form a hydroxide.
Ans: False
Magnesium is _________ reactive than aluminium.
Ans: more
Metals ___________ hydrogen in the series DO NOT react with acids to produce hydrogen gas.
Ans: Below
Tin is ___________ reactive than lead.
Ans: More
Sodium is __________ reactive than calcium.
Ans: More
What are the products of the reaction between potassium and cold water?
Ans: Hydrogen, potassium oxide
Copper reacts with dilute hydrochloric acid.
Ans: False
What are the products of the reaction between calcium and cold water?
Ans: Potassium hydroxide and hydrogen
Magnesium can displace calcium from calcium chloride solution.
Ans: False
Lead is ________ reactive than zinc.
Ans: More
Alloys are made up of ________________________.
Ans: More than 1 type of atom
What are the products of the reaction between zinc and steam?
Ans: Zinc oxide, hydrogen
Zinc can displace copper from copper sulphate solution.
Ans: True
ALL metals are ___________ conductors electricity and heat.
Ans: Good
What is/are the condition/s necessary for rusting to occur?
Ans: Presence of water, presence of air
Which of the following is NOT a method to prevent rusting?
Ans: Coating with water
Metals are ________________.
Ans: Ductile, Strong, Malleable
Magnesium reacts with dilute hydrochloric acid to form ______________
Ans: Hydrogen, magnesium chlorine
Metals have ____________ densities because there is very little space between the atoms
Ans: High
AIRWhich of the following gases is most common in air?
Ans: Oxygen
Why are catalytic converters fitted to car exhausts?
Ans: to decrease the amount of nitrogen oxides emitted
In which pair do both pollutants cause damage to buildings?
Ans: nitrogen dioxide and sulphur dioxide
What is air?
Ans:L Mixture of elements and compound
Which of the following sets contains three pollutants found in air?
Ans: carbon monoxide, nitrogen dioxide, sulphur dioxide
Which one of the following does not involve combination with oxygen?
Ans: photosynthesis in plant
Air contains about 21% oxygen by volume. When a sample of river water was boiled, the air expelled was found to contain 30% oxygen. What is the best explanation of the difference in oxygen content?
Ans: Air is more soluble in water than nitrogen
Iron will not rust if it is kept _____________.
Ans: Dry
Which of the following gases cannot be removed from the exhaust gases of a petrol powered car by its catalytic converter?
Ans: Carbon dioxide
Which substance, commonly present in car exhaust fumes, does not pollute the atmosphere?Ans: Nitrogen oxides
Pure Physic AnswerLight
An illuminated object placed 10 cm in front of a convex lens of focal length 8 cm forms a 4 times magnified image on a screen. What is the distance between the object and the screen?
Ans: 40cm
The two types of reflection are ________________ .
Ans: Regular and diffused
In a plane mirror the image is ____________________ .
Ans: The same size as the object
If a convex lens is used as a magnifying glass to view an object, which of the following statements is incorrect?
Ans: The image and the observer are on the same side of the lens.
Refraction is the process by which __________________ .
Ans: Light bends
The depth of a pool is 6.0 m. What is its apparent depth if the refractive index of the water is 1.33?
Ans: 4.5
An image in a mirror is __________________________ .
Ans: a virtual image
For a regular reflection ________________
Ans: the angle of incidence of every ray that hits the surface is equal
The area of a square is magnified by 9 times when viewed through a magnifying glass. What is the linear magnification produced by the magnifying glass?
Ans: 9
The refractive index of glass is 1.5. What is the speed of light in glass (in multiple of 108 m/s) ?
Ans: 2
When light enters a less dense medium from a denser medium, the light ray bends __________________________ .
Ans: away from normal
A virtual image __________________________ .
Ans: cannot be seen on screen
An object is placed in front and within the focal length of a converging lens. Which of the following descriptions about the image formed is incorrect?
Ans: the image is real
A pool appears shallower than it is because _________________.
Ans: light ray bend when theyt travel from water to air
An example of regular reflection is when ______________________ .
Ans: Light shine on a plane mirror
A man of height 1.8 m stands 0.5 m in front of a vertical plane mirror. What is the minimum length of mirror, which will permit the man to see his whole body?
Ans: 0.9m
A ground glass surface cannot form image of an object by reflection because _________________ .
Ans: light from the object is reflected randomly in different directions by the ground glass surface
The image of an object formed is smaller than object when the object is placed 17 cm from a converging lens. Placed at a distance of 15 cm, the image of the object becomes slightly bigger than the object. What is the approximate focal length of the lens?
Ans: 8
Which of the following statements is incorrect?
Ans: A ray may always enter air from glass at any angle of incidence
An object of height 4 cm is placed 18 cm in front of convex lens of focal length 12 cm. A real image is formed 36 cm on the other side of the lens. What is the height of the image?
Ans: 8cm
Themal propertiesCalculate the amount of heat required to raise the temperature of 0.8 kg of copper from 35°C to 60°C. (Specific heat capacity of copper = 400 J kg-1 C-1)
Ans: 8kJ
Which of the following is NOT a reason for the use of Freon liquid in refrigerators?
Ans: It has low boiling point
Some gas trapped in a cylinder is compressed at constant temperature by a piston. Which of the following will not change?
Ans: mass
Which of the following does NOT take place when steam condenses into water?
Ans: The size of the water molecules decrease
0.2 kg of water at 70°C is mixed with 0.6 kg of water at 30°C. Assuming that no heat is lost, find the final temperature of the mixture.
Ans: 40°C
Heat energy is supplied at the same rate to 250 g of water and 250 g of ethanol. The temperature of the ethanol rises faster. This is because the ethanol _______________ .
Ans: has a smaller specific heat capacity than water
Some gas is heated in a sealed container. Which of the following does not increase?
Ans: The average kinetic energy of gas molecules
200 g of water at 25°C is poured into a container. The water is cooled until it turns into ice. If the rate of heat release is 7.3 x 10 J s-1, find the time taken to turn all the water into ice. (Specific latent heat of fusion of ice = 3.34 x 105 J kg-1, specific heat capacity of water = 4 200 J kg -1 C-1).
Ans: 20 minutes
Blister as a result of contact with steam is more severe than blister as a result of contact with boiling water. This is because ________________ .
Ans: the specific latent heat of steam is higher than the specific heat capacity of water
Iron has a higher specific heat capacity than copper. When heat is supplied at the same rate to two identical blocks of iron and copper, which of the following will take place?
Ans: The temperature rise in the iron block is slower than the copper block.
A refrigerator turns 550 g of water at 15°C into ice at-5°C. How much heat is absorbed by the refrigerator? (Specific latent heat of fusion of ice = 3.34 x 105 J kg-1, specific heat capacity of water = 4 200 J kg -1 C-1).
Ans: 224kJ
1.8 kJ is required to melt 30 g of a certain solid. The specific latent heat of fusion of the solid, in Jkg-1, is _____________ .
Ans: 60 000
Why does the pressure of a fixed mass of gas increase when it is heated at constant volume? (J94 P1 Q13)
Ans: The average speed of the molecules increases.
800 g of water is cooled from 88°C to X°C. Given that 2.1 x 105 J of heat is released, find the value of X. (Specific heat capacity of water = 4 200 J kg-1C-1)
Ans: 25.5°C
The temperature inside a spacecraft which has landed on the Moon is the same as it was on the Earth. Which property of an aluminium block would have a different value on the Moon compared with that on the Earth? (J96 P1 Q14)
Ans: Its mass
The air in a large paper bag is heated. The bag is then found to rise through the surrounding cold air. This is because
Ans: Bag has become less dense
A student observes the Brownian motion of smoke particles in air with a microscope. She sees moving points of light. These points of light come from
Ans: a smoke particles only moves randomly
There is no rise in temperature when latent heat is supplied to melt the ice. Which of the following explains this observation?
Ans: Latent heat is used to overcome the attractive force between molecules
A metal block of mass 200 g is heated from 20°C to 55°C. If the specific heat capacity of the metal is 380 J kg -1 C-1 , how much heat is absorbed by the block? (Specific heat capacity of water = 4 200 J kg -1 C-1)
Ans: 2660J
The Brownian motion of smoke particles is caused by (N94 P1 Q12)
Ans: collisions between smoke particles and air molecules.
As the temperature is raised, molecules gain energy and vibrate more vigorously about their fixed positions. Eventually they have enough energy to overcome the strong forces between them so that they can move past each other, although weaker forces still do not allow them complete freedom of movement.' Which process is described in the above statement? (J95 P1 Q11)
Ans: A solid melting
An electric kettle is rated at 800 W. Calculate the rise in temperature of 2.5 kg of water if the electric kettle is switched on for 5 minutes. (Specific heat capacity of water = 4 200 J kg -1 C-1)
Ans: 22.9°C
The motion of the molecules of two gases causes them to mix. What is this mixing called?(J97 P 1 Q 11)
Ans: Diffusion
Which of the following substances has the lowest specific heat capacity?
Ans: Aluminium
A plastic container contains 600 g of water. The water is heated by a 1.5 kW heater for t seconds. If the temperature of the water increases by 75°C, find the value of t. (Specific heat capacity of water = 4 200 J kg-1C-1)
Ans: 126s
2 kg of liquid X at 90°C is allowed to cool. If the specific heat capacity of the liquid is 600 J kg-1 C-1and 9 000 J of heat energy is released, find the final temperature of the liquid.
Ans: 82.5°C
When the temperature of a gas rises at constant volume, its molecules _________________________. (N92 P1 Q12)
Ans: move with greater average speed.
200 g of water at 100°C is poured into a copper container of mass 25 g. The copper container contains 1 kg of water at 0°C What is the final temperature of the mixture? (Specific heat capacity of water = 4 200 J kg-1 C-1) (Specific heat capacity of copper = 390 J kg-1 C-1)
Ans: 16.6°C
Calculate the amount of heat needed to convert 3 kg of ice at 0°C to water at 30°C. (Specific latent heat of fusion of ice = 3.34 x 105 J kg-1, specific heat capacity of water = 4 200 J kg -1 C-1).
Ans: 1.38MJ
Which of the following statements about latent heat is true?
Ans: Heat used to weaken the bonds between molecules.
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