Sumilla
Supuesto 2: en el caso del literal b) del numeral 19.2, el legislador ubica a la con- con-tratación a través de catálogos electrónicos de acuerdo marco como un supuesto
2. La subcontratación en los contratos del Estado
P, Q, S R, T
3
1(h) [Able to explain the difference in the voltage of the cell]
Suggested answer:
The distance between Cu and metal S is further / greater than the distance between Cu and metal P in the electrochemical series.
3
1(i)
[Able to draw the labeled apparatus set-up completely]
Suggested answer:
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Question
Rubric
Score
2 (a) [Able to record all the five readings accurately to one decimal point]:
t1 = 55.0 s, t2 = 48.0 s, t3 = 42.0 s, t4 = 37.0 s, t5 = 33.0 s, 3 (b) [Able to construct a table and transfer all the five readings from (a) correctly
with unit for each heading.. The values for
time
(c) [Able to give the operational definition correctly]
Rate of reaction is inversely proportional to the time taken for the mark
“X” to be no longer visible // Rate of reaction
∝ time
1
3
(d) [ Able to do the following:
• Draw a graph of suitable size / using suitable scale (occupying about 75% of graph paper)
• Label the axes concentration / mol dm-3 and
time
1 / s
-1• Plot the five points correctly from the table constructed in (b)
• Draw a straight line (linear) graph ]
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(d) [ Able to state
the relationship between concentration and the rate of reaction correctly]
(ii) An increase in concentration (of sodium thiosulphate solution) will increase the rate of reaction.
3
(e) [Able to predict the time taken using the graph drawn]
Suggested answer : 30 s 3
(f) [Able to state and explain the observation correctly.]
A yellow precipitate is formed.
The reaction of hydrochloric acid and sodium thiosulphate solution produces sulphur, sulphur dioxide and water. // The sulphur produced from the reaction forms the yellow precipitate.
3
(g) [Able to state the relationship between the manipulated variable and the responding variable and the direction correctly]
The higher / lower the concentration of sodium thiosulphate solution, the shorter / longer the time taken for the mark “X” to be no longer visible.
3
(h) [Able to state three variables and the way to control them correctly]
Suggested answer:
Time taken for the mark
“X” to be no longer visible // thiosulphate solution // size of conical flask // concentration and volume of hydrochloric acid used // total volume of reacting mixture
Reject : Use of “Quantity” or
“amount of “ hydrochloric acid / reacting mixture.
Solutions of same temperature are used // use conical flasks of same size // use the same concentration and volume of hydrochloric acid //
keep the total volume of reacting mixture the same.
6
(i) [Able to explain phenomena using relevant
knowledge of chemistry]
Suggested answer :
Fanning increases the concentration of oxygen blown over glowing charcoal //
Fanning causes the glowing charcoal to be exposed to more oxygen. 3
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Question
Rubric
Score
3(a) How do different metals in contact with iron affect the rusting of iron? // What is the effect of different metals in contact with iron on the rusting of iron nails
?
3
(b) Iron nail rusts when it is in contact with a less electropositive metal. Iron nail
does not rust when it is in contact with a more electropositive metal 3 (c) MV : Different metals in contact with iron nail
RV: Rusting of iron
CV: Type of (iron) nail, medium in which iron nail is kept, temperature
3
(d) Name one metal more electropositive (magnesium) than iron and one metal less electropositive (copper) than iron.
Materials : Iron nails, magnesium ribbon, copper foil, hot jelly solution containing potassium hexacyanoferrate(III) solution, sandpaper.
Apparatus : test tubes, test tube rack,
3
(e) Procedure :
1. Clean / Rub three iron nails with sandpaper.
2. Two iron nails are coiled / wound separately with magnesium ribbon and copper foil.
3. The three nails are each put / dip / immersed into labelled test tubes A, B and C containing hot jelly solution with potassium
hexacyanoferrate(III) solution separately .
4. The test tubes are put on a test tube rack under room condition for a few days.
5. The test tubes are observed and the results are recorded.
3
(f) Tabulation of data : Suggested answer(any one )
Pair of metal Observation
Iron nail only Iron nail coiled with
magnesium ribbon Iron nail coiled with
copper foil
Tets tube Pair of metal Observation A Iron nail only
B Iron nail coiled with magnesium ribbon C Iron nail coiled with
copper foil
3
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Question
Rubric
Score
4 (a) Is vulcanised rubber more elastic than unvulcanised rubber ? //
How does the elasticity of vulcanised rubber differ from unvulcanised rubber ? //
Does vulcanisation increase the elasticity of rubber?
3
(b) MV : Types of rubber // Vulcanised and unvulcanised rubber RV: Length of rubber strip
CV : Size of rubber strip, mass of weight
3
(c) Vulcanised / Unvulcanised rubber is more elastic than unvulcanised /
vulcanised rubber. 3
(d) Materials : Vulcanised rubber strip, unvulcanised rubber strip Apparatus: Retort stand and clamp, (bulldog) clips, ruler, 10 g, 20 g, 30 g , 40 g and 50 g weights,
3
(e) Procedure :
1. (Using bulldog clips,) hang a vulcanised rubber strip and an unvulcanised rubber strip onto a retort stand each.
2. The (initial) lengths of the two rubber strips are measured.
3. A 10 g weight is hung to each of the two strips and the lengths of the
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Question
Rubric
Score
5(a) How effective are // How is the effectiveness of soaps and detergents in hard water ? //
What is the effectiveness of soaps and detergents in hard water ? //
Is the cleansing action of a detergent / soap more effective than that of a soap / detergent in hard water ? //
Is soap as effective as detergent in hard water ?
3
(b) Detergents are effective in hard water. Soaps are less / not effective in hard water. //
Detergent is a more effective cleansing agent than soap in hard water.
3
(c) MV : Different types of cleansing agent / Detergent and soap RV: (Removal of) oily stain on a cloth
CV: Volume and concentration of magnesium sulphate solution, volume and concentration of detergent and soap, type of stain / oil stain on cloth, temperature of magnesium sulphate // calcium sulphate solution.
3
(d) Materials : Soap solution, detergent solution, two pieces of cloth with oily stains, magnesium sulphate // calcium sulphate solution Apparatus : measuring cylinder, basin // [any suitable container such as a basin]
3
(e) Procedure :
1. 50 cm3 of 5% soap solution and 50 cm3 of 5% detergent solution are separately poured into two beakers containing 20 cm3 of magnesium sulphate solution / hard water.
2. A small piece of cloth with oily stains is dipped / immersed / put into each beaker.
3. Each cloth is washed with the cleansing agent / soap or detergent in the beaker.
4. The cleansing action of the soap and detergent is observed and compared // The oily stain remaining on the cloth is observed and compared.
5. The results are recorded in a table.
3