SCIE 4001
Section A - Multiple Choice
Section A - Multiple Choice Answers
Multiple Choice on Section B Matter and Materials
Multiple Choice on Section B Matter and Materials Answers
Section B - Matter and Materials
Section C - Energy
Section D - Structures and Mechanisms
 

Section B Matter and Materials

QUESTION

(a) Mary who is eight years old was helping her mother to make orange juice. While the mother left the kitchen, she mistakenly poured the whole pack of granulated sugar into the juice. She stirred the juice vigorously for five minutes but the sugar did not all dissolve. When her mother came back, she was told that she added too much sugar. As Mary’s teacher, explain fully what has happened to her orange juice? (4 marks)
(b) Jane has always watched her mother baking cakes. She asked her mother how adding baking powder to the ingredients makes the cake rise. Her mother explained that it is part of the ingredients in the recipe. Jane was not satisfied.
(i) Explain fully the importance of adding baking powder to the cake ingredients.    (4 marks)

(ii) Complete the following word equation:

Acid + ____________  →   Water  + __________                                    (2 marks)

(ii) The above equation represents the process of __________________ (1 mark)

(c) With the aid of a diagram, describe how you will find the volume of a bunch of keys (4marks)    

Answer points–
(a) (i) Water is made up of molecules in constant random motion with spaces between them.
(ii) Sugar is a solid whose molecules are arranged in a rigid matrix. On first addition to the water the surface molecules of the sugar break away from the rigid matrix and become ‘more like a liquid’ fitting in the spaces between the water molecules.
(iii) Stirring assists the sugar molecules to break the bonds holding them in the solid matrix.
(iv) The ‘free’ sugar molecules fit into the spaces between the water molecules (dissolving).
(v) Adding more sugar filled all the spaces between the water molecules (saturation) so solid sugar could not dissolve.
(vi) The drink can be described as SATURATED.

(b) (i)(1) Baking powder is sodium bicarbonate (NaHCO3)
(2) Solid organic acids (like tartaric and gluconic) are added directly to the mixture.
(3) Solid acidic substances (like complex phosphates of calcium or sodium) are added directly.
(4) When water is added these acids react with sodium bicarbonate to release carbon dioxide, water and a sodium salt. H+ + NaHCO3 → Na+ + CO2 + H2O (if you don’t understand ignore)
(5) On heating (in the oven) any remaining sodium bicarbonate decomposes to release carbon dioxide.
(6) The carbon dioxide released from the reaction and heating is a gas and causes gas spaces in the batter (reaction causes batter to rise before baking and heating causes batter to rise due to expansion and decomposition of sodium bicarbonate) and so baked cake ‘rises’.
(ii) Acid + Base → Water + Salt
(ii) Neutralization

answersc) Apparatus: Measuring cylinder, thread or thin string.
(i) Add water to the measuring cylinder so that the keys can be completely submerged in the water.
(ii) Read the measuring cylinder
(iii) Use a thin string to gently lower the keys so that it is completely immersed in the water.
(iv) Take the new reading from the measuring cylinder.
(Note to Students: The volume of water does not increase – the reading increases because he keys displace their own volume of water)
(v) The volume of the keys is the difference between the two readings.

 

Unit 1 Matter and Materials

QUESTION

(a) Angela hates her chore of cleaning the bathtub in the house. She cannot understand why she has to clean it three times a week. With the aid of word equations give a full explanation of why the bathtub gets dirty very quickly. (5 marks)
(b) Study the table below and use the information to help you answer questions (i), (ii) and (iii)
Density of some common materials

Material Density( g/cm3)
Rubbing Alcohol 0.79
Glycerin 1.26
Corn oil 0.93
Water 1.00
Wood 0.85
Rubber 1.34
Cork 0.25

Anita created a density column in a graduated measuring cylinder using four substances from the table above.
(i) Which liquid will settle at the bottom of the graduated cylinder? Why? (2 marks)
(ii) Which liquid in the above demonstration will remain at the top? (1 mark)
(iii) Which liquid with a volume of 1 cm3 has the largest mass? (2 marks)
(c) Explain briefly how a mixture of ethanol and water which are miscible can be separated? (5 marks)

Answer points
(a) The non-scientific answer (and it will get no marks) – people bathe there… etc…. The scientific answer is that the water used is hard water.
Hard water may have calcium and magnesium ions and sulphate or hydrogen carbonate ions.
Soap is sodium stearate and reacts with the calcium/magnesium sulphate/ hydrogen carbonate to produce a scum.
X Y + sodium stearate (soap) = X stearate (scum) + sodium Y
where X = calcium or magnesium and Y = hydrogen carbonate or sulphate
(you can write the equation like calcium sulphate + sodium stearate (soap) = calcium stearate (scum) + sodium sulphate)
Also when hard water evaporates it leaves behind solids - the calcium/magnesium sulphate/ hydrogen carbonate. The hydrogen carbonate becomes carbonate which is the mineral in limestone and dolomite rocks.

(b) (i) Glycerin – it is the densest. (Actually some of these liquids will dissolve each other and not form layers! – but don’t tell them that)
(ii) The rubbing alcohol will float. (– it is the least dense).
(iii) Glycerin – it is the densest. Density = Mass/Volume.

answers(c) Ethanol and water (miscible liquids – liquids which dissolved each other to completely mix) can be separated by fractional distillation.
The ethanol/water mixture is placed in a flask and heated.
The fractionating column is made up of glass beads.
Alcohol boils at a lower temperature than water so a thermometer is used at the top of the column to make sure the temperature stays at the boiling point of the alcohol (so no water boils).
A condenser is used to change the alcohol vapour to liquid alcohol.
The distillate is pure ethanol and collected in a flask.
(So now you know – tell the man who making the babash how to distill it efficiently!)


 

 

 

 

 

 

 

 

 

 

Unit 1 Matter and Materials

(a) Answer points–
(i) Sound travel through the air at about 330m/s. This means for distances like the classroom the sound is heard a fraction of a second after it is produced by the tap.
(ii) Diffusion of gas is a slow process where fluid (liquids and gas) molecules spread out
(iii) It may take several seconds or minutes before the gas molecules diffuse across the room to the person’s nose.
(iii) Wind in the direction of the person move the molecules faster (THIS IS NOT DIFFUSION) and similarly wind in the opposite direction may make the time longer (THIS IS NOT DIFFUSION)

(b) Answer points–
(i) Metals (like almost all materials) expand when heated.
(ii) Metals conduct heat faster than glass.
(iii) The metal cover will expand quicker than the glass and thus get ‘slack’.
(iv) Some types of glass expand by a small amount. Metals tend to expand by a greater amount the glass and thus the metal cover gets ‘slack’.

(c) Answer points–
(i) The burner is hot and the pot is cold so heat is transferred to the bottom of the pot.
(ii) This heat is conducted from the pot bottom to the bottom layer of the water.
(iii) As the water gets hot it expands.
(iv) The density of the bottom layer decreases so it rises.
(v) Water from the top layers flow downwards to take the place of the rising water.
(vi) A convection current is created.

(d) Answer points–
(i) Magnets have two poles: like poles repel and unlike poles attract
(ii) Magnets attract magnetic materials (usually iron based)
(iii) The only true test for an object being a magnet is if it repels another magnet.
(Iv) Try bringing the ends of the needle together in pairs(XY. XZ and YZ). Switch the ends of the pairs. The two that repel each other are magnets.

 

answer
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answers

(a) (i) Answer points–
(i) Water is made up of molecules in constant random motion with spaces between them.
(ii) Koolaid is a solid whose molecules are arranged in a rigid matrix. On first addition to the water the surface molecules of the koolaid break away from the rigid matrix and become ‘more like a liquid’ fitting in the spaces between the water molecules.
(iii) Stirring assists the koolaid molecules to break the bonds holding them in the solid matrix.
(iv) The ‘free’ koolaid molecules fit into the spaces between the water molecules (dissolving).
(v) The same process occurred for the sugar.
(vi) Adding more sugar filled all the spaces between the water molecules (saturation) so solid sugar could not dissolve.
(vii) The drink can be described as SATURATED.

(b) (i)(1) Baking powder is sodium bicarbonate (NaHCO3)
(2) Solid organic acids (like tartaric and gluconic) are added directly to the mixture.
(3) Solid acidic substances (like complex phosphates of calcium or sodium) are added directly.
(4) When water is added these acids react with sodium bicarbonate to release carbon dioxide, water and a sodium salt. H+ + NaHCO3 → Na+ + CO2 + H2O (if you don’t understand ignore)
(5) On heating (in the oven) any remaining sodium bicarbonate decomposes to release carbon dioxide.
(6) The carbon dioxide released from the reaction and heating is a gas and causes gas spaces in the batter (reaction causes batter to rise before baking and heating causes batter to rise due to expansion and decomposition of sodium bicarbonate) and so baked cake ‘rises’.
There is another anwer that has to do with yeast but it is not in this course. Yeast converts sugars to alcohol and releases carbon dioxide,which does the same action.

(c) Answer points–
(i) Leg B represents the solid ice becoming liquid water.
(1) Both solid and liquid are present at this time
(2) The temperature remains at 0°C until all the ice is molten.
(3) The ice absorbs heat (called latent heat of fusion) for the melting process to occur.
(4) The molecules gain freedom of movement from rotation and vibration only to translation, rotation and vibration.
(5) The molecules get closer and the volume decreases (an anomaly – melting ice contracts but other substances expand)
(ii) Leg B represents warming the water to boiling point.
(1) The volume increases as the spaces between the water molecules get larger.
(2) The molecules move faster.
(3) Some molecules gain enough energy to become a gas (water vapour) and escape the bulk of the liquid.

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answers

(a) Answer points–
(i) 1. The mixture is probably a suspension or an emulsion (the liquid equivalent of a suspension).
2. The solid particles in a suspension (or the liquids in and emulsion) settle out when it is not disturbed for some time.
3. Shaking will distribute the particles more evenly in the suspension (or mix the liquids in an emulsion).
(ii) The differences:
1. The suspension has tiny undissolved solid particles but all the particles in the solution are dissolved.
2. The suspension may be separated by filtration or allowing it to stand undisturbed but the solution cannot.
3. A solution contains only molecules whereas the suspension has solid particles with many molecules.
4. A solution is transparent but a suspension is cloudy and individual particles can be seen with magnification (hands lens or microscope)
(iii)    X Y + sodium stearate (soap) = X stearate (scum) + sodium Y
where X = calcium or magnesium and Y = hydrogen carbonate or sulphate
(you can write the equation like
calcium sulphate + sodium stearate (soap) = calcium stearate (scum) + sodium sulphate)

(b) Answer points–
(i) 1. Rubbing alcohol
2. Materials which are denser than a liquid will sink but less dense materials will float in the liquid. The following will sink in rubbing alcohol (density – 0.79): wood (density – 0.85), rubber (density – 1.34), aluminium (density – 2.70) and plastic (density – 1.17) but cork (density – 0.25) will float. (for your own analysis: glycerin (1.26) corn oil (0.93) and water (1.00) – wood (0.85) and cork (0.25) will both float)
(ii) 1. Glycerin
2. Glycerin (density – 1.26)  - rubber (density – 1.34) will sink but plastic (density – 1.17) will float
(iii) Any of the following pairs (but I think they only were aware of the first):
1. Water and Rubbing Alcohol
2. Water and Glycerin
3. Glycerin and corn oil
Reason: They have different boiling points so the one with the lower boiling point will be the distillate.

 

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Concept by Kishore Lal. Programmed by Kishore Lal... Copyright © 2015 Kishore Lal. All rights reserved.