5 Solids, liquids and gases

Transcription

1 5 Solids, liquids and gases Practical work a) Identifies two different methods ( mark each), e.g. Take several readings and work out a mean average Calibrate the thermometer against fixed point, such as boiling temperature of water Links ideas with theory ( mark per method): Calculating an average reduces the impact of random errors Calibrating means the size of the error can be calculated and readings can be adjusted b) States one benefit, e.g. sharing tasks Explains the benefit e.g. students concentrate on one task Links to this experiment, e.g. more accurate readings of time and temperature Total 7 a) Smoke particles are large enough to be seen The smoke particles are small enough to show Brownian motion b) The lamp lights up the smoke particles So the Brownian motion/movement can be seen c) Small brightly lit particles Constantly moving in random directions Total 6 3 Using scales: place on a level surface so it takes a true reading zero the scales using the tare button Measuring cylinder: keep eye level with water level to avoid parallax Take readings before and after adding the brass weight as the difference is the mass s volume Total 4 4 Any four from: States variables to measure: weight of the bottle, area of the bottle s base (both points needed for mark) Describes how to use equipment: measure mass in grammes using the scales States how to convert the scale reading to weight (in newtons): divide mass (in grammes) by 00 Describes experimental set-up: place the bottle on the square paper and draw round the base Describes how to collect data: calculate complete squares included in the outline and half the partially included squares States how to use data: pressure = weight/ area Total 4 Hodder & Stoughton 03 33

2 Mark scheme Calculations and diagrams a) Steel has a greater density than water it is the mass of a fixed volume which is important b) volume = area length = = 0.6 m 3 (the unit must be included to get the mark) c) mass = density volume mass of pile A = = 440 kg d) B has a small area at the bottom. This means that the pressure is greater, so the point sinks into the ground more easily Total 8 a) volume = 5.5. = 5 m 3 density = mass/volume = 7500/5 = 500 kg/m 3 b) i) weight = mass gravitational field strength = = N pressure = force/area and area = 5.5 =.5 m pressure = /.5 = 6000 N/m (lose mark for the wrong unit) c) The largest pressure will be exerted when the box stands on the smallest area This happens when the box stands on the end which measures. m x.5 m Total 9 3 a) 35 C = = 408 K b) P /T = P /T 00/408 = P /90 P = 00 90/408 = 7 kpa c) At a higher temperature the molecules move faster They hit the walls of the lamp harder and more often Total 8 34 Hodder & Stoughton 03

3 4 a) pressure/kpa b) i) volume/cm 3 Good choice of scale each of the x- and y-axes should take up at least 50% of the length of the paper Axes labelled Points plotted accurately Smooth curve drawn Draw lines as shown on the graph 68 kpa ± kpa 7 cm 3 ± cm 3 c) With less volume the molecules hit the walls of the tube more often The pressure depends on the number of collisions, so it rises d) P V = P V 00 0 = P 0 P = 400 kpa Total 5 a) CO is a greenhouse gas which contributes to global warming b) The cap rock must not be porous, as we do not want the gas to escape c) i) efficiency = useful energy/energy put in With low efficiency more energy is wasted as heat So for the same coal used less electricity is generated, and it costs more d) density = mass/volume = kg/ m 3 = kg/m 3 (lose mark for the wrong unit) e) i) f) i) i P V = P V = 60 V V = /60 = m 3 density = mass/volume = kg/5 000 m 3 = 0 kg/m 3 The volume reduces because molecules are closer together in a liquid than a gas (Think what the second mark is for many students will write that the volume gets smaller, and not say why. The volume is actually 6 times smaller as the density is 6 times larger.) You should draw two diagrams: in the gas state the molecules are far apart and randomly arranged in the liquid state the molecules are in contact and randomly arranged The CO floats above the oil as it is less dense CO has a density of 780 kg/m 3 and oil a density of 850 kg/m 3 Total 8 Hodder & Stoughton 03 35

4 Mark scheme 6 a) i) b) i) c) i) P = height density g = = Pa total pressure = = Pa P = F/A F = P A = = 4800 N (lose mark for the wrong unit) P V = P V = V V = 0.4 l Any two points for mark each: Without breathing out the pressure in the lung stays high As the diver rises the pressure outside the lung drops So the large pressure will damage the lung Total 3 Longer-answer questions Two similarities for mark each: one degree in each scale is the same temperature change; both have fixed zero points Two differences for mark each: the zero point is different; Kelvin values are never negative but Celsius can be; Kelvin readings are 73 degrees higher than Celsius readings Answer states how to convert readings, e.g. subtract 73 from a Kelvin reading to get Celsius reading, so 73 kelvin = 0 degrees Celsius Pollen grains in water constantly move and change direction randomly this is Brownian motion Since the pollen grains change direction they must be hitting/hit by unseen particles/atoms All pollen grains change direction so the particles/atoms must surround them/be everywhere Pollen grains change direction all the time so the unseen particles/ atoms must be in constant motion The unseen particles/atoms must be very small/too small to see 3 As the bubbles move towards the surface, they increase in size The shape of the bubble does not change/stays a sphere Water pressure presses on the bubble equally in all directions Boyle s law states that pressure volume is constant for a gas Since water pressure is less near the water surface, so the air in the bubble expands 36 Hodder & Stoughton 03

5 4 Molecules bouncing off the ball s walls cause gas pressure in the ball When the ball is pumped up, there are more molecules inside the ball There are more collisions on the walls inside the ball so pressure increases pressure/temperature = constant The temperature is lower in the ball taken outside Molecules in a cooler gas move more slowly/have fewer collisions with the container walls Total 6 5 pressure = force/area Objects sink through mud if they exert a high pressure on its surface Pressure is reduced if the area of the tyre in contact with the mud increases or the object weighs less The tractor is heavier but exerts a smaller pressure than the car The area of the tractor s tyres touching the ground must be more than six times that of the car as the tractor weighs six times more than the car (saying the tyres are six times larger does not gain a mark) Hodder & Stoughton 03 37