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mock specific Flashcards

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1
Q

what two things does the rate of a chemical reaction depend on?

A
  1. the collision frequency

2. the energy transferred during a collision

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2
Q

what are four things the rate of reaction depends on?

A
  1. temperature
  2. the concentration of a solution or the pressure of a gas
  3. surface area
  4. the presence of a catalyst
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3
Q

How does a change in temperature affect the rate of reaction? Why?

A

in order for a reaction to occur, the particles have to collide. increasing the temperature increases the speed the particles move at, and so they collide more frequently, so an increase in temperature increases the rate of a reaction

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4
Q

what effect does concentration have on rate of reaction? Why?

A

in order for a reaction to occur, particles have to collide. the more concentrated a solution is, the more particles there are per unit volume, so there are more frequent collisions. this means that an increase in concentration increases the rate of a reaction

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5
Q

what effect does pressure have on the rate of a reaction? Why?

A

in order for a reaction to take place, particles must collide. the higher the pressure, the more particles there are per unit volume, so there are more frequent collisions. this means that an increase in pressure increases the rate of reaction

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6
Q

what effect does surface area have on the rate of a reaction?

A

in order for a reaction to occur, particles have to collide. increasing the surface area to volume ratio of a solid will increase the amount of the solid exposed to the other reactants, so more frequent collisions will occur. this means that an increase in surface area to volume ratio increases the rate of a reaction

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7
Q

what is a catalyst?

A

a substance that speeds up the rate of a reaction, without being used up in the reaction itself

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8
Q

are catalysts part of the overall reaction equation?

A

no

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9
Q

how do catalysts work?

A

by decreasing the activation energy needed for the reaction to occur. they do this by providing an alternative reaction pathway with a lower activation energy.

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10
Q

give an example of a biological catalyst

A

enzymes - they catalyse reactions in living things

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11
Q

what is the formula for the mean rate of reaction?

A

rate of reaction = amount of reactant used or amount of product formed / time

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12
Q

how do you find the rate of a reaction at one particular point in time?

A

you have to plot a graph and find the gradient at that time

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13
Q

what are the three ways to measure the rate of a reaction?

A
  1. precipitation and colour change
  2. change in mass (usually gas given off)
  3. the volume of gas given off
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14
Q

what units would you use to measure a product or reactant if it’s a gas?

A

cm^3

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15
Q

what units would you use to measure a product or reactant if it’s a solid?

A

grams

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16
Q

what is the most common measurement of time when calculating rate of reaction?

A

seconds

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17
Q

what are common examples of the units used for the rate of a reaction

A

cm^3/s, g/s, or mol/s

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18
Q

how do you measure the rate of a reaction using precipitation and colour change? (4 points)

A
  1. you can record the visual change in a reaction if the initial solution is transparent and the product is a precipitate which clouds the solution (it becomes opaque)
  2. you can observe a mark through the solution and measure how long it takes for it to disappear - the faster the mark disappears, the quicker the reaction
  3. if the reactants are coloured and the products are colourless (or vice versa), you can time how long it takes for the solution to lose (or gain) its colour
  4. the results are very subjective - different people might not agree over the exact point when the mark ‘disappears’ or the solution changes colour. Also, if you use this method, you can’t plot a rate of reaction graph from the results
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19
Q

how do you measure the rate of a reaction using a change in mass? (5 steps)

A
  1. measuring the speed of a reaction that produces a gas can be carried out using a mass balance
  2. as the gas is released, the mass disappearing is measured on the balance
  3. the quicker the reading on the balance drops, the faster the reaction
  4. if you take measurements at regular intervals, you can plot a rate of reaction graph and find the rate quite easily
  5. this is the most accurate of the three methods because the mass balance is very accurate, but it has the disadvantage of releasing gas straight into the room
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20
Q

how do you measure the rate of a reaction using the volume of gas given off?

A
  1. this involves the use of a gas syringe to measure the volume of gas given off
  2. the more gas given off during a given time interval, the faster the reaction
  3. gas syringes usually give volumes accurate to the nearest cm^3, so they’re quite accurate. you can take measurements at regular intervals and plot a rate of reaction graph using this method too. you have to be quite careful though - if the reaction is too vigorous, you can easily blow the plunger out of the end of the syringe
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21
Q

what do magnesium and HCl react to produce?

A

Hydrogen gas

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22
Q

what are the 6 steps to using the reaction between magnesium and HCl to investigate the effect of concentration on the rate of reaction?

A
  1. start by adding a set volume of dilute hydrochloric acid to a conical flask and carefully place on a mass balance
  2. now add some magnesium ribbon to the acid and quickly plug the flask with cotton wool
  3. start the stopwatch and record the mass on the balance. take readings of the mass at regular intervals
  4. plot the results in a table and work out the mass lost for each reading. now you can plot a graph with time on the x-axis and loss of mass on the y-axis
  5. repeat with more concentrated acid solutions. variables such as the amount of magnesium ribbon and the volume of acid used should be kept the same each time - only change the acid’s concentration. This is to make your experiment a fair test
  6. the three graphs show that a higher concentration of acid gives a faster rate of reaction
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23
Q

what are the 6 steps to using the reaction between sodium thiosulfate and HCl to investigate the effect of concentration on the rate of reaction?

A
  1. Sodium Thiosulfate and HCl are both clear solutions. They react together to form a yellow precipitate of sulfur
  2. start by adding a set volume of dilute sodium thiosulfate to a conical flask
  3. place the flask on a piece of paper with a black cross drawn on it. add some dilute HCl to the flask and start the stopwatch.
  4. now watch the black cross disappear through the cloudy sulfur and time how long it takes to fully disappear
  5. the reaction can be repeated with solutions of either reactant at different concentrations (but only change the concentration of one reactant at a time). the depth of the liquid must be kept the same each time
  6. The higher the concentration, the quicker the reaction and therefore the less time it takes for the mark to disappear
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24
Q

why should the reaction between sodium thiosulfate and HCl be carried out in a well-ventilated place?

A

because it releases sulfur dioxide

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25
Q

what do sodium thiosulfate and HCl react together to produce?

A

sulfur - a yellow, cloudy precipitate

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26
Q

how do you find the mean rate for a whole reaction?

A

you work out the overall change in the y-axis of the graph (amount of product formed or reactant used up), and divide this by the total time taken for the reaction

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27
Q

how does a reversible reaction reach equilibrium? (high-mark question)

A
  1. in a reversible reaction, as the reactants react, their concentrations fall, so the forward reaction will slow down. But as more and more products are made and their concentrations rise, the backward reaction will speed up
  2. after a while the forward reaction will be going at exactly the same rate as the backward one - the system is at equilibrium
  3. at equilibrium, both reactions are still happening, but there’s no overall effect (it’s a dynamic equilibrium). This means the concentrations of reactants and products have reached a balance and won’t change
  4. equilibrium is only reached in a closed system
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28
Q

can a reaction be at equilibrium with unequal amounts of reactants and products?

A

yes - equilibrium doesn’t mean that the amounts of reactants and products are equal

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29
Q

what does it mean if the position of equilibrium lies to the right?

A

the concentration of the products is greater than that of the reactants

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30
Q

what does it mean if the position of equilibrium lies to the left?

A

the concentration of reactants is greater than that of the products

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31
Q

what conditions does the position of equilibrium depend on?

A
  1. the temperature
  2. the pressure (in gases)
  3. the concentration of the reactants and products
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32
Q

is the reaction from hydrated copper sulfate to anhydrous copper sulfate + water endothermic or exothermic?

A

endothermic

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33
Q

is the reaction from anhydrous copper sulfate + water to hydrated copper sulfate endothermic or exothermic?

A

exothermic

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34
Q

what is le chatalier’s principle?

A

the idea that if you change the conditions of a reversible reaction at equilibrium, the system will react to counteract that change

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35
Q

what can le chatalier’s principle be used for?

A

it can be used to predict the effect of any changes you make to a reaction system

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36
Q

what happens if you lower the temperature of a reversible reaction at equilibrium?

A

the equilibrium will move in the exothermic direction to produce more heat. this means you’ll get more products for the exothermic reaction and fewer products for the endothermic reaction

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37
Q

what happens if you raise the temperature of a reversible reaction at equilibrium?

A

the equilibrium will move in the endothermic direction to try and decrease the temperature. You’ll get more products for the endothermic reaction and fewer products for the exothermic reaction

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38
Q

which reactions at equilibrium are affected by pressure?

A

those involving gases

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39
Q

what happens if you increase the pressure of a reversible reaction at equilibrium?

A

the position of equilibrium shifts towards the side where there are fewer molecules of gas - it tries to reduce the pressure

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40
Q

what happens if you decrease the pressure of a system at equilibrium?

A

the position of equilibrium shifts towards the side where there are more molecules of gas in an attempt to increase the pressure again

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41
Q

what happens if you change the concentration of either the reactants or the products of a system at equilibrium?

A

the system will no longer be at equilibrium, so it responds to bring itself back to equilibrium

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42
Q

what happens if you increase the concentration of the reactants in a system at equilibrium?

A

the system makes more products to counteract the change

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43
Q

what happens if you decrease the concentration of products in a system at equilibrium?

A

the system reduces the amount of reactants to counteract the change

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44
Q

what is a hydrocarbon?

A

any compound that is formed from carbon and hydrogen atoms only

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45
Q

what is the general formula for alkanes?

A

CnH2n+2,

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46
Q

what are alkanes?

A

a homologous series of saturated hydrocarbons

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47
Q

what is a homologous series?

A

a group of organic compounds that react in a similar way

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48
Q

what is the formula for Butane?

A

C4H10

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49
Q

what are the properties of shorter hydrocarbons?

A
  • less viscous
  • more volatile (lower boiling points)
  • more flammable
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50
Q

what are the properties of longer hydrocarbons?

A
  • more viscous
  • less volatile (higher boiling points)
  • less flammable
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51
Q

what are short-chain hydrocarbons used for? why?

A

they are used as ‘bottled gases’ - stored under pressure as liquids in bottles - because of their low boiling points

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52
Q

what is the equation for the complete combustion of a hydrocarbon?

A

hydrocarbon + oxygen -> carbon dioxide + water

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53
Q

during the combustion of a hydrocarbon, what happens to the carbon and hydrogen?

A

they are both oxidised

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54
Q

why are hydrocarbons used as fuels?

A

they release a lot of energy when they combust completely

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55
Q

write a balanced symbol equation for the complete combustion of methane

A

CH4 + 2O2 -> CO2 + 2H20

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56
Q

write a balanced symbol equation for the complete combustion of propane

A

C3H8 + 5O2 -> 3CO2 + 4H2O

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57
Q

how is crude oil made?

A

from the remains of an ancient biomass, made up mainly of plankton, that’s been buried in mud

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58
Q

what type of fuel is crude oil?

A

a fossil fuel

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59
Q

what does crude oil consist of?

A

different lengths of hydrocarbons and a bit of sulfur

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60
Q

what are the 4 steps to separating hydrocarbons by fractional distillation?

A
  1. the oil is heated until most of it has turned into gas. The gasses enter a fractionating column, and everything that remains liquid is drained off
  2. in the fractionating column there’s a temperature gradient (it’s hot at the bottom and cooler as you go up)
  3. the longer hydrocarbons have high boiling points. They condense back into liquids early on, when they’re near the bottom. The shorter hydrocarbons have lower boiling points. They condense and drain out much later on, near to the top of the column where it’s cooler.
  4. you end up with the crude oil mixture separated out into different fractions. Each fraction contains a mixture of hydrocarbons that all contain a similar number of carbon atoms, so have similar boiling points
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61
Q

what fuels are obtained from the fractional distillation of crude oil, in order from the highest boiling point (collected at the bottom) to the lowest boiling point (collected at the top)

A

bitumen, heavy fuel oil, diesel oil, kerosene, petrol, LPG (liquefied petroleum gas)

62
Q

what are organic compounds?

A

compounds containing carbon atoms

63
Q

what is cracking?

A

splitting up long-chain hydrocarbons

64
Q

why do we use cracking?

A

short-chain hydrocarbons are flammable so make good fuels and are in high demand. However, long-chain hydrocarbons form thick gloopy liquids like tar which aren’t very useful, so we use cracking to turn a lot of the longer alkane molecules produced from fractional distillation into smaller, more useful ones.

65
Q

what are some of the products of cracking useful as?

A

fuels, e.g. petrol for cars and paraffin for jet fuel

66
Q

what does cracking produce other than alkanes?

A

alkenes

67
Q

which are more reactive: alkanes or alkenes?

A

alkenes

68
Q

what are alkenes used for?

A

they’re used as a starting material when making lots of other compounds and can be used to make polymers

69
Q

what is the test for alkenes?

A

bromine water - when in the presence of an alkene it turns from bright orange to colourless

70
Q

what type of reaction is cracking?

A

a thermal decomposition reaction - it breaks molecules down by heating them

71
Q

what are the two methods of cracking?

A
  1. catalytic cracking

2. steam cracking

72
Q

what are the 3 steps to catalytic cracking?

A
  1. you heat and vaporise long-chain hydrocarbons
  2. then the vapour is passed over a hot powdered aluminium oxide catalyst
  3. the long-chain molecules split apart on the surface of the specks of catalyst
73
Q

how do you perform steam cracking?

A

vaporise long-chain hydrocarbons, mix them with steam and then heat them to a very high temperature

74
Q

what is the word equation for cracking?

A

long-chain hydrocarbon molecule -> shorter alkane molecule + alkene

75
Q

how do you balance a chemical equation for cracking?

A

make sure that there is the same number of carbon molecules on both sides

76
Q

what is the general formula for alkenes?

A

CnH2n

77
Q

what are the 4 gases that you need to know tests for?

A
  1. chlorine
  2. oxygen
  3. carbon dioxide
  4. hydrogen
78
Q

what is the test for chlorine?

A

damp litmus paper - chlorine bleaches it

79
Q

what is the test for oxygen?

A

glowing splint - relights

80
Q

what is the test for carbon dioxide?

A

bubbling it through limewater - positive test turns cloudy

81
Q

what is the test for hydrogen?

A

lit splint - squeaky pop

82
Q

what happened in the first phase of earth’s history (according to the most common theory)?

A

volcanoes erupted and gave out gases

83
Q

how do we think the early atmosphere was formed?

A

from volcanoes erupting and releasing lots of gases

84
Q

what was the early atmosphere like?

A

it was probably mostly carbon dioxide, with virtually no oxygen. This is quite like the atmospheres of Mars and Venus today

85
Q

what gases do volcanoes release?

A

mostly nitrogen, but also water vapour and small amounts of methane and ammonia

86
Q

how did nitrogen get in the atmosphere?

A

volcanic activity released nitrogen, which built up in the atmosphere over time

87
Q

according to one theory, what happened in the second phase of Earth’s history?

A

oceans, algae and green plants absorbed carbon dioxide

88
Q

how were the oceans formed? In what phase of the earth’s history did this happen?

A

oceans were formed when the water vapour in the atmosphere condensed, and this happened in the second phase

89
Q

how was carbon dioxide removed from the atmosphere?

A
  1. lots of carbon dioxide was removed from the early atmosphere as it dissolved in the oceans. This dissolved carbon dioxide then went through a series of reactions to form carbonate precipitates that formed sediments on the seabed.
  2. green plants and algae evolved and absorbed some of the carbon dioxide so that they could carry out photosynthesis. Later, marine animals evolved. Their shells and skeletons contained carbonates from the oceans
  3. some of the carbon these organisms took in from the atmosphere and oceans became locked up in rocks and fossil fuels after the organisms died
90
Q

what happens when plants, plankton and marine animals die?

A

they fall to the seabed and get buried by layers of sediment. over millions of years, they become compressed and form sedimentary rocks, oil, and gas - trapping the carbon within them and helping to keep carbon dioxide levels in the atmosphere reduced

91
Q

what is the name for things like coal, crude oil and natural gas that are made when plants, plankton and marine animals die?

A

fossil fuels

92
Q

what are crude oil and natural gas formed from?

A

deposits of plankton

93
Q

what do crude oil and natural gas do when they are trapped in rocks?

A

they form reservoirs under the seabed

94
Q

what is coal?

A

a sedimentary rock made from thick plant deposits

95
Q

what type of rock is limestone?

A

sedimentary

96
Q

what is limestone made of?

A

calcium carbonate deposits from the shells and skeletons of marine organisms

97
Q

according to one theory, what happens in the third phase of the Earth’s history?

A

green plants and algae produce oxygen

98
Q

which plant evolved first? how long ago did it evolve?

A

algae evolved first, about 2.7 billion years ago

99
Q

how did photosynthesis affect the development of life?

A

it caused oxygen levels to build up in the atmosphere over time, so that more complex life (like animals) could evolve

100
Q

how long ago did the atmosphere reach a composition similar to what it is today?

A

about 200 million years ago

101
Q

what is the composition of the atmosphere today?

A

approximately 80% nitrogen, 20% oxygen and small amounts of other gases (each only makes up less than 1% of the atmosphere), mainly carbon dioxide, noble gases and water vapour

102
Q

what allows the earth to be warm enough to support life?

A

greenhouse gases like carbon dioxide, methane and water vapour, which act like an insulating layer in the Earth’s atmosphere

103
Q

what is the greenhouse effect?

A

all particles absorb certain frequencies of radiation. Greenhouse gases don’t absorb the incoming short wavelength radiation from the sun -but the do absorb the long wavelength radiation that gets reflected back off the earth. The longwave radiation is thermal radiation, so it results in warming of the surface of the earth. This is the greenouse effect.

104
Q

name 4 forms of human activity that affect the amount of greenhouse gases in the atmosphere?

A
  1. deforestation
  2. burning fossil fuels
  3. agriculture
  4. creating waste
105
Q

how does deforestation affect the amount of greenhouse gases in the atmosphere?

A

fewer trees means less CO2 is removed from the atmosphere via photosynthesis

106
Q

how does burning fossil fuels affect the amount of greenhouse gases in the atmosphere?

A

carbon that was ‘locked up’ in these fuels is released as CO2

107
Q

how does agriculture affect the amount of greenhouse gases in the atmosphere?

A

more farm animals produce methane through their digestive processes

108
Q

how does creating waste affect the amount of greenhouse gases in the atmosphere?

A

more landfill sites and more waste from agriculture means more CO2 and methane released by decomposition of waste

109
Q

why is it hard to fully understand the Earth’s climate?

A

it’s so complex, and there are so many variables, that it’s very hard to make a model that isn’t oversimplified

110
Q

describe 4 ways climate change could have dangerous consequences

A
  1. an increase in global temperature could lead to polar ice caps melting - causing a rise in sea levels, increased flooding in coastal areas and coastal erosion
  2. changes in rainfall patterns (the amount, timing and distribution) may cause some regions to get too much or too little water. This, along with changes in temperature, may affect the ability of certain regions to produce food
  3. the frequency and severity of storms may also increase
  4. changes in temperature and the amount of water available in a habitat may affect wild species, leading to differences in their distribution
111
Q

what are carbon footprints?

A

a measure of the amount of carbon dioxide and other greenhouse gases released over the full life cycle of something.

112
Q

why can it be really difficult to measure the total carbon footprint of something?

A

there are many different factors to consider - for example, you would have to count the emissions released as a result of sourcing all the parts, and in making it, not to mention the emissions produced when you actually use it and finally dispose of it

113
Q

why can a rough calculation of carbon footprints be useful?

A

it can give a good idea of what the worst emitters are, so that people can avoid them in future

114
Q

describe 5 things that can be done to reduce a carbon footprint

A
  1. renewable energy sources or nuclear energy could be used instead of fossil fuels
  2. using more efficient processes could conserve energy and cut waste. Lots of waste decomposes to release methane, so this will reduce methane emissions
  3. governments could tax companies or individuals based on the amount of greenhouse gases they emit
  4. there’s also technology that captures the CO2 produced by burning fossil fuels before it’s released into the atmosphere - it can then be stored deep underground in cracks in the rock such as old oil wells
115
Q

why is reducing carbon footprints difficult?

A
  1. there’s still a lot of work to be done on alternative technologies that result in lower CO2 emissions
  2. a lot of governments are also worried that making these changes will impact on the economic growth of communities - which could be bad for people’s well-being, especially for countries that are still developing
  3. because not everyone agrees, it’s hard to make international agreements to reduce emissions. Most countries don’t want to sacrifice their economic development if they think that other’s won’t do the same
  4. individuals in developed countries need to make changes to their lifestyle, but it’s hard to get people to make changes if they don’t want to and if there isn’t enough education provided about why the changes are necessary and how to make them
116
Q

why does burning fossil fuels release carbon dioxide and water vapour into the atmosphere?

A

fossil fuels, such as crude oil and coal, contain hydrocarbons. During combustion, the carbon and hydrogen in these compounds are oxidised, which releases carbon dioxide and water vapour

117
Q

what is produced by the incomplete combustion of fossil fuels?

A

during incomplete combustion, some of the fuel doesn’t burn. This means that solid particles (called particulates) or soot (carbon) and unburnt fuel are released and carbon monoxide can be produced as well as carbon dioxide

118
Q

what problems can particulates in the air cause?

A
  • if particulates are inhaled, they can get stuck in the lungs and cause damage. This can then lead to respiratory problems
  • they’re also bad for the environment - particulates and the clouds they help to produce reflect sunlight back into space. This means that less light reaches the earth, causing global dimming
119
Q

what problems are caused by carbon monoxide being released?

A
  • carbon monoxide is really dangerous because it can stop your blood from doing its proper job of carrying oxygen around the body
  • it does this by binding to the haemoglobin in your blood that normally carries O2 - so less oxygen is able to be transported round your body
  • a lack of oxygen in the blood can lead to fainting, a coma or even death
  • carbon monoxide doesn’t have any colour or smell, so it’s very hard to detect. This makes it even more dangerous
120
Q

when is sulfur dioxide (SO2) released?

A

during the combustion of fossil fuels, such as coal, that contain sulfur impurities - the sulfur in the fuel becomes oxidised

121
Q

how are nitrogen oxides created?

A

from a reaction between the nitrogen and oxygen in the air, cause by the heat of the burning (this can happen in the internal combustion engines of cars)

122
Q

what happens when sulfur dioxide and nitrogen oxides mix with clouds?

A

they form dilute sulfuric acid or dilute nitric acid. This then falls as acid rain

123
Q

what effects does acid rain have?

A

it kills plants and damages buildings and statues. It also makes metal corrode.

124
Q

how can sulfur dioxide and nitrogen oxides be bad for human health?

A

they cause respiratory problems if they’re breathed in

125
Q

how can you test for sulfur impurities in a fuel?

A

you bubble the gases from combustion through a solution containing universal indicator - if the fuel contains sulfur, the gases will contain SO2 which will form sulfuric acid and turn the Universal indicator red

126
Q

What is potable water?

A

Water that contains sufficiently low levels of dissolved salts and microbes to be safe to drink

127
Q

What is the difference between pure water and potable water?

A

Pure water only contains H2O molecules, whereas potable water can contain lots of other dissolved substances

128
Q

What three things are necessary for water to be potable?

A
  1. The levels of dissolved salts aren’t too high
  2. It has a pH between 6.5 and 8.5
  3. There isn’t any harmful bacteria or microbes present
129
Q

What is fresh water?

A

Water that doesn’t have much dissolved in it

130
Q

What two things can water be collected as when it rains?

A
  1. Surface water (in lakes, rivers and reservoirs)

2. Groundwater (in rocks called aquifers that trap water underground)

131
Q

In warm areas of the UK, such as the south-east, where does most of the domestic water supply come from and why?

A

Most of the domestic water supply comes from ground water, because surface water tends to dry up first, especially in warm areas

132
Q

Describe the two stages to treating fresh water to make it safe to drink

A
  1. Filtration - a wire mesh screens out large twigs etc, and then gravel and sand beds filter out any other solid bits
  2. Sterilisation - the water is sterilised to kill any harmful bacteria or microbes. This can be done by bubbling chlorine gas through it or by using ozone or ultraviolet light
133
Q

Why are some chemicals added to the water supply? Why is this controversial?

A

Chemicals can be added to the water supply, such as fluoride (which is good for teeth). This is controversial, because people aren’t given any choice over whether they consume them or not

134
Q

What processes can be used to desalinate seawater?

A
  1. Distillation

2. Processes that use membranes - like reverse osmosis

135
Q

Where is seawater used to provide potable water? Why is it used there?

A

In some very dry countries, such as Kuwait, there’s not enough surface or ground water and so instead seawater must be used

136
Q

What are the steps to testing and purifying a seawater sample in the lab?

A
  1. First, test the pH of the water using a pH meter. If the pH is too high or too low, you’ll need to neutralise it. You do this by adding some acid (if the sample’s alkaline) or some alkali (if the samples acidic) until the pH is 7
  2. Set up the equipment so that the seawater is suspended in a round-bottomed flask above a bunsen burner, with a tube running out the top of the flask and through a condenser, before leading into another container
  3. As the water in the flask heats up, it’ll evaporate and enter the condenser as steam
  4. The drop in temperature inside the condenser, due to the cold water around it, will cause the steam to condense back into liquid water
  5. Collect the water running out of the condenser in a beaker
  6. Measure the pH of the water with a pH meter to check it’s neutral
  7. You can tell whether there were salts in your original sample by looking to see whether there are any crystals in the round bottomed flask once the water’s been distilled
137
Q

What happens in reverse osmosis?

A

The salty water is passed through a membrane that only allows water molecules to pass through. Ions and larger molecules are trapped by the membrane so separated from the water

138
Q

Why isn’t it practical to use seawater to produce large quantities of fresh water?

A

Desalination (both distillation and reverse osmosis) need a lot of energy, so they’re really expensive and not very practical

139
Q

what are three things that we use water for in the home?

A

having a bath/shower, flushing the toilet, doing the washing up

140
Q

where does water go when you flush it down the drain?

A

into the sewers and towards sewage treatment plants

141
Q

what are two types of waste water that agricultural systems produce?

A
  1. nutrient run-off from fields

2. slurry from animal farms

142
Q

why does sewage need to be treated?

A

any organic matter and harmful microbes need to be removed before it can be put back into freshwater sources like rivers or lakes, otherwise it would make them very polluted and would pose health risks

143
Q

why does industrial waste water have to undergo additional stages of treatment before it is safe to release it into the environment?

A

it can contain harmful chemicals

144
Q

what are the 6 steps to treating waste water at sewage treatment plants?

A
  1. before being treated the sewage is screened - grit and large bits of material (like twigs or plastic bags) are removed
  2. then it’s allowed to stand in a settlement tank and undergoes sedimentation - the heavier suspended solids sink to the bottom to produce sludge while the lighter effluent floats on the top
  3. the effluent in the settlement tank is removed and treated by biological aerobic digestion. This is when air is pumped through the water to encourage aerobic bacteria to break down any organic matter - including other microbes in the water
  4. the sludge from the bottom of the settlement tank is also removed and transferred into large tanks. Here it gets broken down by bacteria in a process called anaerobic digestion
  5. anaerobic digestion breaks down the organic matter in the sludge, releasing methane gas in the process. The methane gas can be used as an energy resource and the remaining digested waste can be used as a fertiliser
  6. for waste water containing toxic substances, additional stages of treatment may involve adding chemicals (e.g. to precipitate metals), UV radiation or using membranes
145
Q

does sewage treatment require more or less processes than treating fresh water?

A

more

146
Q

does sewage treatment or desalination of salt water use more energy?

A

desalination uses more energy

147
Q

give a reason why sewage treatment might be used instead of the desalination of salt water in areas where there’s not much fresh water?

A

sewage treatment uses a lot less energy, so it’s cheaper

148
Q

name a place that is treating waste water and recycling it back into drinking supplies?

A

Singapore

149
Q

why might people oppose the idea of treating sewage to provide drinking water?

A

people don’t like the idea of drinking water that used to be sewage

150
Q

describe how a reaction reaches equilibrium [2 marks]

A

when a reversible reaction is in a closed system

Chemistry (16 decks)

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