An aquifer is a rock that stores water underground.

True or False? Water from natural sources such as rivers and lakes is always clean and safe to drink.

False. Water from natural sources can contain pollutants such as harmful microbes, nitrates from fertilisers and dissolved metal ions, and must be treated before drinking.

State two domestic uses of water.

Two domestic uses of water are drinking and cooking (also accept gardening and general sanitation).

Dissolved carbon dioxide from rainwater .......... the pH of water because it makes the water slightly ......... .

Dissolved carbon dioxide from rainwater lowers the pH of water because it makes the water slightly acidic .

Give two examples of man-made pollutants found in water sources.

Two examples of man-made pollutants are fertilisers (e.g. nitrates and phosphates) and pesticides (also accept household and industrial waste).

What is a pollutant in the context of water?

A pollutant is a substance found in water that is harmful or undesirable. Pollutants can be natural (e.g. bacteria) or man-made (e.g. fertilisers and pesticides).

True or False? Metal ions such as Ca 2+ and Mg 2+ can be found dissolved in natural water sources.

True. Metal ions including Ca 2+ , Mg 2+ , K + and Na + dissolve into water when it flows over rocks, and are examples of naturally occurring substances in water.

Water has three main categories of use: .......... uses (drinking and cooking), .......... uses (watering crops) and .......... uses (as a solvent or coolant).

Water has three main categories of use: domestic uses (drinking and cooking), agricultural uses (watering crops) and industrial uses (as a solvent or coolant).

Why are nitrates and phosphates from fertilisers considered water pollutants?

Nitrates and phosphates are man-made pollutants because they enter water sources through runoff from farmland and can be harmful to aquatic life and human health.

What does it mean to abstract water?

Abstracting water means obtaining it from natural sources such as rivers, lakes, reservoirs or underground aquifers.

Give two reasons why the global demand for water has increased over the last 100 years.

The global demand for water has increased because of a growing population and greater use of water in agriculture and industry .

True or False? Climate change could lead to water shortages in the UK.

True. Climate change could disrupt rainfall patterns and reduce fresh water availability, leading to water shortages and higher water costs in the UK.

Water is distributed through .......... to areas that need it for drinking, growing crops and .......... .

Water is distributed through pipes to areas that need it for drinking, growing crops and sanitation .

State three ways that people can reduce their personal water consumption.

Three ways people can reduce water consumption are: Taking showers instead of baths Turning off taps when not in use Watering plants with leftover bath or sink water

What is meant by a sustainable water supply?

A sustainable water supply is one that meets current water needs without depleting water sources or damaging the environment for future generations.

True or False? Building dams and reservoirs to abstract water always has a positive environmental impact.

False. Dams and reservoirs can flood land and destroy habitats, which is why ensuring a sustainable water supply requires careful consideration of environmental impacts.

Four methods of abstracting water include collecting .......... , building dams and .......... , collecting water from rivers and lakes and pumping water from .......... .

Four methods of abstracting water include collecting rainwater , building dams and reservoirs , collecting water from rivers and lakes and pumping water from underground .

Why is it important to ensure water distribution is sustainable?

Sustainable distribution is important because pipes are expensive and visually unsightly, and treatment plants containing sewage can smell and pose a hazard to human health.

What are the three stages of treating water for drinking?

The three stages of treating water are: Sedimentation Filtration Chlorination

What is sedimentation in water treatment?

Sedimentation is the process where water is allowed to stand in tanks so that mud, sand and other solid particles sink to the bottom due to gravity.

During filtration, water is passed through layers of .......... and .......... which trap small .......... particles.

During filtration, water is passed through layers of sand and gravel which trap small solid particles.

True or False? Sand and gravel filters are sufficient to remove bacteria and microorganisms from water.

False. Bacteria and microorganisms are too small to be trapped by sand and gravel filters. Chlorination is used to kill these microorganisms.

What is chlorination ?

Chlorination is the careful addition of chlorine to treated water to kill bacteria and other microorganisms.

Why is chlorination necessary in water treatment?

Chlorination is necessary because bacteria are too small to be removed by filtration. Chlorine kills harmful microorganisms and prevents bacterial diseases such as cholera and typhoid.

Give one example of a soluble impurity and one example of an insoluble impurity found in untreated water.

An example of an insoluble impurity is soil or plant matter. An example of a soluble impurity is dissolved calcium compounds or inorganic pollutants.

True or False? Sedimentation removes both soluble and insoluble impurities from water.

False. Sedimentation only removes insoluble particles that settle to the bottom due to gravity. Soluble impurities remain in the water at this stage.

Drinking untreated water can lead to bacterial diseases such as .......... and .......... .

Drinking untreated water can lead to bacterial diseases such as cholera and typhoid .

What is fluoridation of water?

Fluoridation is the process of adding fluoride ions to drinking water, primarily to reduce tooth decay in the population.

State two ways in which fluoride helps prevent tooth decay.

Fluoride helps prevent tooth decay by: Increasing the rate of remineralisation (replacement of minerals in enamel) Reducing the ability of bacteria to produce acid

Tooth decay occurs when the .......... on teeth reacts with acid and dissolves. This process is called .......... . The reverse process is called .......... .

Tooth decay occurs when the enamel on teeth reacts with acid and dissolves. This process is called demineralisation . The reverse process is called remineralisation .

Fluorosis is a condition caused by excessive fluoride intake, characterised by the formation of white patches on tooth enamel.

True or False? Adding fluoride to water is considered by some people to be a form of mass medication.

True. Mass medication means giving medication to everyone regardless of whether they need it. Some people argue fluoridating water is unethical because individuals have not given their consent .

Give two disadvantages of adding fluoride to drinking water.

Two disadvantages of adding fluoride to drinking water are: High fluoride levels can be toxic and have been linked to stomach cancer and infertility It can cause fluorosis in children exposed to too much fluoride

Fluoride is added to drinking water primarily to prevent tooth decay.

True. This is true because fluoride helps prevent tooth decay by increasing the rate of remineralisation , reducing the ability of bacteria to produce acid, and altering the structure of tooth enamel in young children to make it more resistant to acid attack.

Fluoride ions are found naturally in water in some areas and in most .......... , so some people argue adding fluoride to water is .......... .

Fluoride ions are found naturally in water in some areas and in most toothpastes , so some people argue adding fluoride to water is unnecessary .

Give two advantages of adding fluoride to drinking water.

Two advantages of adding fluoride to drinking water are: It helps prevent tooth decay and protect enamel from demineralisation It alters the structure of enamel in young children making it resistant to acid attack

What is desalination ?

Desalination is the removal of salt from seawater to produce fresh water suitable for drinking.

State two methods used in desalination.

Two methods used in desalination are distillation and reverse osmosis .

In reverse osmosis, salt water is pushed through a .......... membrane at high .......... , so only .......... molecules can pass through.

In reverse osmosis, salt water is pushed through a semi-permeable membrane at high pressure , so only water molecules can pass through.

True or False? Desalination is a cheap and energy-efficient way to produce drinking water.

False. Desalination is an expensive process because it consumes large amounts of energy . This also means it produces more greenhouse gases than traditional water treatment methods.

Why is desalination particularly useful in countries such as Saudi Arabia?

Desalination is useful in countries such as Saudi Arabia because they have limited fresh water sources such as rivers and streams and little rainfall , but have access to a coastline and seawater.

What is reverse osmosis ?

Reverse osmosis is a desalination process where salt water is forced through a semi-permeable membrane at high pressure. The membrane allows water molecules through but blocks larger ions and molecules.

Reverse osmosis removes salt from seawater by forcing it through a semi-permeable membrane at high pressure.

True. This is true because the semi-permeable membrane only allows water molecules to pass through, because it blocks larger molecules and ions such as salt, producing fresh water from seawater.

The salty water left behind after desalination is a .......... and must be disposed of .......... to avoid harming the environment.

The salty water left behind after desalination is a pollutant and must be disposed of carefully to avoid harming the environment.

Give two reasons why desalination is not available to poorer countries.

Desalination is not available to poorer countries because it is an expensive process requiring large amounts of energy. The cost of building and maintaining desalination plants is also very high.

What are miscible liquids?

Miscible liquids are liquids that are fully mixed together and do not form separate layers. They can be separated by distillation if they have different boiling points .

Describe the process of distillation of salt water.

The salt water is heated so the water boils and produces vapour. The vapour rises and passes through a condenser where it cools and condenses into pure liquid water collected in a beaker. The salt remains behind in the flask.

During distillation, the water vapour passes through a .......... where it .......... and turns back into liquid water that is collected in a .......... .

During distillation, the water vapour passes through a condenser where it condenses and turns back into liquid water that is collected in a beaker .

True or False? Distillation can be used to separate two miscible liquids with different boiling points.

True. Distillation works because the liquid with the lower boiling point evaporates first. For example, ethanol (lower boiling point) separates from water when the mixture is heated.

Why is distillation an expensive method of producing pure water from salt water?

Distillation is expensive because it requires a large amount of energy to heat the salt water and maintain the process, making it costly at a large scale.

During distillation of saltwater, the water vapour is collected and condensed to give pure water.

True. This is true because when the salt water is heated , only the water boils and evaporates, because the salt remains behind in the flask. The water vapour passes through the condenser where it cools, condenses, and is collected as pure water.

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Water (WJEC GCSE Science (Double Award): Chemistry): Flashcards

Exam code: 3430

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FrontComposition of Water
What is an aquifer?

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Cards in this collection (98)

What is an aquifer?
An aquifer is a rock that stores water underground.
True or False?
Water from natural sources such as rivers and lakes is always clean and safe to drink.
False.
Water from natural sources can contain pollutants such as harmful microbes, nitrates from fertilisers and dissolved metal ions, and must be treated before drinking.
State two domestic uses of water.
Two domestic uses of water are drinking and cooking (also accept gardening and general sanitation).
Dissolved carbon dioxide from rainwater .......... the pH of water because it makes the water slightly ..........
Dissolved carbon dioxide from rainwater lowers the pH of water because it makes the water slightly acidic.
Give two examples of man-made pollutants found in water sources.
Two examples of man-made pollutants are fertilisers (e.g. nitrates and phosphates) and pesticides (also accept household and industrial waste).
What is a pollutant in the context of water?
A pollutant is a substance found in water that is harmful or undesirable. Pollutants can be natural (e.g. bacteria) or man-made (e.g. fertilisers and pesticides).
True or False?
Metal ions such as Ca²⁺ and Mg²⁺ can be found dissolved in natural water sources.
True.
Metal ions including Ca²⁺, Mg²⁺, K⁺ and Na⁺ dissolve into water when it flows over rocks, and are examples of naturally occurring substances in water.
Water has three main categories of use: .......... uses (drinking and cooking), .......... uses (watering crops) and .......... uses (as a solvent or coolant).
Water has three main categories of use: domestic uses (drinking and cooking), agricultural uses (watering crops) and industrial uses (as a solvent or coolant).
Why are nitrates and phosphates from fertilisers considered water pollutants?
Nitrates and phosphates are man-made pollutants because they enter water sources through runoff from farmland and can be harmful to aquatic life and human health.
What does it mean to abstract water?
Abstracting water means obtaining it from natural sources such as rivers, lakes, reservoirs or underground aquifers.
Give two reasons why the global demand for water has increased over the last 100 years.
The global demand for water has increased because of a growing population and greater use of water in agriculture and industry.
True or False?
Climate change could lead to water shortages in the UK.
True.
Climate change could disrupt rainfall patterns and reduce fresh water availability, leading to water shortages and higher water costs in the UK.
Water is distributed through .......... to areas that need it for drinking, growing crops and .......... .
Water is distributed through pipes to areas that need it for drinking, growing crops and sanitation.
State three ways that people can reduce their personal water consumption.
Three ways people can reduce water consumption are:
1. Taking showers instead of baths
2. Turning off taps when not in use
3. Watering plants with leftover bath or sink water
What is meant by a sustainable water supply?
A sustainable water supply is one that meets current water needs without depleting water sources or damaging the environment for future generations.
True or False?
Building dams and reservoirs to abstract water always has a positive environmental impact.
False.
Dams and reservoirs can flood land and destroy habitats, which is why ensuring a sustainable water supply requires careful consideration of environmental impacts.
Four methods of abstracting water include collecting .........., building dams and .........., collecting water from rivers and lakes and pumping water from .......... .
Four methods of abstracting water include collecting rainwater, building dams and reservoirs, collecting water from rivers and lakes and pumping water from underground.
Why is it important to ensure water distribution is sustainable?
Sustainable distribution is important because pipes are expensive and visually unsightly, and treatment plants containing sewage can smell and pose a hazard to human health.
What are the three stages of treating water for drinking?
The three stages of treating water are:
1. Sedimentation
2. Filtration
3. Chlorination
What is sedimentation in water treatment?
Sedimentation is the process where water is allowed to stand in tanks so that mud, sand and other solid particles sink to the bottom due to gravity.
During filtration, water is passed through layers of .......... and .......... which trap small .......... particles.
During filtration, water is passed through layers of sand and gravel which trap small solid particles.
True or False?
Sand and gravel filters are sufficient to remove bacteria and microorganisms from water.
False.
Bacteria and microorganisms are too small to be trapped by sand and gravel filters. Chlorination is used to kill these microorganisms.
What is chlorination?
Chlorination is the careful addition of chlorine to treated water to kill bacteria and other microorganisms.
Why is chlorination necessary in water treatment?
Chlorination is necessary because bacteria are too small to be removed by filtration. Chlorine kills harmful microorganisms and prevents bacterial diseases such as cholera and typhoid.
Give one example of a soluble impurity and one example of an insoluble impurity found in untreated water.
An example of an insoluble impurity is soil or plant matter. An example of a soluble impurity is dissolved calcium compounds or inorganic pollutants.
True or False?
Sedimentation removes both soluble and insoluble impurities from water.
False.
Sedimentation only removes insoluble particles that settle to the bottom due to gravity. Soluble impurities remain in the water at this stage.
Drinking untreated water can lead to bacterial diseases such as .......... and .......... .
Drinking untreated water can lead to bacterial diseases such as cholera and typhoid.
What is fluoridation of water?
Fluoridation is the process of adding fluoride ions to drinking water, primarily to reduce tooth decay in the population.
State two ways in which fluoride helps prevent tooth decay.
Fluoride helps prevent tooth decay by:
1. Increasing the rate of remineralisation (replacement of minerals in enamel)
2. Reducing the ability of bacteria to produce acid
Tooth decay occurs when the .......... on teeth reacts with acid and dissolves. This process is called ........... The reverse process is called .......... .
Tooth decay occurs when the enamel on teeth reacts with acid and dissolves. This process is called demineralisation. The reverse process is called remineralisation.
What is fluorosis?
Fluorosis is a condition caused by excessive fluoride intake, characterised by the formation of white patches on tooth enamel.
True or False?
Adding fluoride to water is considered by some people to be a form of mass medication.
True.
Mass medication means giving medication to everyone regardless of whether they need it. Some people argue fluoridating water is unethical because individuals have not given their consent.
Give two disadvantages of adding fluoride to drinking water.
Two disadvantages of adding fluoride to drinking water are:
1. High fluoride levels can be toxic and have been linked to stomach cancer and infertility
2. It can cause fluorosis in children exposed to too much fluoride
Fluoride is added to drinking water primarily to prevent tooth decay.
True.
This is true because fluoride helps prevent tooth decay by increasing the rate of remineralisation, reducing the ability of bacteria to produce acid, and altering the structure of tooth enamel in young children to make it more resistant to acid attack.
Fluoride ions are found naturally in water in some areas and in most .........., so some people argue adding fluoride to water is .......... .
Fluoride ions are found naturally in water in some areas and in most toothpastes, so some people argue adding fluoride to water is unnecessary.
Give two advantages of adding fluoride to drinking water.
Two advantages of adding fluoride to drinking water are:
1. It helps prevent tooth decay and protect enamel from demineralisation
2. It alters the structure of enamel in young children making it resistant to acid attack
What is desalination?
Desalination is the removal of salt from seawater to produce fresh water suitable for drinking.
State two methods used in desalination.
Two methods used in desalination are distillation and reverse osmosis.
In reverse osmosis, salt water is pushed through a .......... membrane at high .........., so only .......... molecules can pass through.
In reverse osmosis, salt water is pushed through a semi-permeable membrane at high pressure, so only water molecules can pass through.
True or False?
Desalination is a cheap and energy-efficient way to produce drinking water.
False.
Desalination is an expensive process because it consumes large amounts of energy. This also means it produces more greenhouse gases than traditional water treatment methods.
Why is desalination particularly useful in countries such as Saudi Arabia?
Desalination is useful in countries such as Saudi Arabia because they have limited fresh water sources such as rivers and streams and little rainfall, but have access to a coastline and seawater.
What is reverse osmosis?
Reverse osmosis is a desalination process where salt water is forced through a semi-permeable membrane at high pressure. The membrane allows water molecules through but blocks larger ions and molecules.
Reverse osmosis removes salt from seawater by forcing it through a semi-permeable membrane at high pressure.
True.
This is true because the semi-permeable membrane only allows water molecules to pass through, because it blocks larger molecules and ions such as salt, producing fresh water from seawater.
The salty water left behind after desalination is a .......... and must be disposed of .......... to avoid harming the environment.
The salty water left behind after desalination is a pollutant and must be disposed of carefully to avoid harming the environment.
Give two reasons why desalination is not available to poorer countries.
Desalination is not available to poorer countries because it is an expensive process requiring large amounts of energy. The cost of building and maintaining desalination plants is also very high.
What are miscible liquids?
Miscible liquids are liquids that are fully mixed together and do not form separate layers. They can be separated by distillation if they have different boiling points.
Describe the process of distillation of salt water.
The salt water is heated so the water boils and produces vapour. The vapour rises and passes through a condenser where it cools and condenses into pure liquid water collected in a beaker. The salt remains behind in the flask.
During distillation, the water vapour passes through a .......... where it .......... and turns back into liquid water that is collected in a .......... .
During distillation, the water vapour passes through a condenser where it condenses and turns back into liquid water that is collected in a beaker.
True or False?
Distillation can be used to separate two miscible liquids with different boiling points.
True.
Distillation works because the liquid with the lower boiling point evaporates first. For example, ethanol (lower boiling point) separates from water when the mixture is heated.
Why is distillation an expensive method of producing pure water from salt water?
Distillation is expensive because it requires a large amount of energy to heat the salt water and maintain the process, making it costly at a large scale.
During distillation of saltwater, the water vapour is collected and condensed to give pure water.
True.
This is true because when the salt water is heated, only the water boils and evaporates, because the salt remains behind in the flask. The water vapour passes through the condenser where it cools, condenses, and is collected as pure water.
When ethanol and water are distilled, the .......... evaporates first because it has a .......... boiling point than water.
When ethanol and water are distilled, the ethanol evaporates first because it has a lower boiling point than water.
What happens to the salt when salt water is distilled?
The salt remains behind in the flask as a solid because only the water evaporates. After all the liquid has evaporated, only the solid solute is left in the flask.
What is solubility?
Solubility is a measure of how much of a substance (the solute) will dissolve in a given volume of liquid (the solvent). It is expressed in g per 100 g of solvent.
What is a saturated solution?
A saturated solution is one in which no more solute can dissolve at a given temperature. Adding more solute will leave undissolved solid at the bottom.
In a solution, the dissolved substance is the .........., the liquid it dissolves in is the .........., and the mixture formed is the .......... .
In a solution, the dissolved substance is the solute, the liquid it dissolves in is the solvent, and the mixture formed is the solution.
True or False?
As temperature increases, the solubility of most solid solutes in water also increases.
True.
As temperature increases, most solids become more soluble in water. This is shown on a solubility curve as an upward slope from left to right.
What does a solubility curve show?
A solubility curve shows how the maximum amount of solute (in g per 100 g of water) that can dissolve changes with temperature. Solubility is on the y-axis and temperature is on the x-axis.
Describe how you would determine the solubility of a solid at room temperature in the laboratory.
Add small amounts of solute to a known volume of water until no more dissolves. Filter the mixture to remove undissolved solid. Evaporate the solvent from the filtrate and weigh the remaining solute to calculate solubility.
When investigating solubility at different temperatures, the temperature at which .......... first appear when the solution is cooled is recorded as the solubility .......... at that temperature.
When investigating solubility at different temperatures, the temperature at which crystals first appear when the solution is cooled is recorded as the solubility point at that temperature.
As temperature increases, the solubility of most solids increases.
True.
This is true because solubility curves show that most solids dissolve more readily at higher temperatures, because more solute can dissolve in a given volume of solvent before the solution becomes saturated.
What is the unit used to express solubility?
Solubility is expressed in g per 100 g of solvent (for example, g per 100 g of water at a given temperature).
What is hard water?
Hard water is water that contains dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions. These ions dissolve when water flows over rocks such as limestone.
True or False?
Hard water forms a lather with soap more easily than soft water.
False.
Hard water is more difficult to lather because the calcium and magnesium ions react with soap to form scum instead of a lather.
Temporary hardness in water is caused by dissolved .......... and can be removed by .......... the water.
Temporary hardness in water is caused by dissolved calcium hydrogencarbonate and can be removed by boiling the water.
What is permanent hard water?
Permanent hard water is water whose hardness cannot be removed by boiling. It is caused by dissolved calcium sulfate (CaSO₄) which does not decompose on heating.
What is scum and how does it form?
Scum is an insoluble solid that forms when the calcium and magnesium ions in hard water react with soap. It wastes soap and leaves an unsightly residue.
Boiling temporary hard water causes the dissolved calcium hydrogencarbonate to .........., forming insoluble .......... which settles as scale.
Boiling temporary hard water causes the dissolved calcium hydrogencarbonate to decompose, forming insoluble calcium carbonate which settles as scale.
Hard water lathers easily with soap.
False.
Hard water does not lather easily with soap because the dissolved calcium (Ca²⁺) and magnesium (Mg²⁺) ions react with soap to form scum, which means more soap is needed to produce a lather compared with soft water.
How can you determine the relative hardness of different water samples?
Hardness is determined by measuring the volume of soap solution needed to produce a permanent lather. The more soap required, the harder the water sample.
Explain why scale forms inside a kettle when temporary hard water is boiled.
When temporary hard water is boiled, the calcium hydrogencarbonate decomposes to form insoluble calcium carbonate (scale) which deposits on the heating element. This scale reduces heating efficiency.
How can permanent hardness be removed from water?
Permanent hardness cannot be removed by boiling. It is removed by ion exchange (passing water through a resin that replaces Ca²⁺ and Mg²⁺ ions with Na⁺ ions) or by adding sodium carbonate (washing soda), which precipitates the calcium and magnesium ions as insoluble carbonates.
State three methods used to soften hard water.
Three methods used to soften hard water are:
1. Boiling
2. Adding washing soda (sodium carbonate)
3. Using an ion-exchange column
What is washing soda and how does it soften hard water?
Washing soda is sodium carbonate (Na₂CO₃). It softens water by reacting with calcium and magnesium ions to form insoluble carbonates that precipitate out.
An ion-exchange column softens water by exchanging .......... and .......... ions in the water for .......... ions from the resin.
An ion-exchange column softens water by exchanging calcium and magnesium ions in the water for sodium ions from the resin.
True or False?
Boiling can remove both temporary and permanent hardness from water.
False.
Boiling only removes temporary hardness because it decomposes calcium hydrogencarbonate. It does not remove permanent hardness caused by calcium sulfate.
(Higher Tier Only) Write a word equation to show what happens when washing soda reacts with calcium ions in hard water.
(Higher Tier Only) The carbonate ions in washing soda react with calcium ions to form an insoluble precipitate:
carbonate ions + calcium ions → calcium carbonate
CO₃^2- (aq) + Ca²⁺ (aq) → CaCO₃ (s)
An ion-exchange column softens water by replacing calcium and magnesium ions with sodium ions.
True.
This is true because the column contains a resin packed with sodium ions, and as hard water passes through, the Ca²⁺ and Mg²⁺ ions are exchanged for sodium ions, because these are the ions that cause hardness. The resin is recharged by flushing with concentrated sodium chloride solution.
Ion-exchange columns are recharged by flushing with concentrated .......... solution, which replaces the .......... and .......... ions with sodium ions.
Ion-exchange columns are recharged by flushing with concentrated sodium chloride solution, which replaces the calcium and magnesium ions with sodium ions.
Give one advantage and one disadvantage of using an ion-exchange column to soften water.
Advantage: it is a continuous process that removes both temporary and permanent hardness.
Disadvantage: the ion-exchange resin is expensive.
Why is it important to use soft water in some industrial processes?
Soft water is important in industry because the calcium and magnesium ions in hard water can interfere with chemical reactions and processes, reducing efficiency.
State two health benefits of drinking hard water.
Two health benefits of drinking hard water are:
1. The calcium compounds help to strengthen teeth and bones
2. They help prevent heart and cardiovascular disease
True or False?
Hard water forms scale inside kettles which makes them more energy efficient.
False.
Scale inside kettles slows down the rate of heat transfer, making the kettle less efficient and causing it to use more energy.
Hard water is more difficult to use for washing because it reacts with soap to form .......... rather than a lather. This means more .......... is wasted.
Hard water is more difficult to use for washing because it reacts with soap to form scum rather than a lather. This means more soap is wasted.
What is scale in the context of hard water?
Scale (also called limescale) is an insoluble solid deposit of calcium carbonate that forms inside appliances such as kettles and pipes when hard water is heated. It reduces heating efficiency.
True or False?
Some brewers prefer to use hard water when brewing beer.
True.
Some brewers prefer hard water because the dissolved mineral ions can improve the flavour of certain beers. Some people also prefer the taste of hard water for drinking.
Explain why scale forming in hot water pipes is a serious problem.
Scale forming in hot water pipes can cause them to become gradually blocked, eventually stopping the flow of water. This can be very expensive to repair.
The calcium compounds in hard water help to strengthen .......... and .......... and may help prevent .......... disease.
The calcium compounds in hard water help to strengthen teeth and bones and may help prevent cardiovascular disease.
Give two disadvantages of hard water related to its reaction with soap.
Two disadvantages of hard water related to soap are:
1. It is harder to form a lather, meaning more soap is needed and costs increase
2. It forms scum with soap, which has an unsightly appearance
What substance is used to compare the hardness of water samples in the laboratory?
Soap solution is used to compare the hardness of water samples. The harder the water, the more soap solution is needed to produce a permanent lather.
In the hardness investigation, soap solution is added .......... cm³ at a time and the flask is .......... for 5 seconds after each addition until a lather forms and lasts for .......... seconds.
In the hardness investigation, soap solution is added 1 cm³ at a time and the flask is shaken for 5 seconds after each addition until a lather forms and lasts for 30 seconds.
What is temporary hard water and how is it identified in this practical?
Temporary hard water is water whose hardness can be removed by boiling. In this practical, it is identified because the volume of soap solution needed to form a lather decreases after boiling.
True or False?
If the volume of soap solution needed to form a lather remains the same before and after boiling, the water sample is soft water.
False.
If the volume of soap solution remains unchanged after boiling but is high, the water has permanent hardness. Soft water requires only a small volume of soap to form a lather.
What apparatus is needed for the hardness investigation?
The apparatus needed includes a conical flask and stopper, a dropping pipette, a measuring cylinder, a stopwatch and soap solution.
A water sample is permanent hard water if it requires a large volume of soap solution to form a lather .......... boiling and the volume of soap required does .......... decrease after boiling.
A water sample is permanent hard water if it requires a large volume of soap solution to form a lather before boiling and the volume of soap required does not decrease after boiling.
Why is it important to use 50 cm³ of each water sample when comparing hardness?
Using the same volume (50 cm³) of each water sample makes the test fair (a controlled variable), so the volume of soap needed can be compared directly between samples.
True or False?
A sample of soft water will require a small volume of soap solution to form a permanent lather both before and after boiling.
True.
Soft water contains few calcium and magnesium ions, so very little soap is used up forming scum. A small volume of soap is enough to form a lather both before and after boiling.
How would you present the results from the hardness practical in graphical form?
The results should be presented as a bar chart showing the volume of soap solution (y-axis) against each water sample (x-axis) for both the unboiled and boiled versions of each sample.

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