chemistry of the environment

Question 1

Describe chemical tests for the presence of
water using anhydrous cobalt(II) chloride and
anhydrous copper(II) sulfate

Answer 1

Anhydrous cobalt(II) chloride and anhydrous copper(II) sulfate are used as chemical indicators to test for the presence of water.

When these indicators are dry, they have a particular color. However, in the presence of water, they undergo a chemical reaction and change color.

Anhydrous cobalt(II) chloride: When anhydrous cobalt(II) chloride is dry, it is blue in color. However, in the presence of water, it reacts to form hydrated cobalt(II) chloride, which is pink in color. Therefore, anhydrous cobalt(II) chloride can be used to test for the presence of water by observing whether the blue color changes to pink in the presence of a sample suspected to contain water.

Question 2

Describe chemical tests for the presence of
water using anhydrous copper(II) sulfate

Answer 2

Anhydrous cobalt(II) chloride and anhydrous copper(II) sulfate are used as chemical indicators to test for the presence of water.

When these indicators are dry, they have a particular color. However, in the presence of water, they undergo a chemical reaction and change color.
Anhydrous copper(II) sulfate: When anhydrous copper(II) sulfate is dry, it is white in color. In the presence of water, it reacts to form hydrated copper(II) sulfate, which is blue in color. Therefore, anhydrous copper(II) sulfate can be used to test for the presence of water by observing whether the white powder turns blue in the presence of a sample suspected to contain water.

Question 3

Describe how to test for the purity of water using
melting point and boiling point

Answer 3

Melting point:
a. Take a clean and dry test tube, and fill it up to around 1/3 with the water to be tested.
b. Insert a thermometer into the tube, ensuring that it does not touch the sides or bottom of the tube.
c. Place the test tube in an ice-water bath, and stir the thermometer until the temperature stabilizes.
d. Note the temperature at which the water starts freezing (when ice crystals begin to form).

Question 4

Describe how to test for the purity of water using
boiling point

Answer 4

Boiling point:
a. Take a clean and dry boiling tube, and fill it up to around 1/3 with the water to be tested.
b. Insert a thermometer into the tube, ensuring that it does not touch the bottom of the tube.
c. Heat the water slowly, while stirring the thermometer.
d. Note the temperature at which the water starts boiling (when bubbles form and rise to the surface).

Question 5

How can we know if water is pure or not using mp and bp?

Question 6

Why is distilled water is used in practical
chemistry rather than tap water

Answer 6

Distilled water is used in practical chemistry rather than tap water because it contains fewer chemical impurities.

Tap water is obtained from natural sources such as rivers, lakes, or groundwater, and may contain various chemical impurities such as minerals, organic matter, and other contaminants that can interfere with chemical reactions or affect the accuracy of measurements. Even after treatment by water treatment plants, tap water can still contain some impurities that can affect experimental results.

Distilled water, on the other hand, is produced by boiling water and collecting the steam, which is then condensed to form pure water. This process removes most impurities, including minerals, organic matter, and other contaminants, resulting in water that is free of chemical impurities.

Since distilled water is free of chemical impurities, it is the preferred choice for many chemical experiments as it ensures the accuracy and reproducibility of results.

Question 7

What substances may come from natural sources that water can contain?

Answer 7

dissolved oxygen
metal compounds
plastics
sewage
harmful microbes
nitrates from fertilisers
phosphates from fertilisers and detergents

Question 8

State a substance that may come from natural sources that are in water that can be beneficial

Answer 8

dissolved oxygen
metal compounds

Question 9

why can metal compounds be beneficial

Answer 9

they can provide essential minerals for life

Question 10

why can dissolved oxygen be beneficial for?

Answer 10

aquatic life

Question 11

what are the possible harmful effect of metal compounds?

Answer 11

theyre toxic

Question 12

what are the possible harmful effect of plastics?

Answer 12

harm in aquatic life

Question 13

what are the possible harmful effects of sewage?

Answer 13

contains harmful microbes which
cause disease

Question 14

what are the possible harmful effects of nitrates and phosphates?

Answer 14

nitrates and phosphates lead to
deoxygenation of water and damage to
aquatic life

Question 15

Describe the treatment of the domestic water

Answer 15

(a) Sedimentation and filtration: In this stage, the water is allowed to settle to remove large particles and sediments. The settled water is then passed through a filter bed to remove any remaining suspended solids and impurities. This process removes the majority of impurities, including sand, silt, and other suspended solids.

(b) Use of carbon to remove tastes and odours: After the filtration stage, the water is passed through a bed of activated carbon, which removes any remaining impurities, including organic matter, chlorine, and other chemicals that can affect the taste and odor of the water.

(c) Chlorination to kill microbes: After the carbon filtration stage, the water is treated with chlorine to kill any remaining bacteria, viruses, and other harmful microbes that may be present in the water. Chlorine is an effective disinfectant that kills a wide range of pathogens, and it is commonly used in water treatment to ensure the safety of the water supply.

Overall, the treatment of domestic water supply involves a series of processes that are designed to remove impurities and ensure that the water is safe for human consumption. These processes may vary depending on the quality of the source water and the specific requirements of the water supply system, but they typically involve sedimentation and filtration, carbon treatment, and chlorination to remove impurities, improve taste and odor, and kill harmful pathogens.

Question 16

what compounds are used as fertilizers?

Answer 16

ammonium salts and nitrates

Question 17

Describe the use of NPK fertilisers to provide the
elements nitrogen, phosphorus and potassium
for improved plant growth

Answer 17

NPK fertilizers are a type of fertilizers that contain the essential plant nutrients nitrogen (N), phosphorus (P), and potassium (K). These nutrients are required by plants for healthy growth and development, and deficiencies can result in stunted growth, poor yields, and other problems.

Nitrogen is required for the formation of proteins, nucleic acids, and chlorophyll, which are essential components of plant cells. Phosphorus is required for energy transfer and the formation of DNA and cell membranes, while potassium plays a role in the regulation of water uptake and other important plant processes.

NPK fertilizers are formulated to provide these essential nutrients in the correct proportions for optimal plant growth. The exact formulation of the fertilizer will depend on the specific requirements of the crop and the soil conditions, but a typical NPK fertilizer might contain around 10% nitrogen, 5% phosphorus, and 10% potassium.

The application of NPK fertilizers can help to improve plant growth and yield by providing the essential nutrients that the plants need. However, it is important to use these fertilizers carefully, as over-application can lead to environmental problems such as pollution of waterways and eutrophication.

Overall, the use of NPK fertilizers is an important tool for improving plant growth and ensuring healthy crops, but it must be used judiciously and with careful consideration of the specific needs of the plants and the environmental impacts of fertilizer use

Question 18

State the composition of clean

Answer 18

78% nitrogen, N2, 21% oxygen, O2
and the remainder as a mixture of noble gases
and carbon dioxide, CO2

Question 19

what is the source of CO2?

Answer 19

carbon dioxide from the complete
combustion of carbon-containing fuels

Question 20

what is the source of methane?

Answer 20

methane from the decomposition of
vegetation and waste gases from digestion in
animals

Question 21

what is the source of oxides?

Answer 21

oxides of nitrogen from car engines

Question 22

what is the source of sulfur dioxide?

Answer 22

sulfur dioxide from the combustion of fossil
fuels which contain sulfur compounds

Question 23

what are the adverse effects of CO2?

Answer 23

higher levels of carbon dioxide leading to increased global warming, which leads to climate change

Question 24

what are the adverse effects of carbon monoxide?

Answer 24

toxic gas

Question 25

what are the adverse effects of particulates?

Answer 25

increased risk of respiratory problems and cancer

Question 26

what are the adverse effects of oxides?

Answer 26

acid rain, photochemical
smog and respiratory problems

Question 27

what are the adverse effects of methane?

Answer 27

higher levels of methane leading
to increased global warming, which leads to
climate change

Question 28

what are the adverse effects of sulfur dioxide?

Answer 28

acid rain

Question 29

Describe how the greenhouse gases carbon
dioxide and methane cause global warming

Answer 29

Carbon dioxide (CO2) and methane (CH4) are greenhouse gases that contribute to global warming by trapping heat in the Earth’s atmosphere. They do this by absorbing and re-emitting thermal energy, which is radiated from the Earth’s surface as heat.

When solar radiation enters the Earth’s atmosphere, some of it is absorbed by the Earth’s surface and some is reflected back into space. However, greenhouse gases like CO2 and CH4 absorb and re-emit some of this thermal energy back towards the Earth’s surface, reducing the amount of thermal energy that is lost to space. This leads to an increase in the Earth’s average temperature, known as global warming.

Carbon dioxide is particularly important in this process because it is the most abundant greenhouse gas and has a long atmospheric lifetime. When CO2 is released into the atmosphere through human activities such as burning fossil fuels or deforestation, it can remain in the atmosphere for hundreds of years, continuing to trap heat and contribute to global warming.

Methane, on the other hand, is a much less abundant greenhouse gas but is more effective at trapping heat than CO2. Methane is produced by natural processes such as the decomposition of organic matter in wetlands, as well as by human activities such as agriculture and the production of fossil fuels. While methane has a shorter atmospheric lifetime than CO2, it is estimated to be 28 times more effective at trapping heat over a 100-year timescale.

Overall, the greenhouse gases carbon dioxide and methane contribute to global warming by reducing the amount of thermal energy that is lost to space, leading to an increase in the Earth’s average temperature. The continued release of these gases into the atmosphere through human activities is a major environmental concern with far-reaching consequences

Question 30

State and explain strategies to reduce the effects
of climate change

Answer 30

planting trees, reduction
in livestock farming, decreasing use of
fossil fuels, increasing use of hydrogen and
renewable energy, e.g. wind, solar

Question 31

State and explain strategies to reduce the effects
of acid rain

Answer 31

use of catalytic converters in
vehicles, reducing emissions of sulfur dioxide
by using low-sulfur fuels and flue gas
desulfurisation with calcium oxide

Question 32

Explain how oxides of nitrogen form in car
engines and describe their removal by catalytic
converters, e.g. 2CO + 2NO → 2CO2 + N2

Answer 32

Oxides of nitrogen (NOx) are formed in car engines due to the high temperature combustion of fuel in the presence of oxygen. The two main oxides of nitrogen are nitrogen oxide (NO) and nitrogen dioxide (NO2).

Catalytic converters are devices fitted to cars that convert harmful exhaust gases into less harmful ones before they are released into the atmosphere. One way that catalytic converters can remove NOx is through a process called reduction. The reduction of NOx occurs in two stages:

First, carbon monoxide (CO) and unburned hydrocarbons in the exhaust gases react with oxygen over a catalyst to produce carbon dioxide (CO2) and water (H2O).

The second stage involves the use of a different catalyst that causes a reaction between the remaining NOx in the exhaust gases and the unreacted hydrocarbons. The NOx is reduced to nitrogen gas (N2) and water vapor (H2O) by the hydrocarbons.

The overall reaction can be written as:

2CO + 2NO → 2CO2 + N2

The catalyst used for this process is typically a mixture of platinum and rhodium. The catalytic converter can only function effectively when it is operating at a high temperature, which is why it is located close to the engine where the exhaust gases are still hot.

Question 33

Describe photosynthesis as the reaction itself

Answer 33

reaction between carbon dioxide and water to produce glucose and oxygen in the presence of chlorophyll and using energy from light

Question 34

State the word equation for photosynthesis

Answer 34

carbon dioxide + water → glucose + oxygen

Question 35

State the symbol equation for photosynthesis

Answer 35

6CO2 + 6H2O → C6H12O6 + 6O2