Chapter 7 Flashcards
(19 cards)
What do you know about the occurrence of water
total water present on the earth is about 1.33 billion cubic kilometers which nearly covers 71% of the earth’s crust. Freshwater only 3% of this total, and even that is not distributed. ^9% resides in glaciers, 30% underground and less than 1% is located above ground on lakes, rivers and swamps.
Sea water contains large amounts of dissolved salts. Sodium chloride is the most abundant salt in sea water. It is present up to 3.45% in it. This makes it unfit for human juice.
What is the importance of water?
Water acts as a lubrication for digestion and joints. The water in saliva helps facilitate chewing and swallowing. Water also regulates our body temperature through perspiration.
Water is crucial for sustaining the chemical and physical processes necessary.
It acts as a cooling agent for automobile engines, nuclear power plants, steal mills and heavy industrial machinery.
Means of transportation on earth.
Used to grow crops.
Animals need water to survive.
It is also used to generate electricity.
What are the properties of water?
Colorless, tasteless, and odourless. Boils at 100 C and freezes at 0 C.
Exists in all three states, solid liquid and gas.
Density of most solids generally decreases on heating and increases on cooling. Water, however, shows strange behaviour in this regard. On cooling, it contracts up to 4 C, at which its density becomes maximum. On further cooling, it expands so density decreases. Because of this, ice floats on water. This is very beneficial for life on earth, as it provides an insulating layer for aquatic life.
It has a high heat capacity. A lot of heat is required to raise the temp of 1 g of water by 1 C. Conversely, much heat is given by even a drop. Thus, water on earth acts as a moderator for daily temperature variations.
Water has a high heat of vaporization, so large amounts of heat is required to evaporate even a small amount of water. This is beneficial because large amounts of heat can be evaporated by small amounts of skin precipitation.
How do you split water/ what is electrolysis?
When electricity is passed through acidified water in a voltameter, water decomposes and gives hydrogen and oxygen. This is electrolysis, and hydrogen is produced at the cathode.
2H2O ____ 2H2 + O2
Splitting of water doubles the amount of hydrogen as compared to oxygen. This means hydrogen and oxygen in water are in a ratio of 2:1.
What is hard and soft water?
Water that easily gives lather with soap and does not form scum is called soft water.
Water that gives little lather or forms scum with soap is hard water.
hardness in water can be categorized into two types, temporary and permanent. Temporary hardness can be removed by boiling, while permanent hardness cannot.
Temp h is caused by dissolved calcium or magnesium hydrogen carbonates. Perm h is caused by the dissolved sulphates and chlorides of calcium or magnesium.
explain how hard water hampers the cleaning action of soap
water becomes cloudy due to the formation of a white precipitate by the reaction of Ca^+2 or Mg^+2 ions present in hard water and soap. This scum, which is often left on some fabrics washed in hard waters, which often lives a grey or yellow hue on white fabrics.
To overcome this, detergents are used which do not produce any scum because they do not react with calcium and magnesium ions in hard water. Also detergent molecules are biodegradable, they do not persist in the environment.
How is raw water treated in a municipal plant?
Sedimentation: water stands in a reservoir, which causes the suspended matter to sink at the bottom.
Coagulation; treatment with slaked lime and alum, which form a gelatinous mass of aluminum hydroxide.
Filtration; water is then passed through sand and gravel, sometimes charcoal to remove odorous compounds.
Chlorination; added to kill any remaining bacteria. The chlorine reacts with the water to form hypochlorous acids [HCIO].
How is water treated in a purification plant
in many countries sewage water is treated in the following way before being allowed to flow into any body of water.
Primary treatmnt; water sits in a sedimentation tank.
secndary treatmnt; passed through sand and gravel treatments.
activated sludge treatment; sewage is placed in tanks and aerated with large blowers which cause large porous clumps to form and absorb contaminants, aerobic bacteria further convert the organic material to sludge, which is stored on land or used as fertilizer.
Chlorination; this kills any remaining bacteria
what are some health effects of the biological contamination of water?
Human wasted contain pathogenic microorganisms transmitted through food, water, and direct contact and can cause typhoid fever, dysentery, and hepatitis. Chemical and bacterial contents in livestock waste can pollute both surface and ground water causing these diseases as well Hepatitis is a viral disease also occasionally spreads through water.
Some waterborne diseases are: Cholera, an intestinal disease caused by bacteria such as the vibrio cholerae and E.coli, which are present in water contaminated with human wastes.
Dysentery is also intestinal, caused by the entamoeba parasite, which is transmitted by faecal contamination of water or food by an encysted organism. Patients have mild to severe cramps, dark stool with mucous and sometimes blood,
what is jaundice, typhoid, and hepatitis?
jaundice is an inflammation of the liver, which causes excess bile to enter the bloodstream and cause the yellowness of the skin and eye. Leads to loss of appetite, weakness, and fatigue.
Typhoid is a dangerous intestinal disease spread by polluted water which has bacteria like salmonella paratyphi, salmonella typhi, and salmonellaenteritidis. Characterized by a continuous fever between 101 F to 104 F and an irregular pulse.
Hepatitis is categorised as hepatitis A, B, C, D, and E. A and E are caused by polluted water. It is the acute inflammation of the liver.
write a word and chemical equation to show the effect of heat on magnesium hydrogen carbonate in an aqueous solution
Magnesium hydrogen carbonate —- Magnesium carbonate + carbon dioxide + water
Mg(HCO3)2 —– 2MgCO3 + CO2 + 2H2O
why is it cooler near a lake than inland during summer?
Rate of evaporation increases with temperature during summer, and since evaporation causes cooling, it is cooler near a lake than inland during summer.
Evaluate the option that ion exchange can be used to remove temporary hardness
Ion exchange resins can be used to remove both temp and perm hardness from water through the use of porous solid ion exchangers. The principle of this method is that Ca and Mg ions that can cause hardness are removed from water by exchanging with other cations from ion exchanges which do not cause hardness. By this way, hardness is removed from water
Hard water causes kettle to fur, which can be removed using an acid. Justify.
because the acid reacts with the calcium carbonate in the limescale, and the resultant soluble salts that can be washed away.
evaluate the advantages of waste water treatment
Saves extra water
recycles used water
makes water sources safer to drink from
treated water can be used for vegetation
cost of removal of polluted water is saved
air pollution is limited to the treatment plant
what is eutrophication?
excessive nutrients like nitrogen and phosphorous is called eutrophication. It can give rise to algal blooms which block sunlight and prevent oxygen from getting into the water, creating a dead zone where no organism can survive.
why is water a universal solvent?
It dissolves more substances than any other due to its polarity of its molecules. This polarity is due to the electronegativity between oxygen and hydrogen atoms.
The hydrogen side carries a slight positive charge while oxygen carries a slight negative charges. This helps water molecules dissociate ionic compounds into positive and negative ions. This way, the positive parts of a substance are attracted to oxygen and the negative parts are attracted to hydrogen. For example, NaCl has positive charged sodium and negatively charged chlorine which are ionic bonds. Although ionic bonds are stronger, the polarity of all water molecules is strong enough to pull the NaCl atoms apart, which, when done, evenly distributes the salt, forming an homogenous solution.
what is capillary action?
Process by which water rises up from the roots to the plant leaves.
two methods to remove permanent water hardness
washing soda
sodium zeolite (ion exchange method)
