LC CHEMSITRY- WATER

REBECCA'S LC CHEMISTRY WATER QUIZLET

hard water

water that does not form a lather easily with soap

advantages of hard water

• tastes better

• contains calcium for bones and teeth

disadvantages of hard water

• creates scum

• wastes soap

soft water

water that forms a lather easily with soap

metals ions most commonly cause of hardness in water

• Ca²⁺ ions

• Mg²⁺ ions

types of hardness in water

• temporary

• permanent

removal of temporary hardness

boiling

causes of temporary hardness

• Ca(HCO₃)₂

formation of temporary hardness

limestone + carbonic acid = calcium hydrogen carbonate, CaCO3 + H2CO3 = Ca(HCO3)2

lime scale formation chemical equation

when heated, Ca(HCO3)2 calcium carbonate forms insoluble CaCO3 (limescale), water, and CO2; Ca(HCO₃)₂ = CaCO₃ + CO₂+ H₂O

permanent hardness

hardness that cannot be removed by boiling

causes of permanent hardness

CaCl₂

removal of permanent hardness

distillation

distillation

• removes all dissolved substances by evaporation and condensation

• expensive on a large scale

washing soda

removes Ca²⁺ and Mg²⁺ ions by precipitating them as CaCO3

ion exchange resin

removes Ca²⁺ and Mg²⁺ ions exchanged for H⁺ and OH⁻

cation exchange resins in homes

exchange positive ions with Na⁺ ions

replenishment of cation resins

pass concentrated NaCl solution through resin

cation exchange resins in labs

exchange positive ions with H⁺ ions

anion exchange resins in labs

exchange negative ions with OH⁻ ions

distilled water

contains no dissolved solids, liquids, or gases

deionised water

contains some dissolved gases

water treatment definition

the process of purifying water for consumption

stages in water treatment

1. screening

2. flocculation

3. settlement

4. filtration

5. chlorination

6. fluoridation

7. pH adjustment

screening

removes large suspended solids and debris using wire mesh

floccuation

aluminium sulfate added to clump together solids

settlement

suspended solids sink in tanks, 90% removed

filtration

large sand beds remove remaining suspended solids

chlorination

chlorine gas added to kill pathogens

fluoridation

NaF added to reduce dental decay

pH adjustment

if water is too acidic, calcium hydroxide Ca(OH)2 added; if too basic, dilute sulfuric acid H2SO4 added

pollution

any harmful addition to the environment

water pollution

reduces dissolved oxygen levels in water

types of water pollution

eutrophication, organic waste, heavy metals

eutrophication

excess nutrients cause algae growth on water surface

natural eutrophication

gradual increase of phosphates and nitrates in water

artificial eutrophication

runoff of fertilisers causes rapid increase of nutrients

harmful effects of eutrophication

algae blocks light; decay increases bacteria, depleting oxygen, killing fish

organic waste

organic substances from homes, farms, factories broken down by bacteria, using oxygen

harmful effects of organic waste

low oxygen kills fish; H2S produced

heavy metals

metals with high relative atomic masses

examples of heavy metals

• Pb²⁺

• Cd²⁺

• Hg²⁺

harmful effects of heavy metals

minamata disease

test for heavy metals

atomic absorption spectrometry

removal of heavy metals (discharge)

precipitation

example of removal of heavy metals

Pb²⁺ removed as lead II chloride PbCl2 using HCl

sewage treatment

removal of contaminants from wastewater

reason for sewage treatment

high BOD and nitrates/phosphates must be treated before release

stages in sewage treatment

primary (physical), secondary (biological), tertiary (chemical)

primary treatment definition

mechanical removal of solids and suspended solids

process of primary treatment

1. screening removes debris

2. sediment tanks remove solids and 33% BOD

3. sewage moves to secondary treatment

secondary treatment definition

biological removal of suspended solids and organic matter

process of secondary treatment

1. aeration tanks use stirrers to aerate sewage

2. aerobic bacteria decompose solids into activated sludge

3. sludge reused or recycled

4. sewage moves to tertiary treatment

tertiary treatment

chemical removal of phosphates and nitrates

process of tertiary treatment

1. phosphates precipitated as AlPO4 using Al2(SO4)3

2. nitrates converted to N2 gas by denitrifying bacteria

3. treated sewage released into waterways

purpose of adding aluminium sulphate

clumping solids

purpose of adding chlorine

kills pathogens

purpose of adding sodium florosilicate

prevents tooth decay

purpose of adding calcium hydroxide

raises pH

purpose of adding sulfuric acid

lowers pH

anion commonly dissolved in water to Ca²⁺ /Mg²⁺ when temporary hardness is involved

hydrocarbonate

anion commonly dissolved in water to Ca²⁺ /Mg²⁺ when sulfate chloride hardness is involved

sulfate