Topic 12D Chemical Reactions
Updated 2008-08-19 R
Please send comments to: J.Elfick@uq.edu.au
See also: Interesting websites
Table of contents
12.12.0 Soaps and synthetic detergents, syndets
12.13.0 Hardness in water
12.12.0 Soaps and synthetic detergents (syndets)
3.79 Prepare soap from fats
12.12.01 Prepare soap by neutralization
12.12.02 Prepare soap by saponification
12.12.03 Surfactants
12.12.04 Detergents
12.12.07 Laundry detergents
12.12.08 Machine dishwashing detergents
12.12.09 Scouring powders
12.12.10 Drain cleaners
12.12.11 Bleaches, disinfectants, deodorizers
12.12.1 Prepare soap with animal fats
12.12.2 Prepare soap with vegetable oils
12.12.3 Tests for glycerol
12.13.9 Prepare an alcohol-based detergent
12.12.03 Surfactants
12.12.03.1a Ionic surfactants
12.12.03.2a Inorganic builders
12.12.03.2b Organic builders
12.12.03.3a Fluorescent whitening agents,optical bleaches, optical whites, fluorescers, "washing blue"
12.12.03.3b Foaming agents
12.12.03.4 Bleaches, sodium perborate bleach
12.12.03.5 Fillers
12.12.03.6 Enzymes
12.13.0 Hardness in water
12.13.0.1 Temporary hardness and permanent hardness
12.13.0.2 Remove hardness
12.13.0.3 Water hardness test
18.2.5 Salinity
12.13.1 Test water to form lather
12.13.2 Prepare hard water
12.13.3 Wash with hard water
12.13.4 Test different waters for hardness
12.13.5 Test hard water to form a lather
12.13.6 Soften hard water by boiling
12.13.7 Soften hard water with chemicals
12.13.8 Use detergents instead of soap solution
12.13.10 Tests for hardness in water with standard soap solution
12.13.11 Tests for metal ions in water, EDTA, chelates
12.12.0 Soaps and synthetic detergents (syndets)
See 16.5.4: Hydrolysis of an ester
Saponification is the process where fats are broken up by sodium hydroxide to form soaps and glycerol (glycerine, propane-1,2,3-triol). Soaps are the alkaline salts of fatty acids. Most soaps are a mixture of sodium stearate and sodium palmitate. Palmitic acid (C15H31.COOH) is found in vegetable oils. Octadecanoic acid, stearic acid [CH3(CH2)16.COOH] is found in mutton fat. Cis octadec-9-enoic acid (oleic acid, red oil, C17H33.COOH, cis-9-octadecanoic acid) occurs as glycerine ester of fats and oils and oxidizes on exposure to air and turns rancid yellow colour. Soft soaps are made from potassium salts and hard soaps are made from sodium salts. Metallic soaps are compounds of fatty acids with metal bases and used for waterproofing. Resin soaps are alkali salts of resins. Soap is not soluble in salt water. Soap dissolves in water to form sodium ions and stearate ions containing along chain of carbon atoms with a negatively charged group at one end that attracts water molecules. The other ends of the long carbon chains do not attract water molecules but can mix with non-polar compounds, e.g. oils and grease, and surround small oil droplets to be carried away in the wash. Dirt particles suspended in the grease and oil are also washed away. The small oil droplets become negatively charges, repel each other and so remain suspended in the washing water.
Sodium stearate is a salt of a weak acid so it produces slightly alkaline solutions, harmful to certain fabrics, when dissolved in water.
R(C=O)O- Na+ + H-OH <--> R(C=O)-OH + Na+OH-
In acid solutions, sodium stearate forms insoluble stearic acid and forms insoluble salts with Ca2+, Mg2+ and Fe3+ that precipitate as a "bath scum" and dark ring around shirt collars.
C17H35(C=O)O-Na+ + H+Cl- --> C17H35(C=O)OH + Na+Cl-
sodium stearate [soluble] + HCl --> stearic acid [insoluble] + NaCl
C17H35(C=O)O-Na+ + Ca2+ --> (C17H35COO-)2Ca2+ + 2Na+
sodium stearate [soluble] + Ca2+ --> calcium stearate [insoluble] + 2Na+
Anionic detergents
The first anionic detergents were sodium salts of alkyl hydrogen sulfates
1. 3[CH3(CH2)10(C=O)OCH2] + 6H2 --> 3CH2(CH2)10CH2OH + HOCH2-HOCH-HOCH2
Glycerol trilaurate reduced to 1-dodecanol (lauryl alcohol) + glycerol
2. CH2(CH2)10CH2OH + HOSO2OH --> CH2(CH2)10CH2O(SO2)OH + H2O
1-dodecanol + sulfuric acid --> alkyl hydrogen sulfate + water
3. CH2(CH2)10CH2OSO2OH + NaOH --> CH3(CH2)10(S=O2)O-Na+ + H2O
Alkyl hydrogen sulfate neutralized with NaOH --> sodium lauryl sulfate [lipophilic chain: CH3(CH2)10, hydrophilic chain: (S=O2)O-Na+] + water
Modern detergents are straight chain alkyl benzene sulfonates that are biodegradable and do not accumulate in the environment.
RCH=CHR' + benzene --> [AlCl3 catalyst] RCHCH2R'- benzene --> + H2SO4 --> RCHCH2R'- benzene-SO3H --> + Na+ OH- --> RCHCH2R'- benzene-SO3-Na+ [lipophilic: RCHCH2R', hydrophilic: -SO3-Na+]
Also, detergents may be cationic, e.g. C18(CH3)3N+Cl-, neutral, e.g. C8 - benzene ring - O(CH2CH2O)5H, amphoteric C18(CH3)2N+CH2CO2-
12.12.01 Prepare soap by neutralization
RCOOH + NaOH --> RCOO-Na+ + H20, R = CH3(CH2)10-16
fatty acid + base --> Salt (soap) + water
12.12.02 Prepare soap by saponification
ester + alkali --> salts of carboxylic acids + alcohols
RCOOR' + NaOH --> RCOO-Na+ + R'OH
RCOOR' + OH- --> RCOO- + R'OH
Substitute KOH for NaOH to produce semi-solid soft soap. Substitute heavy metals to produce heavy metal stearates for lubricating oil, detergents and plastic manufacture, e.g. PVC
ester (fat) + base --> salt of fatty acid (soap) + alcohol, e.g. glycerol (glycerine), CH2OHCH(OH)CH2OH
Salt of fatty acids from beef tallow, sodium stearate CH3(CH2)16COO-Na+
Salt of fatty acid from palm oil, sodium palmitate CH3(CH2)14COO-Na+
1. Use double decomposition to make metallic soaps. Separately boil a strong soap solution and an equally strong solution of a metallic salt, e.g. chloride or sulfide of Al, Cu, Fe, Mn, Zn . Mix the solutions and gather the soap on a linen cloth. Metallic soaps are used for varnishes, and waterproofing.
2. Make laundry soap. Melt lard at low heat and add sodium hydroxide solution, 200 g per litre, while stirring at constant low heat. until saponification occurs. If the soap does not separate from the solution, add more sodium hydroxide solution. To purify the soap, after separation pour off the sodium hydroxide solution, add water to the soap mass and heat until it dissolves and separate again with concentrated sodium hydroxide solution or common salt, sodium chloride. Remelt the soap in a water bath, heat gently to expel water then pour into moulds.
3. Make a hot-stirred soap with potassium hydroxide. Olive oil 100 parts, solid potassium hydroxide 20 parts, deionized water 100 parts, 90% ethanol 20 parts. Boil the mixture in a steam bath until oil is saponified. Dissolve the soap formed in 300 parts deionized water then "salt out" the soap by adding 25 parts solid sodium hydroxide and 5 parts solid sodium carbonate in 80 parts deionized water.
12.12.03 Surfactants
CH3-CH=CH2 propylene --> CH3-CH(CH3)-CH2-CH(CH3)-CH2-CH(CH3)-CH=CH(CH3) propylene tetramer
--> CH3-CH(CH3)-CH2-CH(CH3)-CH2-CH(CH3)-CH=CH(CH3)benzine-SO3-Na+, alkylbenzene sulfonate (ABS), i.e. RSO3-Na+, similar to soap, RCOO-Na+
Surfactant molecule = hydrophobic, water insoluble chain of fatty acids + hydrophilic, water-soluble, charged end
1. Anionic surfactants have negative charge at the water-soluble end. Used in most domestic detergents and especially for washing glass, e.g. sodium dodecyl benzene sulfonate CH3(CH2)11C6H4SO2O-Na+.
Anionic surfactant molecules concentrate on the surface layers of water to lower the surface tension and allow the water to wet hydrophobic surfaces. The long hydrocarbon tail is soluble in non-polar substances, e.g. oil and the sulfonate group at the other end is soluble in water. So the surfactant molecule can lie across the oil water interface. The molecules aggregate into micelles with the hydrocarbon tails towards the centre leading to emulsification of oily dirt and its removal from the fabric being washed
2. Cationic surfactants have positive charge at the water-soluble end. Used in mild antiseptic throat medicine, algaecides, fabric softeners and washing plastics, e.g. CH3(CH2)15N(CH3)3+Br-
3. Non-ionic detergents have polyethylene oxide group in he molecule. The non-ionic polar groups in the molecule, e.g. -C2H4-O-C2H4-OH, form hydrogen bonds with water.
4. Amphoteric surfactants have positive and negative charge depending on pH. Used in hair conditioners
Surfactant system
1. Ionic surfactants | Non-ionic surfactants
2. Inorganic builders | Organic builders
3. Fluorescent whitening agents | Foaming agents
4. Bleaches
5. Fillers
6. Enzymes
12.12.03.1a Ionic surfactants
alpha olefin + benzene --> alkylbenzene + sulfuric acid (sulfonation) --> sulfonic acid + water
12.12.03.1b Non-ionic surfactants
1. Coconut diethanolamide
RCOOH + H2NCH2CH2OH -->RCONHCH2CH2OH + H2O (condensation reaction)
coconut oil fatty acids + monoethanolamine --> coconut diethanolamide (alkylamide) + water
2. Synthetic fatty alcohol ethoxylate
RCH2OH + (n-1) CH2OCH2 --> RCH2(OCH2CH2)nOH (condensation polymerization)
fatty alcohol + ethylene oxide --> fatty alcohol ethoxylate
12.12.03.2a Inorganic builders
1. sodium tripolyphosphate, STPP, buffers water to milder pH and sequesters hard water ions, deflocculating action to keep clay type dirt in suspension
surface active agent surfactant
2Na2HPO4 + NaH2PO4 --> Na5P3O10 + 2H2O
disodium monohydrogen phosphate + monosodium dihydrogen phosphate --> pentasodium triphosphate (sodium tripolyphosphate)
However, zeolite /sodium carbonate / polycarboxylate builders, e.g. "Zeolite NAA" may replace polyphosphates where there is concern that adding phosphate to polluted water will cause growth of algae that cuts off the light to waterweeds and lead to fish death. In some countries there is an agreement to limit to < 5% phosphorus in detergents.
2. Sodium silicate (water glass) removes magnesium and some calcium and inhibits corrosion in washing machines.
12.12.03.2b Organic builders
cellulose + sodium hydroxide + chloroacetic acid --> sodium carboxymethyl cellulose
It acts as an anti-deposition agent on cellulose based fabrics, e.g. cotton and rayon, by increasing the negative charge in the fabric which then repels the negatively charged dirt particles.
12.12.03.3a Fluorescent whitening agents, optical bleaches, optical whites, fluorescers, "washing blue"
Blueing refers to the practice of adding "washing blue" to the washing water of sheets to neutralize any yellow colour by adding more blue colour so that the dry sheets would appear whiter. Cotton naturally ages to a yellow colour which does not fully reflect blue light from incident sunlight. These chemicals convert invisible ultraviolet light to visible blue light to give fabrics greater uniformity of reflectance and appear "whiter". A white shirt on sale in a shop may already contain fluorescers but they get washed out.
12.12.03.3b Foaming agents
Foam may be important in some detergents to hold up particles of removed dirt, e.g. in carpet and hair shampoos, but the suds may cushion the impact of blades in front loading washing machines and may expand up to cause shot circuits. Some detergents contain a "low suds" foaming agent because people think that a non-foaming detergent is not doing anything! Some detergents include soap to act as a water softener and surface active agent and also to rapidly collapse foam during the rinse cycle after wash. Soap for these purpose my be replaced by silicones.
12.12.03.4 Bleaches, sodium perborate bleach
Sodium perborate in water releases the powerful oxidizing agent hydrogen peroxide that removes most stains without harming textile fibres or removing dyes. However, sodium perborate is effective only at high temperatures and the enzyme catalase in some stains may destroy sodium perborate at low temperatures. The boron in detergent runoff in sewers may be poisonous to citrus crops. Bleach activators can bleach at lower temperatures, e.g. penta acetyl glucose, tetra acetyl ethylene diamine (TAED) sodium percarbonate, nonoyloxy benzene sulfonate (NOBS).
12.12.03.5 Fillers
Calcium carbonate and other components provide bulk to the product.
12.12.03.6 Enzymes
Include alkaline proteases coated with polyethylene glycol that melts in the wash, amylases to break down starch glue and lipases to hydrolyse dirty fat.
12.12.04 Detergents
1. Detergents have the same action as soap but do not form precipitates with calcium and magnesium salts and so can be used in hard water.
2. Surfactants, surface active agents, are organic molecules with a lipophilic end and a polar end that emulsify and disperse oil and grease. Surfactants also lower the surface tension to improve the wetting of clothes so that dirt may be more easily removed. Surfactants do not precipitate in hard water. Cationic surfactants may act as fabric softeners.
3. Wetting agents, e.g. sodium lauryl sulfate, allow soap suds to form easily.
4. Builders, e.g. sodium tripolyphosphate, remove calcium and magnesium ions as a complex through chelation or by exchange these ions for sodium ions. Other builders used to avoid phosphate pollution by wastewater are sodium carbonate, sodium citrate and sodium silicate. Also, sodium aluminium silicate, a zeolite, may be used for calcium ion exchange.
5. Bleaches may be hypochlorite bleaches that allow chlorine to act as an oxidizing agent, or, to avoid pollution by residual chlorine, sodium perborate. NaBO3, may be substituted to allow bleaching by hydrogen peroxide produced by hydrolysis of the sodium perborate.
6. Enzymes may remove stains, e.g. protease enzymes to hydrolyse protein stains and amylase enzymes to dissolve starch based stains.
12.12.07 Laundry detergents
Dose 25 g/30 L TO 100 G /64 L
Percentage formulation: Anionics 15 - 35%, Non-ionics zero to 15%, Surfactants 15 to 49%, Phosphate (% STPP, inorganic builder sodium tripolyphosphate) zero to 30% (being replaced by zeolites) typical 4.5 g P per wash, self-regulation maximum 7.8 g P per wash, Zeolite (%) 10 to 30%, Alkaline builder 15 to 30%, Calcium carbonate mostly zero, used as a filler, Sodium carbonate to break up fatty soils, Sulfate zero to 30%, Enzyme zero to 1.5%, Bleach activator zero or various including perborate, Water 3 to 15%
Examine the labels of soaps, detergents, shampoos and washing powders and list their contents.
12.12.08 Machine dishwashing detergents
Example 1.: Phosphates >30%, Oxygen based bleaching agents 5-15%, Polycarboxylates <5%, Non-ionic surfactants <5%, Phosphonates, enzymes protease [may produce allergic reaction] amylase <5%
Detergent may be classified as IRRITANT [irritating to eyes and skin] With extremely hard waters above 26oC.
Example 2.: Anhydrous sodium tripolyphosphate >30%, Anhydrous sodium metasilicate 30% [dangerous if swallowed!] Anhydrous sodium carbonate 37.5% [ may dissolve glass] Low foam non-ionic surfactants < 0.5%, Sodium dichloriisocyanurate (56-64% available chlorine) 2% [may dissolve plastic] Corrosion inhibitors 9.5% [Includes aluminium salts, otherwise aluminium may be dissolved in machine dishwashing detergents]
12.12.09 Scouring powders
Abrasive powder 80% (screened silica, feldspar, calcite, limestone) sodium carbonate, surfactant + (chlorine bleach)
12.12.10 Drain cleaners
Sodium hydroxide + aluminium filings. They react in water to produce heat and saponify fat to release hydrogen.
12.12.11 Bleaches, disinfectants, deodorizers
Sodium, potassium, calcium, magnesium hypochlorites. Household bleach is usually 5% sodium hypochlorite NaOCl (made from chlorine gas + sodium hydroxide solution until pH = 7.).
12.12.1 Prepare soap with animal fats
Do not prepare soap in containers made of aluminium because aluminium reacts with sodium hydroxide. Use clean dripping from a butcher shop or boil hard animal fat (tallow) in water and remove the separated oil from the surface. Clean the separated fat by strain heated fat through layers of cloth. Weigh sodium hydroxide pellets equal to one third of the weight of fat. Weigh sodium chloride equal to twice the weight of fat. Melt the fat and slowly add sodium hydroxide solution with continuous stirring. Heat gently to avoid boiling over. Boil for 30 minutes then add the sodium chloride while stirring. This is called "salting out". When the mixture cools soap separates as a floating layer, skim off the soap, heat it again, and pour it into moulds, e.g. trays of match boxes. The reaction is much quicker if the fat is already dissolved in methylated spirit before adding the sodium hydroxide.
12.12.2 Prepare soap with vegetable oils
Pour 5 mL olive oil, 5 mL 30% sodium hydroxide solution and 3 mL ethanol into a small beaker. Put the small beaker into a lager beaker of water. Heat the larger beaker while stirring the smaller beaker for 20 minutes. Take out the small beaker and heat it directly to form a creamy paste. Add 5 mL hot saturated sodium chloride solution and stir. This is called salting out and it removes excess alkali. Leave to cool. Remove the solid that separates on the top of the mixture and wash the solid with water. Shake the solid with water and note whether it behaves in the same way as common soaps. Repeat the experiment with potassium hydroxide instead of sodium hydroxide to saponify the fat. Compare the behaviour of the two soaps when used for washing.
12.12.3 Tests for glycerol
Neutralize 10 mL of the sodium hydroxide solution with drops of dilute hydrochloric acid and filter. Evaporate most of the filtrate in a watch glass over boiling water then add 5 mL ethanol. Evaporate most of the solution. Heat the residue with solid potassium hydrogen sulfate. The sharp odour of acrolein, burning fat odour, confirms the presence of glycerol.
CH2OR1-CHOR2-CH2OR3+ 3NaOH -->CH2OH-CHOH-CH2OH + NaOR1-NaOR2-NaOR3
triglyceride fat + sodium hydroxide --> glycerol + soap
12.13.0 Hardness in water
Hardness indicates the tendency of water to precipitate soap or form scale on heated surfaces and is expressed as the sum of Ca and Mg and
usually reported in equivalents of Ca carbonate. Fe, Al, Zn and Mn also can contribute to hardness and should be considered if present in unusual amounts. Hardness in water is a nuisance because it makes washing difficult and causes a precipitate of "fur" in kettles and "scale" in boilers. However, hard water is not dangerous to health. Some water authorities add salts to the town water supply to prepare it harder because it is believed that this may precipitate some harmful bacteria and other micro-organisms. Also, hard water may supply calcium in the diet. Natural spring water is often hard. The salts of fatty acids are insoluble in water except the sodium and potassium salts. When soap is added to water containing metal ions, other than sodium and potassium, ions, insoluble soaps form so removing the fatty acid ions from solution but forming a floating scum on the water.
The five units of measure commonly used in water analysis work: 1. milligrams per litre (mg / l), 2. parts per million (ppm), 3. grains per US gallon (gpg), 4. equivalents per million (epm), 5. grains per imperial gallon (gpg imp).
In USA, hard water contains dissolved hardness minerals above 1 GPG (grains per gallon). USA levels of hardness: soft water < 1 grain per gallon, slightly hard =1 to 3.5 grains per gallon, moderately hard = 3.5 to 7 grains per gallon, hard (very hard) = 7 to 10.5 grains per gallon, extremely hard > 10 grains per gallon. GPG (gpg) is a unit of weight, 1/7000 of a pound, 1 gpg = 17.1 ppm or 1 grain per gallon is equivalent to 17.1 mg/L. The hardness of water is a measure of the amount of minerals, primarily calcium and magnesium, it contains. Water softening, which removes these minerals from the water, may be desirable if large quantities of detergent are needed to produce a lather when doing laundry, or scale is present on the interior of piping or water tanks, laundry sinks or cooking utensils. Water that contains more than 200 mg / l (200 ppm) as calcium carbonate (12 grains per gallon) is considered to be hard and may cause plumbing and laundry staining problems. Three grains per gallon equals about 50 ppm. Methods used to soften hard water for home use are zeolite softening and reverse osmosis. Hardness expressed in mg / l as CaCO3: 0 - 100 soft, 100 - 200 moderate, 200 - 300 hard, 300 - 500 very hard, 500 -1,000 extremely hard. Zeolite softening, ion exchange, exchanges calcium and magnesium ions in the water for sodium ions in the zeolite grains. When the exchange capacity of the zeolite is exhausted, it can be regenerated by passing a strong sodium chloride solution through it causing it to give up the calcium and magnesium ions and take up a new supply of sodium ions. However, only calcium, magnesium and small amounts of iron will be removed from the water so people on salt restricted diets or with high blood pressure may not be able to drink it. Reverse osmosis units remove water hardness through a straining action as hard water passes through a membrane that allows water molecules and only trace levels of contaminants to pass through it. Reverse osmosis units are slow and produce more waste water.
Hardness should not be confused with salinity. Water can be very soft with low levels of Ca and Mg, yet have a high salinity value from dissolved Na salts. Most ground waters have hardness values of less than 2000 mg/L. Hardness range in mg / L: 0-60 soft, 61-120 moderately hard, 121-180 hard, >180 very hard.
12.13.0.1 Temporary hardness and permanent hardness
Temporary hardness occurs when calcium hydrogen carbonate or magnesium hydrogen carbonate dissolves in water. When water with temporary hardness is boiled, the hydrogen carbonates decompose to form insoluble carbonates. They precipitate from the solution to leave "soft" water that forms a lather easily.
calcium hydrogen carbonate(aq) --> carbon dioxide + water(l) + calcium carbonate(s)
Permanent hardness in water occurs when calcium sulfate or magnesium sulfate dissolves in water. Boiling water with permanent harness does not affect the hardness.
12.13.0.2 Remove hardness
See also 16.4.4: EDTA
Remove permanent or temporary hardness in water by adding sodium carbonate crystals (washing soda) to precipitate the calcium ions or magnesium ions as carbonates.
Other methods are used for removing metal ions:
1. Add calcium hydroxide.
2. Add sodium hexametaphosphate, e.g. Calgon, that reacts with the calcium and magnesium ions to produce soluble substances that do not react with soap.
3. Add chelating agents, e.g. Versene, the tetra sodium salt of ethylene-diamine tetra ethanoic acid, EDTA, that combines with unwanted metal ions.
4. Pass water through an ion exchange resin in an ion exchange column, e.g. zeolite (Permutit) that removes the calcium and magnesium ions from the water as insoluble solids. These chemicals "soften" water by removing all minerals to form demineralized water that is as free from ionic substances as deionized water.
The last two processes do not form a scum that can discolour laundry. The Permutit process is the best for producing drinking water.
The hardness of water depends on how much calcium and magnesium salts are present. In natural stretches of water, these salts are mainly hydrogen carbonates, besides sulfates, silicates, chlorides, nitrates and phosphates in much smaller amounts. On boiling the water, the hydrogen carbonates are almost entirely precipitated as insoluble carbonates, so the hardness caused by these salts decreases. The remaining hardness is non-carbonate hardness, permanent, hardness.
Ca(HCO3)2 --> CaCO3 + CO2 + H2O (in boiling water)
The sum of the carbonate (temporary) hardness and non-carbonated (permanent) hardness is the total hardness of water. It is expressed in degrees of hardness. One degree of hardness corresponds to a content of 10 mg of calcium oxygen per litre of water. In Germany this is symbolized by dH. Water with a hardness less than 4o dH is described as very soft. Water with a hardness of 8 to 12o dH is described as moderately hard, between 12 and 18o dH fairly hard, between 18 and 30o dH as hard, and above 30o dH very hard. Water hardness is important technically and from the point of view of health hygiene. It affects the taste of food and drink. Water with a hardness greater than 25o dH acts as a laxative. An increase in the hardness of water causes an increase in how much soap is used because of the formation of insoluble calcium and magnesium soaps that neither foam nor clean. Hardness also causes precipitation of chalk, boiler scale, in pipes and vessels. Very soft water tastes insipid and exerts a bad effect on tooth and bone formation.
12.13.0.3 Water hardness test
The test-tube of the water hardness test set is filled up to the 5 mL graduation mark with the water sample, a level spoonful of indicator powder is added, and the mixture is stirred. If calcium or magnesium salts are present, the water sample turns red-violet, in their absence it turns green. If a red-violet coloration is produced, i.e. if the water possesses a definite hardness, the tablets, each corresponding to 5o dH, added in succession until the colour of the water sample turns to green. Each individual tablet must be completely dissolved before the next one is added. To help this process, the tablets are crushed with the special tamping rod provided for this purpose. Since one table corresponds to 5 degrees of hardness, the exact end point from red-violet to green will usually be greatly exceeded. Repeat the test by first dissolving in the water sample one 5o dH tablet fewer than used in the preliminary test. As many 1o dH tablets are then added until the colour of the water sample just turns green. The degree of hardness of the water is obtained by adding up the hardness values of the tablets used, e.g. if three 5o dH tablets and two 1o dH tablets were used to produce the 0 colour change, the water has a total hardness of 17o dH. The hardness value of the tablets is shown on the package containing them. To find hardness exactly, i.e. to within 0.5o dH, fill the test-tube to the 10 mL mark, add two level spoonfuls of indicator powder, stir, and add tablets with half the hardness value, i.e. 2.5o or 0.5o dH, until the colour just turns green.
12.13.1 Test water to form a lather
1. Prepare soap solution by dissolving 1 g of shavings of plain laundry soap in 100 mL of methylated spirit. Put 5 mL of deionized water or demineralized water in a test-tube. Test the solution by adding one drop of soap solution to the water. Put a stopper on the tube and shake the tube vigorously. If no lather occurs, add another drop of soap solution and shake again. Continue until a lather appears. Record the number of drops of soap solution needed to prepare a good lather.
2. Add soap flakes one by one to 25 mL of the water in a test-tube with a stopper.
The flakes are usually uniform in size. Count how many flakes must be added to the sample to form a good lather by shaking.
12.13.2 Prepare hard water
See also 8.4.2: Heat limewater (calcium carbonate)
1. Temporary hardness
Pass carbon dioxide through limewater or blow through limewater until it turns milky, then turns clear again because of the excess carbon dioxide.
2. Permanent hardness
Dissolve 1 g per of magnesium sulfate-7-water crystals, Epsom Salts, in water. Dissolve 1 gram per of calcium sulfate-2-water crystals in water.
12.13.3 Wash with hard water
Only the sodium and potassium salts of fatty acids are soluble in water, but most are insoluble. If soap is added to water containing metal salts, insoluble soaps form as a greasy scum of calcium or magnesium stearate on the water and the soap cannot be used to remove grease and oil. The scum requires the use of extra soap to remove it and the dirt. This water is called "hard water" because it is hard to prepare a lather in it.
Try to wash the hands with hard water and soap. Use three samples of dirty cloth. Wash each simultaneously and with the same amount of soap in: tap water, hard water, groundwater or stream water. Dry the cloths and compare the results.
12.13.4 Test different waters for hardness
Test different liquids for formation of a lather: Dilute solution of magnesium sulfate-7-water crystals, Dilute solution of calcium hydrogen carbonate, Suspension of calcium carbonate, tap water, rainwater or tank water, mineral water.
12.13.5 Test hard water to form a lather
1. Boil for 5 minutes, 5 mL of: 1. temporary hard water, containing calcium or magnesium hydrogen carbonate 2. permanent hard water, containing other soluble calcium or magnesium salts Test the liquids for formation of a lather.
2. Add sodium carbonate crystals (washing soda) to 5 mL of: 1. temporary hard water 2. permanent hard water. Test the liquids for formation of a lather.
3. Add a commercial water softener, e.g. Calgon, to: 1. temporary hard water 2. permanent hard water. Test the liquids for formation of a lather.
12.13.6 Soften hard water by boiling
Boiling temporarily hard water softens it by decomposing the calcium or magnesium hydrogen carbonates.
1. Test tap water for hardness. Boil the water sample for 5 minutes. A precipitate of calcium carbonate may form.
2. After cooling the water, test for hardness again. Note if a lather forms with less soap than before boiling.
3. Prepare temporary hard water and repeat the experiment.
4. Prepare permanently hard water and repeat the experiment.
Ca(HCO3)2(aq) <--> CaCO3(s) + H2O(l) + CO2(g)
12.13.7 Soften hard water with chemicals
Adding sodium carbonate crystals (washing soda) removes both temporary hardness and permanent hardness in water.
1. Temporarily hard water: Test the harness. Add sodium carbonate crystals (washing soda) and shake. Note whether a precipitate forms. Test the hardness again.
Ca(HCO3)2(aq) + Na2CO3(aq) -->CaCO3(s) + 2NaHCO3(aq)
2. Permanently hard water: Prepare permanently hard water. Test the hardness. Add sodium carbonate crystals (washing soda) and shake. Note whether a precipitate forms. Test the hardness again.
CaSO4(aq) + Na2CO3(aq) --> CaCO3(s) + Na2CO3(aq)
MgSO4(aq) + Na2CO3(aq) --> MgCO3(s) + Na2SO4(aq)
3. Repeat the above experiments with Calgon or other commercially available chemical that softens water. Enter the results of the experiments on water softening in the table below. What can be concluded about the hardness of the different types of water used every day? What is the best way to treat the water used every day?
Type of water used and number of drops of soap solution to form lather
1. Untreated deionized water
2. Untreated tap water
3. Untreated temporary hard water
4. Untreated permanent hard water
5. Boiled temporary hard water
6. Boiled permanent hard water
7. Add sodium carbonate crystals (washing soda) to temporary hard water
8. Add sodium carbonate crystals (washing soda) to permanent hard water
9. Add Calgon to temporary hard water
10. Add Calgon to permanent hard water
12.13.8 Use detergents instead of soap solution
1. Wash clothes with 1. soap solution 2. household detergents. Compare the results. Some household detergents do not form lathers, so test the detergent before using it in this experiment.
2. Use two strips of cotton fabric weighted at one end. Put one strip in pure water and put the other strip in 0.1% surfactant solution. The pure water does not wet the cotton fabric so the strip remains upright. The surfactants wets the cotton fabric so it sinks.
3. Pour an equal thickness layer of olive oil into jars of pure water and a 0.1% surfactant solution. Close the jars, shake them and leave to stand. The oil rises to the surface of the pure water but remains emulsified and dispersed in the detergent solution.
12.13.9 Prepare an alcohol-based detergent
1. Mix 3 drops of dodecan-1-ol (lauryl alcohol) with 2 drops of concentrated sulfuric acid in a test-tube. BE CAREFUL! Dodecanyl sulfate gel forms. Add 2 mL water and 1 drop of phenolphthalein solution.
Add drops of 10% sodium hydroxide solution and stir until the solution is just alkaline. Evaporate to dryness on a watch glass to prepare solid detergent. Shake the solid with water and note whether it behaves in the same way as common soaps.
2. Prepare dodecanyl sulfate and add phenolphthalein as before. Neutralize with 10% solution of triethanolamine. Shake this liquid detergent with water and note whether it behaves in the same way as common soaps.
H2SO4CH3(CH2)10CH2OH --> CH3(CH2)10CH2OSO2OH
dodecan-1-ol --> dodecanyl sulfate
NaOHCH3(CH2)10CH2OSO2OH --> CH3(CH2)10CH2OSO2ONa
dodecanyl sulfate --> sodium dodecanyl sulfate
12.13.10 Tests for hardness in water with a standard soap solution
Prepare a soap solution for estimating of hardness in water
Solution 1.: Dissolve 100 g of pure powdered soap in 1 of 80% methylated spirit. Leave it for a day.
Solution 2.: Dissolve 0.5 g of calcium carbonate in hydrochloric acid, density = 1.19. Add dilute ammonia solution so that litmus paper just turns blue. Dilute to 500 mL. (One mL is equivalent to 1 mg of calcium carbonate.) Titrate the Solution 1. in the burette against Solution 2. Dilute 1. with 80% ethyl alcohol until 1 mL of the resulting solution is equivalent to 1 mL of solution 2. after making allowance for the lather. This is the amount of standard soap solution needed to form a permanent lather in 50 mL of deionized water. One cubic centimetre of the adjusted solution is equivalent to 1 mg of calcium carbonate.
12.13.11 Tests for metal ions in water, EDTA, chelates
The different forms of hardness are expressed as "calcium carbonate hardness". EDTA is [ethylene diamine tetra-acetic acid, HOOCCH2)2N(CH2)2N(CH2COOH)2]. The disodium salt of EDTA combines with metals to form chelates. Chelates are compounds where a multidentate ligand, e.g. as an enolate anion of a -diketone, is bound to a central atom of a coordination complex. EDTA is a complexone and is used in special soaps to remove metal contamination and as a chelating agent for analytical determination of metal contamination. It is available as "EDTA (0.5 M)" which is a concentrated volumetric solution for dilution to prepare 1 litre of 0.5 M standard solution.
1. Prepare a 0.01 M EDTA solution by dissolving 1.861 g in 500 mL water. Prepare a pH 11 buffer solution by adding 7.0 g ammonium chloride solution to 57 mL of concentrated aqueous ammonia solution. Dilute to 100 mL. BE CAREFUL! Prepare an approximate 0.01 M solution MgCl2.6H2O by dissolving 2 g in 1 litre
2. Eriochrome Black T or Erio T indicator is the indicator for determining Ca2+, Mg2+ and Zn2+ with EDT. Dissolve 0.2 g EDTA powder in aqueous ammonia solution. Pour 100 mL of the water to be tested in a conical flask on white paper. Add 1.0 mL of the Mg2+ solution, 3 drops of "Erio T" indicator solution and 1 mL of the buffer solution. Add drops of EDTA solution until a blue colour appears. 1 mL EDTA solution / 1.0 mg CaCO3.
Ca2+ + H2EDTA2 <--> CaEDTA2- + 2H+