Percentage Purity of Sulphuric Acid

 

Process:

ð  Weigh 2 g of the sample accurately in weighing bottle.

ð  Transfer the same sample in a 500 ml. volumetric flask.

ð  Made the solution up to 500 ml. with distilled water.

ð  Pipette out 10 ml. from the same solution using volumetric pipette and transfer it into a conical flask.

ð  Add 2 – 3 drops of phenolphthalein indicator.

ð  Titrate it against 0.1(1/10)N NaOH (sodium hydroxide).

   

Chemical Reaction:

2NaOH_(aq) + H₂SO_{4 (aq)} à Na₂SO_{4 (aq)} + 2H₂O_(aq)

Calculation:

            1000 ml 1 NaOH   ≡  49 g H₂SO₄

1000 ml 0.1 N NaOH   ≡  4.9 g H₂SO₄

1 ml 1 N NaOH  ≡  0.0049 g H₂SO₄

 

% Purity =  Burette Reading (BR) X Eq.Wt.

                                            4

 % Purity =  (BR) X 49

                           4

 % Purity =  (BR) X 12.25

                     

Answer: % Purity of H₂SO₄ is (BR) X 12.25

A Bird’s Eye View of Dyeing

           The colouration of cotton is in regular practice since the ancient era. This colouration is termed “Dyeing” which is the decorating of textile materials by applying basic principles of chemistry. So, it can also be defined as “Applied Chemistry”. Cotton must be well pretreated for achieving perfect dyeing. Well pretreated means, well desized, scour and bleach. Also, whiteness is majorly concentrated for dyeing operations. One would select full white fabric for dyeing pale shades. Dark shades application do not require full bleach fabric, so the supervisor can proceed for half bleach only.

            The textile materials are coloured with dye or pigments with desired colour fastness is termed as “Dyeing”. The said operation was performed with natural dyes prior, but nowadays natural dyes have been replaced by synthetic dyes. The first synthetic dye was discovered by Perkin in 1856. Travelling from ancient to today’s world, cotton has locked its popularity. Therefore, the dyeing of cotton is also at the same level as industrial practices. Cotton dyeing can be performed in various forms. 

Various terms related to dyeing operation are commonly used, therefore, what they mean is important to know.

Self-Shade

            When cotton, in any form, is dyed with a single dye to produce full shade, is known as “Self-Shade”.

Compound Shade

             When cotton, in any form, is dyed with a mixture of two or more dyes to produce full shade, is known as “Compound Shade”.

Solid Shade

            When the warp and weft, both yarns are of the same textile material, then the obtained shade due to dyeing is known as “Solid Shade”

Per cent Shade

            The amount of dye present on the textile material after dyeing is termed as “Percent Shade”. Thus, if 1 g of dye is utilized for 100 g of textile material, then it is said to be 1% shade. This does not suggest that the material has 1 g of dye on it for its 100 g of weight.

Per cent Exhaustion

             At the end of dyeing, the amount of the dye taken up by the textile material from the dye liquor is calculated as “Percent Exhaustion”. Thus, if a dyer wants to produce 1% shade on 200 g fabric, he required 2 g of dye which is the concentration at starting of dyeing. At the end of dyeing, if liquor contains 0.2 g of dye in it. That means 1.8 g dye has been taken up by textile, so the exhausted dye is 90%. As the exhaustion is higher, dye waste is lower.

Material to Liquor (M:L) Ratio

            The requirement of the total quantity of water depends on the weight of the textile material. On the weight of the material, the dyer takes the water. This total quantity of water on the weight of the material is known as “Material to Liquor Ratio”. If dyer is writing 1:30 M:L ratio, means 1 g of textile material requires 30 ml of water to dye it or 1 kg of the same requires 30 kg of water. A low ratio must be preferred as it reduces water consumption.

Standing Bath

              During dyeing, when the exhaustion is very low, a major amount of dye is not used and so it is wasted. Dyer utilizes the same bath again for another lot with the same shade requirement. Such stored dye baths are termed “Standing Bath”. Particularly, this type of bath is used in sulphur, indigo, and an azoic class of dyes.

Cross Dyeing

            When manufactured textile material contains different kinds of fibres, like cotton and polyester blend, then the dyeing is performed with a single bath with the mixture of dyes or with two baths by dyeing each component in a separate bath. This dyeing is termed “Cross Dyeing”.

Reserve Dyeing

            Dyeing of a blend like cotton and polyester is done by reactive dye will result in the dyeing of cotton only, and polyester will be undyed. This happens due to the affinity of reactive dye towards cotton only, not to the polyester. Thus polyester is reserved for dyeing. This operation is known as “Reserve Dyeing”.

Topping

            The dyed fabric is over-dyed with another dye of a different class or same class to obtain a deeper shade or brighter shade for generating a multicolour effect. This over-dyeing process is termed “Topping”. It helps in producing deeper shade by reducing the cost.

Tailing Effect

            The shade of dye during dyeing is weakened on some specific machines. So the shade becomes lighter than the dyed area of the material. So the dyeing results in dark and light shades. This effect is “Tailing Effect”

Stripping

            After dyeing, if the material is uneven dyed or shade is darker than required is achieved, dyestuff present on the material has to be removed completely. Removal of dyestuff is termed as “Stripping”.

Parameters of Dyeing

            Cotton dyeing is complicated chemistry compare to synthetic dyeing. As the natural fibre, cotton has many variables affecting the dyeing procedure. Generally, the dyer tries to exhaust maximum dye onto the material. Such exhaustion is affected by various parameters. Such parameters are:

• Not in Control of Dyers

1. Fibre Shape Factor (S):
2. Ratio of the bimolecular rate constant (R_F)

• In Control of Dyers (Fully/Partially)

1. Dye Dissolution: The dye must be pasted with cold water and then pouring warm water with high-speed stirring. This solution must be prepared before utilizing it in dyeing. The pH of the water should be neutral, and the water must be soft. The recommended level for the water used in dyeing.

Total Hardness	50 – 55 ppm
pH	7.0 + 0.5
Copper	0.05 mg/l
Iron	0.05 mg/l
Chloride ions	300 mg/l

 

2. Exhaustion of Dye: Exhaustion (substantivity) of the dyes affected by dye structure,  concentration of the dye, temperature of the dye bath, and pH. If the dye structure is planner then the exhaustion will be high compare to the complex structure. As the exhaustion is high, migration will decrease, and uneven dyeing increases. So the substantivity between dye and fibres must be proper.
3. Temperature: Temperature affects the dyeing process based on the class of dyes utilized for the dyeing. It depends essentially on the heat of dyeing of various dyes. An increase in the temperature will result in a low substantivity ratio and reactivity will increase which reduces the efficiency. 
4. pH: As dyer change the pH, the substantivity of individual dye is affected. pH profile will decide the fixation which required sufficient time required for reacting the dye with fibre.  
5. Liquor Ratio: M:L ratio is largely under the control of dyer. As the amount of liquor reduces, depth of shade, concentration of dye must increases. So the ratio of substantivity decreases.
6. Electrolyte concentration: The rate of reaction and efficiency increases with the increase in electrolyte concentration. It also affects the reactivity of dye in little amount with precipitation or aggregation. So there must be some limit on the electrolyte concentration.

Classification of Dyes

ð According to Chemical Constitution: The colour index listed several chemical classes. A dye may have a single or multiple functional or chemical groups in its structure. They are unlimited and regularly developed by dye manufacturers. Some reported classes are:

Nitro	Diphenylmethane	Thiazole	Aminoquinone
Nitroso	Triphenylmethane	Indamine	Hydroxyketone
Monoazo	Anthraquinone	Indophenol	Indigoid
Disazo	Xanthene	Azine	Phthalocyanine
Triazo	Acridine	Oxazin	Chorotiazinyl
Polyazo	Quinolone	Sulphur	Vinyl sulphone
Stilbene	Methine	Lactone

 

ð According to Methods of Application: The dyes are classified into two broad categories, viz. readymade and ingrain dyes. Readymade dyes are further classified into water-soluble and insoluble categories. Ingrain dyes are developed on the surface or insitu by coupling intermediate compounds which are not true dyes. Classification is as follows:

 

Mechanism of Dyeing

            The dyeing mechanism deals with various theories, such as kinetic theory, molecular theory, and thermodynamic theory. These theories are utilized for explaining the physic-chemical principle involved in dyeing. So, the mechanism of dyeing is divided into four fundamentals phenomena which are:

1)      Exhaustion: Migration of dye particles from dye solution to the fibre surface.

2)      Adsorption: Dye particles are locking their position on the surface of the fibre.

3)      Absorption: Dye particles travelled/diffused to the inner structure of the fibre from its surface.

4)      Fixation: Dye attached with the fibre and permanently locked its position in the fibre.

 

By keeping all the above parameters in mind, dyes are selected for the dyeing based on:

1)      Compatibility

2)      Consistency

3)      Reproducibility

4)      Right first time      

Selection of Thickeners for Printing (Textiles)

 

ð  Thickeners used in textile printing are high molecular weight compounds giving viscose pastes in water.

ð  These impart stickiness and plasticity to the printing paste which preserve the sharpness of the printed design and prevent blurring effect by capillary action.

ð  Four significantly different approaches may be used to produce thickeners, using:

(1)   a low concentration of a polymer of high relative molecular mass (r.m.m.)

(2)   a high concentration of a material of lower r.m.m. or of highly branched chain structure

(3)   an emulsion of two immiscible liquids, similar to the emulsions used as cosmetic creams, or a foam of air in a liquid

(4)   a dispersion of a finely divided solid, such as bentonite.

ð  In the selection of thickening agents, it is necessary to take into account requirements other than viscosity, which can usefully be classified in five categories:

(1)   Print paste stability

(2)   Good adhesion of the dried thickener film

(3)   Minimum effect on colour yield

(4)   Ease of removal

(5)   Acceptable cost.

 

ð  Print paste stability:- The thickener must be stable and compatible with the dyes and auxiliaries to be used. If a cationic dye is added to a thickener with anionic charges, the interaction is likely to change the viscosity and to produce insoluble complexes. The pH of the print paste must be considered, as some polymers are only usable within a limited pH range and form gels when acids or strong alkalis are added. The micro-organisms responsible are present in the air, and thickeners provide nutrients and ideal conditions for their growth and reproduction. They produce enzymes that break down the polymer, with a consequent and often rapid fall in viscosity.

 

ð  Properties of the dried thickener film:- Drying usually follows printing, and the fabric may be creased and flexed over rollers and tension rails before fixation of the print occurs. The thickening agent is deposited on the fabric surface as a dry film that sticks fibres together and contains colorant. Good adhesion to the fibre is required in order to avoid loss of colorant during mechanical handling. Otherwise particles of coloured film may break off, leaving white spots in coloured areas and possibly giving coloured spots in unprinted areas. The deposition of polymer films on a fabric inevitably causes some stiffening, and washing is normally required after fixation of the dye to remove thickening agent and any loose dye. Fortunately, many synthetic thickeners do not form such hard films as do the natural polymers.

 

ð  Effect on colour yield:- Printers have found that the fixation of dye is usually best achieved by steaming. Steam condenses on to the film of thickening agent, which swells and contains a miniature dye bath on the fibre surface. Some dye dissolves, and the next step is the diffusion of dye through the swollen film to the fibre surface. Any affinity between the molecules of dye and thickening agent will reduce the speed of this diffusion process as well as the extent of dye transfer to the fibre. If both molecules have ionic charges of the same sign, the speed and efficiency of the process will be higher because of the mutual-repulsion effect. In addition to any effect on dye fixation, the thickener will significantly affect the penetration of print paste into the yarn and fabric structure, and this may have a dominant effect on colour yield.

 

ð  Ease of preparation and removal:- The time taken to prepare a thickener, and the precautions required to ensure that the paste has satisfactory and consistent properties, are variables that have greater significance today than in the past. The extent to which a thickening agent is removed in a high-speed washing process, especially after a high-temperature steaming operation, is also a vital consideration in the selection of thickening agents. It is also difficult to redisperse starches and remove them from the printed fabric. The removal of thickening agents can also be facilitated by introducing a second component in the thickener.

 

ð  Cost:-  Traditionally, when labour costs were low, it was common to look only at the cost of the thickening agent itself and the cheapest materials were widely used. It must already be obvious, however, that it is essential to consider many other aspects to decide which material will give the required quality at the lowest overall cost. The concentration to be used, cost of preparation, stability, print penetration, colour yield and ease of removal can in total be more important than the basic price of the polymer. The biological oxygen demand of the effluent, due to thickener removed in the washing-off operation, can also be a vital parameter. 

ð  The inter relationship between Low and High solid Thickening properties

 

Characteristic Property	Type of Thickening
	Low solids	High solids
Flow	Short	Long
Effect of increasing shear on viscosity	Viscosity falls off rapidly	Little or no falling off of viscosity
Yield of dye	Generally high	Usually of a lower order than low solids thickenings
Levelness of print	More difficult to achieve than with high solids thickenings	Generally good
Viscosity	High	Medium-low
Handling of dried or baked print	Flexible film giving moderate-good handle	Film tends to be hard, brittle and many crack off fabric
Nature of polysaccharide chains	Very long and straight with little or no side batching	Shorter than low solids types. Heavily branched, coiled in solution
Price of made-up thickening	Relatively low	More expensive than low solids type
Chemical resistance	There is no clear demarcation between the two types