Prepare a range of Calamine suspensions and determine the effects of various additives on the stability of the suspensions.
Methodology The formula for the different suspensions were as follows (each was made in duplicate): A: Calamine 7. 5g Zinc Oxide 2. 5g Glycerin 2. 5ml Water to 50ml B: Calamine 7. 5g Zinc Oxide 2. 5g Bentonite 1. 5g Glycerin 2. 5ml Water to 50ml C: Calamine 7. 5g Zinc Oxide 2. 5g Bentonite 1. 5g Sodium Citrate 0.
25g Glycerin 2. 5ml Water to 50ml D: Calamine 7. 5g Zinc Oxide 2. 5g Sodium Citrate 0. 25g Glycerin 2. 5g Water to 50ml E: Calamine 7. 5g Zinc Oxide 2.
5g Sodium Citrate 1g Glycerin 2. 5ml Water to 50ml The solid compounds were weighed in weighing boats, and some of the distilled water was added to the glycerin. The suspensions were made up using pestle and mortar, transferred to a measuring cylinder and made up to volume with water. They were then left to stand and they were to be observed after three days. The roles of the different additives in the suspensions are: Zinc oxide – an active ingredient; a mild astringent Glycerin – a wetting agent Bentonite – a thickening agent; increases viscosity and decreases sedimentation rate
Sodium Citrate – an electrolyte (flocculating agent; causes flocculation) – dependent on concentration Results and Discussion Calamine Suspension Sedimentation Volume (ml) No.
Of turns to Re-suspend 5 min 15 min 30 min 60 min 90 min 120 min 72 hours The results for suspensions D and E were taken from group C3b, since the results were insufficient By plotting a graph of the sedimentation ratio against time, for all the suspensions, the stability cam be compared for all five of the suspensions. The most stable formulation was Suspension C, as it was the suspension with the least amount of sedimentation over the course of three days.
This is due to the small amount of flocculating agent that was added to cause flocculation, which causes a increase in rate of sedimentation compared to that of Suspension A, which contained no additives. The Bentonite increased the viscosity of the suspension thus also slowing down the rate of sedimentation. Suspension C had the least number of turns to re-suspend the particles after three days. This is due to the addition of the flocculating agent that allowed the particles to aggregate together to form clusters, which trapped small volumes of the liquids to allow for easy re-dispersion when shaken.
The suspensions with the most number of turns to re-suspend the particles was Suspension D. This These additives are required to increase the stability of the calamine suspension. Flocculation increases attraction (or decreases repulsion) between the particles. Sedimentation is faster in a flocculated system, where the sediment volume is larger, thus caking cannot occur as the clusters of the particles trap small volumes of the continuous phase, thus making re-dispersion easier. Experiment B: Preparation of bismuth subnitrate suspensions (5g/100ml) containing increasing amounts of phosphate ions Aim.
Determine the effect of increasing the concentration of electrolyte (as a flocculating agent) on suspension stability Bismuth subnitrate suspensions were to be stabilised by employing potassium phosphate as the flocculating agent. Methodology 5g of bismuth subnitrate was weighed in weighing boats and transferred to 100ml measuring cylinders. The appropriate suspending medium provided was added and the measuring cylinder was stoppered and shaken to disperse the bismuth subnitrate particles in the liquid medium. The suspensions were left to stand, and the sediment volume was measured three days later.
Results and Discussion Concentration of electrolyte, KH2PO4 (mM) Volume of sediment (3 days later; ml) Sediment Ratio, R No. Of turns taken to re-disperse suspension (3 days later) 1 2 1 2 Mean 1 2 Mean Volume of sediment Total suspension volume Plotting a graph of electrolyte concentration against sediment ratio shows the expected trend when adding increasing electrolyte concentrations to the suspension. The number of turns taken to re-suspend the suspension can be compared to the increasing concentrations of the electrolyte.
Bismuth subnitrate particles are positively charged, addition of phosphate ions (flocculating agent) result in adsorption of the anions onto bismuth subnitrate particles. This reduces the positive charge on the particles. Increasing the phosphate ion concentration causes further reduction in the positive charge as more anions adsorb onto the particles. Eventually, all the positive charge on the particles is neutralised by the adsorbed anionic charge and the net charge is zero. Further addition of phosphate ions causes the charge to become negative.
The positive charges on the particles in the suspension repel each other, thus there is no flocculation. When an electrolyte (negative charges) is added, the repulsive forces between the particles is reduced, so that flocculation can occur. When excess electrolyte is added, the charge on the particle is reversed, thus the strong repulsive forces may cause deflocculation. In this case, caking can occur, where no continuous phase is trapped between the particles, thus making re-dispersion very difficult.
Typical curve of repulsion and attraction between particles. Is Potassium Phosphate a good flocculating agent? Pp is negative – bismuth is positive What is the optimal concentration range of electrolyte needed to stabilise the bismuth subnitrate suspension? Are the suspensions easy to re-disperse? Conclusion Aims met – what was deduced? Pourable Needs to be re-dispersible in a few numbers of turns. Not too much electrolyte (sodium critrate or potassium phosphate) Not too much thickening agent (Bentonite) as want it to be pourable.
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