Calcium hydroxide equivalent mass

The equivalent of a base is that mass of it which contains one replaceable hydroxyl group, i.e. 17.008 g of ionisable hydroxyl 17.008 g of hydroxyl are equivalent to 1.008 g of hydrogen. The equivalents of sodium hydroxide and potassium hydroxide are the mole, of calcium hydroxide, strontium hydroxide, and barium hydroxide half a mole. 

In the case of the calcium hydroxide, since calcium has a charge of +2 and the coefficient of the term is 2, the number of reference species is 4. Thus, we have now two possible values for the same reaction. In this situation, there are two alternatives the 2 or the 4 as the number of reference species. As mentioned previously, either can be used provided, when one is chosen, all subsequent calculations are based on the one particular choice however, adopt the convention wherein the number of reference species to be chosen should be the smallest value. Thus, the number of reference species in the second reaction is 2, not 4— and all the equivalent masses of the participating substances are obtained by dividing each balanced term of the reaction by 2 Fe(HC03)2/2, 2Ca(OH)2/2, Fe(OH)2/2, 2CaCOf2 and 2H2O/2. 

The solids produced from the coagulation reactions are Al(OH)3, Fe(OH)3 and CaCOj. Referring to the reactions of alnm, the equivalent mass of aluminum hydroxide is 2A1(0H)3/6 = 26.0. The ferric hydroxide is produced through the use of copperas and the ferric salts. Its equivalent mass from the use of copperas [Eqs. (12.89) through (12.91)] is Fe(OH)3/2 = 53.4 and from the use of the ferric salts, its equivalent mass is 2Fe(OH)3/6 = 35.6. Calcium carbonate is produced from the reaction of copperas, Equation (12.89). From this reaction, the equivalent mass of calcium carbonate is 2CaC03/2 = 100. 

When synthetic mixtures of calcium silicate hydrate and calcium hydroxide were used, the series of curves obtained all indicated curve breaks, at about 500°C. These were caused by calcium hydroxide decomposition, as was shown by authentic mass-loss curves for the pure compounds. By taking the vertical distance from the point at which the straight-line curve starts to change due to evolution of the combined water from the calcium silicate hydrate to the point where it resumes the calcium silicate decomposition drop, and calculating the calcium hydroxide from the loss in mass of water equivalent to this vertical distance, one obtained a good estimate of the amount of calcium hydroxide in all cases. 

Another concentration measure sometimes encountered is normality (symbolized by N). Normality is defined as the number ot equivalents per liter of solution, where the definition of an equivalent depends on the reaction taking place in the solution. For an acid-base reaction, the equivalent is the mass of acid or base that can furnish or accept exactly 1 mole of protons (H ions). In Table 11.2 note, for example, that the equivalent mass of sulfuric acid is the molar mass divided by 2, since each mole of H2SO4 can furnish 2 moles of protons. The equivalent mass of calcium hydroxide is also half the molar mass, since each mole of Ca(OH)2 contains 2 moles of OH ions that can react with 2 moles of protons. The equivalent is defined so that 1 equivalent of acid will react with exactly 1 equivalent of base. 

---