C03 EXPERIMENT 7 DETERMINATION OF TOTAL ALKALINITY OF SODA ASH Principle One-ten

Question

C03 EXPERIMENT 7 DETERMINATION OF TOTAL ALKALINITY OF SODA ASH Principle One-tenth molar hydrochloric acid is sta ndardized against primary standard sodium carbonate. Phenolphthalein is used to approximate the halfway point of the titra- tion, and then either modified methyl orange indicator or bromenesol green indi- cator is used to detect the final end point: the last indicator is used with boiling of the solution near the end point to remove co2 (see discussion of Figure 8.11). Al ternatively, the hydrochloric acid is standardized against sodium by- droxide from Experiment 6 using phenophthalein indicator. soda ash sample is titrated with the hydrochloric acid solution, with the addition of 2 mol hydro- gen per mole Nazcos. Equations CO H2CO3 H2O CO2 t Solutions and Chemicals Required 1. Provided. 0.2% phenolphthalein in 90% ethanol, either modified methyl orange (mixture of methyl orange and xylene cylanole FF available from East man Kodak C bromcresol green in 0.001 M NaOH, and either pri- many standar Nazcos oj standardized 0.1 M NaOH. If you are to use this solution in Experiment 7 to standardize the HC, your instructor will advise you to save the remaining solution after completing this experiment. In that event, you should prepare and stan- dardize the HCl within one week of standardizing the

Explanation / Answer

Number of moles = mass/molar mass

mass of Na2CO3 = 106 gm/mol

Thus, number of moles of Na2CO3 = 0.2 gm / 106 gm/mol

= 0.002 moles

Now, mass = number of moles * molar mass

mass of CaCO3 = 0.002 moles * 100 gm/mol

= 0.2 gm

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