Substance Z is sodium carbonate because the relative atomic mass of X calculated is 22. 99. The actual relative atomic mass of sodium is 22. 99. Hence, we can conclude X is sodium. 6) If de-ionized water was added into the volumetric flask beyond the calibration mark, the exact concentration of the solution of standard Z will decrease but the number of moles of substance Z will still remain the same.
Assuming that the volume of the solution of substance Z made is still 250 cm3, the number of moles calculated in that 250 cm3 solution of substance Z will be less because of the decrease in concentration. When the number of moles calculated decreases, the mass of one mole of substance Z will increase because of the equation (). Number of moles is inversely proportional to mass of one mole of substance Z or relative molecular mass of substance Z.
7) If an air bubble is initially entrapped in the burette tip and is passed from the burette during the titration, the recorded volume of HCl used will increase although the actual volume used to reach the end point of the titration is still the same. The calculated number of moles of HCl used will increase. The number of moles of Substance Z calculated will also increase. The calculated mass of one mole of substance Z will be lower because of the equation (). The number of moles is inversely proportional to the mass of one mole of substance Z or relative molecular mass of substance Z.
Discussion Element X was correctly identified as sodium and substance Z is sodium carbonate. The relative atomic mass of element X was accurately determined. The percentage error of the calculation is zero. Conclusion The relative molecular mass of substance Z can be correctly identified by knowing the amount of hydrochloric acid that reacted with a known amount of Substance Z. Substance Z is sodium carbonate with a calculated relative molecular mass of 105. 99g.
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