Final answer:
The concentration of HCl is 14.584 g/dm3 and 0.4 M. The percentage purity is 1.4298%, and the impurity is 98.5702%. The mass of impurities in 25.5g of the impure acid is 25.1354g.
Step-by-step explanation:
In this experiment, the determination of the concentration and percent purity of hydrochloric acid (HCl) is carried out through a titration with sodium hydroxide (NaOH). Given that 25cm3 of hydrochloric acid neutralizes 25 cm3 of 0.4 M NaOH, the concentration of the acid can be calculated.
Concentration of the Hydrochloric Acid
(i) To find the concentration in g/dm3, we must ascertain the amount of HCl that reacts with NaOH. Since the volume and molarity of NaOH are given, the number of moles of NaOH can be calculated.
Number of moles NaOH = Volume (L) × Molarity (mol/L) = 0.025 × 0.4 = 0.01 mol
Since the reaction between HCl and NaOH is a 1:1 ratio (HCl + NaOH → NaCl + H2O), the moles of HCl will also be 0.01 mol. To find the concentration in g/dm3, we convert the number of moles to mass using the molar mass of HCl.
Mass of HCl = Moles × Molar Mass = 0.01 mol × 36.46 g/mol = 0.3646 g
Since this is for 25cm3, for a dm3 (1000cm3), it will be: Concentration = (0.3646 g/25 cm3) × 1000 = 14.584 g/dm3
(ii) The molar concentration (mol/dm3) is the same as the number of moles in 1 dm3, which is 0.4 M as derived from the initial information.
Percentage Purity and Impurity of the Acid
(b) The mass of pure HCl is calculated above as 0.3646 g for 25cm3. So, the initial mass of impure acid dissolved to make 1 L is given as 25.5 g. Percentage purity can be calculated as:
Percentage purity = (Mass of pure HCl / Mass of impure HCl) × 100 = (0.3646 g / 25.5 g) × 100 = 1.4298%
(c) Percentage impurity = 100% - Percentage purity = 100% - 1.4298% = 98.5702%
(d) The mass of impurities in the impure acid can be calculated by:
Mass of impurities = Mass of impure HCl - Mass of pure HCl = 25.5 g - (25.5 g × 0.014298) = 25.5 g - 0.3646 g = 25.1354 g