Question

Question 2 (2.0 pts): a) In the gravimetric (mass) analysis method, the stage of performing the analyte precipitation reaction with reagents is very important, in order to create a large-sized precipitate that is easy to filter. State at least three ways to reduce supersaturation when performing a precipitation reaction. b) Determine the concentration of Ca² in 200 mL of tap water sample as follows: precipitate Ca2 with excess NH4C2O4. Proceed, filter, wash and calcine the CaC2O4.H2O precipitate at 1000 °C to a constant mass, obtaining a weighed mass of 0.1830 g. Calculate mol/Lit concentration and ppm concentration of Ca2 in tap water sample. Know the calcination diagram of CaC2O4.H2O as shown below, giving molar masses of Ca = 40, C = 12 and O = 16. CaCO3 L High |

Answer 1

In gravimetric analysis, reducing supersaturation is important to create a large-sized precipitate. Three ways to reduce supersaturation are slow addition of reagents, agitation, and controlling temperature. To determine the concentration of Ca²⁺ in tap water, precipitate Ca²⁺ with
`NH_4C_2O_4`, filter, wash, and calcine the precipitate, and then calculate the molar concentration and ppm concentration of Ca²⁺ in the sample.

In gravimetric (mass) analysis, reducing supersaturation during precipitation reactions is important to create a large-sized precipitate that is easy to filter. Here are three ways to reduce supersaturation:

1. Slow addition of reagents: Add reagents slowly to allow for controlled and gradual formation of the precipitate.
2. Agitation: Agitate the reaction mixture to promote an even distribution of reagents and prevent localized supersaturation.
3. Controlling temperature: Lowering the temperature of the reaction mixture can help reduce supersaturation.

To determine the concentration of Ca²⁺ in a tap water sample, you need to precipitate Ca²⁺ with excess
`NH_4C_2O_4`, filter the precipitate (
`CaC_2O_4`·
`H_2O`), wash and calcine it at 1000°C. Given that the weighed mass of the precipitate is 0.1830 g, you can calculate the molar concentration (mol/L) and the concentration in parts per million (ppm) of Ca²⁺ in the tap water sample using the molar masses of Ca, C, and O and the stoichiometry of the reaction.