Question

A chemistry graduate student is given 500.mL of a 0.70M chloroacetic acid HCH2ClCO2 solution. Chloroacetic acid is a weak acid with =Ka×1.310−3. What mass of NaCH2ClCO2 should the student dissolve in the HCH2ClCO2 solution to turn it into a buffer with pH =3.40? You may assume that the volume of the solution doesn't change when the NaCH2ClCO2 is dissolved in it. Be sure your answer has a unit symbol, and round it to 2 significant digits.

Answer 1

Given =) ka for HCH2C1602 = 1.3x10-3 concentration of HCH2C1C02 = 0.70m . pH=3.40 we know that pH of acidic buffer pH e praf log (Ng CH2 CIC027 . o THCH2 C1 CO2 3-40 = -logkat dog (nac H2 CIC02] d 0.70m 3.40 = - log 1-3410-3 +log [Nachz CIC02] 0.7om 3-4 0 = 2886 +log [NaCH2 CICO2) 070m 0.514 = 09 (Na CH2 C1 CO2] 0 0.70m

(NaCH₂ C1 (O2) = 3: 266 0.70m. [na CH2 C1002]- 3.266X0.70M (NO CH2C1CO2 = 2:2862 m No. of mol of NacHa alco2 = Molarity x volume(4) = 2.2 862 X 0.5 mol = 101431 mol Majs of NICH2 CICO2 = no. of mol . x molar mars = 01:1431X 116.4788 = 133.159 mass of = 1.34102 g Ang Na CM2C1CO2 1