Question

Describe how to make 2.0L of a 2.00 M solution of sodium carbonate from solid sodium carbonate(s).

b. Describe how you can make a buffer with sodium carbonate(s) by adding hydrochloric acid.
c. How many mL of 1.00 M HCl(aq) are needed to be added to 10.00 g of sodium carbonate to make a buffer at pH =10.00. Ka of HCO3- is 4.7 x 10-11.

Answer 1

Ques a) moles of solid sodium carbonate(s) required = 2M x 2L = 4 moles

so, mass of solid sodium carbonate(s) to be mixed in 2 L of solution = 4 x 40= 160 gm

Ques b) when solid sodium carbonate(s) and  hydrochloric acid are mixed, then following reaction occurs:

Na2CO3 + HCl --> HCO3-  + NaCl

so, here buffer solution of HCO3- /CO3-2 can be made, if after the above reaction, some amount of carbonate anion is left in the solution.

Ques C) 10.00 g of sodium carbonate= 0.25 moles of sodium carbonate= 250 millimoles of sodium carbonate

mL of 1.00 M HCl(aq) be V. So millimoles of HCl used= 1 X V= V millimoles

Na2CO3 + HCl --> HCO3-  + NaCl

250-V 0 V

using Henderson–Hasselbalch equation:

PH = Pka + Log([Salt]/[Acid])

10 = 10.3279 + Log([250-V]/[V ])

after simplification, we get V= 170.5 ml