Question

Calculate ph of a buffer solution prepared by dissolving 30g of na2co3 in 500ml

Answer 1

Answer:

Hydrochloric acid reacts with Sodium carbonate to neutralise the base as follows:

Na_2CO_3 + HCl  >  NaCl + H_2CO_3

Moles of Na2CO3 = m /M = 30 /105 = 0.28 mol

Moles of HCl = V(L) * M = (0.15) * 1 = 0.15 mol

Mole of Na2CO3 left = 0.28 – 0.15 = 0.13 mol

Concentration of left Na2CO3 = 0.13 / (0.500 + 0.15) M

Concentration of Salt = 0.15 / (0.500 + 0.15) M

pH of buffer = pK a + log [salt] /[Base]

pK a = - log [ka] = - log [5.63 * 10^-^1^1 ] = 10.32

pH = 10.32 + log [0.15] /[0.13]  = 10.32 + 0.11 = 10.43

Thus, pH of buffer is 10.43

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