Which one of the following is a buffer solution? 0.10 M KCN 0.20 M CH3COOH 1.0 M HNO3 and 1.0 M NaNO3 0.40 M HCN and 0.10 KCN 0.50 M HCl and 0.10 NaCl

0.40 M HCN and 0.10 KCN

Explanation:

A buffer solution is defined as the aqueous mixture of a weak base and its conjugate base or vice versa.

For the systems:

0.10 M KCN 0.20 M CH3COOH: Acetic acid, CH₃COOH is a weak acid and KCN is the conjugate base of HCN. Here, you have a weak acid and a conjugate base but not the conjugate base of the acetic acid or the weak acid of KCN. Thus, it is not a buffer.

1.0 M HNO3 and 1.0 M NaNO3. HNO₃ is a strong acid. Thus, this system is not a buffer.

0.40 M HCN and 0.10 KCN. Here, you have HCN, the weak acid, and KCN, its conjugate base. Thus, it is a buffer.

0.50 M HCl and 0.10 NaCl. HCl is a strong acid, thus, its mixture with NaCl is not a buffer.

answer: the enthalpy of the overall chemical reaction is +87.88 kj or +88 kj.

according to hess's law, the overall enthalpy of a reaction is the difference between the sum of enthalpy values of all the products and the sum of enthalpy values of all the reactants.

δh(reaction) = ∑nδh(products) - ∑nδh(reactants)

δh(reaction) = [δh +δh] - [δh]

δh(reaction) = [1(-287.02) + 1(0) ] - [1(-374.9)] kj = +87.88 kj

here, δh (pcl3) = -287.02 kj, δh(cl2) = 0, δh(pcl5) = -374.9 kj

therefore, enthalpy of the overall reaction is +87.88 kj or +88 kj.