when titrating a mixture of sodium carbonate and sodium hydroxide with HCl,?

Question

why is it that all the sodium hydroxide reacts first followed by the sodium carbonate? is it because the dissociation of sodium hydroxide blocks the dissociation of the weaker base, sodium carbonate, due to common ion effect, sodium ions being the common ion?

Answer 1

Yes but the bigger reason is that NaOH is a strong base while Na2CO3 is only a basic salt.

Answer 2

Actually, for number 2, NaOH can't be used as a primary standard because it is not completely pure. A primary standard is something used to measure the molarity of something else because its purity is reliable and accepted to be 100%. You could titrate a known molarity sodium hydroxide solution with HCl to calculate the hydrochloric molarity but you could NOT use NaOH as a standard. However, you would have to use a different primary standard just to figure out the molarity of the NaOH.