ðˈʌs, wˈʌn stˈændɚd səlˈuːʃən ɪz nˈiːdᵻd ˈiː.dʒˈiː. ˌeɪtʃsˌiːˈɛl ɪnðə dᵻɹˈɛkt taɪtɹˈeɪʃən, wˌaɪl tˈuː ɑːɹ nˈiːdᵻd ˈiː.dʒˈiː. ˌeɪtʃsˌiːˈɛl ænd nˈɑː ˌoʊˈeɪtʃ ɪnðə bˈæktaɪtɹˈeɪʃən.
Thus, one standard solution is needed (e.g. HCl) in the direct titration, while two are needed (e.g. HCl and NaOH) in the back-titration.