Zadanie 1a
Hydrochloric acid, HCl(aq), and hydroiodic acid, HI(aq), ionize completely in water, whereas propanoic acid, CH3CH2COOH(aq), ionizes only partly. 25.0 cm3 of 0.200 mol dm−3 HCl(aq) was titrated with sodium…
Acid-base indicators and their colour change
Explain indicators as weak acids whose conjugate pair differs in colour, write the equilibrium HIn ⇌ H+ + In- and use Le Chatelier's principle to explain the colour change, noting that the end point lies near the pKa of the indicator.
Tę umiejętność sprawdza 9 zadań wzorowanych na arkuszach IB z lat 2022–2026.
Zadania sprawdzające tę umiejętność: 9 Otwórz w wyszukiwarce z filtrami
Zadanie 4c
The titration curve below was obtained when the sodium hydroxide solution was added to 25.0 cm3 of the unknown organic acid in part (b). State, with a reason, which indicator would be appropriate for this titration, using section 18 of the data booklet.
- Materiał graficzny
Zadanie 1a
Each indicator contains more than one benzene ring. (i) State one functional group, other than the phenyl group, that is present in all three indicators. (ii) Deduce the colour of light absorbed by bromothymol blue in acidic conditions and by bromophenol blue…
- Materiał graficzny
Zadanie 1d
Cresolphthalein is a weak acid that can be represented as HIn. Using an equation, explain why the colour of a solution containing cresolphthalein depends on its pH.
- Materiał graficzny
Zadanie 33
An indicator, HIn, is a weak acid with pKa = 5.0. HIn is yellow and its conjugate base, In−, is blue. HIn(aq) ⇌ H+(aq) + In−(aq) Which statements are correct? I. At pH 2.0 the indicator appears yellow. II. At pH 5.0 the…
Zadanie 5a
In a titration, 25.00 cm3 of a 0.120 mol dm−3 solution of a weak monoprotic organic acid, HA, was neutralized by adding sodium hydroxide solution, NaOH(aq), from a burette. The pH curve obtained is shown. (i) Determine the…
- Materiał graficzny
Zadanie 10a
4-Nitrophenol is used as an acid-base indicator. It exists as two forms, X and Y, which differ in colour. Explain which form, X or Y, predominates at pH 11.
- Materiał graficzny
Zadanie 13b
4-Nitrophenol can act as an acid-base indicator. Its acid form, HIn, is colourless and its conjugate base, In−, is yellow. Explain how 4-nitrophenol acts as an acid-base indicator as the pH increases.
- Materiał graficzny
Zadanie 1d
The presence of calcium nitride in the product can be demonstrated by adding water. The nitride is hydrolysed to form calcium hydroxide and ammonia. (i) Calculate coefficients that balance the equation for the reaction: __ Ca3N2(s) + __ H2O(l) →…