Further Aspects of Acids & Bases (DP IB Chemistry: HL)

Iron(III) ions can react with cyanide ions to form ferricyanide ion via the following equation

Fe³⁺ + 6CN^- → [Fe(CN)₆]^3-  

State which of the reactants is behaving as a Lewis base and justify your answer.

State the definition of a Brønsted-Lowry acid and the equation which demonstrates how ethanoic acid, CH₃COOH (aq) , behaves as a Brønsted-Lowry acid when reacting with ammonia, NH₃ (aq).

Sketch a graph to indicate the change in pH during a titration of 25.0 cm³ of 0.100 mol dm^-3 hydrochloric acid, HCl (aq) , with 0.100 mol of ammonia, NH₃ (aq).

The end point in a titration can be identified using a suitable indicator.

Ethanoic acid, CH₃COOH (aq) , is titrated with 0.16 mol dm^-3 potassium hydroxide and the following graph is obtained.

Explain why the equivalence point is greater than pH 7 for this titration.

Explain what is meant by a buffer solution and describe where the ‘buffer region’ on the graph would occur. 

Explain the shape of the pH curve up to the equivalence point. 

Explain why potassium hydroxide can act as a Brønsted-Lowry base and Lewis base.

This question is about Brønsted-Lowry acids and bases.
 

When an acid and a base react they produce a conjugate base and a conjugate acid. 

acid + base  ⇋  conjugate base + conjugate acid 

Write an equation to show how hydrochloric acid behaves as a strong acid when it reacts with water, and state the role of water in this reaction.

Ethanoic acid is a weak acid. Hydrogen carbonate ions can also act as a weak acid if in an aqueous solution.

Explain how a solution containing ethanoic acid and ethanoate ions can act as a buffer. 

A student performed a titration of 25.0 cm³ of 0.100 mol dm^-3 hydrochloric acid, HCl (aq) , with 0.100 mol of sodium hydroxide, NaOH (aq).
 

Draw the expected pH curve on the graph and indicate the equivalence point for this.

  

The student repeated the titration using two different chemicals, 25.0 cm³ of 0.100 mol dm^-3 nitric acid, HNO₃ (aq) , and 0.100 mol dm^-3 ammonia, NH₃ (aq).
 

State the equation for reaction between nitric acid and water, this reaction and identify the conjugate acid formed in the reaction. 

The image below shows the hexaaquaaluminium ion, [Al(H₂O)₆]³⁺. Explain why this can behave as an acid.

25.0 cm³ of 0.100 mol dm^-3 propanoic acid, CH₃CH₂COOH (aq) , is titrated with of 0.100 mol dm^-3 sodium hydroxide. The pH curve for this titration is shown below.

The student used the pH range of the indicators to determine which was the best one to use for this titration. 

The end point of an indicator depends on its pK_a 

A buffer solution contains a mixture of propanoic acid and its salt. A small amount of nitric acid is added to the buffer.

Write an equation, including state symbols, showing how this buffer can resist the change in pH.

Ammonia reacts with boron trifluoride to form an adduct, a molecule made from the combination of two others.

NH₃ + BF₃ →  NH₃BF₃

Identify the Lewis acid and base and the type of bond formed between a Lewis acid and base.

Explain the role of water, in terms of Lewis acid-base theory, in the following equations:

NH₃ (aq) + H₂O (l)   NH₄⁺ (aq) + OH^- (aq)

'All Brønsted-Lowry acids are Lewis acids but not all Lewis acids are Brønsted Lowry acids.'

Evaluate whether this statement is true, giving an appropriate example.

In the nitration of benzene, identify a species which acts as a Lewis base.

Sketch the titration curve when 50 cm³ of 0.1 mol dm^-3 HNO₃ (aq) is titrated against 25 cm³ of 0.1 mol dm^-3 NH₃ (aq).

Select a suitable indicator for the titration from table 22 of the Data booklet.

Calculate the pH of 0.1 mol dm^-3 ammonia using section 21 of the Data booklet.

Deduce, using section 21 of the Data booklet whether the pH of 0.1 mol dm^-3 ethylamine would be higher or lower than 0.1 mol dm^-3 ammonia solution.

Indicators are solutions of weak acids or bases. Methyl red has the molecular formula C₁₅H₁₅N₂O₂.

Draw the structure of the conjugate base of methyl red.

What will be seen if a few drops of methyl red are added during a titration of 50 cm³ of 0.1 mol dm^-3 HCl (aq) against 25 cm³ of 0.1 mol dm^-3 NaOH ( aq). 

The pKa of methyl red is 5.1. Explain how this relates to the acid-base character of methyl red when added to water.

Using section 21 of the Data booklet, discuss the relationship between the chemical structures and acidity of chloroethanoic acid, dichloroethanoic acid and trichloroethanoic acid.

This question is about acid buffers.

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20 cm³ of 0.05 mol dm^-3 dichloroethanoic acid was reacted with 10 cm³ of 0.10 mol dm^-3 sodium hydroxide. Suggest, with a reason, a pH value for the resulting solution.