Theories & Reactions of Acids & Bases (DP IB Chemistry: SL)

Malonic acid is a naturally occurring acid found in fruits and vegetables and is shown in Figure 1.

Figure 1 

The first dissociation of malonic acid is:

C₃H₄O₄ (aq) + H₂O (l) ⇌ C₃H₃O₄^- (aq) + H₃O⁺ (aq)

Identify one conjugate acid-base pair from the equation.

The equilibrium constant for the first dissociation of malonic acid is 1.48 x 10^-3.

State, with a reason, the strength of malonic acid.

The anion C₃H₃O₄^- may be classified as amphiprotic. Explain the meaning of amphiprotic and write equations, using C₃H₃O₄^-_, to illustrate your answer.

Under the right conditions, malonic acid can react with ethanol to form diethyl malonate, a diester.

Draw a displayed formula for diethyl malonate showing all the bonds.

Salicylic acid has the structure shown below in Figure 1.                             

Figure 1

Draw the structure of the conjugate base of salicylic acid, showing all the atoms and all the bonds.

Predict what would be seen if a small amount of copper (II) oxide was added to an aqueous solution of salicylic acid, HOC₆H₄COOH, and warmed.

Write a balanced equation for the reaction.

Suggest, with a reason, whether salicylic acid is likely to be soluble in water.

Determine the relative molecular mass, M_r, of salicylic acid using Table 6 from the Data book.

Write balanced equations to show the separate reactions between ethanoic acid and calcium carbonate, CaCO₃, magnesium oxide, MgO, and aluminium hydroxide, Al(OH)₃.

In Table 1 below, suggest the names and formulae of the acids and bases needed to make the specified salts.

Table 1

The ethanoate ion, CH₃COO^-, carbon dioxide, CO₂, and the ethoxide ion, CH₃CH₂O^-, all contain carbon oxygen bonds. 

Deduce the order in carbon to oxygen bond length from shortest to longest and explain your answer.

Ethanoic acid, CH₃COOH, shows two absorptions in an infrared spectrum that are not present in the spectrum of ethanol.

Using Table 26 of the Data book, state the wavenumber range of these absorptions and the bonds that cause them.

Glycolic acid, C₂H₄O₃, is a colourless, odourless crystalline solid that is highly soluble in water and behaves as a Brønsted–Lowry acid.

The systematic IUPAC name for glycolic acid is 2-hydoxyethanoic acid.

Draw the structural formula for its conjugate base, showing all the atoms and bonds.

Write an equation for the reaction between glycolic acid, C₂H₄O₃, and limescale, CaCO₃. State and explain one observation you would make.

State one reason why you would use glycolic acid to remove the limescale in a kettle at home, but not hydrochloric acid.

An alkaline solution is formed when sodium hydrogencarbonate is dissolved in water.

Write an equation for the reaction and explain why the solution is alkaline.

 State whether the HCO₃^- ion is behaving as a Brønsted–Lowry acid or as a base and give a reason for your answer.

Carbon dioxide gas dissolves in rainwater to form carbonic acid. State the formula of the conjugate base of carbonic acid.

Carbonic acid and sulfuric acid can be described as diprotic acids. Explain the meaning of diprotic.

Explain why an ammonium ion can not behave as a Brønsted-Lowry base.

State and explain the acid-base character of aqueous ammonia at 298 K.

Acids can be classed as monoprotic, diprotic and triprotic. Sulfuric acid is a diprotic acid. 

The second ionisation step is for the ionisation of sulfuric acid is as follows.

HSO₄^- (aq) + H₂O (aq) ⇌ SO₄^2- (aq) + H₃O⁺ (aq)

Suggest why the second ionisation step reaches equilibrium.

Sodium hydrogen carbonate solution, NaHCO₃ (aq) , can act as an amphiprotic species. State the equation for the reaction fo NaHCO₃ (aq) with the following compounds:

Using your answer to part a) i) and ii), explain why NaHCO₃ is amphiprotic. 

Phosphine is usually prepared by heating white phosphorus, one of the allotropes of phosphorus, with concentrated aqueous sodium hydroxide.

The equation for the reaction is.

P₄ (s) + 3OH⁻ (aq) + 3H₂O (l) → PH₃ (g) + 3H₂PO₂⁻ (aq)

Identify the amphiprotic species in this reaction giving the formulas of both species it is converted to when it behaves in this manner.

1.68 g of white phosphorus was used to make phosphine

Oxalic acid, H₂C₂O₄ , is a weak diprotic acid and can be used in titrations. State the equation for the reaction of oxalic acid with sodium hydroxide. 

The ionisation of oxalic acid occurs in two steps. State equations for both of these steps. 

Tartaric acid shown below behaves as a Brønsted-Lowry acid when it reacts with calcium hydroxide, Ca(OH)₂. Sketch the structure of the salt formed from this reaction. 

Using ionic equations state how HPO₄^2- can behave as an amphiprotic and amphoteric species.

Gallium oxide behaves as an amphoteric oxide. State two equations to show how gallium oxide reacts with a strong monoprotic acid and strong base.

Reaction with strong monoprotic acid .........................................................................................................................................

Reaction with strong base .........................................................................................................................................

Identify the Br∅nsted-Lowry acids in the following reaction.

CH₃CH₂O^- (aq) + H₂O (l) CH₃CH₂OH (aq) + OH^- (aq)