Carboxylic acids (Edexcel IGCSE Chemistry (Modular): Unit 2)

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Butanoic acid behaves like other acids.

Which is the correct statement about the reactions of butanoic acid?

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This question is about alcohols, carboxylic acids and their reactions.

The boxes give some information about a carboxylic acid. Complete the boxes by giving the missing information.

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Ethanol can be oxidised to produce a carboxylic acid.

i) Give the names of the two reagents used in this oxidation reaction.

(2)

1. ..............................................................
2. ..............................................................

ii) Which of these colour changes occurs during the reaction?

(1)

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Alcohols and carboxylic acids can be heated together to form esters.

i) State why it is better to heat the mixture using a water bath rather than directly with a Bunsen burner flame.

(1)

ii) An ester has the structural formula CH₃CH₂COOCH₃ Which of these is the name of this ester?

(1)

What is the empirical formula of butanoic acid?

Methanoic acid is the first member of the homologous series of carboxylic acids.

Give two general characteristics of a homologous series.

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In some areas when water is boiled, the inside of kettles become coated with a layer of calcium carbonate. This can be removed by adding methanoic acid.

i) Complete the equation.

............ HCOOH + CaCO₃ → Ca(HCOO)₂ + ................. + .................

(2)

ii) Methanoic acid reacts with most metals above hydrogen in the reactivity series. Complete the word equation.

zinc + methanoic acid → ............................................ + ............................................

(2)

iii) Aluminium is also above hydrogen in the reactivity series. Why does methanoic acid not react with an aluminium kettle?

(1)

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Draw the displayed formula for the ester formed when methanoic acid reacts with ethanol. 

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Give the name, molecular formula and empirical formula of the fourth acid in this series.

name ...........................................................................................................................

(1)

molecular formula .......................................................................................................

(1)

empirical formula ........................................................................................................

(1)

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Ethanoic acid is a carboxylic acid used in vinegar. 

Which of these statements is true about ethanoic acid?

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When a bottle of wine is left open, ethanoic acid and water can form as a result of ethanol reacting with the oxygen in the air.

i) Complete the equation for this reaction.

......................  +   O₂. →    CH₃COOH   + ........................

(2)

ii) Which calculation shows the percentage by mass of hydrogen in ethanoic acid?

(A_r of hydrogen, H = 1, M_r of ethanoic acid, CH₃COOH = 60)

(1)

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Propanoic acid, C₂H₅COOH,  belongs to the same homologous series as ethanoic acid. 

It can react with sodium hydroxide to form sodium propanoate, C₃H₅NaO₂ and water. 

i) Draw the structure of a molecule of propanoic acid, showing all covalent bonds. 

(2)

ii) Write a balanced symbol equation for the reaction between propanoic acid and sodium hydroxide.

(1)

Describe a chemical test that could be done to show that propanoic acid is acidic. 

This question is about carboxylic acids. Solutions of carboxylic acids react with magnesium metal to form hydrogen gas. A student uses this apparatus to investigate the time taken to produce 10 cm³ of hydrogen gas from different carboxylic acids.

This is the student’s method.

• pour some carboxylic acid solution into a conical flask

• add some magnesium powder

• quickly connect the gas syringe and start a timer

• record the time taken to collect 10 cm³ of hydrogen gas

The student repeats the method with three other carboxylic acids.

i) All the carboxylic acids are of the same concentration. Give two other variables the student should control in his investigation.

(2)

ii) Give a reason why it is important to connect the gas syringe quickly.

(1)

The table shows the student’s results.

i) Calculate the mean (average) time for propanoic acid to produce 10 cm³ of hydrogen gas.

(2)

mean time = ............................................................................. s

ii) Deduce the relationship between the number of carbon atoms in the molecule and the time taken to produce 10 cm³ of hydrogen gas.

(1)

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An ester is formed by adding ethanoic acid to ethanol in the presence of sulfuric acid. Give the displayed formula of the ester produced when ethanoic acid reacts with ethanol.

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This question is about the reactions of organic compounds A - E shown in Figure 1. 

Figure 1 

Name compound C. 

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Name the two products formed when E reacts with sodium.

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Which compound reacts with compound A to produce compound C? 

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Which compound dissolves in water to produce a neutral solution?

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Alcohol A has the structural formula, CH₃CH₂OH.

Which product is formed when alcohol A is oxidised using acidified potassium dichromate (VII)?

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When alcohol A reacts with propanoic acid, an ester, B is formed. 

CH₃CH₂OH + CH₃CH₂COOH → B + H₂O

Give the name and structural formula of B.

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Propanoic acid reacts with sodium carbonate.

Write the balanced symbol equation for the reaction.

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Propanoic acid also reacts with magnesium 

2CH₃CH₂COOH (aq) + Mg (s) → (CH₃CH₂COO)₂Mg (aq)  + H₂ (g) 

An excess of magnesium was added to 50 cm³ of 1.0 mol / dm³ and the hydrogen gas produced was collected in a gas syringe. 

Calculate the volume, in cm³, of hydrogen gas produced in this reaction.

 Volume of hydrogen gas collected .................................................... cm³

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Propanoic acid is a carboxylic acid. Its formula is CH₃–CH₂–COOH.

 i) Propanoic acid is the third member of the homologous series of carboxylic acids.

Give the name and structural formula of the fourth member of this series.

  Name ..............................................................

  Formula ..............................................................

(2)

ii) Members of a homologous series have very similar chemical properties.

  State three other characteristics of a homologous series.

(3)

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Carboxylic acids can be made by the oxidation of alcohols.

 i) Draw the structural formula of the alcohol which can be oxidised to propanoic acid. Show all atoms and bonds.

(1)

ii) Name a reagent, other than oxygen, which can oxidise alcohols to carboxylic acids.

(2)

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Complete the following equations for some of the reactions of propanoic acid.

 i) Zinc + propanoic acid → .................. .................. + hydrogen

(1)

 ii) Calcium oxide + propanoic acid → .................. + ..................

 (1)

 iii) LiOH + CH₃CH₂COOH →  .................. + ..................

 (1)

 iv) ......CaCO₃ + ......C₂H₅COOH →  .................. + .................. +  ..................

(1)

A piece of magnesium was added to 100 cm³ of an aqueous acid. The time taken for the metal to react completely was measured. 

This experiment was repeated using different aqueous acids. The same volume of acid was used in each experiment and the pieces of magnesium used were identical. 

In one experiment the reaction was carried out at a different temperature.

 Explain the following in terms of collision rate between reacting particles.

 i) Why is the rate in experiment C slower than the rate in experiment A? 

(2)

ii) Why is the rate in experiment B faster than the rate in experiment A?

(2)

iii) Why is the rate in experiment D faster than the rate in experiment A?

(3)

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Carboxylic acids contain the group

Ethanoic acid is a typical carboxylic acid. It forms ethanoates.

Complete the following equations.

Mg + ......CH₃COOH → ............................... + ...............................

(2)

sodium hydroxide + ethanoic acid → ........................  ........................ + ........................

(1)

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Ethanoic acid reacts with ethanol to form an ester. Give the name of the ester and draw its displayed formula. Show all of the bonds.

Maleic acid is an unsaturated acid. 5.8 g of this acid contained 2.4 g of carbon, 0.2 g of hydrogen and 3.2 g of oxygen.

i) How do you know that the acid contained only carbon, hydrogen and oxygen?

 (1)

ii) Calculate the empirical formula of maleic acid.   Number of moles of carbon atoms = ................................

  Number of moles of hydrogen atoms = ................................

 Number of moles of oxygen atoms = ................................

 The empirical formula is ......................................................................................

 (3)

iii) The mass of one mole of maleic acid is 116 g. What is its molecular formula?

 (2)

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Maleic acid is dibasic. One mole of acid produces two moles of H⁺. Deduce its structural formula.