A salt X is formed and a gas is evolved when ethanoic acid reacts with sodium hydrogencarbonate. Name the salt X and the gas evolved. Describe an activity and draw the diagram of the apparatus to prove that the evolved gas is the one which you have named. Also, write the chemical equation of the reaction involved.
Salt formed: Sodium ethanoate (\(CH_3COONa\))
Gas evolved: Carbon dioxide (\(CO_2\))
Activity:
Take a test tube and add a small amount of sodium hydrogencarbonate.
Add ethanoic acid (acetic acid) to it through a thistle funnel.
A brisk effervescence appears due to evolution of \(CO_2\).
Pass the gas produced through lime water using a delivery tube.
The lime water turns milky, confirming the presence of \(CO_2\).
Chemical equation:
\[ CH_3COOH + NaHCO_3 \rightarrow CH_3COONa + H_2O + CO_2 \]
(a) What are hydrocarbons? Give examples.
(b) Give the structural differences between saturated and unsaturated hydrocarbons with two examples each.
(c) What is a functional group? Give examples of four different functional groups.
(a) Hydrocarbons: Compounds made up of carbon and hydrogen atoms only. Examples: methane (\(CH_4\)), ethane (\(C_2H_6\)).
(b) Structural differences:
Saturated hydrocarbons: Contain only single bonds between carbon atoms.
Examples:
Methane: \(CH_4\)
Ethane: \(CH_3-CH_3\)
Unsaturated hydrocarbons: Contain at least one double or triple bond.
Examples:
Ethene: \(CH_2=CH_2\)
Ethyne: \(CH\equiv CH\)
(c) Functional group: An atom or group of atoms that gives characteristic chemical properties to a compound.
Examples:
Hydroxyl group (−OH)
Carboxyl group (−COOH)
Aldehyde group (−CHO)
Ketone group (\(C=O\))
Name the reaction which is commonly used in the conversion of vegetable oils to fats. Explain the reaction involved in detail.
Reaction name: Hydrogenation reaction
Explanation:
Vegetable oils contain unsaturated hydrocarbons (double bonds). When hydrogen gas is passed through the oil in the presence of a nickel catalyst and moderate heat, the double bonds are converted into single bonds. This forms saturated fats, which are solid at room temperature.
Chemical representation:
\[ R−C = C−R + H_2 \xrightarrow{Ni} R−CH−CH−R \]
This process converts liquid oils into semi-solid or solid fats such as vanaspati ghee.
(a) Write the formula and draw the electron dot structure of carbon tetrachloride.
(b) What is saponification? Write the reaction involved in this process.
(a) Carbon tetrachloride:
Formula: \(CCl_4\)
Electron dot structure:
C is surrounded by four Cl atoms with shared electron pairs as single covalent bonds (represented diagrammatically).
(b) Saponification:
Saponification is the process in which an ester reacts with a base to form a salt of a carboxylic acid (soap) and alcohol.
Reaction:
\[ CH_3COOC_2H_5 + NaOH \rightarrow CH_3COONa + C_2H_5OH \]
Esters are sweet-smelling substances and are used in making perfumes. Suggest some activity and the reaction involved for the preparation of an ester with a well-labeled diagram.
Activity to prepare an ester:
Take 1 mL ethanol and 1 mL glacial acetic acid in a test tube.
Add a few drops of concentrated sulphuric acid.
Warm the mixture in a water bath for 10–15 minutes.
Pour into a beaker containing water and smell the sweet fruity ester formed.
Reaction:
\[ CH_3COOH + C_2H_5OH \xrightarrow{Conc.\ H_2SO_4} CH_3COOC_2H_5 + H_2O \]
Diagram: (The setup includes a test tube containing reactants, placed in a water bath and heated gently.)
A compound C (molecular formula \(C_2H_4O_2\)) reacts with Na-metal to form a compound R and evolves a gas which burns with a pop sound. Compound C on treatment with an alcohol \(A\) in the presence of an acid forms a sweet-smelling compound S (molecular formula \(C_3H_6O_2\)). On addition of NaOH to C, it also gives R and water. S on treatment with NaOH solution gives back R and A. Identify C, R, A, S and write the reactions involved.
Identification:
C = Ethanoic acid (\(CH_3COOH\))
R = Sodium ethanoate (\(CH_3COONa\))
A = Methanol (\(CH_3OH\))
S = Methyl ethanoate (\(CH_3COOCH_3\))
Reactions involved:
1. Reaction of C with Na:
\[ 2CH_3COOH + 2Na \rightarrow 2CH_3COONa + H_2 \]
2. Esterification reaction:
\[ CH_3COOH + CH_3OH \xrightarrow{Conc.\ H_2SO_4} CH_3COOCH_3 + H_2O \]
3. Reaction of C with NaOH:
\[ CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O \]
4. Saponification of ester S:
\[ CH_3COOCH_3 + NaOH \rightarrow CH_3COONa + CH_3OH \]
Look at Figure 4.1 and answer the following questions:
(a) What change would you observe in the calcium hydroxide solution taken in tube B?
(b) Write the reaction involved in test tubes A and B respectively.
(c) If ethanol is given instead of ethanoic acid, would you expect the same change?
(d) How can a solution of lime water be prepared in the laboratory?
(a) The calcium hydroxide solution (lime water) in tube B will turn milky.
(b) Reactions involved:
In test tube A:
\[ 2CH_3COOH + Na_2CO_3 \rightarrow 2CH_3COONa + H_2O + CO_2 \]
In test tube B:
\[ Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O \]
With excess CO₂, milkiness disappears:
\[ CaCO_3 + H_2O + CO_2 \rightarrow Ca(HCO_3)_2 \]
(c) No. Ethanol does not react with sodium carbonate, so no CO₂ is produced and no milky appearance is observed.
(d) Lime water is prepared by dissolving calcium oxide in water and decanting the clear supernatant liquid.
How would you bring about the following conversions? Name the process and write the reaction involved.
(a) Ethanol to ethene
(b) Propanol to propanoic acid
(a) Ethanol to ethene — Dehydration
Ethanol is heated with concentrated sulphuric acid at 443 K to form ethene.
\[ CH_3CH_2OH \xrightarrow[443K]{Hot\ conc.\ H_2SO_4} CH_2 = CH_2 + H_2O \]
(b) Propanol to propanoic acid — Oxidation
Propanol is oxidised using alkaline potassium permanganate (KMnO₄).
\[ CH_3CH_2CH_2OH \xrightarrow{Alk.\ KMnO_4,\ Heat} CH_3CH_2COOH \]
Draw the possible isomers of the compound with molecular formula \(C_3H_6O\) and also give their electron dot structures.
The possible isomers of \(C_3H_6O\) are:
(1) Propanone
Structure: \(CH_3−CO−CH_3\)
Electron dot structure includes a carbonyl group with each carbon bonded appropriately (diagrammatic representation).
(2) Propanal
Structure: \(CH_3−CH_2−CHO\)
Electron dot structure shows the aldehyde group with proper valence electrons around O and C.
Explain the given reactions with examples:
(a) Hydrogenation reaction
(b) Oxidation reaction
(c) Substitution reaction
(d) Saponification reaction
(e) Combustion reaction
(a) Hydrogenation reaction:
Unsaturated hydrocarbons add hydrogen in the presence of nickel catalyst.
\[ RC = CR + H_2 \xrightarrow{Ni} RCH−CHR \]
(b) Oxidation reaction:
Ethanol is oxidised to ethanoic acid by alkaline KMnO₄.
\[ CH_3CH_2OH \xrightarrow{Alk.\ KMnO_4,\ Heat} CH_3COOH \]
(c) Substitution reaction:
Chlorine replaces hydrogen in methane in presence of sunlight.
\[ CH_4 + Cl_2 \xrightarrow{h u} CH_3Cl + HCl \]
(d) Saponification reaction:
Esters react with alkali to form soap and alcohol.
\[ CH_3COOC_2H_5 + NaOH \rightarrow CH_3COONa + C_2H_5OH \]
(e) Combustion reaction:
Carbon compounds burn in oxygen to produce \(CO_2\), \(H_2O\), heat and light.
\[ CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O + \text{Heat} \]
An organic compound A on heating with concentrated \(H_2SO_4\) forms a compound B which on addition of one mole of hydrogen in the presence of Ni forms a compound C. One mole of compound C on combustion forms two moles of \(CO_2\) and three moles of \(H_2O\). Identify the compounds A, B and C and write the chemical equations of the reactions involved.
Identification of compounds:
The combustion products indicate that compound C is \(C_2H_6\) (ethane).
Since C is formed by hydrogenation of B, B must be \(C_2H_4\) (ethene).
Compound A forms B on dehydration, so A is \(C_2H_5OH\) (ethanol).
Reactions involved:
1. Dehydration of ethanol:
\[ C_2H_5OH \xrightarrow{Hot\ conc.\ H_2SO_4} C_2H_4 + H_2O \]
2. Hydrogenation of ethene:
\[ C_2H_4 + H_2 \xrightarrow{Ni} C_2H_6 \]
3. Combustion of ethane:
\[ 2C_2H_6 + 7O_2 \rightarrow 4CO_2 + 6H_2O + \text{Heat} \]