VCE Chemistry Qualitative Tests [4.1] Workbook Solutions PDF

Website: contoureducation.com.au | Phone: 1800 888 300 Email: [email protected] VCE Chemistry ¾ Qualitative Tests [4.1]...

Website: contoureducation.com.au | Phone: 1800 888 300 Email: [email protected] VCE Chemistry ¾ Qualitative Tests [4.1] Workbook Solutions Outline: Qualitative Physical Tests Pg 2-23 Qualitative Chemical Tests Pg 24-45 Introduction to Qualitative Tests Carbon to Double Bonds (C = C) Tests Melting Point/Boiling Point Hydroxyl Group Tests Solubility Carboxyl Tests pH (Potential of Hydrogen) 1  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Section A: Qualitative Physical Tests Sub-Section: Introduction to Qualitative Tests Context So far, we’ve been able to see the structure molecules, such as the two molecules below: In practice, you will only see this: Discussion: How can we determine what functional groups each molecule has? Chemical ____________________ Properties. ____________________ Physical Properties. [4.1] 2  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Let’s first look at physical properties! Physical Properties Definition: A characteristic of a substance that can be observed/measured without changing the identity of a substance. Examples: melting point, boiling point, viscosity. Discussion: What physical properties can be easily tested of a molecule? Melting/boiling point _____________________________ Solubility _____________________________ _____________________________ Colour _____________________________ pH NOTE: While viscosity can be tested, it is impractical to do so! Space for Personal Notes [4.1] 3  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Sub-Section: Melting Point/Boiling Point Exploration: States of Matter Consider two unknown substances, one is methane (CH4 ) and one is heptane (C7 H16 ), which look like the following: Which is more likely to have stronger intermolecular bonds? [Methane]/[Heptane] Which is more likely to pack closer together? [Methane]/[Heptane] Which is more likely to be a liquid at the same temperature? [Methane]/[Heptane] Substance 𝑨 Substance 𝑩 [Methane]/[Heptane] [Methane]/[Heptane] NOTE: This idea also links to melting point determination which will be investigated properly later! Space for Personal Notes [4.1] 4  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Question 1 Walkthrough. Henry has two vials of substances, one containing ethanol, and the other containing ethanal. At SLC, the substances look like the below. Determine the likely identity of each of the compounds. Substance 𝑨 Substance 𝑩 Gaseous in state. Liquid in state. Identity: Identity: Ethanal Ethanol Your turn! Question 2 For each of the following, determine the likely identity of each of the compounds at a given temperature. a. At 50℃, both methyl methanoate and ethanol are present. Substance 𝑨 Substance 𝑩 Gaseous in state. Liquid in state. Identity: Identity: Methyl methanoate Ethanol b. At 200℃, both ethanoic acid and ethanedioic acid are present. Substance 𝑨 Substance 𝑩 Liquid in state. Gaseous in state. Identity: Identity: Ethanedioic acid Ethanoic acid [4.1] 5  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] c. At 103℃, both pentan-1-amine and pentanone are present. Substance 𝑨 Substance 𝑩 Gaseous in state. Liquid in state. Identity: Identity: Pentanone Pentan-1-amine Sub-Section: Solubility Context Another separating factor of organic molecules is their solubility in water. Intermolecular bonding of water: Hydrogen bonding. What happens if wine (ethanol) is mixed with water? Do they dissolve? [Yes]/[No] [4.1] 6  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Solubility & Miscibility Soluble Definition: A solid can become incorporated into a liquid to form a solution. Miscible Definition: Two liquids are miscible if they can mix to form one homogeneous solution. In the context for VCE Chemistry ¾, solubility and miscibility are roughly the same! What makes something soluble in water? Exploration: Solubility in Water Consider a beaker of water. How do the bonds form? (Label Below) Consider Ethanol: Polarity: [Polar]/[Non-Polar] Stronger Intermolecular Bonding: [Dispersion Forces]/[Dipole-Dipole]/[Hydrogen Bonding] [4.1] 7  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Consider a beaker of ethanol liquid (𝐂𝟐 𝐇𝟓 𝐎𝐇(𝐥)). How do the bonds form? (Label Below) Both water and ethanol form hydrogen bonds with themselves. What if the two liquids are mixed? When ethanol and water are mixed, they initially form two layers. Eventually they both form hydrogen bonds with each other and ________________ dissolve together! [4.1] 8  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Let’s look at a similar scenario, but with another compound instead! Exploration: Hexane Consider hexane (C6 H14 ): Polarity: [Polar]/[Non-Polar] Stronger Intermolecular Bonding: [Dispersion Forces]/[Dipole-Dipole]/[Hydrogen Bonding] When hexane and water are mixed, again, two layers will initially form: Can hexane and water undergo the same type of intermolecular bonds? [Yes]/[No] Will they dissolve? [Yes]/[No] [4.1] 9  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Key Takeaways Polar and polar molecules will dissolve (as they both undergo dipole-dipole/hydrogen bonding with each other). Non-polar and non-polar molecules will dissolve (as they both undergo Dispersion Forces only with each other). Polar and non-polar molecules will not dissolve (as one undergoes Dispersion Forces only while the other undergoes stronger dipole-dipole/hydrogen bonding with itself. As such, we see that like dissolves with like. Exploration: Solubility With Water Stronger Stronger Solubility in Molecule intermolecular bond intermolecular bond Water with itself with water [Dispersion Forces]/ [Dispersion Forces]/ [Soluble]/ [Dipole-Dipole]/ [Dipole-Dipole]/ [Insoluble] [Hydrogen Bonds] [Hydrogen Bonds] Alkanes [Dispersion Forces]/ [Dispersion Forces]/ [Soluble]/ [Dipole-Dipole]/ [Dipole-Dipole]/ [Insoluble] [Hydrogen Bonds] [Hydrogen Bonds] Alkene [Dispersion Forces]/ [Dispersion Forces]/ [Soluble]/ [Dipole-Dipole]/ [Dipole-Dipole]/ [Insoluble] [Hydrogen Bonds] [Hydrogen Bonds] Haloalkane [4.1] 10  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] [Dispersion Forces]/ [Dispersion Forces]/ [Soluble]/ [Dipole-Dipole]/ [Dipole-Dipole]/ [Insoluble] [Hydrogen Bonds] [Hydrogen Bonds] Alcohol [Dispersion Forces]/ [Dispersion Forces]/ [Soluble]/ [Dipole-Dipole]/ [Dipole-Dipole]/ [Insoluble] [Hydrogen Bonds] [Hydrogen Bonds] Ketone [Dispersion Forces]/ [Dispersion Forces]/ [Soluble]/ [Dipole-Dipole]/ [Dipole-Dipole]/ [Insoluble] [Hydrogen Bonds] [Hydrogen Bonds] Carboxylic acid [Dispersion Forces]/ [Dispersion Forces]/ [Soluble]/ [Dipole-Dipole]/ [Dipole-Dipole]/ [Insoluble] [Hydrogen Bonds] [Hydrogen Bonds] Amine [Dispersion Forces]/ [Dispersion Forces]/ [Soluble]/ [Dipole-Dipole]/ [Dipole-Dipole]/ [Insoluble] [Hydrogen Bonds] [Hydrogen Bonds] Amide [4.1] 11  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] [Dispersion Forces]/ [Dispersion Forces]/ [Soluble]/ [Dipole-Dipole]/ [Dipole-Dipole]/ [Insoluble] [Hydrogen Bonds] [Hydrogen Bonds] Aldehyde [Dispersion Forces]/ [Dispersion Forces]/ [Soluble]/ [Dipole-Dipole]/ [Dipole-Dipole]/ [Insoluble] [Hydrogen Bonds] [Hydrogen Bonds] Ether [Dispersion Forces]/ [Dispersion Forces]/ [Soluble]/ [Dipole-Dipole]/ [Dipole-Dipole]/ [Insoluble] [Hydrogen Bonds] [Hydrogen Bonds] Benzene Question 3 Classify whether the following will be soluble or insoluble in water. a. Methanol c. Propan-2-amine [Soluble]/[Insoluble] [Soluble]/[Insoluble] b. Ethane d. Cyclohexane [Soluble]/[Insoluble] [Soluble]/[Insoluble] [4.1] 12  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Question 4 Classify whether the following will be soluble or insoluble in hexane (C6 H14 ). a. Octane c. Glycerol [Soluble]/[Insoluble] [Soluble]/[Insoluble] b. Ethanol d. Butanamide [Soluble]/[Insoluble] [Soluble]/[Insoluble] Exploration: Comparing Solubility Consider ethanol vs butan-1-ol: Ethanol (𝐂𝟐 𝐇𝟓 𝐎𝐇) Butan-𝟏-ol (𝐂𝟒 𝐇𝟗 𝐎𝐇) Forms [Stronger]/[Weaker] intermolecular bonds. Forms [Stronger]/[Weaker] intermolecular bonds. [Greater]/[Lesser] proportion of molecule can [Greater]/[Lesser] proportion of molecule can form hydrogen bonds. form hydrogen bonds. [More]/[Less] soluble in water. [More]/[Less] soluble in water. [4.1] 13  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] NOTE: Extent of solubility is related to how polar the molecule is, rather than how large the molecule is! Question 5 In each scenario, circle which molecule has greater solubility in water. a. Chloromethane - dipole-dipole b. 1-butanol − hydrogen bonds c. Ethanol – more polar [4.1] 14  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Question 6 The properties of ethanol and octanol are to be investigated. a. Determine whether each of the following is likely to be soluble in water. i. Ethanol: [soluble]/[insoluble] in water. ii. Octanol: [soluble]/[insoluble] in water. b. Justify your answer to part a. _____________________________________________________________________________________ _____________________________________________________________________________________ Ethanol is soluble as it contains the hydroxyl group which can form hydrogen bonds with water. However, as octanol has a long non-polar chain, majority of the molecule cannot form _____________________________________________________________________________________ hydrogen bonds, and thus is insoluble in water. _____________________________________________________________________________________ _____________________________________________________________________________________ NOTE: While it depends on the functional group present, the turning point is roughly four carbons long where the non-polar chain starts to become too long and the substance is deemed ‘non-polar’ and insoluble in water. Space for Personal Notes [4.1] 15  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Let’s look at another question together! Question 7 Walkthrough. Four substances, ethane, chloroethane, ethanol and octane were present in separate vessels, but Hunter has accidentally mislabelled them, and thus their identities are no longer known. However, the following information is known about the substances. Identify each of the substances. Vessel 𝑨 𝑩 𝑪 𝑫 Solubility in water Soluble Soluble Insoluble Insoluble State of matter at Gas Liquid Liquid Gas SLC Substance Chloroethane Ethanol Octane Ethane Your turn! Question 8 Three substances, methane, octan-2-ol and ethanol are investigated. The following information is known about the substances. Identify each of the substances. Vessel 𝑨 𝑩 𝑪 Solubility in water Soluble Insoluble Insoluble State of matter at SLC Liquid Gas Liquid Substance Ethanol Methane Octan-1-ol [4.1] 16  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Question 9 Four substances, propane, octan-1-amine, ethan-1-amine, ethanamide are to be investigated. The following information is known about the substances. Identify each of the substances. Vessel 𝑨 𝑩 𝑪 𝑫 Solubility in water Soluble Insoluble Soluble Insoluble State of matter at Gas Gas Liquid Liquid SLC Substance Ethan-1-amine Propane Ethanamide Octan-1-amine Question 10 Additional. Both ethanoic acid and butan-1-ol have a similar boiling point of roughly 110-118℃, and they are both relatively soluble in water. Propose a test that could be made to distinguish between the two substances. _____________________________________________________________________________________ pH testing. _____________________________________________________________________________________ Any of the hydroxyl/carboxyl chemical tests. Space for Personal Notes [4.1] 17  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Sub-Section: 𝐩𝐇 (Potential of Hydrogen) Exploration: 𝐩𝐇 levels of each functional group According to the Bronsted Lowry Definition, acids and bases are both associated with hydrogen ions (H + ), whereby: The acid is said to [accept]/[donate] hydrogen ions (H + ). The base is said to [accept]/[donate] hydrogen ions (H + ). Which functional group acts as an acid/base? Molecule Acid/Base? Molecule Acid/Base? [Acid]/[Base] [Acid]/[Base] /[Neither] /[Neither] Alkanes Amine [Acid]/[Base] [Acid]/[Base] /[Neither] /[Neither] Alkene Amide [Acid]/[Base] [Acid]/[Base] /[Neither] /[Neither] Haloalkane Aldehyde [4.1] 18  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] [Acid]/[Base] [Acid]/[Base] /[Neither] /[Neither] Alcohol Ether [Acid]/[Base] [Acid]/[Base] /[Neither] /[Neither] Benzene Ketone [Acid]/[Base] /[Neither] Carboxylic acid Carboxylic Acid: [4.1] 19  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Amine: NOTE: Carboxylic Acids → acidic, Amines → basic! ALSO NOTE: Amides are very weak bases, and are only slightly basic. You do not have to know why! Discussion: How can we quickly test if something is an acid/base? Method Type of Test Use pH Meter/Indicator. Physical test React it with acid/base. Chemical test Let’s keep only focusing on physical tests for now! How do we use indicators? Space for Personal Notes [4.1] 20  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Exploration: Indicators The pH ranges of different indicators can be found on page 𝟓 of the databook. Colour change from lower to Name 𝐩𝐇 range higher 𝐩𝐇 in range Thymol blue (𝟏𝐬𝐭 change) 1.2-2.8 Red → Yellow Methyl orange 3.1-4.4 Red → Yellow Bromophenol blue 3.0-4.6 Yellow → Blue Methyl red 4.4-6.2 Red → Yellow Bromothymol blue 6.0-7.6 Yellow → Blue Phenol red 6.8-8.4 Yellow → Red Thymol blue (𝟐𝐧𝐝 change) 8.0-9.6 Yellow → Blue Phenolphthalein 8.3-10.0 Colourless → Pink Consider Methyl Orange: Question 11 Walkthrough. Determine the colour of bromothymol blue if it is placed in: a. A basic environment with a pH of 10. b. A neutral environment with a pH of 7. Blue Green [4.1] 21  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Question 12 Determine the colour of phenol red if it is placed in: a. A basic environment. c. A neutral environment. Red Orange b. An acidic environment. Yellow Question 13 Additional. Determine the colour of thymol blue when it’s placed in: a. A basic environment with pH = 10. c. A neutral environment with pH = 7. Blue Yellow b. An acidic environment with pH = 1. Red Let’s use this to identify what functional groups are present! Question 14 Walkthrough. Three compounds, pentane, ethanoic acid and ethanamine are to be investigated, which are all liquid at SLC. The following information about them is given when they are mixed with water with methyl red indicator added. Identify each of them. Vessel 𝑨 𝑩 𝑪 Solubility in water Soluble Soluble Insoluble Colour of water Red Yellow Yellow Substance Ethanoic acid Ethanamine Pentane [4.1] 22  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Your turn! Question 15 Three compounds, ethanal, octan-1-ol and ethanoic acid. The following information about them is given, whereby they attempted to be mixed with water with bromothymol blue indicator added. Identify each of them. Vessel 𝑨 𝑩 𝑪 Solubility in water Soluble Soluble Insoluble Colour of water Yellow Blue Blue Substance Ethanoic acid Ethanal Octan-1-ol Question 16 Three compounds, propanone, propan-1-amine, propanamide. The following information about them is given, whereby they attempted to be mixed with water with thymol blue indicator added. Identify each of them. Vessel 𝑨 𝑩 𝑪 Solubility in water Soluble Soluble Soluble Colour of water Blue Yellow Green Substance Propan-1-amine propanone propanamide So far, we’ve looked at physical tests, now let’s look at chemical tests! [4.1] 23  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Section B: Qualitative Chemical Tests Sub-Section: Carbon to Carbon Double Bonds (𝐂 = 𝐂) Tests Exploration: Alkene vs Alkanes Reactions Consider molecules with C = C bonds (alkenes): Saturation level: [Saturated]/[Unsaturated] Type of reaction it can undergo: Addition reaction ______________________________ If brown bromine liquid (𝐁𝐫𝟐 (𝐥)) is added to an alkene: What happens to the colour of the solution? Turns colourless. Consider molecules with no C = C bonds (alkanes): [4.1] 24  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Saturation level: [Saturated]/[Unsaturated] Can alkanes undergo addition reactions? [Yes]/[No] Here is a video showing the reaction which takes place! (Play at 1.5 × speed) Video Link (Video 𝟏): https://youtube.com/playlist?list=PL2hVhOVQpiYQ2b13f_T2Kx3G- _oc8oeVy&si=8sywpRZidB2TH3B4 NOTE: To determine if a molecule has C = C double bonds, we can add a halogen to it and see if there is a colour change! ALSO NOTE: The same thing works with halogens like Iodine (I2 ). Generally, it does not work as well with halogens like Fluorine (F2 ) and Chlorine (Cl2 ) as they are gases at SLC! REMINDER: The colours for different halogens can be found on page 𝟓 of the databook. Question 17 Walkthrough. A test tube contains either butane or but-1-ene. When iodine is added to the test tube, the solution turns brown. Identify the substance present. Justify your answer by writing any reaction(s) which may take place. _____________________________________________________________________________________ Butane – if it turns brown, the iodine did not react, meaning the molecule is saturated. _____________________________________________________________________________________ NOTE: If it changes to the same colour of the halogen, it means no reaction has taken place! [4.1] 25  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Question 18 Test tube 𝐴 and test tube 𝐵 both contain a colourless hydrocarbon at the beginning, and both have bromine liquid added to them. The experiment along with the results are shown below. Given that the test tubes contain either propane or propene, identify which substance is in test tube 𝐴 and 𝐵, giving justification for your reasoning. a. Test tube 𝐴 Substance: Propene ______________________________ Justification: _____________________________________________________________________________________ Colour does not stay brown, meaning Br2 reacted away, meaning compound is unsaturated. _____________________________________________________________________________________ b. Test tube 𝐵 Propane Substance: ______________________________ Justification: _____________________________________________________________________________________ Colour does stays brown, meaning Br2 did not react away, meaning compound is saturated. _____________________________________________________________________________________ [4.1] 26  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Exploration: Degree of Unsaturation Consider the following molecules. But-𝟏-ene Buta-𝟏, 𝟐-diene 𝐧𝐮𝐦𝐛𝐞𝐫 𝐨𝐟 𝐂 = 𝐂 𝐛𝐨𝐧𝐝𝐬 = 𝐚𝐦𝐨𝐮𝐧𝐭 𝐨𝐟 𝐈𝟐 𝐚𝐝𝐝𝐞𝐝 Question 19 Walkthrough. Consider a mixture with buta-1,3-diene (C4 H6 ). Fluorine gas is added until the molecule is fully saturated. a. Complete the equation for the reaction which takes place. b. Find the theoretical mass of fluorine which reacts with 8.30 𝑔 of buta-1,3-diene. _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ [4.1] 27  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] What if we don’t know the number of double bonds? Degree of Unsaturation Definition: The amount of C = C bonds present in a molecule. Active Recall: Find the integer ratio of the following: 𝟎. 𝟎𝟓𝟔𝟖: 𝟎. 𝟏𝟕𝟎𝟑 1: 3 Question 20 Walkthrough. 0.0250 𝑚𝑜𝑙 of an unknown colourless hydrocarbon 𝑌 which only contains carbon-carbon single bonds or carbon-carbon double bonds are placed into a test tube. Drops of brown iodine (I2 ) are added until a brown colour remains. The amount of iodine added was 19.0 𝑔. Determine the degree of unsaturation present in the hydrocarbon. _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ Space for Personal Notes [4.1] 28  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Question 21 An unknown hydrocarbon is known to be 5 carbons long is to be investigated. A 0.0100 𝑚𝑜𝑙 sample of the hydrocarbon is mixed with 0.730 𝑔 of hydrogen chlorine gas (HCl) and goes to completion with no reactants left over. a. Calculate the degree of unsaturation present in the molecule. _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ b. Draw a potential structural formula of the molecule and name it. penta − 1,3 − diene is a potential isomer From here the iodine number can be calculated! Space for Personal Notes [4.1] 29  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Exploration: Iodine Number Consider the following molecule (C4 H6 ) and complete the equation. If there is 100 𝑔 of buta-1,2-diene present, find the mass of iodine used. _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ What is the final mass of the product? 100 𝑔 + 940 𝑔 = 1040 𝑔 𝒎(𝐦𝐨𝐥𝐞𝐜𝐮𝐥𝐞 𝐛𝐞𝐟𝐨𝐫𝐞 𝐫𝐞𝐚𝐜𝐭𝐢𝐨𝐧) + 𝒎(𝐢𝐨𝐝𝐢𝐧𝐞) = 𝒎(𝐦𝐨𝐥𝐞𝐜𝐮𝐥𝐞 𝐚𝐟𝐭𝐞𝐫 𝐫𝐞𝐚𝐜𝐭𝐢𝐨𝐧) Rearranging: 𝒎(𝐢𝐨𝐝𝐢𝐧𝐞) = 𝒎(𝐦𝐨𝐥𝐞𝐜𝐮𝐥𝐞 𝐚𝐟𝐭𝐞𝐫 𝐫𝐞𝐚𝐜𝐭𝐢𝐨𝐧) − 𝒎(𝐦𝐨𝐥𝐞𝐜𝐮𝐥𝐞 𝐛𝐞𝐟𝐨𝐫𝐞 𝐫𝐞𝐚𝐜𝐭𝐢𝐨𝐧) This is known as the __________________________. iodine number Iodine Number Definition: The number of grams of iodine that reacts with __________ 100 𝑔 of a chemical substance. It is typically used to determine the degree of unsaturation in large molecules such as fats. Formula: 𝐢𝐨𝐝𝐢𝐧𝐞 𝐧𝐮𝐦𝐛𝐞𝐫 = 𝒎(𝐦𝐨𝐥𝐞𝐜𝐮𝐥𝐞 𝐚𝐟𝐭𝐞𝐫 𝐫𝐞𝐚𝐜𝐭𝐢𝐨𝐧) − 𝒎(𝐦𝐨𝐥𝐞𝐜𝐮𝐥𝐞 𝐛𝐞𝐟𝐨𝐫𝐞 𝐫𝐞𝐚𝐜𝐭𝐢𝐨𝐧) [4.1] 30  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Let’s have a look at an example together! Question 22 Walkthrough. A sample of 100 𝑔 of fat was reacted with iodine, whereby the final mass of the sample was 601 𝑔. Given that the molar mass of the compound was 304 𝑔/𝑚𝑜𝑙, find the degree of unsaturation. _____________________________________________________________________________________ Iodine number = 601𝑔 − 100𝑔 = 501𝑔 _____________________________________________________________________________________ 𝑚(𝐼2) = 501𝑔 _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ TIP: The iodine number essentially calculates the mass of iodine which reacts with the reactant. Your turn! Question 23 A sample of 100 𝑔 of fat is reacted with iodine, whereby the mass of the product is 320 𝑔. a. Find the iodine number. _____________________________________________________________________________________ b. Find the amount of iodine (in 𝑚𝑜𝑙) this corresponds to. _____________________________________________________________________________________ _____________________________________________________________________________________ [4.1] 31  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Question 24 A sample of fat which has a molar mass of 882 𝑔/𝑚𝑜𝑙 is to be investigated. When 100 𝑔 of the fat is reacted with iodine, the mass of the final product produced is 215 𝑔. a. Find the iodine number. _____________________________________________________________________________________ b. Find the degree of unsaturation of the molecule. _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ Question 25 Additional Question. A sample of fat which has a molar mass of 480 𝑔/𝑚𝑜𝑙 is to be investigated. When 100 𝑔 of the fat is reacted with iodine, the mass of the final product produced is 470 𝑔. Find the degree of unsaturation of the molecule. _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ _____________________________________________________________________________________ Study Design: Laboratory analysis of organic compounds Measurement of the degree of unsaturation of compounds using iodine. [4.1] 32  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Sub-Section: Hydroxyl Group Tests Discussion: What type of reactions can alcohols undergo? Oxidation reactions ________________________________. ________________________________. Esterification reactions Let’s first look at oxidation! REMINDER: Don’t forget! Type of Reaction Reaction Full Oxidation of Primary Alcohol Oxidation of Secondary Alcohol Oxidation of Tertiary Alcohol [4.1] 33  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Exploration: Dichromate & Permanganate Tests Oxidising agents (acidified MnO4 − (aq) or Cr2 O7 2− (aq)) reactions: Colour Changes: (Hint: Look at page 5 of the databook.) Reaction 𝐌𝐧𝐎𝟒 − (𝐚𝐪) → 𝐌𝐧𝟐+ (𝐚𝐪) Colour Purple Pale pink/colourless Reaction 𝐂𝐫𝟐 𝐎𝟕 𝟐− (𝐚𝐪) → 𝟐𝐂𝐫 𝟑+ (𝐚𝐪) Colour Orange Green The video below shows the colour changes in action. Video Link (Videos 𝟐 & 𝟑): https://youtube.com/playlist?list=PL2hVhOVQpiYQ2b13f_T2Kx3G- _oc8oeVy&si=8sywpRZidB2TH3B4 Consider if propan-1-ol, propan-2-ol, and 2-methyl-propan-2-ol have acidified potassium dichromate added to them: Which one does not oxidise? [propan-𝟏-ol]/[propan-𝟐-ol]/[𝐦𝐞𝐭𝐡𝐲𝐥𝐩𝐫𝐨𝐩𝐚𝐧 − 𝟐 − 𝐨𝐥] If the experiment looks like this, match the test tube to the substance. propan-𝟏-ol propan-𝟐-ol 𝟐-methyl-propan-𝟐-ol Test Tube [𝑨]/[𝑩]/[𝑪] Test Tube [𝑨]/[𝑩]/[𝑪] Test Tube [𝑨]/[𝑩]/[𝑪] How can we tell between propan-𝟏-ol and propan-𝟐-ol? [4.1] 34  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] What do they form as they oxidise? 𝐚𝐜𝐢𝐝𝐢𝐟𝐢𝐞𝐝 𝐨𝐱𝐢𝐝𝐚𝐧𝐭 Propanoic acid Propan-1-ol → ______________________. 𝐚𝐜𝐢𝐝𝐢𝐟𝐢𝐞𝐝 𝐨𝐱𝐢𝐝𝐚𝐧𝐭 Propanone Propan-2-ol → ______________________. What test can we do to distinguish between the two products? pH test (indicator) (Doesn’t really work though because we’ve added acidified oxidant already so both should be acidic already). / Esterification. Let’s look at a question together! Question 26 Walkthrough. A mixture of substances containing butanoic acid, butan-1-ol, butan-2-ol and 2-methylbutan-2-ol are investigated. They are placed into random vessels 𝐴-𝐷. Bromothymol blue indicator is added to each vessel and the colour is observed. The indicator is then removed to restore the colour of each solution back to colourless before acidified permanganate ions is then added to them afterwards. Observations for each vessel is depicted below. Vessel 𝑨 𝑩 𝑪 𝑫 Colour of solution after bromothymol Blue Blue Yellow Blue blue indicator is added. Colour of solution after acidified Purple Colourless Purple Colourless permanganate added. Substance butanoic acid 2-methylbutan-2-ol Identify two of the substances above. [4.1] 35  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Key Takeaways Primary and Secondary Alcohols can get oxidised. Tertiary Alcohols and other functional groups cannot get oxidised! Your turn! Question 27 Two separate test tubes, ethanol and ethanoic acid which are both colourless by themselves have acidified permanganate added to them. Predict the colour of the test tube after the acidified permanganate is added. Ethanol Colour After Ethanoic Acid Colour After Colourless Purple Question 28 A mixture of substances containing propan-2-ol, 2-methylpropan-2-ol, octan-1-ol and octan-2-one are investigated. They are placed into random vessels 𝐴-𝐷. Each of the solutions have acidified dichromate added to them, and their colours observed are shown below. Observations for each vessel is depicted below. Identify each of the substances. Vessel 𝑨 𝑩 𝑪 𝑫 Solubility in Water Soluble Insoluble Soluble Insoluble Colour of solution after acidified Orange Orange Green Green dichromate added. Substance 2-methylpropan-2-ol Octan-2-one Propan-2-ol Octan-1-ol [4.1] 36  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Question 29 Additional. Two separate test tubes, propan-2-ol and propanal which are both colourless by themselves have acidified dichromate added to them. Predict the colour of the test tube after the acidified dichromate is added. Propan-𝟐-ol Colour After Propanal Colour After Green Green NOTE: Technically, both alcohols and aldehydes can get oxidised! To overcome this, we need to look at esterification reactions! What about Esterification Reactions? Exploration: Esterification of Alcohols Consider ethanol (C2 H5 OH): To allow for the esterification reaction to occur, the following must be added: Carboxyl Reactant: ____________________________ Catalyst: Concentrated H2 SO4 ____________________________ Esterification reaction example: 𝐇𝟐 𝐒𝐎𝟒 (𝐥) 𝐂𝐇𝟑 𝐂𝐎𝐎𝐇(𝐥) + 𝐂𝐇𝟑 𝐂𝐇𝟐 𝐎𝐇(𝐥) → 𝐂𝐇𝟑 𝐂𝐎𝐎𝐂𝐇𝟐 𝐂𝐇𝟑 (𝐥) + 𝐇𝟐 𝐎(𝐥) Issue: carboxylic acids, alcohols, esters, and water are all colourless. How do we know if a reaction has occurred? Are there any properties of esters? Esters smell fruity! [4.1] 37  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Key Takeaways C = C bonds When adding a halogen (e.g. Br2 or I2 ), we test for if the compound contains __________________. When adding H + (aq)/MnO− 4 (aq) or H (aq)/Cr2 O7 (aq), we test for if the compound + 2− ______________________. can oxidise ester , and thus if the When adding a carboxylic acid, we test for if the compound can form an __________ hydroxyl molecule contains a ________________ group! Question 30 Walkthrough. For each of the following, indicate if a reaction will occur if acidified permanganate is added vs. a carboxylic acid. a. Indicate if a reaction will occur if the following reagents are added with the suitable catalyst to ethanol. Acidified Permanganate Added Carboxylic Acid Added [Reaction Occurs]/[No Reaction Occurs] [Reaction Occurs]/[No Reaction Occurs] b. 2-methylpropan-2-ol is then investigated. i. Indicate if a reaction will occur if the following reagents are added with suitable catalyst to 2-methylpropan-2-ol. Acidified Permanganate Added Carboxylic Acid Added [Reaction Occurs]/[No Reaction Occurs] [Reaction Occurs]/[No Reaction Occurs] i. Draw the ester which forms when 2-methylpropan-2-ol is reacted with ethanoic acid. [4.1] 38  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] NOTE: While tertiary alcohols cannot be oxidised, they can still form an ester with a carboxylic acid! Your turn! Question 31 For each of the following, indicate if a reaction will occur if acidified permanganate is added vs a carboxylic acid with suitable catalysts. a. Propan-1-ol Acidified Permanganate Added Carboxylic Acid Added [Reaction Occurs]/[No Reaction Occurs] [Reaction Occurs]/[No Reaction Occurs] b. Propan-2-ol Acidified Permanganate Added Carboxylic Acid Added [Reaction Occurs]/[No Reaction Occurs] [Reaction Occurs]/[No Reaction Occurs] c. 2-methylbutan-2-ol Acidified Permanganate Added Carboxylic Acid Added [Reaction Occurs]/[No Reaction Occurs] [Reaction Occurs]/[No Reaction Occurs] d. Ethanal Acidified Permanganate Added Carboxylic Acid Added [Reaction Occurs]/[No Reaction Occurs] [Reaction Occurs]/[No Reaction Occurs] [4.1] 39  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] e. Propan-2-one Acidified Permanganate Added Carboxylic Acid Added [Reaction Occurs]/[No Reaction Occurs] [Reaction Occurs]/[No Reaction Occurs] f. Ethan-1-amine Acidified Permanganate Added Carboxylic Acid Added [Reaction Occurs]/[No Reaction Occurs] [Reaction Occurs]/[No Reaction Occurs] NOTE: While adding carboxylic acid can test if the molecule is an alcohol, it can also form an amide with amines! Extension: Can we distinguish between ethanoic acid reacting with ethanol and ethan-𝟏-amine? Ethanoic Acid + Ethanol: 𝐂𝐇𝟑 𝐂𝐎𝐎𝐇(𝐥) + 𝐂𝐇𝟑 𝐂𝐇𝟐 𝐎𝐇(𝐥) → 𝐂𝐇𝟑 𝐂𝐎𝐎𝐂𝐇𝟐 𝐂𝐇𝟑 (𝐥) + 𝐇𝟐 𝐎(𝐥) Ethanoic Acid + Ethanamine: 𝐂𝐇𝟑 𝐂𝐎𝐎𝐇(𝐥) + 𝐂𝐇𝟑 𝐂𝐇𝟐 𝐍𝐇𝟐 (𝐥) → 𝐂𝐇𝟑 𝐂𝐎𝐍𝐇𝐂𝐇𝟐 𝐂𝐇𝟑 (𝐥) + 𝐇𝟐 𝐎(𝐥) [Can Distinguish]/[Cannot Distinguish] If so, how? If not, why not? Esters smell fruity/good, amides do not smell. NOTE: Amide formation reaction is not in the study design, so you most likely won’t be tested on this idea! [4.1] 40  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Sub-Section: Carboxyl Tests Discussion: What type of reactions can carboxylic acids undergo? Esterification ________________________________. Amide formation (not tested) ________________________________. Acid/base ________________________________. Let's first look at the Esterification of carboxylic acids! Exploration: Esterification of carboxylic acids Consider ethanoic acid (CH3 COOH): To allow for the esterification reaction to occur, the following must be added: Reactant: Alcohol ____________________________. Catalyst: ____________________________. Concentrated H2 SO4 Esterification reaction example: 𝐇𝟐 𝐒𝐎𝟒 (𝐥) 𝐂𝐇𝟑 𝐂𝐎𝐎𝐇(𝐥) + 𝐂𝐇𝟑 𝐂𝐇𝟐 𝐎𝐇(𝐥) → 𝐂𝐇𝟑 𝐂𝐎𝐎𝐂𝐇𝟐 𝐂𝐇𝟑 (𝐥) + 𝐇𝟐 𝐎(𝐥) Esters smell fruity Indication of esterification reaction occurred: ____________________. [4.1] 41  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] NOTE: This reaction is very similar to the previous one, but this time, instead of adding a carboxylic acid to test for alcohols, we add an alcohol to test for carboxylic acids! Question 32 Four separate mixtures either contain pentan-1-ol, 3-methylpentan-3-ol, pentan-3-one or pentanoic acid. A couple of tests are taken, and the observations are shown below. Identify each mixture. Mixture 𝑨 𝑩 𝑪 𝑫 Acidified Solution is purple Solution is purple Solution is purple Solution is permanganate added. colour. colour. colour. colourless. Ethanol is added. No observations. No observations. Smells fruity. No observations. Ethanoic acid is No observations. Smells fruity. No observations. Smells fruity. added. Substance Pentan-3-one 3-methylpentan-3-ol Pentanoic acid Pentan-1-ol Question 33 Additional. Eddie is drinking his favourite drink but is curious as to whether propanoic acid is present in his food. a. Propose a chemical test he can execute to identify if propanoic acid is present. Justify your reasoning. _____________________________________________________________________________________ React with an alcohol (e.g. ethanol) and see if an ester forms, which is _____________________________________________________________________________________ indicated by the fruity smell produced when an ester is formed. _____________________________________________________________________________________ b. He runs into an issue, as his favourite drink is pineapple juice which already smells fruity regardless. Identify another test he can execute to test for the presence of the propanoic acid. _____________________________________________________________________________________ Acid/base test. [4.1] 42  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Exploration: Carbonate Test To not rely on the product ‘smelling fruit,’ the carbonate test can be used instead! Carbonate and hydrogen carbonates act as a base! Consider ethanoic acid (𝐂𝐇𝟑 𝐂𝐎𝐎𝐇): Reaction with Sodium carbonate: 2CH3 COOH(aq) + Na2 CO3 (s) → 2CH3 COONa + CO2 (g) + H2 O(l) Reaction with Sodium hydrogen carbonate: CH3 COOH(aq) + NaHCO3 (s) → CH3 COONa(aq) + CO2 (g) + H2 O(l) Observations: Bubbles forming (CO2 (g)). Video Link (Video 𝟒): https://youtube.com/playlist?list=PL2hVhOVQpiYQ2b13f_T2Kx3G- oc8oeVy&si=8sywpRZidB2TH3B4 If the substance is a: Acid Not an Acid [Bubbles Form]/[No Observation] [Bubbles Form]/[No Observation] Are there any downsides to this test? Any acid (not just carboxylic acid) such as nitric acid will also react! NOTE: You are not expected to understand these reactions as acid-base reactions are only tested in VCE Chemistry ½ and are not in the Chemistry ¾ study design, but it’s good to know these for your SACs! Space for Personal Notes [4.1] 43  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Question 34 Four separate mixtures either contain butan-1-ol, butanoic acid, octanoic acid or butanamide. A couple of tests are taken, and the observations are shown below. Identify each mixture. Mixture 𝑨 𝑩 𝑪 𝑫 State of matter Liquid Solid Liquid Liquid Acidified dichromate Solution is orange in Solution is orange Solution is green in Solution is orange added. colour. in colour. colour. in colour. Sodium carbonate Bubbles formed Bubbles formed No observations No observations Substance Butanoic acid Octanoic acid Butan-1-ol butanamide Question 35 Emily has two mixtures, one which is comprised of butanol, the other comprising of butanoic acid. She wishes to distinguish between them using different types of tests. a. Propose one physical test she can execute to distinguish between the two mixtures. Explain how they will be distinguished. _____________________________________________________________________________________ pH test with indicator – butanoic acid will be acidic. _____________________________________________________________________________________ b. Propose two chemical tests she can execute to distinguish between the two mixtures. Explain how they will be distinguished. _____________________________________________________________________________________ Carbonate test – butanoic acid will react to form bubbles. _____________________________________________________________________________________ Add acidified permanganate/dichromate – alcohol will react and change colour. _____________________________________________________________________________________ Add alcohol – carboxylic acid will react and form an ester (smells fruity). add carboxylic acid – alcohol will react and form an ester (smells fruity). _____________________________________________________________________________________ [4.1] 44  [4.1] Website: contoureducation.com.au Phone: 1800 888 300 Email: [email protected] Key Takeaways Physical Tests: Tests For Test Conducted Molar Mass / Size of Molecule State of Matter Solubility Add water pH Add indicator Chemical Tests: Tests For Tests Conducted C = C Bonds Bromine/Iodine Test Add H + (aq)/MnO4 − (aq) or H + (aq)/ Cr2 O72− (aq) (reacts if primary or secondary alcohol) Hydroxyl Group Carboxylic Acid Add ________________________________ (forms smelly ester) (reacts for primary/secondary/tertiary alcohol) Alcohol Add _______________ (forms smelly ester) Carboxyl Group Carbonate Add _______________ (forms bubbles) Add H + (aq)/MnO4 − (aq) or Aldehyde H + (aq)/ Cr2 O72− (aq) Study Design: Laboratory analysis of organic compounds Qualitative tests for the presence of carbon-carbon double bonds, hydroxyl and carboxyl functional groups. [4.1] 45