HSC Chemistry Module 8: Applying Chemical Ideas Practice Questions

Question 6 ⭐⭐⭐

During a gravimetric analysis investigation, you found that the mass of a sample containing KCl weighed 0.628g. This solution was treated with AgNO₃ and the subsequent AgCl precipitate weighed 1.345g. Calculate the percentage of K that was in the original sample (4 marks)

(L1.3: Conduct investigations and/or process data involving: Gravimetric analysis, Precipitation titration)

Question 7 ⭐⭐⭐🔥

The %w/w I^– in a 0.6712g sample was determined by a Volhard titration. After adding 50.00 mL of 0.05619 M AgNO₃ and allowing the precipitate to form, the remaining silver was back titrated with 0.05322 M KSCN, requiring 35.14 mL to reach the end point. Report the %w/w I^– in the sample. 

Question sourced from LibreTexts

(L1.3: Conduct investigations and/or process data involving: Gravimetric analysis, Precipitation titration)

Question 8 ⭐⭐⭐

Describe the steps used to determine the concentration of a solution using colorimetry (5 marks). 

(L1.4: Conduct investigations and/or process data to determine the concentration of coloured species and/or metal ions in aqueous solution, including but not limited to, the use of: Colourimetry, UV spectrophotometry, Atomic absorption spectroscopy)

Question 9 ⭐⭐

The following graph has two peaks, labelled ‘a’ and ‘b’. Answer the following questions using the graph below. (3 marks)

Graph sourced from Chou et. al. (2017)

a) What does the first peak represent?

b) What does the second peak represent? 

c) How would you use this graph to quantify the sun protection factor (SPF) of a new sunscreen brand? 

(L1.4: Conduct investigations and/or process data to determine the concentration of coloured species and/or metal ions in aqueous solution, including but not limited to, the use of: Colourimetry, UV spectrophotometry, Atomic absorption spectroscopy)

Question 10 ⭐⭐⭐

Draw a diagram depicting how atomic absorption spectroscopy works. Explain the principle behind this procedure. (4 marks) 

(L1.4: Conduct investigations and/or process data to determine the concentration of coloured species and/or metal ions in aqueous solution, including but not limited to, the use of: Colourimetry, UV spectrophotometry, Atomic absorption spectroscopy)

Analysis of Organic Substances

Question 11 ⭐

Explain how you used bromine water to test for the presence of a carbon-carbon single or double bond. Include relevant structural equation(s). (3 marks)

(L2.1: Conduct qualitative investigations to test for the presence of organic molecules of the following functional groups: Carbon-carbon double bonds, Hydroxyl groups, Carboxylic acids)

Question 12 ⭐⭐

Susan used sodium to identify primary, secondary and tertiary hydroxyl groups. Here are her results: 

Identify which samples contain either primary, secondary and tertiary hydroxyl groups (3 marks). 

(L2.1: Conduct qualitative investigations to test for the presence of organic molecules of the following functional groups: Carbon-carbon double bonds, Hydroxyl groups, Carboxylic acids)

Question 13 ⭐

What is the importance of calcium hydroxide when testing for the presence of carboxylic acid using sodium carbonate? (3 marks)

(L2.1: Conduct qualitative investigations to test for the presence of organic molecules of the following functional groups: Carbon-carbon double bonds, Hydroxyl groups, Carboxylic acids)

Question 14 ⭐⭐⭐

Identify the organic compound using the 1H NMR graph below. (3 marks)

Image sourced from Chemicalbook

(L2.2: Investigate the processes used to analyse the structure of simple organic compounds addressed in the course, including but not limited to: Proton and carbon-13 NMR, Mass spectroscopy, Infrared spectroscopy)

Question 15 ⭐⭐

Identify the structural formula of the organic compound illustrated in the ¹³C graph below. (3 marks)

(L2.2: Investigate the processes used to analyse the structure of simple organic compounds addressed in the course, including but not limited to: Proton and carbon-13 NMR, Mass spectroscopy, Infrared spectroscopy)

Question 16 ⭐⭐

Identify the structural formula using the following mass spectroscopy graph. (3 marks)

(L2.2: Investigate the processes used to analyse the structure of simple organic compounds addressed in the course, including but not limited to: Proton and carbon-13 NMR, Mass spectroscopy, Infrared spectroscopy)

Question 17 ⭐⭐⭐

Identify the molecular formula of the organic compound using the spectroscopic data provided. Justify your answer. (4 marks)

(L2.2: Investigate the processes used to analyse the structure of simple organic compounds addressed in the course, including but not limited to: Proton and carbon-13 NMR, Mass spectroscopy, Infrared spectroscopy)

Chemical Synthesis and Design

Question 18 ⭐⭐⭐🔥

Consider the Haber process, whereby atmospheric nitrogen and hydrogen are converted synthetically into ammonia as described in the equilibrium equation below: 

Evaluate the importance of monitoring the availability of reagents and reaction conditions in this process with relation to yield and purity. (7 marks). 

(L3.1: Evaluate the factors that need to be considered when designing a chemical synthesis process, including but not limited to: Availability of reagents, Reaction conditions, Yield and purity, Industrial uses, Environmental, social and economic issues)

Question 19 ⭐⭐

Describe examples of industrial uses of products that are made from a named chemical synthesis process. (4 marks) 

(L3.1: Evaluate the factors that need to be considered when designing a chemical synthesis process, including but not limited to: Availability of reagents, Reaction conditions, Yield and purity, Industrial uses, Environmental, social and economic issues)

Question 20 ⭐⭐⭐

Elucidate the structure of the compound from the following spectroscopic data. Provide reasoning for your answer. (7 marks)

(Challenge Question)

Many industries release by-products into the environment, and if not done correctly this can cause harm. By monitoring these environments, the safety of all living organisms is ensured to prevent illness, disease or other negative impacts. Water bodies in particular are crucial to every species survival, and if these become polluted with high concentrations of detergents, salinity or toxic metals it can cause detrimental effects on all those relying on the water source.

Question 2

Question 3

It is possible to conduct a flame test for Pb²⁺, producing a blue-white flame, but other analytical methods may be more reliable as the colour is not always very distinct. Additionally, due to its toxic nature, these tests should only be conducted with proper safety procedures.

Question 4

Question 5

Question 6

Question 7

Question 8

Colorimetry uses the light absorbed by a coloured solution to determine its concentration, which is done through the following steps. First, the appropriate wavelength needs to be selected, through choosing the colour that a solution will absorb the most light of (complementary colour). Next, a set of standard solutions of known concentrations need to be prepared and analysed using the colorimeter. The measured absorbance of each standard is used to create a calibration curve. The calibration curve should be a linear relationship following Beer-Lambert’s Law. Now, the unknown solution can be measured and the absorbance recorded. Using the recorded absorbance, the corresponding concentration can be identified on the calibration curve. Through following these steps, the concentration of an unknown solution can be determined using colorimetry.

Question 9 

a) The first peak is a strong peak at a lower-wavelength, indicating a higher energy excitation state (typically from conjugated double bonds or aromatic rings).

b) The second peak is a weaker peak at a higher-wavelength, attributed to a lower energy excitation state (occurring from atoms like oxygen, nitrogen or sulfur).

c) Sunscreen provides most protection when it is absorbing the UV rays. Therefore, SPF 50 has the greatest absorbance in the wavelength range shown and would be the most effective in preventing sun damage to the skin.

Question 10

Atomic Absorption Spectroscopy (AAS) is an analytical technique based on the principle that free metal atoms absorb light at specific wavelengths and can be used to determine the concentration of metal ions in solution. It works by spraying a diluted sample containing the metal ion of interest into a hot flame or graphite furnace, which converts the metal ions into free atoms in the gaseous state. A hollow cathode lamp will emit light of wavelength particular to the metal being analysed and the free metal atoms in the flame will absorb some of this light. As each element absorbs a unique wavelength, the detector measuring the absorbance at the wavelength can identify the metal and the concentration.

Question 11

Bromine water can be used to distinguish between alkenes (C=C) and alkanes (C-C). Bromine water is reddish-brown in colour and when added to a solution containing either an alkane or an alkene it reacts like so; alkanes are fully saturated and do not react with the bromine, so the solution will stay reddish-brown, while alkenes react with bromine and the solution will change to a colourless solution. The reaction with alkenes (C=C) can be shown using the following example equation:

C₂​H₄ +Br₂​ → C₂​H₄Br₂​

Question 12

The readiness of the reaction with sodium depends on the level of branching. Primary alcohols have no branching, whilst secondary alcohols have some and tertiary alcohols have the highest level of branching. Hence primary alcohols will react the fastest (sample 2), secondary alcohols next (sample 3) and tertiary alcohols will react the slowest (sample 1).

Question 13

When a carboxylic acid is reacted with sodium carbonate, CO₂ gas will form. However if it is unknown that the solution is a carboxylic acid, the gas formed can be bubbled through calcium hydroxide. If the solution turns milky due to the calcium carbonate precipitate, then it is confirmed that the gas was CO₂ and the solution was a carboxylic acid.

Question 14

Question 15

Question 16

Question 17

C₄H₈O

The mass spec indicates a molar mass of 72g/mol of the compound and the peak on the IR spec around 1680-1750 indicates a ketone or aldehyde. Removing the C=O  from the mm (72-28) leaves a mass of 44, which indicates a C₃H₈ split.

Question 18

The Haber process is known for its synthesis of ammonia, and to optimise yield and purity the availability of reagents and reaction conditions must be monitored. Monitoring the reagents ensures that the ratio of nitrogen to hydrogen is maintained to favour the forward reaction, producing ammonia and increasing the overall yield. If there are insufficient reagents, the production slows and the overall yield is reduced. 

The reaction is exothermic, so a lower temperature would favour the forward reaction but would also slow the rate of reaction. If the temperature is too high, it can reduce the purity. A higher pressure favours the forward reaction and also improves the purity. An iron catalyst is favoured as it increases the rate of reaction improving the yield.

Hence, by monitoring the availability of reagents and the reaction conditions, the desired yield and purity can be achieved.

Question 19

The Haber process produces ammonia which is used in the agriculture industry to produce fertilisers, improving soil fertility and crop yields. Additionally the production of plastics and synthetic fibres such as nylon are made using ammonia-derived constituents and these fibres are used in textiles, ropes and machine parts.

Question 20

The IR spec indicates a carboxylic acid is likely due to the very broad O-H peak and the strong C=O peak. The H₁ NMR indicates four distinct hydrogen environments, two triplets (however one is closer to an electronegative elements), one hexlet and one singlet at around 12ppm (indicative of the OH group). The C₁₃ NMR indicates four carbon environments. This makes butanoic acid seem likely, and the parent compound molar mass indicating 88 g/mol from the mass spec matches butanoic acid.