ijmb model questions vol1 2023 chemistry | Practical

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Question 1 View Details
Three unknown inorganic salts are labelled X, Y and Z. Each salt is soluble in water. Using the apparatus provided, you are to carry out the qualitative tests described below to identify the metal cation present in each sample.
Question Parts
(a)
Perform a flame test on each sample. Record the colour of the flame observed for X, Y and Z.
(b)
Dissolve a small amount of each sample in distilled water and add a few drops of 0.1 M NaOH solution. State whether a precipitate forms and describe its appearance (colour, solubility).
(c)
Using the observations from (a) and (b), identify the most likely metal ion in each sample from the list: Na⁺, K⁺, Ca²⁺, Cu²⁺, Fe³⁺. Provide a brief justification for each identification.
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Question 2 View Details
A 0.500 g sample of an unknown chloride compound is dissolved in distilled water and the solution is diluted to 250.0 mL. The solution is then titrated with 0.100 M AgNO₃ using the Mohr method (potassium chromate indicator). The titration data are shown below: | Volume of AgNO₃ added (mL) | Observation | |---------------------------|-------------| | 0 – 20 | No colour change | | 20 – 23.5 | Light pink appears, deepens with more AgNO₃ | | 23.5 | Permanent pink colour (endpoint) | Using this information, answer the following questions:
Question Parts
(a)
Write the balanced chemical equation for the reaction between chloride ion and silver nitrate in the Mohr method.
(b)
Calculate the concentration of chloride ions (mol L⁻¹) in the original solution before dilution.
(c)
Determine the percentage by mass of chloride present in the original 0.500 g sample.
(d)
Discuss two possible sources of error in this titration and explain how each error would affect the calculated percentage of chloride.
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Question 3 View Details
A white crystalline solid labelled X is supplied for analysis. The following observations were recorded during the practical investigation. | Observation | Result | |-------------|--------| | Appearance | White crystalline solid | | Melting point| 800 °C (sharp) | | Solubility in water | Insoluble | | Solubility in dilute HCl | No reaction | | Electrical conductivity of a saturated aqueous suspension | Very low (virtually non‑conducting) | | Flame test | No characteristic colour | | Density (measured by displacement of water) | 2.6 g cm⁻³ | Using the data above, answer the questions that follow.
Question Parts
(a)
State the most likely type of chemical bonding present in compound X.
(b)
Justify your answer by referring to at least three of the observed properties.
(c)
Predict two additional physical properties of X that are consistent with the identified bonding type and briefly explain why they are expected.
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Question 4 View Details
A sample of an unknown solid Y weighing 0.240 g is dissolved in excess distilled water. The solution is titrated with 0.2000 M hydrochloric acid (HCl) using phenolphthalein as the indicator. The colour changes from pink to colourless at the endpoint after 24.50 mL of the acid has been added. The reaction between Y and HCl is known to be: Y + 2 HCl → YCl₂ + H₂↑ where each molecule of Y contains one replaceable –OH group. Answer the following questions.
Question Parts
(a)
Calculate the number of moles of HCl that were required to reach the endpoint.
(b)
Determine the number of moles of Y present in the weighed sample.
(c)
Calculate the experimental molar mass of Y using the mass of the sample and the moles obtained.
(d)
The theoretical molar mass of pure Y is 98.0 g mol⁻¹. Calculate the percent purity of the sample.
(e)
Discuss two possible sources of error that could affect the accuracy of the purity determination.
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