neco 2018 chemistry | Practical

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Question 1 View Details
A mass spectrometer was used to determine the isotopic composition of element X. The data obtained are shown in the table below. Isotope (mass number) | Isotopic mass (u) | Relative abundance (%) ----------------------|-------------------|------------------------ 58 | 57.9353 | 68.0 60 | 59.9338 | 30.5 61 | 60.9310 | 1.5 Using this information, answer the following questions:
Question Parts
(a)
Calculate the experimentally determined average atomic mass of element X.
(b)
The accepted atomic mass of X in the periodic table is 58.9332 u. Calculate the percent error of your experimental value.
(c)
Suggest two possible sources of error that could have contributed to the discrepancy between the experimental and accepted values.
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Question 2 View Details
A 0.250 g sample of an unknown metal M was placed in a conical flask and reacted with excess dilute hydrochloric acid according to the equation: M + 2HCl → MCl₂ + H₂(g) The experiment was carried out at 25 °C and atmospheric pressure of 760 mmHg. The volume of hydrogen gas collected over water was 112.0 mL. The vapour pressure of water at 25 °C is 23.8 mmHg. Using the data above, answer the following questions:
Question Parts
(a)
Calculate the number of moles of dry hydrogen gas collected.
(b)
Determine the molar mass of the metal M.
(c)
Identify the metal by comparing the calculated molar mass with values in the periodic table (give the nearest whole‑number atomic mass).
(d)
State two experimental precautions that should be observed to improve the accuracy of the molar‑mass determination.
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Question 3 View Details
You are provided with three solid samples labelled (i) copper(II) sulfate pentahydrate, (ii) magnesium oxide and (iii) carbon tetrachloride. For each sample you are required to perform the following investigations: 1. Dissolve a small amount of the solid in distilled water and test the electrical conductivity of the resulting solution using a conductivity tester. 2. Observe the solubility of the solid in water. 3. Record the melting point (or boiling point for the liquid) using a melting point apparatus. Based on your observations answer the sub‑questions.
Question Parts
(a)
Classify each compound as predominantly ionic, covalent or metallic on the basis of the observations obtained.
(b)
Using the electronegativity values Cu = 1.90, O = 3.44, S = 2.58 and H = 2.20, calculate the percent ionic character of the Cu–O bond in copper(II) sulfate using the formula \(\%IC = (1 - e^{-0.25(\Delta\chi)^2}) \times 100\). Show all steps.
(c)
Briefly discuss how the observed physical properties support the classification you gave in part (a).
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Question 4 View Details
A 0.500 g sample of an unknown metal carbonate (MCO₃) is placed in a clean, dry crucible. The crucible is heated strongly until no further change in mass occurs and a solid residue remains. The gaseous product is collected over water. The volume of gas measured at 25 °C and 760 mmHg is 112.0 mL. The vapour pressure of water at 25 °C is 23.8 mmHg. Assume the gas collected is carbon dioxide released by the decomposition reaction: \[\text{MCO}_{3(s)} \rightarrow \text{MO_{(s)}} + \text{CO}_{2(g)}\] Answer the following:
Question Parts
(a)
Calculate the number of moles of CO₂ collected (dry gas). Show all working and state any assumptions.
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