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*CHEMISTRY PRACTICAL*
(3a) Hydrated ethanedioc acid (oxalic acid) is a primary standard because it is a stable solid with a known composition, and it does not undergo any change in composition when exposed to air. On the other hand, sodium hydroxide (NaOH) is not a primary standard because it is highly hygroscopic, meaning it absorbs moisture from the air, which can alter its composition.
(3bi)
(i)Analytical balance
(ii)Volumetric flask
(iii)Pipette (e.g., burette or volumetric pipette)
(iv)Measuring cylinder
(3bii) To calculate the mass of H2C2O4·2H2O required, we need to calculate the number of moles required and then multiply it by the molar mass.
Number of moles = concentration x volume (in dm³)
= 0.108 mol dm⁻³ x 2.0 dm³
= 0.216 mol
Molar mass of H2C2O4·2H2O = (2 x 1.0) + (2 x 12.0) + (4 x 16.0) + (2 x 18.0)
= 2.0 + 24.0 + 64.0 + 36.0
= 126.0 g mol⁻¹
Mass required = number of moles x molar mass
= 0.216 mol x 126.0 g mol⁻¹
= 27.22 g
(3c) One chemical substance that produces carbon(IV) oxide and a black residue when strongly heated is sugar (sucrose).
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CHEMISTRY OBJ
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21-30: DBCCAAACBB
31-40: DCBCDABAAA
41-50: BACADADCAA
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(1a)
(1) Al(NO₃)₃: Aluminum nitrate
(2) HClO₃: Chloric acid
(1b)
Given:
– Mass of Na₃PO₄ = 355 g
– Volume of solution = 3.5 dm³
– Molar mass of Na₃PO₄ = (23.0 × 3) + 31.0 + (16.0 × 4) = 69 + 31 + 64 = 164 g/mol
Number of moles of Na₃PO₄ = Mass / Molar mass = 355 / 164 = 2.16 mol
Concentration (mol/dm³) = Moles / Volume = 2.16 / 3.5 = 0.617 mol/dm³
(1c)
Ionization energy is the minimum energy required to remove the most loosely bound electron from an isolated gaseous atom in its ground state.
(1d)
Ionization energy generally increases across a period in the periodic table. This is because the nuclear charge increases, pulling the electrons closer to the nucleus and making it harder to remove an electron.
(1e)
(1) H⁻, H, H⁺: H⁻ > H > H⁺ (H⁻ has the largest radius due to extra electrons, while H⁺ has the smallest due to loss of an electron).
(2) Si, Cl, P: Cl < P < Si (Atomic radius decreases across a period, so Si has the largest radius).
(1f)
(1) 2-fluoro-3-methylpent-2-ene:
F
|
CH₃-C=C-CH₂-CH₃
|
CH₃
(2) 2,2-dimethylbutane:
CH₃
|
CH₃-C-CH₂-CH₃
|
CH₃
(1g)
1. Melting Point: A pure substance has a sharp and constant melting point.
2. Boiling Point: A pure substance has a sharp and constant boiling point.
(1h)
1. Concentration of Reactants: Higher concentration increases the rate of reaction.
2. Temperature: Increasing temperature increases the rate of reaction.
(1i)
Faraday's second law states that the mass of a substance deposited or liberated during electrolysis is directly proportional to its chemical equivalent weight (molar mass divided by the number of electrons involved in the reaction).
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(2ai)
-The volume of gas molecules is negligible compared to the volume of the container.
-Collisions between gas molecules are perfectly elastic (no energy loss).
(2aii)
Mass of gas = 0.8 g
Volume = 560 cm³ = 0.560 dm³
Temperature (T) = 0 °C = 273 K
Pressure (P) = 1 atm = 101325 N/m²
Gas constant (R) = 8.31 J K⁻¹ mol⁻¹
Using the ideal gas equation:
PV = nRT
n = PV / RT
n = (101325 N/m² × 0.560 × 10⁻³ m³) / (8.31 J K⁻¹ mol⁻¹ × 273 K)
n = 56.742 / 2268.63 = 0.025 mol
Molar mass = Mass / Moles = 0.8 g / 0.025 mol = 32 g/mol
(2b)
(i) Ionization energy increases across a period.
(ii) Oxygen has a lower ionization energy than nitrogen because oxygen has four electrons in the 2p orbital, while nitrogen has three. The extra electron in oxygen causes repulsion, making it easier to remove. Nitrogen has a half-filled 2p orbital, which is more stable and requires more energy to remove an electron.
(2c)
(i) HOCl is acidic: It can donate a proton (H⁺) in solution, forming OCl⁻. The presence of the electronegative chlorine atom makes the O-H bond more polar, facilitating proton donation.
(ii) NaOH is basic: It dissociates in water to form Na⁺ and OH⁻ ions. The OH⁻ ions make the solution basic by accepting protons (H⁺)
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