How do you do these HSC multiple choice questions? (1 Viewer)
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fluffchuck
Active Member
15:
All reactions are 1:1 with CO2 so by n=m/M, the smaller M is, the greater the moles of CO2 and hence the greater the volume. Calculating the molecular weights of the reactants, we see that option D (NaHCO3) has the least molecular weight (84.01 grams/mole).
Therefore, D.
17:
From the chemistry data sheet:
Total cell potential = (1.36 V) - (0.16 V) = 1.20 V,
Therefore, A.
18:
Energy = 1360 kJ/mol
m(ethanol) = 1 kg = 1000 g = 1000/46.07 moles = 21.7 moles
Energy (released in combustion of 21.7 moles) = 21.7 mol x 1360 kJ/mol = 19512 kJ
Km travelled = (19512 kJ)/(2270 kJ/km) = 13 km .
Therefore, B.
All reactions are 1:1 with CO2 so by n=m/M, the smaller M is, the greater the moles of CO2 and hence the greater the volume. Calculating the molecular weights of the reactants, we see that option D (NaHCO3) has the least molecular weight (84.01 grams/mole).
Therefore, D.
17:
From the chemistry data sheet:
Total cell potential = (1.36 V) - (0.16 V) = 1.20 V,
Therefore, A.
18:
Energy = 1360 kJ/mol
m(ethanol) = 1 kg = 1000 g = 1000/46.07 moles = 21.7 moles
Energy (released in combustion of 21.7 moles) = 21.7 mol x 1360 kJ/mol = 19512 kJ
Km travelled = (19512 kJ)/(2270 kJ/km) = 13 km .
Therefore, B.
Last edited:
15) first write 2 different chemical equations one for the compounds with co3 and another for hco3 (only need to write two equations because na and k are in the same group so essentially will have the same molar ratios). From that you see everything has a coefficient of 1 for the mole ratio. since moles = mass/molecular mass, and volume for co2 = moles x 24.79, the greatest co2 volume is when the moles is the highest value, which is when molecular mass is the smallest. So from the choices given D has the smallest value for molecular mass.
17) In the potassium dichromate you can't immediately tell which part is involved in the reaction with so2, but you have to consider that when you have redox reactions, you must have both an oxidation and reduction reaction. So since so2 is a reactant if u look on the reduction sheet on the right hand side you'll find the reaction and it can be seen it is undergoing oxidation. So that means potassium dichromate has to undergo reduction (So the dichromate part undergoes reduction, since the cathode reaction has to be below the anode reaction in these galvanic cell questions). If you add up the values Ecell=-0.16+1.36 = 1.2
19) First find the heat energy released by burning 1 kg of ethanol by finding the value for mCAT in molar heat of combustion = mcAT/moles. Then divide the value u found by 2270.
17) In the potassium dichromate you can't immediately tell which part is involved in the reaction with so2, but you have to consider that when you have redox reactions, you must have both an oxidation and reduction reaction. So since so2 is a reactant if u look on the reduction sheet on the right hand side you'll find the reaction and it can be seen it is undergoing oxidation. So that means potassium dichromate has to undergo reduction (So the dichromate part undergoes reduction, since the cathode reaction has to be below the anode reaction in these galvanic cell questions). If you add up the values Ecell=-0.16+1.36 = 1.2
19) First find the heat energy released by burning 1 kg of ethanol by finding the value for mCAT in molar heat of combustion = mcAT/moles. Then divide the value u found by 2270.
In a neutralisation reaction, if one of the components is a strong acid or a strong base, the reaction will go to completion regardless if one of the reactants is a weak acid or weak base. So essentially since both reactions go to completion and they all have 1:1 mole ratios, the volume of NaOH needed will be the same for the acetic acid