Answer and Explanation:
Aspirin is odorless, but when left exposed to air in the environment, it gradually hydrolyzes into salicylic acid and acetic acid as that is the precursor for synthesizing Aspirin.
Using this hydrolyzed aspirin for titration would not be advised, because it would affect the reading of the titration. Ordinarily, apsirin is a weak acid and direct titration of aspirin is problematic because it hydrolyzes pretty fast to salicylic acid— leading to an unwanted side reaction which may or may not go to completion. Therefore, excess base must be added and heat is supplied to the mixture so that neutralization and hydrolysis are complete. The remaining base is then titrated. This is called back titration.
Now, in back titration, instead of using solution whose concentration is expected to be known, we rather use excess volume of reactant which has been left over after the completion of a reaction with the analyte.
In this case, we use an alkali, preferably NaOH (1.0 mol/dm³). Te unused NaOH remaining after the hydrolysis is titrated against a standard HCl (0.1 mol/dm³). Then from the reaction equation of the aspirin and sodium hydroxide, the amount of NaOH required for the hydrolysis can be calculated.
Answering whether the titration goes up or down, it would be observed that the titration reading would GO DOWN because the exposed aspirin used has experienced some form of hydrolysis before it was used for titration, so the hydrolysis reaction it would undergo with acetyl-salicylic acid would be minimal, and this would affect the titration reading.
But if the aspirin wasn't left exposed to the environment, the reading would go up since more hydrolysis would take place in this case.
The biological macromolecule that is made of those monomers is C. Protein.
Answer:
a. 50KCal
b. 400KCal
c. Same as (a) above
Explanation:
Given
To raise the temperature of 1kg of liquid water at 1°C requires 1KCal
To raise the temperature of 1kg of ice or water vapour by 1°C requires 0.5KCal
To melt 1kg of ice at 0°C requires 80KCal
To evaporate 1kg of liquid water sitting at 100°C requires 540KCal
a. How much heat is required to raise the temperature of 5 kg of liquid water by 20 C?
To raise the temperature of 5 kg of ice by 20°C requires:
5 kg * (0.5 kcal / kgC) * 20C
= 50 KCal
b. How much heat is required to melt 5 kg of ice at 0 C?
To melt an ice of 5 kg of ice at 0 C requires:
5 kg * (80 kcal / kg)
= 400 KCal
c. Same as (a) above
The last option, fossil fuels are non-renewable sources.
Answer:
(A)
Explanation:
The enthalpy of formation of a substance is the enthalpy of the reaction where this substance is formed by its constituents species. So, for MnO2, the enthalpy of formation is the enthalpy of the reaction:
Mn(s) + O2(g) --> MnO2(s)
By the Hess' law, when a reaction follows steps, the enthalpy of the overall reaction is the sum of the enthalpy of the steps. In this sum, the intermediaries must be canceled, so, some changes may have to be done in the reactions. If the reaction is inverted, the signal of the enthalpy inverts too, and if it's multiplied by some constant, the enthalpy is multiplied too.
2MnO2 (s) --> 2MnO(s) + O2(g) ΔH = 264 kJ (must be inverted)
MnO2(s) + Mn(s) --> 2 MnO(s) ΔH = -240 kJ
O2(g) + 2MnO(s) --> 2MnO2(s) ΔH = -264 kJ
MnO2(s) + Mn(s) --> 2 MnO(s) ΔH = -240 kJ
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MnO is canceled, and 2MnO2 - MnO2 = MnO2 in the products because it was where have more of it:
O2(g) + Mn(s) --> MnO2(s)
ΔH = -264 + (-240) = -504 kJ
