The freezing point of a solution in which 2.5 grams of NaCl is added t0 230 ml of water is : - 0.69°C
<h3>Determine the freezing point of the solution </h3>
First step : Calculate the molality of NaCl
molality = ( 2.5 grams / 58.44 g/mol ) / ( 230 * 10⁻³ kg/ml )
= 0.186 mol/kg
Next step : Calculate freezing point depression temperature
T = 2 * 0.186 * kf
where : kf = 1.86°c.kg/mole
Hence; T = 2 * 0.186 * 1.86 = 0.69°C
Freezing point of the solution
Freezing temperature of solvent - freezing point depression temperature
0°C - 0.69°C = - 0.69°C
Hence the Freezing temperature of the solution is - 0.69°C
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Taking into account the definition of calorimetry, the mass of the sample is 478.41 grams.
Calorimetry is the measurement and calculation of the amounts of heat exchanged by a body or a system.
Sensible heat is defined as the amount of heat that a body absorbs or releases without any changes in its physical state (phase change).
So, the equation that allows to calculate heat exchanges is:
Q = c× m× ΔT
where Q is the heat exchanged by a body of mass m, made up of a specific heat substance c and where ΔT is the temperature variation.
In this case, you know:
- Q= -543 J because the energy is releases
- c= 0.227
- m= ?
- ΔT= Tfinal - Tinitial= 10 C - 15 C= -5 C
Replacing:
-543 J= 0.227 × m× (-5 C)
Solving:
<u><em>m=478.41 grams</em></u>
In summary, the mass of the sample is 478.41 grams.
Learn more about calorimetry:
Answer:
The answer is given below
Explanation:
Cys 278 residue is the only available cysteine which is alkylated by the addition of N-Ethylmaleimide or NEM (alkylating agent). It works by only alkylating the sulfhydryls. In this case, Cys 278 residue is the only one which has exposed cysteine residue.
While the other residues have their sulfhydryls group either involved in the synthesis of disulfide bonds of proteins or their Cys residues are intrinsically placed in the proteins and cannot be alkylated with NEM.
NEM cannot alkylate if its protein is not available in the free form or it is in bounded form. For NEM to alkylate Cys 278, it should be free and should have sulfhydryls available for alkylation.
Alkylation: it is the transfer of alkyl groups. Alkyl groups contain Hydrogen and Carbon in their structure.
The grams of aluminium oxide are formed when 350 kj heat are released is calculated as follows
1mole = 850Kj
what about 350kj
=1mole x350/850 = 0.412 moles
mass of Al = moles of Al x molar mass of Al
= 0.412mol x 27 g/mol = 11.124 grams
