An engineer designing a new type of engine needs a liquid that can be heated and cooled quickly with as little exchange of energ
2 answers:
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Answer : A= 0.5, B = 0.25 , C = 0.125, D = 0.015625 and E = 0.00390625
Explanation :
Half life of a substance is defined as the amount of time taken by the substance to reduce to half of its original amount.
Here n represents the number of half lives.
The amount of substance that remains after n half lives can be calculated using the given formula,
So when we have n =1,
Fraction of substance that remains = 0.5¹ = 0.5.
That means after first half life over, the amount of substance that remains is 0.5 times that of original.
Therefore we have A = 0.5
When n = 2, we have 0.5² = 0.25
So when 2 half lives are over, the amount of substance that remains is 0.25 times that of original
Therefore B = 0.25
When n = 3, we have 0.5³ = 0.125
So when 3 half lives are over, the amount of substance that remains is 0.125 times that of original.
Therefore we have C = 0.125
When n = 6 , we have 0.5⁶ = 0.015625
So D = 0.015625
When n = 8, we have 0.5⁸ = 0.00390625
Therefore E = 0.00390625
The values for A, B, C, D and E are 0.5, 0.25, 0.125, 0.015625 and 0.00390625 respectively.
The compounds can react with OH⁻ and HCO₃⁻ only C₅H₆N pyridinium
<h3><em>Further explanation </em></h3>In an acid-base reaction, it can be determined whether or not a reaction occurs by knowing the value of pKa or Ka from acid and conjugate acid (acid from the reaction)
Acids and bases according to Bronsted-Lowry
Acid = donor (donor) proton (H + ion)
Base = proton (receiver) acceptor (H + ion)
If the acid gives (H +), then the remaining acid is a conjugate base because it accepts protons. Conversely, if a base receives (H +), then the base formed can release protons and is called the conjugate acid from the original base.
From this, it can be seen whether the acid in the product can give its proton to a base (or acid which has a lower Ka value) so that the reaction can go to the right to produce the product.
The step that needs to be done is to know the pKa value of the two acids (one on the left side and one on the right side of the arrow), then just determine the value of the equilibrium constant
Can be formulated:
K acid-base reaction = Ka acid on the left : K acid on the right.
or:
pK = acid pKa on the left - pKa acid on the right
K = equilibrium constant for acid-base reactions
pK = -log K;
K value> 1 indicates the reaction can take place, or the position of equilibrium to the right.
There is some data that we need to complete from the problem above, which is the pKa value of some compounds that will react, namely:
pyridinium pKa = 5.25
acetone pKa = 19.3
butan-2-one pKa = 19
Let's look at the K value of each possible reaction:
pka H₂O = 15.74, pka of H₂CO₃ = 6.37)
- 1. C₅H₆N pyridinium
* with OH⁻
C₅H₆N + OH- ---> C₅H₅N- + H₂O
pK = pKa pyridinium - pKa H₂O
pK = 5.25 - 15.74
pK = -10.49
K values> 1 indicate the reaction can take place
* with HCO3⁻
C₅H₆N + HCO₃⁻-- ---> C₅H₅N⁻ + H₂CO₃
pK = 5.25 - 6.37
pK = -1.12
Reaction can take place
- 2. Acetone C₃H₆O
* with OH-
C₃H₆O + OH⁻ ---> C₃H₅O- + H₂O
pK = 19.3 - 15.74
pK = 3.56
Reaction does not happen
* with HCO₃-
C₃H₆O + HCO₃⁻ ----> C₃H₅O⁻ + H₂CO₃
pK = 19.3 - 6.37
pK = 12.93
Reaction does not happen
- 3. butan-2-one C₄H₇O
* with OH-
C₄H₇O + OH- ---> C₄H₆O- + H₂O
pK = 19 - 15.74
pK = 3.26
Reaction does not happen
* with HCO₃⁻
C₄H₇O + HCO₃⁻ ---> C₄H₆O⁻ + H₂CO₃
pK = 19 - 6.37
pK = 12.63
Reaction does not happen
So that can react with OH⁻ and HCO₃⁻ only C₅H₆N pyridinium
<h3><em>Learn more </em></h3>
the lowest ph
the concentrations at equilibrium.
the ph of a solution
Keywords : acid base reaction, the equilibrium constant
