A buffer is usually composed of either:
- a weak base combined with its conjugate acid, or
- a weak acid combined with its conjugate base
Now, examining each of the choices:
1- KOH and NH3: since they are both bases, thus this mixture is not a buffer
2- HBr and NaCl: since HBr is a strong acid while NaCl is the salt of another different acid, thus this mixture is not a buffer
3- HCl and HBr: these are both considered to be strong acid, thus this mixture is not a buffer
4- HCHO2 and NaCHO2: as for HCH02, it is considered a weak base while NaCHO2 is considered its conjugate base, thus this mixture is a buffer
<u>Answer:</u> The concentration of reactant after the given time is 0.0205 M
<u>Explanation:</u>
Rate law expression for first order kinetics is given by the equation:
![k=\frac{2.303}{t}\log\frac{[A_o]}{[A]}](https://tex.z-dn.net/?f=k%3D%5Cfrac%7B2.303%7D%7Bt%7D%5Clog%5Cfrac%7B%5BA_o%5D%7D%7B%5BA%5D%7D)
where,
k = rate constant = 
t = time taken for decay process = 11.0 min = 660 s (Conversion factor: 1 min = 60 s)
![[A_o]](https://tex.z-dn.net/?f=%5BA_o%5D)
= initial amount of the reactant = 0.400 M
[A] = amount left after decay process = ?
Putting values in above equation, we get:
![4.50\times 10^{-3}s^{-1}=\frac{2.303}{660s}\log\frac{0.400}{[A]}](https://tex.z-dn.net/?f=4.50%5Ctimes%2010%5E%7B-3%7Ds%5E%7B-1%7D%3D%5Cfrac%7B2.303%7D%7B660s%7D%5Clog%5Cfrac%7B0.400%7D%7B%5BA%5D%7D)
![[A]=0.0205M](https://tex.z-dn.net/?f=%5BA%5D%3D0.0205M)
Hence, the concentration of reactant after the given time is 0.0205 M
The properties of elements are determined by their group/family. Usually, its the area they are located on the periodic table. The valence electrons also determine reactivity, etc.
Answer:
B. Lower than 100 °C because hydrogen sulfide has dipole-dipole interactions instead of hydrogen bonding.
Explanation:
Boiling point is a physical property which is usually a product of breaking intermolecular bonds.
Both dipole-dipole attractions are intermolecular bonds and they have serious effect on boiling point of a substance.
Hydrogen bonds are very strong intermolecular bonds compared to dipole-dipole attractions. In hydrogen bonding hydrogen atom is directly joined to a highly electronegative atom.
Dipole-Dipole attraction exists between molcules that are polar. Such molecules line up such that the positive pole of one molecule attracts the negative pole of another.
Hydrogen bonds in water are much stronger than the dipole-dipole attraction of hydrogen sulfide.
You have to move higher; potential energy depends on height and mass.
