Formic acid is the simplest carboxylic acid with a structure of HCOOH and has a pka of 3.75. The pka refers to the acidity of the molecule, which in this example refers to the molecules ability to give up the proton of the O-H. A decrease in the pka value corresponds to an increase in acidity, or an increase in the ability to give up a proton. When an acid gives up a proton, the remaining anionic species (in this case HCOO-) is called the conjugate base, and an increase in the stability of the conjugate base corresponds to an increase in acidity.
The pka of a carboxylic can be affected greatly by the presence of various functional groups within its structure. An example of an inductive effect changing the pka can be shown with trichloroacetic acid, Cl3CCOOH. This molecule has a pka of 0.7. The decrease in pka relative to formic acid is due to the presence of the Cl3C- group, and more specifically the presence of the chlorine atoms. The electronegative chlorine atoms are able to withdraw the electron density away from the oxygen atoms and towards themselves, thus helping to stabilize the negative charge and stabilize the conjugate base. This results in an increase in acidity and decrease in pka.
The same Cl3CCOOH example can be used to explain how dipoles can effect the acidity of carboxylic acids. Compared to standard acetic acid, H3CCOOH with a pka of 4.76, trichloroacetic acid is much more acidic. The difference between these structures is the presence of C-Cl bonds in place of C-H bonds. A C-Cl bond is much more polar than a C-H bond, due the large electronegativity of the chlorine atom. This results in a carbon with a partial positive charge and a chlorine with a partial negative charge. In the conjugate base of the acid, where the molecule has a negative charge localized on the oxygen atoms, the dipole moment of the C-Cl bond is oriented such that the partial positive charge is on the carbon that is adjacent to the oxygen atoms containing the negative charge. Therefore, the electrostatic attraction between the positive end of the C-Cl dipole and the negative charge of the anionic oxygen helps to stabilize the entire species. This level of stabilization is not present in acetic acid where there are C-H bonds instead of C-Cl bonds since the C-H bonds do not have a large dipole moment.
To understand how resonance can affect the pka of a species, we can simply compare the pka of a simple alcohol such as methanol, CH3OH, and formic acid, HCOOH. The pka of methanol is 16, suggesting that is is a very weak acid. Once methanol gives up that proton to become the conjugate base CH3O-, the charge cannot be stabilized in any way and is simply localized on the oxygen atom. However, with a carboxylic acid, the conjugate base, HCOO-, can stabilize the negative charge. The lone pair electrons containing the charge on the oxygen atom are able to migrate to the other oxygen atom of the carboxylic acid. The negative charge can now be shared between the two electronegative oxygen atoms, thus stabilizing the charge and decreasing the pka.
Answer:
(a) = $34.123
(b) = $8.532
(c) Additional cost of fluorescent bulb is justified
Explanation:
Cost of electricity = $0.17 per kW·h
(a) For a 100 watt bulb which is the same as 100/1000 or 0.1 kW, the cost per hour =
0.1 × 0.17 = $0.017/h
and for 5.5 hours = 0.017×5.5 = $0.0935
The annual cost, which is 365 days, we have
Annual cost = $0.0935 × 365 = $34.123
(b) For the energy efficient 25-watt bulb, we have
25/1000 = 0.025kW
Power cost per annum =
0.025kW×$0.17 per kW·h×5.5×365 = $8.532
(c) Total cost of incandescent bulb = $0.89 total cost of using the incandescent bulb is $34.123 + $0.89 = $35.02
Total cost of using the energy efficient fluorescent bulb is about $3.49
Total cost of using the energy efficient bulb = $8.532 + $3.49 = $12.02
Total cost of incandescent bulb = $35.02 while total cost of energy efficient bulb is = $12.02
$12.02 <$35.02
Additional cost of fluorescent bulb is justified
Answer:
Choice A: approximately 
.
Explanation:
Note that the unit of concentration, 
, typically refers to moles per liter (that is: 
.)
On the other hand, the volume of the two solutions in this question are apparently given in 
, which is the same as 
(that is: 
.) Convert the unit of volume to liters:
.
.
Calculate the number of moles of 
formula units in that 
of the 
solution:
.
Note that (sulfuric acid) is a diprotic acid. When one mole of completely dissolves in water, two moles of 
ions will be released.
On the other hand, 
(sodium hydroxide) is a monoprotic base. When one mole of formula units completely dissolve in water, only one mole of 
ions will be released.
ions and ions neutralize each other at a one-to-one ratio. Therefore, when one mole of the diprotic acid dissolves in water completely, it will take two moles of to neutralize that two moles of produced. On the other hand, two moles formula units of the monoprotic base will be required to produce that two moles of . Therefore, and formula units would neutralize each other at a two-to-one ratio.
.
.
Previous calculations show that 
of was produced. Calculate the number of moles of formula units required to neutralize that
.
Calculate the concentration of a 
solution that contains exactly 
of formula units:
.
