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.
The heat of reaction (i.e. combustion) of butane (
) when reacted with oxygen (
) is -2658 kJ/mol butane, and the chemical reaction is given by:
+
--->
+
The mass of butane required in the reaction is based on the heat produced by the reaction, which is given to be -1,500 kJ. The minus sign is added because the reaction releases heat (exothermic), which means that the products are in a "lower energy state" than the reactants.
Dividing this with the heat of reaction per mole of butane reacted would give the number of moles butane required. Then, multiplying the answer with the molar mass of butane which is 58 grams/mole, will give the mass of butane required.
Moles of butane = [(-1,500 kJ)/(-2658 kJ/mol butane)]
Moles of butane = 0.5643 moles butane
Mass of butane = 0.5643 moles butane * 58 grams/mol butane
Mass of butane =
32.73 grams butane
The mass of carbon dioxide (
) can be determined by multiplying the moles of butane (
) with the mole ratio of (
) produced to the (
) reacted, and then with the molar mass of (
), which is 44 grams/mole.
Mass of carbon dioxide produced = 0.5643 moles butane * [4 moles
/ 1 mole
] * 44 grams/mole
Mass of carbon dioxide produced
= 99.32 grams Thus, the mass of butane required is 32.73 grams, and the mass of carbon dioxide produced from the reaction of this amount of butane is 99.32 grams.
Answer:Hydrogen is placed such because it exhibits some similar characteristics of both group1 and group VII elements.
Explanation:
The reason why hydrogen is similar to group 1 metals:
#It has same valence electron and inorder achieve octet state it can lose that electron and forms H+ ion
#It acts as a good reducing agent similar to group1 metals
#It can also halides
Similarity to halogens:
#hydrogen can also gain one electron to gain noble gas configuration. It can combine with other non metals to form molecules with covalent bonding.
#It exists as diatomin molecule,H2
#Have the same electronegativity nature
#its reaction with other metal
The empirical formula of hydrocarbon is CH2
The molecular formula of the hydrocarbon is C6H12
<u><em>Explanation</em></u>
Hydrocarbon is made up of carbon and hydrogen
<h3><u><em> </em></u>Empirical formula calculation</h3>
Step 1: find the moles CO2 and H2O
moles =mass/molar mass
moles of CO2 = 6.59 g/ 44 g/mol = 0.15 moles
moles of H2O = 2.70 g / 18 g/mol = 0.15 moles
Step 2: Find the moles ratio of Co2:H2O by diving each mole by smallest mole(0.15)
that is for CO2 = 0.15/0.15 =1
For H2O = 0.15/0.15 =1
therefore the mole ratio of Co2 : H2O = 1:1 which implies that 1 mole of Co2 and 1 mole of H2O is formed during combustion reaction.
From the the law of mass conservation the number of atoms in reactant side must be equal to number of atoms in product side
therefore since there 1 atom of C in product side there must be 1 atom of C in reactant side.
In addition there is 2 H atom in product side which should be the same in reactant side.
From information above the empirical formula is therefore = CH2
Molecular formula calculation
[CH2}n= 84 g/mol
[12+ (1x2)] n = 84 g/mol
14 n = 84 g/mol
n = 6
multiply the each subscript in CH2 by 6
Therefore the molecular formula = C6H12
Sun isn't actually planet but star. Really big ball made of gases. Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%). Sun is the biggest object in our Solar System. It's 99.86% of the total mass of the Solar System.
... wikipedia is really grat if you have questions like that ;)
