The molar concentration of the original HF solution : 0.342 M
Further explanation
Given
31.2 ml of 0.200 M NaOH
18.2 ml of HF
Required
The molar concentration of HF
Solution
Titration formula
M₁V₁n₁=M₂V₂n₂
n=acid/base valence (amount of H⁺/OH⁻, for NaOH and HF n =1)
Titrant = NaOH(1)
Titrate = HF(2)
Input the value :

There are some standard numbers that help us describe the structure of an atom and help us categorize them. Those are the atomic number, the mass number and the numbers of electrons in an atom (or ion). Atoms are electrically neutral, hence they have the same number of protons as electrons. If an atom has a charge and has thus become an ion, it is because electrons joined it or left. For example in this case, since the ion has +2 charge, 2 electrons left it and thus the ion has 4 electrons (2 electrons less than its protons). The mass number is the sum of the protons and neutrons of an atom (that are in the nucleus). In this case, this yields a mass number of 13 for this ion. The atomic number of an atom (or ion) is the total number of protons in the nucleus. Protons do not leave the nucleus except for radioactive reactions and thus the atomic number of an atom (or ion) does not change in chemical reactions. In this case, the ion has an atomic number of 6.
0.24 moles of oxygen must be placed in a 3.00 L container to exert a pressure of 2.00 atm at 25.0°C.
The variables given are Pressure, volume and temperature.
Explanation:
Given:
P = 2 atm
V = 3 litres
T = 25 degrees or 298.15 K by using the formula 25 + 273.17 = K
R = 0.082057 L atm/ mole K
n (number of moles) = ?
The equation used is of Ideal Gas law:
PV = nRT
n = 
Putting the values given for oxygen gas in the Ideal gas equation, we get
n = 
= 0.24
Thus, from the calculation using Ideal Gas law it is found that 0.24 moles of oxygen must be placed in a container.
Ideal gas law equation is used as it tells the relation between temperature, pressure and volume of the gas.