Advertisements
Advertisements
प्रश्न
Explain formula mass with an example.
Advertisements
उत्तर
- The formula mass of a substance is the sum of atomic masses of the atoms present in the formula.
- In substances such as sodium chloride, positive (sodium), and negative (chloride) entities are arranged in a three-dimensional structure in a way that one sodium (Na+) ion is surrounded by six chlorides (Cl–) ions, all at the same distance from it and vice versa. Thus, sodium chloride does not contain discrete molecules as the constituent units.
- Therefore, NaCl is just the formula that is used to represent sodium chloride though it is not a molecule.
- In such compounds, the formula (i.e., NaCl) is used to calculate the formula mass instead of molecular mass.
e.g. Formula mass of sodium chloride = atomic mass of sodium + atomic mass of chlorine
= 23.0 u + 35.5 u
= 58.5 u
APPEARS IN
संबंधित प्रश्न
The number of molecules in 22.4 cm3 of nitrogen gas at STP is ______.
Which of the following has the largest number of atoms?
Calculate the molecular mass of the following in u.
NH3
Calculate the molecular mass of the following in u.
CH3COOH
Calculate the molecular mass of the following in u.
C2H5OH
Solve problem:
The mass of an atom of hydrogen is 1.008 u. What is the mass of 18 atoms of hydrogen?
Solve problem:
Calculate the number of an atom of the following (Given: Atomic mass of I = 127 u).
254 u of iodine (I)
Solve problem:
Calculate the number of an atom of the following (Given: Atomic mass of I = 127 u).
254 g of iodine (I)
Solve the problem:
The natural isotopic abundance of 10B is 19.60% and 11B is 80.40 %. The exact isotopic masses are 10.13 and 11.009 respectively. Calculate the average atomic mass of boron.
24 g of carbon reacts with some oxygen to make 88 grams of carbon dioxide. Find out how much oxygen must have been used.
Solve problem:
Calculate the number of atoms of the following. (Average atomic mass : N = 14 u, S = 32 u)
0.4 mole of nitrogen
Solve problem:
Calculate the number of atoms of the following. (Average atomic mass : N = 14 u, S = 32 u)
1.6 g of sulfur
Solve problem:
Calculate the number of moles of magnesium oxide, MgO in
- 80 g, and
- 10 g of the compound.
(Average atomic masses of Mg = 24 and O = 16)
Solve problem:
Calculate the mass of sulfur dioxide produced by burning 16 g of sulfur in excess of oxygen in the contact process. (Average atomic mass : S = 32 u, O = 16 u)
Explain the need of the term average atomic mass.
Which of the following is/are true with respect to carbon-12.
Which one of the following is used as a standard for atomic mass.
Define relative atomic mass.
Calculate the average atomic mass of naturally occurring magnesium using the following data.
| Isotope | Isotopic atomic mass | Abundance (%) |
| Mg24 | 23.99 | 78.99 |
| Mg25 | 24.99 | 10.00 |
| Mg26 | 25.98 | 11.01 |
The reaction between aluminium and ferric oxide can generate temperatures up to 3273 K and is used in welding metals.
(Atomic mass of Al = 27 u Atomic mass of O = 16 u)
\[\ce{2Al + Fe2O3 -> Al2O3 + 2Fe}\]; If, in this process, 324 g of aluminium is allowed to react with 1.12 kg of ferric oxide.
- Calculate the mass of Al2O3 formed.
- How much of the excess reagent is left at the end of the reaction?
An element has a bee structure with cell edge of 288 pm. The density of element is 7.2 g cm-3. What is the atomic mass of an element?
Boron has two isotopes 10B and 11B with atomic masses 10 and 11, respectively. If its average atomic mass is 10.81, the abundance of 10B is ____________.
How many moles of ammonia are present in 5.6 cm3 of ammonia gas at STP?
What is the average mass of an element if it has two isotopes, one of mass 6.015 u with 8.24 % and other of mass 7.016 u with 91.26% respectively?
It is found that in 11.2 L at 0°C and 1 atm, of any gaseous compound of 'X', there is never less than 15.5 gm of 'X'. It is also found that 11.2 L of vapours of 'X' at 0°C and 1 atm, weighs 62 gm. The atomicity of 'X' is ______.
