Atomic Mass

Q.

How do you calculate the number of molecules in a substance?

Q.

What is the atomic mass of Calcium?

Q. On analysis it was found that black oxide of copper and red oxide of copper contain 80% and 89%of copper respectively. Show that this data is in accordance with law of multiple proportions.

Q.

The number of atoms in $0.1\text{mol}$triatomic gas is:

1. $1.806\times {10}^{23}$

2. $6.02\times {10}^{22}$

3. $1.8\times {10}^{22}$

4. $3.6\times {10}^{23}$

Q.

The total number of atoms in 8.5g of NH₃

1. 9.033 X 10²³

2. 3.011 X 10²³

3. 1.2044 X 10²³

4. None of these

Q.

Gram Atomic mass is just the atomic mass expressed in grams ...ie, atomic mass with gram as units. Our book says that gram atomic mass and gram atom are the same thing (similarly for gram molecule and gram molecular mass) . But later a formula is given that : Gram atom = mass in grams / Atomic mass [RAM].

There are questions also that use this formula ( similarly for gram molecule) in which we have to find the number of "gram atoms " in a given mass of substance.

So what is the real meaning of gram atom and the formula ( and is is similar for gram molecules) ?

Q.

In order to prepare $500\mathrm{ml}$ of $0.2\mathrm{M}$ $\mathrm{NaOH}$, the mass of $\mathrm{NaOH}$ required is

Q.

X, Y, and Z are the three elements in $3^{rd}$ a period of the periodic table. Oxides of X, Y, and Z are basic, amphoteric, and acidic. What will be its correct order in atomic number?

1. $\mathrm{X}<\mathrm{Y}<\mathrm{Z}$

2. $\mathrm{Y}<\mathrm{X}<\mathrm{Z}$

3. $\mathrm{Z}<\mathrm{Y}<\mathrm{X}$

4. $\mathrm{X}<\mathrm{Z}<\mathrm{Y}$

Q.

0.7 g of iron reacts directly with 0.4 g of sulphur to form ferrous sulphide. If 2.8 g of iron dissolves in dilute HCl and excess of sodium sulphide solution is added, 4.4 g of iron sulphide is precipitated. If it obeys the law of constant composition, what is the ratio of weights of Fe : S ?

1. 7:4

2. 6:4

3. 4:7

4. 8:4

Q.

What is the molar mass of helium gas?

Q.

The mass of an atom of C is

1. $1g$

2. $1.99\times {10}^{-23}g$

3. $\frac{1}{12}$

4. $1.99\times {10}^{-20}g$

Q.

How many Atoms do Carbon have?

Q.

What is the atomic mass of neon?

Q. A chemical element (X) is represented by ${}_Z{X}^A$. If ‘X’ is any element, then what do ‘A’ and ‘Z’ stand for?

1. Z - Atomic number; A - Mass number
2. Z - no. of neutrons; A - no. of electrons
3. Z - Mass number; A - Atomic number
4. Z - no. of protons; A - no. of electrons

Q.

Ordinary chlorine has two isotopes${}_{17}^{35}Cl$ and${}_{17}^{37}Cl$ in the ration of 3:1 Calculate the relative atomic mass of chlorine.

Q.

An atom is 10 times heavier than $\frac{1}{{12}^{th}}$ of mass of a C-12 . The mass of the atom in amu is:

1. 10
2. 120
3. 12
4. 1.2

Q.

Write the relation between mass number and atomic number.

Q.

Potassium nitrate on strong heating decomposes as under:
2KNO₃ $\stackrel{∆}{\to }$ 2KNO₂ + O₂
Calculate:
(i) weight of potassium nitrite formed.
(ii) weight of oxygen formed when 5.05 g of potassium nitrate decomposes completely.
(K = 39, O = 16, N = 14)

Q.

Calculate the mass of 0.1 mole of carbon dioxide.

[Atomic mass: S = 32, C = 12 and O=16 and Avogadro's Number = 6 x 10²³]

1. 2.9 g

2. 3.7 g

3. 4.4 g

4. 5.2 g

5. 6.3 g

Q.

The molecular formula for eelemental sulphur si $S_8$. In a sample of 5.12 g of slphur:
(a) how many moles of sulphur are present ?
(b) HOw many molecules and atoms are present?

Q.

Calculate:

a) the gram molecular mass of chlorine if 308 cm cube of it at STP weighs 0.979 grams

B) the volume of 4 gram of H2 at 4 atmospheres.

C) the mass of oxygen in 2.2 litres of carbon dioxide at STP

Q. Assertion: The Relative Atomic mass of aluminium is 27
Reason: An atom of aluminium is 27 times heavier than 1/12th of the mass of the C – 12 atom.,

1. A and R are correct, R explains the A.
2. A is correct, R is wrong.
3. A and R are correct, R doesn’t explain A.
4. A is wrong, R is correct.

Q. The chemical formula of the ionic compound containing ${Fe}^{3+}$ and $(S{O}_4{)}^{2-}$is____.

1. ${Fe}_{2}S{O}_4$
2. ${Fe}_3(S{O}_4{)}_2$
3. ${Fe}_2(S{O}_4{)}_3$
4. ${Fe}_{3}S{O}_4$

Q.

Write the chemical formula for Caustic potash. Also, calculate the molecular mass of Caustic potash.

1. $KOH,56gmo{l}^{-1}$
2. $KOH,57gmo{l}^{-1}$
3. $KOH,58gmo{l}^{-1}$
4. $KOH,59gmo{l}^{-1}$

Q. How many g atoms of hydrogen are present in 0.02 mole of cuso4.5h20?

Q.

Give the values for the following,

Gram atom of Chlorine= ____g of Chlorine.

Q. Gram molecular mass of ammonia is:

1. 20g
2. 17g
3. 18g
4. 22g

Q.

Liquids mix more slowly than gases. Why?

Q.

For 20 g hydrogen, the number of atoms present is 20.

1. True

2. False

Q.

Calculate the actual mass of 0.25 gram atom of calcium.