State the two important laws of chemical combination. How Dalton’s atomic theory explains the two Laws?

With the help of example, explain the law of conservation of mass.

What is meant by the law of conservation of mass? If 12 g of C is burnt in the presence of O₂, how much CO₂ will be formed?

[Atomic mass of C = 12 u, O = 16 u]

20g silver nitrate solution is added to 20g of sodium chloride solution. What change in mass do you expect after the reaction and why?

Which postulate of Dalton’s atomic theory can explain the law of constant proportions?

A liquid compound X of molecular mass 18 u can be obtained from a number of natural sources. All the animals and plants need liquid X for their survival. When an electric current is passed through 200 grams of pure liquid X under suitable conditions, then 178 grams of gas Y and 22 grams of gas Z are produced. Gas Y is produced at the positive electrode whereas gas Z is obtained at the negative electrode. Moreover, gas Y supports combustion whereas gas Z burns itself causing explosions.

(a) Name (i) liquid X (ii) gas Y, and (iii) gas Z

(b) What is the ratio to the mass of element Z to the mass of element Y in the liquid X?

(c) Which law of chemical combination is illustrated by this example?

(d) Name two sources of liquid X.

(e) State an important use of Y in our life.

One of the forms of a naturally occurring solid compound P is usually used for making the floors of houses. On adding a few drops of dilute hydrochloric acid to P, brisk effervescence are produced. When 50 g of reactant P was heated strongly, than 22 g of a gas Q and 28 g of a solid R were produced as products. Gas Q is the same which produced brisk effervescence on adding dilute HCl to P. Gas Q is said to cause global warming whereas solid R is used for white-washing.

(a) What is (i) solid P (ii) gas Q, and (iii) solid R.

(b) What is the total mass of Q and R obtained from 50 g of P?

(c) How does the total mass of Q and R formed compare with the mass of P taken?

(d) What conclusion do you get from the comparison of masses of products and reactant?

(e) Which law of chemical combination is illustrated by the example given in this problem?

During an experiment hydrogen (H₂) and oxygen (O₂) gases reacted in an electric are to produce water as

follows: 2H + O₂ 2H₂O

The experiment is repeated three times and data tabulated as shown below:

During 3^rd experiment the researcher forgot to list masses of H₂ and O₂ used. So, if the law of constant proportion is correct then find mass of O₂ used during 3^rd experiment.

In a compound such as water, the ratio of the mass of hydrogen to the mass of oxygen is always:

Four students A, B, C and D verified the law of conservation of mass by performing chemical reaction between barium chloride and sodium sulphate. All of them took 107.2 g barium chloride solution and 116.1g of sodium sulphate solution and mixed them in the beaker of mass 150 g. They reported their results as follows:

The correct observation is that of student.