Laws of Mass Conservation

Q.

What is a balanced chemical equation? Why should chemical equations be balanced?

Q.

Why do chemical equations need to be balanced?

Q. The law of conservation of mass is valid for all of the following, except:

1. Precipitation reactions
2. Nuclear reactions
3. Decomposition reactions
4. Neutralization reactions

Q. 4 g equimolar mixture of $NaOH$ and $N{a}_{2}C{O}_3$ contains x g of $NaOH$ and y g of $N{a}_{2}C{O}_3$.The value of x to the nearest integer (in g) is

Q. 0.2g of organic compound on complete combustion produces 0.18 g of water, the % of hydrogen in it is

1. 5
2. 10
3. 15
4. 20

Q.

Silver nitrate reacts with sodium chloride to form sodium nitrate and silver chloride. It is found that 6.8 g of silver nitrate reacts with 2.4 g of sodium chloride and forms 3.4 g of sodium nitrate. Applying the law of conservation of mass, calculate the weight of silver chloride formed.

Q. Which of the following is the best example of the law of conservation of mass?

1. When 12 g of carbon is heated in a vacuum, there is no change
   in mass.
2. A sample of air increases in volume when heated at constant pressure but its mass remains unaltered.
3. 12 g of carbon combines with 32 g of oxygen to form 44 g of carbon dioxide.
4. The weight of a piece of platinum is the same before and after heating in air.

Q.

By heating 10g of $CaC{O}_3$, 5.6g of CaO is formed. What is the moles of $C{O}_2$ obtained in this reaction?

1. 1

2. 0.1

3. 10

4. 0.01

Q.

Dalton’s atomic theory successfully explained (i) Law of conservation of mass (ii) Law of constant composition (iii) Law of radioactivity (iv) Law of multiple proportion ?

1. $\left(\mathrm{i}\right),\left(\mathrm{ii}\right)\mathrm{and}\left(\mathrm{iii}\right)$

2. $\left(\mathrm{i}\right),\left(\mathrm{iii}\right)\mathrm{and}\left(\mathrm{iv}\right)$

3. $\left(\mathrm{ii}\right),\left(\mathrm{iii}\right)\mathrm{and}\left(\mathrm{iv}\right)$

4. $\left(\mathrm{i}\right),\left(\mathrm{ii}\right)\mathrm{and}\left(\mathrm{iv}\right)$

Q.

A gaseous alkane is burnt completely in oxygen. The volume of $O_2$required for complete combustion to the volume of $C{O}_2$ formed is 7:4. Determine the formula for alkane. [Alkane is $C_n{H}_{2n+2}$]

1. 

2. 

3. 

4. 

Q. When 0.0976 g of magnesium was heated in air, 0.1627 g of magnesium oxide $\left(MgO\right)$ was produced. What is the mass of oxygen needed to produce 0.1627 g of $MgO$?

1. $0.0651\text{g}$
2. $0.0782\text{g}$
3. $0.0440\text{g}$
4. $0.0200\text{g}$

Q. A mixture of pure $AgCl$ and $AgBr$ is found to contain a total of 60.94% $Ag$ by mass. What is the mass % of chlorine in the mixture?
(Molar mass of Ag = 108 g/mol, Cl = 35.5 g/mol, Br = 80 g/mol)

1. 9.64%
2. 4.85%
3. 8.45%
4. 7.23%

Q.

Which of the following reactions is not correct according to the law of conservation of mass ?

(a) $2Mg\left(s\right)+O_2\left(g\right)\to 2MgO\left(s\right)$

(b) $C_3{H}_8\left(g\right)+O_2\left(g\right)\to C{O}_2\left(g\right)+H_{2}O\left(g\right)$

(c) $P_4\left(s\right)+5O_2\left(g\right)\to P_4{O}_{10}\left(s\right)$

(d) $C{H}_4\left(g\right)+2O_2\left(g\right)\to C{O}_2\left(g\right)+2H_{2}O\left(g\right)$

Q. An unbalanced chemical reaction is a violation of the law of:

1. Conservation of mass
2. Reciprocal proportions
3. Constant proportions
4. Multiple proportions

Q.

As magnesium burns in oxygen to produce magnesium oxide, there is no change in mass. Explain.

Q. The enthalpy change involved in oxidation of glucose is $-2880{\text{kJ mol}}^{-1}$. 25% of this energy is available for muscular work. If $100\text{kJ}$ of muscular work is needed to walk one km, then the maximum distance (in km) that a person will be able to walk after taking $150\text{g}$ of glucose is:

Q. 1 gram of a metal carbonate $\left(M_{2}C{O}_3\right)$ on treatment with excess $HCl$ produces 0.01186 mole of $C{O}_2$. The molar mass of $\left(M_{2}C{O}_3\right)$ in $gmo{l}^{-1}$ is

1. $1186$
2. $84.3$
3. $118.6$
4. $11.86$

Q. why is the law of conservation of mass not applicable for nuclear reactions ?

Q.

If molar mass of compound B is $x$, then find $\frac{x}{2}$

Q. 10.0 g of $CaC{O}_3$ on heating gave 4.4 g of $C{O}_2$ and x g of $CaO$. Applying the law of conservation of mass, calculate the mass of $CaO$.

1. 6.5 g
2. 5.6 g
3. 4.2 g
4. 5.3 g

Q. According to the Dalton's atomic theory : The relative number and kinds of atoms are constant in a given compound. Explain that statement ?

Q.

What mass of Silver chloride will be obtained by adding an excess of Hydrochloric acid to a solution of 0.34g of Silver nitrate? ($\mathrm{CI}=35.5,\mathrm{Ag}=108,\mathrm{N}=14,\mathrm{O}=16,\mathrm{H}=1)$

Q. When $Fe{S}_2$ is burnt in air, it converts to $F{e}_2{O}_3$ as, $Fe{S}_2\left(s\right)+O_2\left(g\right)\to F{e}_2{O}_3\left(s\right)+S{O}_2\left(g\right)$, the change in percentage by weight of iron in the process is: $\left(\text{Atomic mass of Fe = 56 u}\right)$

1. $23\%$ increase
2. $12\%$ decrease
3. $12\%$ increase
4. No change

Q.

Aluminum carbide reacts with water according to the following equation ${\mathrm{Al}}_4{\mathrm{C}}_3+12{\mathrm{H}}_2\mathrm{O}\to 4\mathrm{Al}{\left(\mathrm{OH}\right)}_3+3{\mathrm{CH}}_4$

(I) What mass of Aluminum hydroxide is formed from 12 g of Aluminum carbide

(ii) What volume of methane at STP is obtained from 12 g of Aluminum carbide relative to molecular weight of Al₄C₃=144 Al(OH)₃=78

Q. The enthalpy change involved in the oxidation of glucose is -2880 kJ mol${}^{-1}$. Twenty five percent of this energy is available for muscular work. If 100 kJ of muscular work is needed to walk one kilometer, what is the maximum distance that a person will be able to walk after eating 125 g of glucose?

1. 5 km
2. 10 km
3. 7.25 km
4. 2.25 km

Q. One mole of $N_2$ and 3 moles of $H_2$ are mixed in a closed container of 2 litre capacity. At equilibrium if the container contains 1.2 moles of $N{H}_3$, the active mass of $N_2$ is:

1. 0.2
2. 0.6
3. 0.4
4. 1.2

Q.

All chemical changes are accompanied by chemical reactions. These reactions are described in sentence form with the help of chemical equations in terms of symbols and formulae of the substance involved. Initially, the equation is in a skeletal form which is then balanced so that the total number of reactant species is the same as that of product species.

Why should a chemical equation be balanced?

Q.

0.22 g of a hydrocarbon (i.e., a compound containing carbon and hydrogen only) on complete combustion with oxygen gave 0.9 g water and 0.44 g carbon dioxide. Are these results in accordance with the law of conservation of mass (atomic mass of C = 12, H = 1, O = 16).

1. True

2. False

Q. When 0.0976 g of magnesium was heated in air, 0.1627 g of magnesium oxide $\left(MgO\right)$ was produced. What is the mass of oxygen needed to produce 0.1627 g of $MgO$?

Q.

In every chemical reaction of a substance X, the mass of the product formed is greater than the mass of X taken for the reaction. What kind of substance is X?