Law of conservation of mass experiment Class 9

4 grams of hydrogen reacts with some oxygen to make 36 grams of water. Figure out how much oxygen must have been used by applying the law of conservation of mass?

Solution:
Word equation –
Hydrogen + Oxygen  →   water
Masses of each substance given –                                   4 g                ?                36 g

According to law of conservation of mass –           Mass of reactants  =  Mass of products
4 + ?       =           36
So,  32 grams of oxygen was used.

Problem : 2

In a chemical reaction 150 g Baking soda mixture containing sodium bicarbonate and vinegar on heating gives 87 g of carbon dioxide gas. What mass of solid residue will left in food?

Solution:
According to law of conservation of mass,
Total mass of reactants = Total mass of products.

Here, baking soda mixture (reactant) on heating gives solid residue and carbon dioxide ( products).Here baking soda mixture (reactant) on heating gives solid residue and carbon dioxide ( products).

MBaking soda = MSolid residue + MCarbon dioxide

Hence,  the mass of solid residue is 150g – 87g = 63g.

Read first –

• What is Matter? What is its Characteristics?
• States of Matter
• Law of Conservation of Mass
• Problems based on Law of Definite Proportions / Constant Composition  
• Law of Definite Proportions / Constant Composition
• Mole Concept – Importance and formulas

Problem : 3
How much oxygen will add with 36 g carbon to give 132 g carbon dioxide assuming complete combustion of carbon?

Solution:
According to law of conservation of mass,
Mass of carbon + Mass of oxygen = Mass of carbon dioxide
36g         +             x               =             132 g
Hence,  the mass of oxygen is 96g.

Problem : 4

A thin strip of iron with a mass of 15.5g is placed into a solution containing 21.0g of copper (II) sulfate and copper begins to form. After some times, the reactions stops because all the copper (II) sulfate has reacted. The iron strip is found to have a mass of 8.5g. The mass of copper formed is found to be 8.60g. What mass of iron (II) sulfate has been formed in the reaction?  

Solution:
Mass of iron = Initial mass – Final mass
=     15.5 – 8.5 = 7.0g
Mass of copper (II) sulfate =  21.0g
Mass of copper  = 8.60g
According to law of conservation of mass,
Mass of iron + Mass of copper (II) sulfate = Mass of copper + Mass of iron (II) sulfate
7.0g       +                  21.0g                      =         8.60g          + Mass of iron (II) sulfate

So,       Mass of iron (II) sulfate    =     19.40g

Problem : 5

Silicon dioxide, made up of elements silicon and oxygen, contains 46.7% by mass of silicon. With what mass of oxygen will 10 g of silicon combine?

Solution:
100g of silicon dioxide contains  46.7 g of silicon,  or  100 – 46.7 ( i.e. 53.3 g) of oxygen.

It means, 10g of silicon will contain (10/100) × 53.3 = 5.33 g of oxygen.

Problem : 6

When 0.0976g of magnesium was heated in air, 0.1618g of magnesium oxide (MgO) was produced. What is the mass of oxygen needed to produce 0.1618g MgO?

Mass is an isolated system. The law of conservation of mass states that the mass can neither be created nor destroyed in a chemical reaction. There is just a rearrangement in the atoms of substances for the formation of compounds. Therefore, the mass of the total system remains constant at any interval of time. This implies that the total masses of reactants is equal to the sum of masses of products and the masses of unreacted reactants. The law of conservation of mass is also termed as the principle of mass conservation.

Mass of the total enclosed system at the beginning of the reaction is equivalent to the mass at the termination of the reaction. 

Mass reactants = Mass products

Experiment to verify the law of conservation of mass

The following experiment can be conducted to verify the law of conservation of mass: 

Things required to perform the experiment: 

• Barium chloride (BaCl2.2H20),
• Sodium sulphate (Na2SO4.10H2O),
• Two beakers of 100 and 150 ml respectively.
• Physical balance
• Two watch glasses
• Spring balance (0-500 g),
• Polythene bag
• Distilled water
• A glass rod.

The reaction can be visualised as a precipitation reaction, where the insoluble salt separates out as a precipitate. The reaction occurs between the Barium Chloride (BaCl22(aq)) and Sodium Sulphate (Na2SO4(aq)). Both the compounds are taken in aqueous solutions, that is water is taken as the solvent. This is a kind of double displacement reaction.

The reaction involved is,

BaCl2(aq)        +        Na2SO4(aq) ————-> BaSO4(aq)        +        2NaCl(aq)
 Colorless                  Colorless                         White Precipitate

Rearranging the equation in the iconic form, we get, 

Ba+(aq)        +        SO42-(aq) —————> BaSO4(s)
                                                                     White Precipitate

The reactants involved in the reaction are barium chloride and sodium sulphate, whereas the products involved are barium sulphate and sodium chloride.

Now, we know, 

Mass of the reactants (barium chloride + sodium sulphate) = Mass of the products (barium sulphate + sodium chloride)

Steps Involved in the Process

• 50 ml distilled water is taken in two 100 mL beakers.
• Weigh the two taken watch glasses on a physical balance.
• A quantity 3.6 g of BaCl2.2H20 is taken in a watch glass.
• Dissolve the quantity of aqueous solution of barium chloride in 50ml of distilled water. The contents are stored in beaker A.
• 8.05 g of Na2SO4.10H2O is taken in another watch glass of a definite mass.
• Dissolve the quantity of aqueous solution of sodium chloride in 50ml of distilled water. The contents are stored in beaker B.
• A 150ml beaker is taken and measured using the spring balance. This beaker will contain the final contents and is labelled as C.
• The solutions contained in the beakers A and B are combined together through constant stirring using a glass rod.
• A precipitate emerges out on the beaker C, owing due to the formation of the compound barium sulphate (BaSO4).
• The total weight of the products can be calculated by measuring the weight of the beaker.
• The content masses of the beakers are measured before and after the reaction.

Assumptions during the experiment

In case of distilled water, density is assumed to be 1g /cc.

Things to take care of before the experiment

• Small quantities of chemicals should be used to perform the reaction.
• Initially, the spring balance pointer should be at the zero marks.
• The reading of spring balance is taken only once its pointer is at the rest position.
• The reading of spring balance should be taken when it is placed in a vertical position.
• Precise quantities of the masses mentioned should be taken.
• Solution of BaCl2 and Na2SO4 should be mixed with constant stirring.

Observations

The following inferences can be drawn from the experiment, 

Mass of aqueous solution of barium chloride (BaCl2) = 3.6 g

Mass of BaCl2 solution = 53.6 g

Mass of aqueous solution of sodium sulphate (Na2SO4.10H2O) = 8.05 g

Mass of Na2SO4 solution =58.05 g

Mass of 50 ml distilled water = 50.0 g

Calculating the total mass of reactants, we have, 

BaCl2 + Na2SO4 = 53.6 + 58.05 

= 111.65 g

Mass of empty 150 mL beaker,m1 =………………….g

Mass of reaction mixture before precipitation, m2= m1+ 111.65 g = ……………………g

Final mass of reaction mixture after precipitation, m3 =……………………. g

Conclusions 

When we compare the mass of reactants with those of products, the two masses are considered to be equivalent. This implies that the observed masses, m2 = m3.  Hence, the law of conservation of mass is preserved. 

Sample Questions

Question 1. Where is the law of conservation applicability found?

Answer: 

Law of conservation of mass can be seen in chemical reactions, like the production of carbon dioxide, or during the process of combustion of wood. It is applicable to all the phenomena occurring in the closed system. 

Question 2. What is a double displacement precipitation reaction?

Answer: 

Double precipitation reactions involve the switching of atoms from two different compounds. In these reactions, there occurs an exchange of ions resulting in the formation of two new compounds. The occurrence of this type of reaction is more evident in case the ionic compounds are dissolved in water as the solvent. The positive ions exchange negative ion partners. Any reaction of this form is, 

AB + CD → AD + CB

Question 3. Which other reaction type can be used to display the law of conservation of mass?

Answer: 

Any combination reaction, where the reactants combine to form a product can be used to verify this law. For example, the production of water from hydrogen and oxygen molecules. 

How will you prove experimentally the law of conservation of mass Class 9?

The chemical reaction takes place in flask. Put cork on the mouth of the flask so that reactants and products do not spill out of flask. The mass of flask and its contents remain the same before as well as after the reaction that proves the law of conservation of mass.

What is the law of conservation of mass give an example class 9?

The law of conservation of mass states that mass in an isolated system is neither created nor destroyed by chemical reactions or physical transformations. According to the law of conservation of mass, the mass of the products in a chemical reaction must equal the mass of the reactants.

Who did experiment on law of conservation of mass?

It was a French chemist named Antoine Lavoisier who formulated the concept of the conservation of mass – the idea that matter can neither be created nor destroyed, only rearranged.