Conservation Of Mass And Quantative

Question 1

What is Thermal Decomposition?

Answer 1

A reaction that breaks down using heat.

Question 2

What is conservation of mass?

Answer 2

The law of conservation of mass states that the mass of reactants is equal to the mass of the products, only change of state can occur

Question 3

Why may it appear mass has decrease despite the law of conservation?

Answer 3

The mass still is there, in some form, a gaseous form, that can’t be measured on a balance as if floats into the surroundings.

Question 4

Why is an excess of a reactant added during an experiment?

Answer 4

To ensure the reaction has reached its full potential.

Question 5

How do we calculate concentration?

Answer 5

concentration (g/dm^3) = mass / volume of solvent

Question 6

What is a limiting reaction?

Answer 6

A limiting reaction is when one reactant is used up before the other, limiting the reaction from progressing

Question 7

What is Theoretical Yield?

Answer 7

The mass of products, in theory, calculated in accordance to the laws of conservation of mass

Question 8

What is percentage yield?

Answer 8

The percentage of products actually made in comparison to initially theorised

Question 9

Why may we not achieve our full potential yield?

Answer 9

• Reactants may not react due to it being a reversible reaction or a slow reaction
• The reaction doesn’t produce the products we expect
• Products are lost if a product is a gas or through filtration

Question 10

What is a limiting reactant?

Answer 10

A reactant that runs out before the rest of the reactants do meaning the reaction can’t progress leaving an excess.

Question 11

A reaction “burned in air” is called

Answer 11

A combustion reaction

Question 12

If the question is “Calculate the mass of Sodium Oxide when 115g of Sodium is burned in air” what is the process of answering?

Answer 12

• Find the excess, in this case it’s oxygen because it’s in great abundance around us, leaving sodium the limiting reactant
• Write the equation out and balance it. 4Na + O2 —> 2Na2O
• Find the Ratio of reactants to products, in this case it’s 4:2 or 2:1
• Find the amount of moles we started with using mol = mass / mr, in this case it’s 5mol
• This means, according to our ratio, every 5 mol of Na, we produce 2.5 mol of Na2O
• We take this to find the mass by doing mass = mol x mr (2.5 x 62 = 155g of Na2O)

Question 13

What is atom economy?

Answer 13

The percentage of the reactants being used to make the desired product, the remainder percentage being waste

Question 14

The formula for atom economy is…

Answer 14

Mr of Desired product/Mr of Reactants x 100

Question 15

How can we tell, without using mathematical equations, that something is 100% atom economic?

Answer 15

There’s only one product, meaning there’s no waste products.

Question 16

Why is atom economy important?

Answer 16

Raw materials are expensive, we can achieve a better atom economy through a more efficient reaction or alternatively, sell the biproducts