R2.1 - how much? the amount of chemical change

Question 1

What is a chemical reaction?

Answer 1

Shows the ratio of products and reactants that can be written as a chemical or symbol equation.

Question 2

What are stoichometric co-efficients?

Answer 2

Numbers in front of products and reactants that are used to balance the equations.

Question 3

What can a mole ratio determine?

Answer 3

1) The mass or volumes of reactants and products.
2) Concentration of products and reactants in a solution.

Question 4

What is Avogadro’s Law?

Answer 4

Equal volumes of all gases under STP contain equal number of moles.

Question 5

What is molar volume?

Answer 5

Volume occupied by 1 mole of a gas

Question 6

How is titration carried out?

Answer 6

1) Use a pipette to measure a known volume of one solution into a conical flask, and add universal indicator.
2) Put the other solution in a burette, which is a calibrated glass tube.
3) Open the burette to allow the solution into the conical flask and mix it.
4) Add indicator and keep mixing until there is a permanent colour change.

Question 7

How is back titration carried out?

Answer 7

1) Known excess of one of the reactants is added to the reaction mixture.
2) Unreacted excess is determined by titration of a standard solution.
3) Subtract the unreacted amount from the original to work out the reacting amount.
- Used when the end point is hard to identify for impure substances.

Question 8

What assumptions are made during a back titration?

Answer 8

1) All of the substance reacts with the acid.
2) Only NaHCO3 reacted with the acid.
3) Took place under standard conditions.

Question 9

What is the equation involving mass, moles and Mr?

Answer 9

moles = mass / Mr

Question 10

What is the equation involving mass, molar volume and volume?

Answer 10

molar volume = moles / volume

Question 11

What is the limiting reactant?

Answer 11

Reactant that gets used up in a reaction and determines the theoretical yield of a product.

Question 12

What is the difference between theoretical and experimental yield?

Answer 12

Theoretical yield - maximum amount of product obtained if 100% of the limiting reactant is converted into products.
Experimental yield - yield that is actually produced from a reaction.

Question 13

How do you work out % yield?

Answer 13

% yield = (experimental yield / theoretical yield) x 100

Question 14

What can cause EY < TY?

Answer 14

• Side reactions
• Decomposition of reactants or products
• Product lost during purifying
• Reversible chemical reaction
• Incomplete reaction

Question 15

Wh cause TY < EY?

Answer 15

• Impurities in a product
• Product not fully dried
• Incomplete reaction

Question 16

How do you work out atom economy?

Answer 16

Atom economy = (Mr of desired product / Mr of sum of reactants) x 100

Question 17

What is green chemistry?

Answer 17

Sustainable design of chemical products and processes that aims to minimize the use and generation of substances that are hazardous to human health and the environment.