C4 Chemical reactions

Question 1

Moles from masses equation

Answer 1

number of moles = mass (g) / Ar or Mr

Question 2

Masses from moles equation

Answer 2

mass (g) = number of moles x Mr/Ar

Question 3

What is the limiting reactant

Answer 3

The reactant that gets used up first in a reaction

Question 4

What is the yield of a chemical reaction?

Answer 4

Describes how much product is made

Question 5

What is the percentage yield of a chemical reaction?

Answer 5

How much product is made compared with the maximum amount that could be made (100%)

Question 6

Factors affecting the yield of a chemical reaction

Answer 6

• The reactants may not be pure
• Some of the product may be lost in handling or left in the apparatus
• The reaction may be reversible, reversible reactions not going to completion
• Losses in separating products from the reaction mixture
• Some reactants may produce unexpected reactions and unwanted products

Question 7

What is the equation for calculating percentage yield?

Answer 7

percentage yield = actual mass of product produced / maximum theoretical mass of product possible x 100%

Question 8

What is the atom economy of a chemical reaction?

Answer 8

A measure of the extent to which the atoms in the starting material (the reactants) end up in the desired product

Question 9

What is the equation for calculating atom economy?

Answer 9

percentage atom economy = relative formula mass of the desired product from equation / sum of the relative formula masses of the reactants from the equation x 100%

Question 10

Concentration equation

Answer 10

concentration (g/dm^3) = amount of solute (g) / volume of solution (dm^3)

Question 11

How can you increase the concentration of an aqueous solution?

Answer 11

• Adding more solute and dissolving it in the same volume of its solution
• Evaporating off some of the water from the solution so you have the same mass of solute in a small volume of solution

Question 12

Law of conservation of mass

Answer 12

States that no atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants

Question 13

Relative formula mass

Answer 13

The relative formula mass of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula

Question 14

Relative formula mass in a balanced chemical reaction

Answer 14

In a balanced chemical equation, the sum of the relative formula masses of the reactants equals the sum of the relative formula masses of the products