C4

Question 1

What is 1mol of atoms equal to? (Avagadro)

Answer 1

6.02x 10[23] carbon atoms

Question 2

How do you find Mr?

Answer 2

add the Ar’s of each element in compound
(e.g CO2 = 1x12 + 2x16 =44 )

Question 3

The amount of moles of a given mass substance is calculated using:

Answer 3

moles = mass/ Mr

Question 4

What is the limiting reactant?

Answer 4

The reacting substance that is completely used up in a chemical reaction

Question 5

The concentration of a solution can be calculated using:

Answer 5

concentration (mol/dm[3]) = amount of solute (mol) / volume (dm[3])

Question 6

how can you convert from cm[3] to dm[3]?

Answer 6

divide by 1000

Question 7

how can you convert from dm[3] to cm[3]?

Answer 7

x 1000

Question 8

how can you convert mol/dm3 to g/dm3?

Answer 8

x Mr

Question 9

how can you convert g/dm3 to mol/dm3?

Answer 9

divide by Mr

Question 10

How do you calculate atom economy?

Answer 10

Total Mr of desired products/ Total Mr of all reactants x100

Question 11

What is atom economy?

Answer 11

A measure of how many reactant atoms form a desired product.

Question 12

what is theoretical yield?

Answer 12

The maximum possible mass of a product that can be made in a chemical reaction

Question 13

why might actual mass not be the maximum theoretical mass?

Answer 13

• the reaction not going to completion, because it is reversible
• some of the product may be lost when it is separated from the reaction mixture
• some of the reactants may react in ways different to the expected reaction
• spillages

Question 14

how can you calculate percentage yield?

Answer 14

mass of product made/ maximum theoretical mass x100

Question 15

How can you calculate volume of a gas?

Answer 15

Number of moles x molar gas volume

Question 16

What is the molar gas volume?

Answer 16

the volume of any gas at standard conditions of 20C and 1 atmosphere pressure, it is a fixed volume of 24dm[3]

Question 17

what apparatus is needed for titrations?

Answer 17

• burette
• pipette and filler
• conical flask and white tile

Question 18

What reagents are needed for titration?

Answer 18

• an acid (hydrochloric, sulfuric or nitric) of unknown concentration
• sodium hydroxide solution of known concentration
• a suitable indicator, for example methyl orange or phenolphthalein
• ## NOTE: known goes in flask, unknown in buerette

Question 19

What is the method for titration?

Answer 19

• Use the pipette and pipette filler to add 25 cm3 of alkali to a clean conical flask.
• Add a few drops of indicator and put the conical flask on a white tile.
• Fill the burette with acid (known) and note the starting volume.
• Slowly add the acid from the burette to the alkali in the conical flask, swirling to mix.
• Stop adding the acid when the
  end-point is reached (when the indicator first permanently changes colour). Note the final volume reading.
• Repeat steps 1 to 5 until you get
  concordant titres

Question 20

what are concordant titres?

Answer 20

Titres within 0.10 cm³ of each other.

Question 21

Explain why a pipette is used to measure the alkali, rather than a measuring cylinder.

Answer 21

The pipette allows the same volume of alkali to be added each time, helping to make the results repeatable.