Topic 5

Question 1

Number of molecules

Answer 1

AC x number of moles

Question 2

Molecular formula

Answer 2

Actual numbers of the atoms of each element in a molecule or compound

Question 3

Empirical formula

Answer 3

The simplest whole number ratio of the atoms of each element in a molecule

Question 4

atom economy

Answer 4

Mr of desired product / sum of Mr of all products x100%

Question 5

% yield

Answer 5

actual yield / theoretical yield x100%

Question 6

Reasons the actual yield is lower than the percentage yield

Answer 6

Product has escaped- gas escaped or dissolved (note: CO2 is quite soluble)
Reaction is incomplete
Unwanted side reactions

Question 7

moles of gas

Answer 7

volume (dm3) / 24

volume (cm3) / 24,000

Question 8

ideal gas equation

Answer 8

pV=nRT

p = pressure (Pa)
V = volume (m3)
n = moles
R = the gas constant (8.31 Jmol-1K-1)
T = temperature (K)

Question 9

dm3 to m3

Answer 9

/1,000

Question 10

cm3 to m3

Answer 10

/1,000,000

Question 11

C to K

Answer 11

+ 273

Question 12

atm to kPa

Answer 12

1 atm = 101 kPa

Question 13

Measurement uncertainty

Answer 13

The potential error involved when using a piece of apparatus to make a measurement.

% uncertainty = total measurement uncertainty / value recorded x100%
Add the uncertainty for each measurement

Question 14

What combination of acids and bases is methyl orange suitable for?

Answer 14

Strong acid-strong base
Strong acid-weak base

Base: yellow
Acid: red
End point: peach-orange colour

Question 15

What combination of acids and bases is phenolphthalein suitable for?

Answer 15

Strong acid-strong base
Weak acid-strong base

Base: pink
Acid: colourless
Endpoint: colourless persists for 5 seconds

Question 16

What are some reasons for error in a titration?

Answer 16

Judgement of the colour change at the endpoint
Jet of burette not filled
Unreliable if only 1 titration carried out