Module 1 Development of Practical Skills in Chemistry
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When there is no uncertainty of graduated apparatus, how can it be calculated?
Half of the smallest graduation
When no uncertainty is provided for digital apparatus, how can it be calculated?
It is assumed to be the resolution of the apparatus e.g., a 2 decimal place weighing balance has an uncertainty of +/- 0.01 in each measurement
Formula for percentage uncertainty
Percentage uncertainty = uncertainty / quantity measured x 100
A mass balance was used twice, what must we do to the uncertainty?
Multiply by 2
List the equipment where uncertainty must be multiplied by two
• Thermometer (when calculating temperature change) • Burette • Mass balance
List ways in which percentage error may be reduced
• Increase amount measured • Increase precision by using a two decimal place weighing balance
Describe the trends in atomic radii across a period
• Protons added to nucleus so nuclear charge increases • Electrons added to same shell • Nuclear attraction on outer shell electrons increases across a period • Electron shells drawn in by nucleus Atomic radii decreases across period
Explain trends in atomic radii down a group
• Number of shells increases • Outer electron is added to new shell further away from nucleus • Shielding effect by inner shells increases down a group • Increase in distance far outweights increase in nuclear charge • Nuclear attraction decreases down a group Atomic radii increases down a group
Which acronym can be used when describing trends in atomic radii
Now = nuclear charge Do = distance from nucleus Something = shells (electron repulsion from inner shells) Amazing = attraction (nuclear)
Describe melting and boiling points between group 1 + 4
Increases gradually
Describe melting and boiling points between group 4 + 5
Decreases sharply (goes from metallic to simple covalent)
Describe melting and boiling points between group 5 + 8
Comparatively low