Exam (elaborations)
Chemistry Student experiment year 11
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High-level assignment graded 19/20. Lost one mark from rationale. Great sample to guide you to achieve a high mark.
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How does changing the masses (0.05g, 0.03g and 0.25g) ofmagnesium ribbons (Mg) effect the amount of hydrogen yield when
reacted with 20ml of 1M hydrochloric acid (HCl)?
Rationale:
Throughout this report, the chemical reaction between magnesium and hydrochloric acid will be
explored. It is an exothermic reaction as hydrogen gas and heat energy is being released. A salt,
magnesium chloride and hydrogen gas are produced meaning that this reaction is an example of a
metal and acid reaction. It is also a single replacement reaction. This particular reaction is
represented through its balanced chemical equation:
M g(s) +2 HC l(aq) → MgC l 2(aq) + H 2 (g)
The theoretical and experimental yield will be compared through using gas laws. In particular, the
ideal gas law equation. The ideal gas equation is: PV =nRT . This equation represents the
relationship between pressure (P), volume, number of moles/volume of gases (n) and the
temperature (T) (Tenny, 2021). Of the five components of the equation, R is known as the universal
gas constant therefore it is always constant so it will be 8.31 J K−1 mol−1 . This is the SI units that
will be used as it is consistent with the other units for the other variables. Avogadro’s law states that
equal volumes of all gases, when the temperature and pressure is constant, have the same number
of molecules (Gregerson, 2019). Thus, molar volume is also associated. It is the volume at which one
mole of any gas occupies (Helmenstine, 2019). Molar volume of a gas varies with temperature and
pressure hence the standard temperature and pressure (STP) is used. The temperature is 0 degrees
Celsius, or 273 kelvin and pressure is at 1atm or 100kPa. Under these conditions, molar volume of
any gas is 22.7 L mol−1 . When molar volume is outside of STP, it becomes dependent on
temperature and pressure (Team 2, 2020).
Research question:
How does changing the masses (0.05g, 0.03g and 0.25g) of magnesium ribbons (Mg) effect the
volume of hydrogen yield when reacted with 20ml of 1M hydrochloric acid (HCl)?
Original Experiment:
The original experiment also explored the reaction between magnesium ribbon and hydrochloric
acid. Only one mass of the magnesium ribbon was used which was 0.08g. The amount of 2M HCl
used was 20ml. This produced 83ml of hydrogen gas as there was only one trial conducted. The
equipment utilised to measure the gas production was a measuring cylinder. This was considered a
limitation as using a burette would have been more efficient and accurate as using a measuring
cylinder will allow hydrogen gas to escape. Hence the volume measured might not have been
accurate and would have been skewed. There were many other limitations to the original
experiment which led to the following modifications.
Modifications to the methodology:
Chemistry Student Experiment
, To ensure that the data collected was relevant and sufficient, the original experiment was:
1. Refined by
a. Implemented three trials of each different reaction instead of only 1 which will produce
more reliable and accurate results. This will also minimise any source of error and
possible sample bias to occur.
b. Using a 50ml ± 0.5ml burette instead of a measuring cylinder as it will provide a more
accurate result of the hydrogen gas production (independent variable) as no gas will
escape.
c. Using 20ml ± 0.5ml of hydrochloric acid for each trial (controlled variable)
2. Extended by
a. Additional magnesium ribbon masses of 0.05g, 0.03g and 0.25g (dependent variable).
Having more masses will increase the validity of the experiment as a larger sample is
used. Each mass will be tested three times so that it will reduce random errors from
occurring. Masses will be measured by using a balance with uncertainty of ± 0.001 g .
The range of the masses has been taken from the sample calculations.
Management of risks, ethical and environmental considerations:
Risk, ethical and environmental considerations: Management:
Spillage of 1MHCl as causes irritation to the skin Wear the appropriate protective equipment
and eyes. such as gloves and eye protection. If spilled it
can be neutralised with base.
Broken equipment. Glass-type equipment such Check conditions of the equipment and
as the burette can cut the skin if broken or not immediately report to the supervisor if there
handled properly. are any damaged equipment.
Environmental consideration: Dispose when the reaction between
HCl is harmful to aquatic organisms magnesium and HCl has fully diluted or pour
water down the drain immediately after the
acid.
Ethical consideration: Handle equipment carefully avoid spills and not
Wastage of materials such as water, HCl and to drop materials. Waste materials will have to
the magnesium ribbons be returned.
Qualitative Observations:
Chemistry Student Experiment
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