Magnesium reacts with dilute hydrochloric acid in a conical flask which is connected to an inverted measuring cylinder in a trough of water. The volume of hydrogen gas produced is measured over a few minutes, and the results are used to plot a graph Show
This is intended as a class practical. It is best if the students work in pairs because setting up and starting the experiment requires more than one pair of hands. One student can add the magnesium ribbon to the acid and stopper the flask, while the other starts the stopclock. During the experiment, one student can take the readings while the other records them. The experiment itself takes only a few minutes. But allow at least 30 minutes to give students time to set up, take readings and draw graph. Hydrogen gas (extremely flammable) is generated in the experiment. Students should not have access to any source of ignition. EquipmentApparatus
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Teaching notesThe equation for the reaction is: magnesium + hydrochloric acid → magnesium chloride + hydrogen Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g) Students follow the rate of reaction between magnesium and the acid, by measuring the amount of gas produced at 10 second intervals. 3 cm of magnesium ribbon typically has a mass of 0.04 g and yields 40 cm3 of hydrogen when reacted with excess acid. 50 cm3 of 1M hydrochloric acid is a six-fold excess of acid. In this reaction, the magnesium and acid are gradually used up. However the acid is in excess, so it is mainly the loss of magnesium (surface area becomes smaller) that causes the change in the rate. If a graph of volume (y-axis) against time (x-axis) is drawn, the slope of the graph is steepest at the beginning. This shows that the reaction is fastest at the start. As the magnesium is used up, the rate falls. This can be seen on the graph, as the slope becomes less steep and then levels out when the reaction has stopped (when no more gas is produced). The reaction is exothermic, but the dilute acid is in excess and the rise in temperature is only of the order of 3.5˚C. There is some acceleration of the reaction rate due to the rise in temperature. Some students might notice the flask becoming slightly warm and they could be asked how this would affect the rate of reaction, and how they might adapt the experiment to make it a ‘fair test’. Additional informationThis is a resource from the Practical Chemistry project, developed by the Nuffield Foundation and the Royal Society of Chemistry. This collection of over 200 practical activities demonstrates a wide range of chemical concepts and processes. Each activity contains comprehensive information for teachers and technicians, including full technical notes and step-by-step procedures. Practical Chemistry activities accompany Practical Physics and Practical Biology. Health & Safety checked, 2016 © Nuffield Foundation and the Royal Society of Chemistry How would you investigate the rate of reaction between magnesium and hydrochloric acid?Students follow the rate of reaction between magnesium and the acid, by measuring the amount of gas produced at 10 second intervals. 3 cm of magnesium ribbon typically has a mass of 0.04 g and yields 40 cm3 of hydrogen when reacted with excess acid. 50 cm3 of 1M hydrochloric acid is a six-fold excess of acid.
What is the reaction between magnesium and hydrochloric acid?The reaction between magnesium and hydrochloric acid combine to form a salt of magnesium chloride and release hydrogen gas. This single replacement reaction is a classic example of a metal reacting in an acid to release hydrogen gas.
How does concentration affect the rate of reaction between magnesium and hydrochloric acid?Grinding up the magnesium into a powder increases the surface area, so the acid has more space to react on. This means the larger surface area, the quicker reaction time. Magnesium reacts very strongly with hydrochloric acid.
Why does hydrochloric acid react faster with magnesium?So we now know that the reaction between warm hydrochloric acid and magnesium has a faster rate of reaction than the reaction between cold hydrochloric acid and magnesium because the particles are moving faster and with greater energy, answer choice (E).
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