This experiment is used by a metal-finishing company to decide the temperature of an acid cleaning bath. Equal strips of magnesium are placed in hydrochlori...
Question 1 Report
This experiment is used by a metal-finishing company to decide the temperature of an acid cleaning bath. Equal strips of magnesium are placed in hydrochloric acid solution at different temperatures. The students record the time until each strip has disappeared. Fig. 1 represents the collision model for a reaction between magnesium and acid particles. In box A, the collision does not have enough energy. In box B, the collision has enough energy to lead to reaction.
(a) State the gas formed when magnesium reacts with hydrochloric acid. [1]
(b) Give the balanced chemical equation for this reaction. [2]
(c) Use the collision model to explain why increasing temperature decreases the time taken for the magnesium to disappear. [3]
(d) Name one variable, other than temperature, that must be controlled in this experiment. [1]
(e) Calculate the mean rate of reaction if a magnesium strip of mass 0.36 g disappears in 90 s. Give the answer in g/s. [2]
(f) Suggest why the company should not use a very high temperature, even if it gives a fast rate reaction. [1]
Answer Details
(a) Magnesium reacting with hydrochloric acid produces hydrogen gas. [1]
(b) The balanced equation is:
\[\mathrm{Mg+2HCl\rightarrow MgCl_2+H_2}\]
[2]
(c) At higher temperature, particles have more kinetic energy. They move faster and collide more often. Also, a greater proportion of collisions have enough energy to react, so magnesium disappears in less time. [3]
(d) One variable that must be controlled is the concentration of hydrochloric acid. The volume of acid, mass or surface area of magnesium, and type of magnesium strip are also acceptable controls. [1]
(e) Mean rate is mass used divided by time:
\[\frac{0.36\text{ g}}{90\text{ s}}=0.004\text{ g s}^{-1}\]
[2]
(f) A very high temperature increases energy costs. It may also make hot acid more hazardous, and hydrogen, which is flammable, would be produced more rapidly. [1]
Download The App On Google Playstore
Everything you need to excel in your exams
