Fair testing: To keep this experiment a fair test you must leave everything constant, but only change one element – the temperature of acid. And for each piece of Magnesium used you must scrape off any oxide that has formed on the surface, in order to get pure magnesium, otherwise you’ll be using magnesium oxide (MgO2). You can tell if magnesium oxide (MgO2) is present because it forms a thin dark grey layer on the surface of the magnesium.
Constants: Everything must be kept the same apart from the temperature of the acid.
Quantities: 5.00g Magnesium for each experiment
20cm3 volume of hydrochloric acid
Conical flask, thistle funnel, delivery tube, balance, stopwatch, trough, burette, magnesium, beaker, measuring cylinder (cm3), hydrochloric acid, safety glasses, water bath, ice.
Repeats and Range: For each test the best way to get an accurate reading is to do the experiment at least 3 times (repeats) and then add up the results and divide the total by 3 to get an average reading of gas collected. We can find the gas collected by using the scale on the Burette. A range of 5 temperatures will be used to help draw a conclusion and at the following temperatures (oC):
- 4 oC (closest as possible to achieve in the lab instead of 0oC)
- 20 oC
- 30 oC
- 40 oC
- 50 oC
I will increase the temperature after 20oC by 10 oC each time until 50 oC is reached, since it will allow me to see the increase in rate of reaction and 5 results should be enough to help me identify a conclusion.
Safety: There are a number of safety issues that apply to this experiment. One of the most important ones is to wear safety goggles at all times. Make sure you don’t boil your acid because it’s extremely dangerous and can burn you if spilt (that’s why we’re using a maximum of 60oC).
I found out from my pilot that I could obtain fair results using the quantities 5.00g of magnesium and 20cm3 hydrochloric acid (concentrated at 1M). But I also discovered a number of errors. For example, gas escaped through the thistle funnel as soon as I began to pour the hydrochloric acid into the conical flask. I could prevent this by covering the thistle funnel with the palm of my hand. But the experiment was successful after that which meant I could carry out the investigation as planned above.
My results table and graph show me that when I increase the temperature of the hydrochloric acid, the rate of reaction also increases.
Altogether I tested 5 different temperatures of hydrochloric acid. 50oC hydrochloric acid, which was the highest temperature that I used, produced the fasted rate of reaction because more gas had been produced. I repeated all 5 temperatures three times to be sure that they were reliable results and in all cases the higher the temperature, the higher the rate of reaction. I had stated this in my prediction.
I believe that the experiment was successful but there were a few problems. Although the initial rate of reaction seemed to fit a pattern there were many errors that could have left me with anomalous results. Firstly, I had realised that gas had escaped through the thistle funnel as soon as the experiment started. Therefore I had to cover the thistle funnel with the palm of my hand. And it took a second or two to start the stopwatch once the experiment had started. I could have been much more accurate by using a gas syringe. To improve the experiment I would put the hydrochloric acid into the conical flask first and then put in the piece of magnesium, which would allow minimal gas to be lost because it saves time from pouring in 20cm3 through the thistle funnel.
Info: from science exercise book, science teacher, and science chemistry book.