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To determine the rate of reaction for:
What effect does the concentration of hydrochloric acid have on the rate of reaction when combined with magnesium powder?
I hypothesise that the volume of hydrogen gas produced will increase at a steep, but steady rate as the concentration of hydrochloric acid increases, until the concentration is equal to 1.0 mol dm-3. Therefore, the rate of reaction will remain constant until this point. I suggest this concentration because the standard concentration of hydrochloric acid used in general experiments is usually 1 mol dm-3. I then theorize that the rate of reaction will gradually decrease until the gradient of the graph (‘effect of increasing concentration of HCl against the volume of hydrogen produced’ – line graph 1) becomes ï¿½0.
Type of Variable
* Time Taken
* Timed using stop clock
* Volume of Hydrogen Gas Produced
* Experiment repeated three time & Average taken
Independent Variable (quantitative)
* Concentration of HCl(aq)
* 8 concentrations were used
* Water bath was used
* Thermometer placed in water bath
* Mass of Magnesium
* Used a 3 d.p. balance
* Surface Area of Magnesium
* Used powder & made sure mass was the same
* Volume of Hydrochloric Acid
* A burette was used to measure volume
* water bath (30oC)
* 500cm3 conical flask
* rubber stopper
* delivery tubing
* measuring cylinder
* clamp stand
* stop clock
* 0.06g magnesium powder
* 20cm3 hydrochloric acid
* 3 d.p. balance
* weighing boat
* burette (x2)
* thermometer in water trough
* safety goggles
1) The magnesium powder should be as pure as possible. It should be stored in a clean and dry environment to ensure that no impurities (such as effects of oxidation) prevent the collection of accurate data.
2) Eye protection is necessary due to the use of hydrochloric acid – tiny bubbles may cause irritation of eyes.
3) Rubber, instead of cork, must be used as the material for the bungs. Cork is too porous and will leak.
4) No naked flames should be present – hydrogen gas is extremely flammable
1. The solutions were prepared with a calculated combination of hydrochloric acid and water, to produce 8 different concentrations of 20cm3 hydrochloric acid
2. The apparatus was set up as shown in the diagram. The trough was half filled with water
3. The measuring cylinder was filled with water, and remained full whilst being turned upside-down (as in diagram)
4. The magnesium powder was added to the conical flask quickly and the bung was replaced as fast as possible to prevent any gas escaping. The stop clock was started.
5. The volume of the gas was then collected in the measuring cylinder, measured and recorded after 30 seconds
6. Steps 3-5 was repeated three times with fresh materials, and an average volume of gas collated was calculated for that concentration
7. This process (steps 1-6) was repeated for the 7 other concentrations (0.25 – 2.00M)
8. The rate of reaction was then calculated for each of the concentrations
* As the magnesium powder reacted with the hydrochloric acid, fizzing on the surface was evidence of a reaction taking place.
From my data and calculations, I determined the rate of reaction (for concentration of HCl: 0.25 to 2.00M) to be between 0.24 and 1.14 (respectively) ï¿½ 11.68%.
The rate of reaction is affected by a number of factors. Increasing the concentration of reactants will usually cause the rate of reaction increase. A higher concentration will mean that there is more of the reactant to collide together and react.
By measuring the volume of gas (hydrogen) evolved at each concentration, I was able to calculate the rate of reaction for each of the concentrations.
The volume of gas evolved increases as the concentration of HCl (aq) increase, as does the rate of reaction (the gradient of line graph 1). However, the graph showing the rate of concentration against average volume of gas (i.e. showing the rate of reaction) begins to level off at 1.25M, and not 1.00M, as I hypothesised.
This could be associated to one or many of the random or systematic errors, resulting in ï¿½11.68% uncertainty for the value of rate of reaction. It could also be that my hypothesis was proved wrong on this account.
There is no standard rate of reaction, as it is different for each trial, since the rate of reaction is dependent on concentration. There is not single rate of reaction for this type of experiment.
Temperature of Hydrochloric Acid
If the temperature increases, it could be the cause of any change in rate of reaction & would mask the effects of the change in concentration
The flask was placed in a water bath set at 30oC in order to keep it at a constant temperature & eliminate this as an independent variable
Volume of Hydrochloric Acid
If the volume varies, it could be responsible for an increase or decrease in the rate of reaction & it would not be a reliable experiment
20cm3 of hydrochloric acid was used for every experiment
Mass of Magnesium Powder
If the mass increases, it would alter the rate of reaction & would cause inaccurate results
0.06g of magnesium powder was used for every experiment