There will be less strong bonds being made and weaker ones in its place, meaning there will be less Na-Cl bonds being made and more H-OH bonds being made. Also, because the strong bonds are less, he total heat given off will be less. Neautralisation reactions are usually exothermic.
Acids are compounds of non-metals with simple molecular structure. They all contain hydrogen (H) covalently bonded to other elements.
Acids are also soluble in water and produce solutions with a pH of less 7. They will turn litmus paper red and turn universal indicator an orange/red colour. Acids react with metals, which are above Copper in the reactivity series, to form a metal and a salt.
Acids react with carbonates to give a salt, carbon dioxide and water. Acid solutions also conduct electricity, but are also decomposed by it, this shows that the acids consist of ions, which suggests that all acids contain H+ ions, acids are also defined as substances that can denote H+ ions.
Bases are the chemicals opposite to acids. Bases take H+ ions rather than give them away. Alkalis are a special kind of base, bases that are soluble in water.
All, alkali’s for ammonia are the hydroxides highly reactive metals. Alkalis have similar properties to acids, they are soluble in water and they are electrolytes.
EXOTHERMIC & ENDOTHERMIC REACTIONS
Exothermic reactions release energy, the amount of heat released is greater than the amount of heat used to start the reaction. Bond making is exothermic and energy is released into its surroundings.
Endothermic reactions absorb energy; the energy continues to be absorbed as long as the reaction continues. Bond breaking is endothermic and energy is absorbed from its surroundings.
Every reaction can be considered as a series of bond breaking steps followed by bond forming steps. All chemical reactions involve bond making and bond breaking.
All bonds have different 'strengths' of energies.
When bonds break in a chemical reaction the energy required to break bonds is absorbed from its surroundings.
Breaking a chemical bond requires energy, to supply energy (heat) to break bonds it becomes an endothermic reaction, forming a chemical bond will release energy. So in a reaction that releases heat (exothermic) there must be net bond formation.
HEAT & ENTHALAPY CHANGES
When a chemical reaction occurs in an open container most of the energy is gained or lost in the form of heat. Heat flows between system and surroundings until the two are at the same temperature.
Under conditions of constant pressure the heat absorbed or released and termed enthalpy or heat content. Enthalpy is not measured directly, we are concerned about the heat added or lost by the system which is the change is enthalpy.
If the system has higher enthalpy at the end of the reaction, then it absorbed heat from the surroundings in an endothermic reaction.
If the system has a lower enthalpy at the end of the reaction then it gives off heat during an exothermic reaction.
The minimum amount of energy needed for two molecules to react when they collide is called Activation Energy.
The more collisions there are between reactants the faster the rate of the reaction
- Clamp Stand
- Measuring cylinder
- Hydrochloric Acid – 1M, 0.8M, 0.6M, 0.4M, 0.2M
- Sodium Hydroxide – 1M
- Water (ml)
- A Beaker
- Polystyrene Cup
- Glass Rod
To keep the experiment fair certain things will need to be done and kept the same whilst one variable is changed. I have chosen to vary the temperature.
Firstly, and most importantly, I will have to get the measurements of the hydrochloric acid, sodium hydroxide and water as accurate as possible.
I will make sure that the amounts of hydrochloric acid are accurate, the sodium hydroxide is the same amount 20ml and I keep it at 1molar all the time, also the amount of water I dilute it with has to be accurately measured as it could interfere with my results.
Secondly, I must make sure I am accurate with measuring the temperature at the beginning of the experiment. Also, when adding the acid in the sodium hydroxide and water I must make sure the stop clock is started at the same time. I must make sure that
I am accurate with starting and stopping the stop clock; otherwise this factor could meddle with my results as well.
When measuring the temperature after the reaction has taken place and the one-minute is up I must make sure this is measured accurately as this is the result, which is most important.
If all these things are carried out hopefully my experiment and results will turn out fair.
Safety is an important aspect in every experiment. In this experiment I will be using acids and alkalis, which means I will have to be very careful with handling the substances. I will have to be careful with handling the hydrochloric acid, as it is a very reactive acid.
I have to make sure these don’t get into my body, as we are not aware of the damage it could cause.
Also, I will need to wear gloves when handling substances. E.g. hydrochloric acid, I will also wear a laboratory overall and goggles just incase any substances are splashed around and goes into the eyes.
These are the main things we should be careful of.
- Collect all the equipment, make sure it is not damaged and set it all up.
- Firstly, with my measuring cylinder, I will measure 20ml of sodium hydroxide.
- I will put the solution in the plastic cup and place the plastic cup into a beaker.
- I will take the temperature of the alkali.
- After, doing that I will add 1ml of hydrochloric acid and start the stop clock for 1minute.
- When the one-minute is up I will measure the temperature again of the solution this will tell me whether heat is given out, is being taken in.
- I will record the results in my table.
- I will repeat this process, but I will use different amounts of hydrochloric acid and I will also dilute sodium hydroxide it with water.
RESULT TABLES FOR NEUTRALISATION EXPERIMENT:
AVERAGE TEMPERATURE & ENTHALPY CHANGE
The formula used to calculate the average temperature is:
Change In Temperature 1 + Change In Temperature 2
= Average Change In Temperature
The enthalpy change has been calculated using the formula:
(DH) Energy Conversion = M × S.F.C × ΔH
M = Mass (20ml)
S.F.C = Specific Heat Capacity of Water (4.2 j k/g)
ΔH = change in temperature (average temperature)
I predicted that as I decrease the amount of Hydrochloric Acid, the amount of heat given off would decrease. From my results I have gathered I can say that the temperature does affect the neutralisation reaction meaning that what I predicted is true. I predicted this because I knew that neutralisation is an exothermic reaction. The biggest change in temperature would be from the strong acid and strong alkali.
I can see from my results that as I decreased the amount of hydrochloric acid that the amount of energy released decreased. However, at the start of my experiment as I measured the temperature it remained constant. I used the same amount of sodium hydroxide throughout my whole experiment. The amount of hydrochloric acid also stayed as the same amount of molars.
My results and scientific knowledge support my prediction very well. They prove that neutralisation reactions are exothermic and heat is given out. My knowledge of Exothermic, endothermic reactions and enthalpy supports my prediction.
Overall, I think that my experiment did go well, and was successful. I achieved the results that I predicted I would gain. I felt I obtained my results as best as I could to create informative graphs. I followed my method correctly therefore, I believe I gained accurate and sufficient results to conclude the experiment and prove my hypothesis.
I feel that my results were 90% accurate. Although I achieved what I predicted, I believe I could have made improvements to my method to gain better results.
Ideally, I would have liked to repeat each experiment one more time to achieve accurate results.
If I conducted this experiment again, I would change some of the experiment, I would change the timing I would allow more time for the reaction to take place so I would get clearer results, I would increase the time by a minute, so hopefully altogether two minutes would be enough for the reaction to fully take place in. The clearer results would enable me to produce accurate graphs.
I would also make sure my measurements were accurate if I was to do the experiment again, I would use a pipette to gain a more precise measurement of the acid and alkali, and in a larger-scale a measuring cylinder.
I believe that my experiment was fair. I followed all of the guidelines that I set out to make a fair test. The only difficulty I had was that I had put a time limit on the reaction-taking place so I would not no when the reaction finished and I could have gained better results if there was not a limit on it.
To gain extra information for my scientific knowledge, I could have used more textbooks to make the information more detailed.
To conclude I feel that that this investigation was carried out very carefully, my results turned out good and my graphs were plotted with great accuracy.
Here's what a teacher thought of this essay
**** A good account of the experiment with clear explanations of the steps followed and detailed background information. A little more careful use of scientific terminology would be be helpful however.