Neutralization investigation
Neutralization investigation Nicky G
I will conduct an investigation into the effect an alkali and an acid have on each other using titration, find out whether neutralization occurs, and what factors effect neutralization if any. I will look at how concentration and type of an acid can affect neutralization.
Acids And Alkalis
Acids and alkalis are substances found everywhere in our daily lives. They both have different properties that can be both harmful and advantageous. Some examples of substances containing alkaline are toothpaste, which is used to fight acid in the mouth built up by bacteria in the mouth digesting sugar, and antacids, which are tablets used to combat acid indigestion. A base is any substance that can neutralize an acid, so an alkali can be called a soluble base as it also dissolves in water. There are other known compounds that can neutralize acids such as zinc carbonate.
Acidic solutions are often found in the kitchen and include cleaning products to fight lime scale build up, and stronger oven spray. All these examples of acidic and alkaline solutions are also examples of neutralization, which occurs equal in our daily lives.
A neutral substance is neither an acid nor an alkali and shares no properties with them. Neutral substances such as pure water tend not to be toxic and corrosive and generally are much safer to handle than acids and alkalis.
When a neutral substance is formed water and salt are always two of the resulting products. The type of salt which is formed is derived from the type of acid used e.g. sulphide makes sulphate salts, nitrogen makes nitrate salts, and chloride makes chlorine salts. This should mean hydrochloric acid and sulphuric acid should leave chloride and sulphide salts as well as pure water.
Some examples of neutralization and its products found in labs:
Nitric acid + magnesium oxide magnesium nitrate (salt) + water
Hydrochloric acid + calcium hydroxide calcium chloride (salt) + water
Some properties of acids:
* Have a sour taste
* React with metals to form hydrogen and salt
* Some are corrosive
* Have a pH of less than 7 (as explained later)
Some properties of alkalis
* Are toxic
* Have a pH greater than 7
* Have a bitter taste
Some examples of acids are:
* Hydrochloric acid, HCL
* Sulphuric acid, H2504
* Nitric acid, HNO3
Some examples of alkalis are:
* Sodium hydroxide, NaOH
* Potassium hydroxide, KOH
* Calcium hydroxide, Ca(OH)2
What are acids and alkalis?
According to Chemistry A-Level by Ted Philips: ''An alkali is a substance which dissolves in water to form hydroxide ions, as it's only negative ion'', and ''An acid is a substance which dissolves in water to form hydrogen ions, as it's only positive ion''.
This means that all alkalis are made up of hydroxide ions, OH-, which are negative, and all acids are made up of hydrogen ions, H+ which are positive. When water is added to an alkali or an acid the molecules in the acid or alkali brake up to form either hydrogen or hydroxide ions. This means that acids and alkalis have different (charges?) and this is why they have different properties.
How are alkalis and Acids measured, and how do they vary?
I now know that acids and alkalis are compounds which dissolve in water to form hydrogen or hydroxide as their only positive and negative ions, however within acids and alkalis the composition of hydrogen or hydroxide ions can give different strengths of acids and alkalis. When we refer to an acid as weak or strong we are referring to the amount of hydrogen ions concentrated within every mole of the substance when it is pure. Concentration means the amount of H+ or OH- ions in acids/alkalis. The more hydrogen ions there are per mole of acid, the more acidic it is. Similarly when we refer to an alkali as weak or strong we are referring to the concentration of hydroxide ions.
Co-ordinated Science defines the strength of an acid: ''in a strong acid, nearly all the acid molecules form ions. In a weak acid, only some of the acid molecules form ions.''
This means that in a weak acid/alkali not all the molecules are strong enough to form into ions and the result is a substance with less ions meaning a lower concentration of ions, and therefore a weaker ionic structure with weaker acidic/alkaline properties.
The concentration of an acid or an alkali is measured on something called the pH scale, which runs from 0-14 with 1 being the strongest acid and 14 being the strongest alkali. (Diagram of pH scale shown below, also table showing typical acids, neutral and base substances and their pHs).
For my investigation I should use one strong acid and one strong alkali. I should use extremes like this so I can get strong results which are easy to test for and therefore very conclusive.
I will use hydrochloric acid, HCl, Sulphuric acid, H SO , and sodium hydroxide, NaOH, as the acid and alkali for my investigation. I choose these three substances because they vary in terms of their strength and were they are on the pH scale- this should give me a range of results, which test the accuracy of the pH scale. Hydrochloric ...
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For my investigation I should use one strong acid and one strong alkali. I should use extremes like this so I can get strong results which are easy to test for and therefore very conclusive.
I will use hydrochloric acid, HCl, Sulphuric acid, H SO , and sodium hydroxide, NaOH, as the acid and alkali for my investigation. I choose these three substances because they vary in terms of their strength and were they are on the pH scale- this should give me a range of results, which test the accuracy of the pH scale. Hydrochloric acid has a pH of 1, while sodium hydroxide has a pH of 14. This means that a neutral pH of 7 lies exactly in-between them and so they should have an equal concentration of hydrogen and hydroxide ions, and should than react to form a salt (which is always a product of neutralization along with water), because the positive and negative ions are of equal strength and therefore cancel/remove each other leaving a substance with no charged ions. Sulphuric acid has a pH reading of 3.5, meaning it is exactly half as strong as sodium hydroxide.
Hydrochloric acid and sodium hydroxide have an ratio of 1:1 which means they are monobasic substances which should neutralize in equal quantities only if they are both of the same concentration (in this case pure). If the hydrochloric acid was placed in a neutral substance which was the same volume as itself, it's strength would half and it would therefore have a ratio of 2:1 with pure sodium hydroxide, as two moles of hydrochloric acid would be of the same strength as one mole of sodium hydroxide and therefore twice as much hydrochloric acid would be needed to neutralize sodium hydroxide.
The reaction of acids and alkalis to each other to form water and salt can be compared to the reactions elements from the periodic table have with each other. Sodium and Sulphide react with each other strongly because they both need to share electrons in order to gain full outer shells. They are at a large distance from each other in the periodic table (groups 1 and 6) and therefore are both very reactive. However, sodium is more reactive than sulphate because it only needs to lose one electron, while sulphide needs to gain two electrons. This means that in the compound that is formed consists of two sulphide ions for every one sodium ion.
The ionic relation of the sodium and sulphide is the same as the ionic relation between sulphuric acid and sodium hydroxide. If the substances are pure than the ratio of sulphuric acid to sodium hydroxide is 1:2 and so for neutralization to occur there needs to be twice as much sulphuric acid as sodium hydroxide.
Acids that form one H+ ion from each acid molecule are called monopratic acids, two acid molecules- diprotic, and three- triprotic.
A strong acid or alkali is always strong even if it is diluted, e.g. hydrochloric acid mixed with water would be called a strong dilute substance. A base like ammonia will always be a weak one because it has a sparse ionic arrangement. The concentration of a substance and the strength of them are only relevant when relating to ionic concentration- not the amount of substance dilution.
Key words: neutralization- when an acid and a base react with each other to give a substance with a pH of exactly 7.
Equipment (with labelled diagram)
The equipment I will use: Burette to 50cm3, pipette to 25cm3, clamp, hydrochloric acid with concentrations of 0.1M, 0.5M, 1M, 1.5M, 2M, sulphuric acid with concentrations of 0.1M, 0.5M, 1M, 1M, 5M, 2M, methyl orange indicator, beaker up to 100ml, funnel, clamp, distilled water in plastic bottle with tube.
Method
I will decide on a scientifically accurate method of obtaining results that will give me reliable results. I will test my method in a preliminary test in when I will measure a set of results for any one concentration of sulphuric acid and hydrochloric acid to check my method works efficiently, and make any changes if necessary.
My first step will be to step up all the equipment as shown in the equipment diagram and put on a lab coat and goggles. I will than add the orange methyl indicator to the sodium hydroxide so I can see when the substance turns neutral. As the indicator is quite strong I only need to add about three drops to the sodium hydroxide and gently turn the beaker to make sure it mixes in.
I will than put the 0.1M sulphuric acid into the burette using a funnel. I will pour the sulphuric acid in slowly so that it does not overflow the funnel and spill out, and will pour it until the bottom of the curve on its surface is exactly in line with 50cm3.
I will than turn the lever on the bottom of the burette so that the sulphuric acid pours into the 25cm3 of sodium hydroxide in the beaker below. Using a prediction table to estimate how much sulphuric acid will roughly be needed to neutralize the sodium hydroxide, I will pour the sulphuric acid in reasonably fast to begin with, and than slow it down to drops when it becomes within 5 cm3 of the predicted amount needed for neutralization.
As soon as the sodium hydroxide turns pink I will turn off the tap and record how much sulphuric acid I had put into the sodium hydroxide to neutralize it. I will then repeat this process three times. If the three results are not within 0.4cm3 of each other than I will look for any mistakes I may be making which could be causing inaccuracy and will repeat the experiment a further three times. If this happens again I will do it another three times, but after this if the results are still not consistent I will have to move onto the next concentration or type of acid.
After each type concentration and type of acid I have measured I will wash the burette out with distilled water. I will make sure the water reaches up to the 50cm3 mark on the burette so that the whole burette is cleaned and will than turn the tap at the bottom of the burette so that no water is left in the burette, as if water was left in it the measurement of the acid added would not be accurate.
I will do this process for all of the different concentrations for 0.1M, 0.5M, 1M, 1.5M, 2M sulphuric acid, and I will than move onto hydrochloric acid, where I will repeat the same process. The range of concentrations I am using is sensible as they are just different enough to show clear differences in the results.
I have already planned and attempted a preliminary test for hydrochloric acid, 1 molar. However, this test did not work well as I found the substance did not turn pink and therefore no neutralization took place. I decided that the most likely reason for this was that the acids were accidentally contaminated in some way. Unfortunately, there was nothing I could think of to change my method to prevent this happening again as I was not entirely sure that this was the reason for the problem, and I could not think of anything that would help prevent this happening again except to be extra careful about which substance I am using.
Variables And Fair Test
The variables that will effect the investigation are the amount of sodium hydroxide that is put into the beaker to begin with, the amount of hydrochloric acid and sulphuric acid added to this, and the ionic composition (strength) of the acids. However, if all of these things change throughout the investigation than the experiment will not be fair or accurate because it means I will be obtaining results for things I am not investigating, and not obtaining enough results to justify a conclusion for the aims I should be investigating. For this reason I shall only use one type of alkali and I will keep the amount of sodium hydroxide the same- 25cm3 of 1M, at all times. I shall than be able to measure the effects of the acids on a constant strength and volume of alkali and make an accurate conclusion on the factors involved in neutralization.
I will change the strength of the acid that I put into the alkali so that I can measure the effect different ionic concentrations have on neutralization. This means I will use acids will a specific number of hydrogen ions in solution make-up. I will use 0.1, 0.5, 1, 1.5 and 2 molar concentrations for the acids. I have chosen these concentrations because they systematically rise so I can see any patterns in my results more clearly. It is important that I test the different properties of acids as thoroughly as possible and so I must look at acids of different strengths. This will allow me to record results that will show whether the strength of an acid is accurately shown by the pH scale.
Each time I have made a measurement I should wash out the burette so that any of the acid that might be left on the side of it is washed off. I will wash the burette with distilled water- it must not be tap water as this does not have a pH of exactly 7 so it will not remove all alkaline or acidic substances from the burette. It is important because if any of the acid is left in the burette it might mix with the next type of acid, meaning it would not be a fair test because the acids would be contaminated. Similarly, I should not mix any of the liquids in the bottles together.
I should also check the labels on each of the acid bottles are correct using litmus paper. The litmus paper is a small strip of blue paper that I can dab into the acid, and it should turn red.
I will use sensible amounts of acids and alkalis.
I will use the same volume and type of indicator, as this is something that should be kept the same so my method remains consistent. If I use different types of indicators in my experiment it will not be a fair test because different indicators have different properties, which gives different results. I will use the same volume of indicator because the amount of indicator may affect its effectiveness, which is something that should be kept the same.
Accuracy
There are various types of indicators I can use. These include universal indicator, phenolphthalein and methyl indicator. These indicators work by reacting with the ions inside the substance that is being made. They are not part of the chemical reaction, they simply measure the reaction. The substances involved cause the reaction chemically and the physical effects of the indictor do not in any way affect the results. So the only the difference between the indictors is how accurately they show the reaction.
I will use orange methyl indicator as an indicator for this investigation because it is more accurate than other types of indicator as it shows the precise amount of hydrochloric acid or sulphuric acid needed to turn the sodium hydroxide neutral. However, I must be careful that I add the acids into the sodium hydroxide very slowly so I can measure the exact amount I have added without adding to much and than not knowing at what point the substance changed colour.
I have carefully selected the equipment I am using for my investigation so that my investigation is accurate and safe.
The burette is very accurate because it has a tap which is easy to control and can add the acids drop by drop. This means if I am attentive I should always be able to measure the exact amount of acid needed to turn the sodium hydroxide neutral. The burette also has measurements going up it in millimetres so I can use accurate units of measurement. However I should be aware that the 0mm measurement is just above the bottom of the burette so I should not empty it completely.
When I am putting acid into the burette I will use a plastic funnel to make sure I put in the acid without spilling any over the side, as this could mean some acid dropping into the sodium hydroxide which would make the test unfair as this would not be measured, or it could land on the table and splash onto someone.
When acid is put into a burette a curved shape appears at the top of the substance. I should measure the correct amount of acid from the bottom of the curve. This is because the density of the acid in the thin burette causes it to sag in the middle, and if I measured it from its highest point, I would be measuring some air which fills the hole were the acid sags. Although this is slightly inaccurate as this means I am not taking into account the small amount of acid either side of the sag, it is the most accurate way I can think of, and as long as I am consistent in my measurements it should not lead to inaccuracy in my results.
I will use two types of acid instead of one because I can than analyse results from two acids with different pH's and this will mean my results will show a wider degree of deviation and will show any miscalculations in the method of the investigation which might not be shown by using only one type of acid. As I will have results for two sets of acids with different properties I will be able to have a larger amount of results which should be different and therefore allow me to make a more scientifically accurate and substantial conclusion. Using two different strengths of acids will show how substances differ, but how which are both acids or alkalis share similar properties.
I will repeat any results that are not similar per every different molar strength of acid I use. I will do this because there may be conditional interferences that I have over-looked and I should try to find what these are (preferably in my preliminary test) and end up with results that reflect a well-planned method which consistent results. I should do every different molar substance three times as this is enough times to show consistency, and should carry on to nine times if my results fail to be consistent. Using repeats also allows for human error that is something that is very hard to completely cover for.
The acids that I use are measured in molar units. The only other way I know of measuring concentration is by using percentages of ions in a concentration, but molar units are much simpler than this.
Safety
There are a few safety issues I should consider when planning my investigation. Both acids and alkalis can be very harmful if they make contact with the skin. Acids and alkalis are corrosive and toxic and can eat away at skin if even small amounts get in contact. The acids and alkalis I'm using for my investigation are especially dangerous because they are strong and can be much more harmful than weak acids/alkalis. I should therefore make sure I'm wearing a lab coat and goggles at all times while I am conducting the investigation so if any acid or alkali touches me I am protected. I should also make sure I'm standing when acids and alkalis are on the tables because if they spill than I am in a better position to move out of the way quickly.
I should be aware of things such as the beaker containing sodium hydroxide being directly below the burette when the acids are pouring, and should make sure any acids or alkalis that get on the table or floor are cleaned up immediately.
However, if I am careful, wear the correct protective clothing, and do not knock or drop anything (especially the large glass burette), than the experiment should be very safe.
Prediction
Using all the information I have researched and any knowledge I had previously I will make a prediction based on my aim. I predict that neutralization will take place when an acid is added to an alkali. I think this because I know through my own knowledge that when acid rain falls into a river, lime is used to neutralize the acid.
I predict that the concentration of the acid will be an important factor on the amount of acid needed to neutralize the alkali. The more hydrogen ions there are in a substance the stronger it will be on the pH scale. This works in a similar way molecules work in a solid object. The denser the molecules in a solid are, the stronger the bonds, and the object will be. Acids work the same, except instead of solidifying they become more acidic as its molecules become stronger.
I predict that less hydrochloric acid will be needed to neutralize 25cm3 of sodium hydroxide than sulphuric acid. I think this because I know that sulphuric acid has a more sparse arrangement of ions, and so when it is added to another aqueous solution like sodium hydroxide only some of its acid molecules will be strong enough to form ions. Hydrochloric acid has denser arrangement of ions so I predict less of this will be needed because the molecules form ions much easier. The sodium hydroxide will remove all of the H+ ions and convert them into water, so the more and stronger the H+ ions are the easier neutralization can take place and the less acid is needed.
I also know that hydrochloric acid has a stronger acidic pH than sulphuric acid, so if I base my prediction on the accuracy of the pH scale I reach the conclusion that less hydrochloric acid is needed to neutralize 25cm3 of sodium hydroxide.
The only factor that affects neutralization is the amount of hydrogen and hydroxide ions present. This can be shown best in an ionic equation as shown below. These equations show that the amount of hydrogen and hydroxide ions present need to be equal in order for neutralization to take place. Using this information I can determine the ratio of the acids, and then work out how much acid is needed to neutralize the alkali.