When Acids React With Alkalis Biology Essay

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In this investigation, I shall be investigating how much energy is transferred as heat when acid reacts with alkalis and whether concentration affects the amount of energy being transferred.

Scientific background information:

Acids are substances with a PH of less than 7. The stronger the acid, the lower the PH number. Acids dissolve in water to form H+ ions. Alkalis are substances with PH of higher than 7. The stronger the alkali the higher the PH number. Alkalis dissolve in water to form OH- ions. Substances with PH scale of 7 are neutral. [1]

Acid and alkalis react to form neutral products such as water. Acid reacting with an alkali causes its PH to fall because the alkali is removed by its reaction with the acid. A reaction in which acidity or alkalinity removed is called a neutralisation reaction. A neutralisation reaction which involves acid and alkali produce a salt and water. The equation is as follows:

Acid + alkali  salt + water [2]

When there is a chemical reaction, energy is usually transferred to or from the surroundings. There are two types of reactions:

Endothermic reactions - Endothermic reactions are reaction that takes in energy from the surroundings, usually in form of heat. This can be noticed by fall in temperature of the surrounding. Example of exothermic reaction is photosynthesis. Endothermic reactions are not very common.

Exothermic reactions - Exothermic reactions are reactions that give out energy, usually in the form of a heat. This can be noticed in change of temperature. Example of exothermic reaction is burning fuels.

energy_transfer1 [3]

When there is a chemical reaction, chemical bonds are either broken or either formed. Endothermic reaction is a type of reaction where products have more energy than the reactants, therefore it is breaking bonds. Energy form the surroundings is used to break the bonds. Breaking of bonds in chemical reaction releases energy. Exothermic reaction is a type of reaction where products have less energy than the reactants. It is reaction where bonds are made. [4]

Hypothesis:

Apparatus:

Thermometer- Thermometer is needed to measure the temperature of the reaction. Measuring the temperature allows us to calculate the energy change of the reaction. Temperature also allows us to tell whether a reaction is endothermic or exothermic.

Copper cup holder - Polythene cup holder as used in the experiment to support the polythene cup to reduce risk of spillages.

Polythene cup (8) - Polythene cups are used in the experiment to carry out the experiment. Polythene cups are used rather than test tubes because they are insulator; they do not conduct heat, no heat is lost to the surrounding, which will mean that the results are more accurate. The use of different paper cups to carry out the experiment will also limit the need for repeated washing which will save time and will also make sure that no neutralised solution is left in the cup.

Measuring cylinder- Measuring cylinders are used in the experiment to measure the appropriate amount of acid/alkali needed. The measuring cylinder used is marked in 'ml' to make the measurements precise. Separate measuring cylinders should also be used in order to make my experiment a fair test. Using the same measuring cylinder to measure the amount of acid and alkali will result in neutralisation taking place in the cylinder rather than the paper cup.

Acid - Acid will be used to carry out a reaction with Alkali.

Alkali- Alkali will be used to carry out a reaction with Acid.

Stopwatch- Stopwatch will be used in the experiment to make sure that we measure the temperature for each test at a particular time; this will make result in my data being reliable

Health and Safety:

Health and safety precautions must be taken while carrying out this experiment.

Wear goggles- It is important to wear goggles to protect our eyes from any spills that could happen. If you are working with higher concentration of acids or alkali, full cover goggles must be used. Acids and alkalis used in the experiment are corrosive and irritant.

Carry out the experiment standing- It is important to carry out the experiment standing, so that there is less chance of injury happening to you. If something happens, i.e. acids spills, you can quickly move from the area.

Positioning of equipment- Acids and Alkalis should be kept in a position where they are not likely to fall or spill. It shouldn't be kept at edge of the table. Equipment such as measuring cylinder which is made out of glass could fall and break easily if placed inappropriately, i.e. edge of the table. Broken pieces of glasses are hazard, it could easily cut someone.

Skin contact- Acid is dangerous and classed as irritant. If there is contact with skin; wash immediately with plenty of water. Acid spilled on skin can make skin irritated, if irritation persists, seek medical attention.

It is also recommended to wear latex gloves as they are thin, see through and will not create difficulty for you while doing the experiment. Latex gloves will create a barrier between the substances and your hand. Wearing gloves protects our hand form the irritation which could be caused by acid.

Wearing goggles and latex gloves will mean that there is maximum skin protection and minimises chances of irritation and rashes from substances coming in contact with the skin. Hands should also be washed after doing the experiment.

Factors:

Independent variables:

The independent variables in the experiment are:

Dependant Variables:

The dependant variables in the experiment are

Controlled variables:

The controlled variables in the experiment are:

Temperature- Temperature definitely affects an exothermic or an endothermic reaction. The experiment should be carried out in room temperature. Furthermore, the temperature in which the acid and alkali are kept at should remain constant, i.e. if an acid that has a higher temperature is being used during the experiment, the rise in temperature will also be higher.

Type of acid- Different type of acid have different properties and can cause different temperatures.

Type of alkali- Similarly, different type of alkali have different properties, if this does not remain constant in my experiment, it could make the result obtained biased.

Amount of acid- It is necessary to use the same amount of acid throughout the experiment,

Amount of alkali-

Concentration of alkali-

Preliminary test:

In order to see if there were any changes necessary to be made in the real experiment, I conducted a preliminary experiment.

Method:

Collect all the apparatus needed as indicated in the apparatus list above.

Prepare the concentrations needed for the experiment. Concentration is worked out by:

Concentration of acid = Mol. (desired molarity) * (Ml needed)

Original molarity

*The formula above only gives the amount of acid needed for a particular concentration. Therefore distilled water should be added to make up the amount that is needed.

Measure the temperature of the acid and the alkali

Pour alkali onto the cup, follow by adding acid. Allow the reaction to occur and measure the temperature of the reaction.

*The change in temperature is worked out by deducting the temperature of the acid before the reaction and temperature during the reaction.

5. Repeat each test three times for reliability.

6. Repeat steps 4-5 for all the concentration of acid that will be used in the experiment.

I am investigating whether a concentration of acid affects neutralisation. The sulphuric acid in the experiment will be diluted to make the concentration weaker. I will use 2.0 molar of sulphuric acid and dilute this eventually down to 0.25 molar. The amount of acid that will be used throughout the experiment is 20 cm3.

Here is how I diluted the concentration.

Molar of H2S04

Volume of sulphuric acid (cm3)

Volume of water (cm3)

0.25

2.5

17.5

0.50

5

15

0.75

7.5

12.5

1.0

10

10

1.25

12.5

7.5

1.50

15

5

1.75

17.5

2.5

2.0

20

0

Results table:

Temperature when mixed with alkali / (temperature change) [°C]

Mol. of acid

Starting temperature of acid and alkali (°C)

Test 1

Test 2

Test 3

Average

0.25

20

21.5 /

25

25

24

0.5

20

24

29

31

28

0.75

20

22

35

34

30.33333

1.0

20

28

32

32

30.66667

1.25

20

31

31.5

31

31.16667

1.50

20

30

30

32

30.66667

1.75

20

30

30

29

29.66667

2.0

20

29

29

30

29.33333

Real test

Temperature when mixed with alkali / (temperature change) [°C]

Mol. of acid

Starting temperature of acid and alkali (°C)

Test 1

Test 2

Test 3

Average

0.25

20

22

24

25

0.5

20

24

26

25

0.75

20

25

24

25

1.0

20

26

25

24

1.25

20

25

25

25

1.50

20

26

26

26

1.75

20

26

27

27

2.0

20

26

28

27

In order to acquire a direct reading of the temperature during the reaction, I would use a digital thermometer. Digital thermo meter also gives result in one decimal place which in turn makes my result precise. The thermometer used in the experiment- mercury thermometers could also be dangerous if it breaks. Mercury thermometers have scale in them which means that there could human errors while reading the temperature. There could also be parallax error while reading the data from the thermometer.

However, using digital thermometer could also result in systematic error and the result might not be reliable.

I would also use measuring cylinders which have a higher accuracy, to measure the amount of acid and alkali. This enables me to have a precise amount of alkali and acid needed.

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