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Chemistry deconstruction: Acid concentration of everyday substances -…
Chemistry deconstruction: Acid concentration of everyday substances
How to measure the concentration of acids?
Stoichiometry
What is stoichiometry?
studies amounts of substances that are involved in reactions
By using reaction observations to deduce and mathematically calculate the amount of reactants involved in the practical
How can stoichmetry help calculating the concentration of acid in substances?
stoichiometry equations for concentration
C = m/V or M = n/V
This refers to concentration equals to the number of moles of solution divided by volume of the solvent
What are household acids ?
Most common acidic house hold products
Cleaning products
CLR Bathroom and Kitchen Cleaner (pH 2.4-2.6) - Bunnings
CLR Calcium Lime Rust Remover (pH 2.10-2.30) – Bunnings and Woolworths
Chemtech 1L Brick Tile And Paver Cleaner – (pH 2) - Bunnings
Peerless JAL 1L One Shot Thick Concentrated Acidic Toilet Bowl Cleaner (pH 1-2) – Bunnings
Foods
Woolworths lemon juice 500ml (pH 2) -Woolworths
Chobani strawberry yogurt (pH 4.3-4.4) - Woolworths
Coles full cream milk 1L (pH 6.5-6.7) - Coles
Skincare products
The ordinary glycolic acid toner 240ml (pH 3.6)- Priceline
The ordinary lactic acid serum 30ml (pH 3.8) - Priceline
Neutrogena Pore Refining Toner 250 mL (pH ~3) – Chemist Warehouse
Possible methods related to stoichiometry
Titration
What is titration?
Method of quantitative chemical analysis to determine the concentration of an identified analyte
What is analyte?
the substance whose quantity or concentration is to be determined
What is a titrant?
A substance with known concentration
What are the equipments needed for titration?
Volumetric flask (200/250ml)
the standard solution is made in this equipment
How to make a standard solution
Measure out a certain amount of liquid, or if the substance is a solid disslove it with water
Add water up to the line
Volumetric buret
Where the titrant is placed in
Buret clamp
To hold the buret in place
Stopper
Beaker (100ml)
Volumetric burrette :
What are the limitations of this method?
How do you eliminate these limitations or errors happening
Ensuring that all controlled variables are controlled in the appropriate manner
Cleaning equipments and using the same equipments
Observing and comparing the color of the solution carefully to obtain color change
Variables
Controlled variables
Type of indicator used, source of lemon juice, concentration of standard solution, quantity of standard solution, equipment used
Uncontrolled variables
Lost of liquid/solution
Dependent variables
None
Independent variable
None
How to perform a titration?
Step 2: Use a volumetric pipette to put 20 ml of the lemon juice into a conical flask, and add 3 drops of Methyl Orange Indicator
The quantity of the lemon juice must be known to allow for the final calculations, and the indicator shows when all the acid has been reacted to by showing when the acidic lemon juice becomes neutral through reacting with the basic standard solution.
Step 3: Fill a burette with the standard solution, then slowly add to the lemon juice and indicator.
Step 4: Once the solution changes colour, record what volume of the standard solution has been added to the solution
The volume of standard solution added will be the volume required to react completely with the lemon juice, from which the concentration of the lemon juice can be calculated.
Step 5: Repeat steps 2-4 until 3 concordant values have been found for the volume of standard solution added.
Repeating the process reduces the effect of random errors and allows for the evaluation of the consistency of the results.
Step 1: Create a standard solution of 0.1 MolL-1 NaOH
This standard solution must be created to know exactly how it reacts and what its concentration is, allowing for the calculation of the concentration of the lemon juice. It also has to be a base so it will react properly with the acid.
Potential risks of handling acids and equipments in the laboratory
Risks of using equipments
Glass equipments might break and cause injuries such as cuts
How do we handle this?
Do not pick up the glass with bare hands or attempt to step on it , instead sweep the glass with a broom or ask for a teachers advice
Disposing glass in the glass container specifically designed for disposing broken glass
Risks of using acid bases
Acid and bases could potentially be corrosive when it comes into contact with human skin and surfaces
How do we prevent this from happening ?
By wearing appropriate safety gear which includes safety goggles , apron, gloves and preferably non slip shoes as spillage might occur
Acids could react very violently with certain chemicals such as metals and bases which might cause explosions or fires
To prevent this from happening we should not be mixing unknown substances together as we do not know how they would react
What is an acid
Acids have a pH that is lower than 7
Strong acids has the pH of pH 0-3
Weak acids has the pH of pH 4-7
Reactions with acids
Acids reacts with bases and solution will neutralise
Acids react with metals to produce salts
Acids usually exist in forms of liquids
How do we measure results accurately?
Some equipments are more reliable on measuring liquids
These equipments includes volumetric flask, volumetric burette and volumetric pipettes
How do we use these equipments?
How to use a volumetric burette?
Fill the buret with the liquid you wish to deliver and read the volume. It is not necessary to adjust the level of the liquid to exactly 0.00 ml, or any other number for that matter. A piece of paper placed behind the buret may make it easier to read. Be careful as the numbers on a buret are opposite to those on a graduated cylinder.
Slowly allow the liquid to drain into the receiving vessel.
Clamp the buret in a buret clamp attached to a ringstand.
Rinse the buret two or three times with the liquid you wish to use. Do this by adding a small amount of liquid into the buret, turning the pipet horizontally and rotating it so that the liquid contacts the entire inside surface of the buret. Let the liquid drain through the stopcock into a waste container.
When the appropriate amount of liquid has been delivered close the stopcock and touch the buret to the side of the vessel to remove any partial drops.
How to use a volumetric flask?
Add your solute to your solution.
Add enough solvent to dissolve the solute.
Keep adding your solvent until it gets close to the line marked on the volumetric flask.
Use a pipette to fill the flask.
Use the meniscus* of the solution and the graduation line on the flask to determine your endpoint.
Place the volumetric flask stopper into the volumetric flask to seal it.
Invert the flask to thoroughly mix the solution.
How to use a volumetric pipette?
Touch the pipet to the surface of the liquid or side of the container to remove any partial drops still clinging to the pipet.
Gently release the seal with your finger and allow the liquid to drain until the liquid level reaches the inscribed mark. This is most easily accomplished by releasing the pressure of your finger and rotating the pipet between your fingers.
Remove the pipet from the liquid and wipe any droplets off the side of the pipet.
Quickly remove the bulb from the pipet (this is why you don't push the pipet into the bulb) and cover the opening with your right index finger.
Place the end of the pipet well below the surface of the liquid to be transferred and gently release the bulb. Liquid should be drawn up into the pipet. Allow the liquid to rise above the inscribed line on the pipet.
Squeeze the bulb and place it over the end of the pipet. The pipet should not be forced into the hole in the pipet bulb. A satisfactory seal can be made if the two are pushed up against each other.
If you are right handed place the pipet in your right hand and the pipet bulb in your left (left handed people do the opposite).
Rinse the pipet two or three times with the liquid you wish to transfer. Do this by drawing a small amount of liquid into the pipet, turning the pipet horizontally and rotating it so that the liquid contacts the entire inside surface of the pipet. Let the liquid drain into a waste container.
Methods of observing data and collecting results
The most common method is to observe reactions with naked eyes
However, during a titration color changes are very subtle and sometimes could not be recognised therefore resulting in inaccurate results and low reliability and validity
To observe the color change easily, simply create a solution with your stand solution and choice of indicator and use it to compare it with the solution that you are testing
Another way is to take a picture before adding base to your solution and compare the color of the before and after