Chemistry - Controlled Assessment P1 Flashcards
What’s the context?
Some farmers need to neutralise their fields to ensure that crops grow.
A farmer will need to know how much alkali (or acid) to add to their fields to ensure their fields are neutralised.
Farmers do want to add more alkali or acid than necessary for the cost implications.
What’s the hypothesis?
As the concentration of the acid increases, the volume of acid required to neutralise the solution decreases.
What’s the explanation to the hypothesis?
Acids and alkali react in a neutralisation reaction.
Increasing the concentration or volume of the alkali will mean more acid is needed to neutralise the alkali.
Increasing the volume of the alkali increases the number of OH- ions so more H+ ions are needed for the reaction to occur.
What are the variables to the experiment?
Independent: concentration of the acid ( mol/dm3)
Dependent: volume of acid in cm3 (needed for neutralisation to occur) (burette or measuring cylinder)
Control: volume of alkali in cm3 (burette or measuring cylinder)
What sources are chosen and why?
I chose More Neutralisation as I feel that it is useful since it has a diagram showing how to set up the burette, has an equation demonstrating an neutralisation reaction and has a pH scale which allows me to see the change in the solution to be experimenting.
However I also chose GCSE Science Methods which I feel is even more useful as it has a simple method closely related to my experiment which I can easily adapt to suit my hypothesis. Additionally, it also has an equipment list and brief risk assessment which I am able to use for my own experiment.
What’s the background?
When an acid and an alkali react, water and a salt are produced.
Water is formed because the OH- ions from the alkali react with the H+ ions in the acid to produce molecules of water H2O.
What’s the method?
1) Gather and set up the equipment
2) Measure 10 ml NaOH (0.5 mol) and pour into conical flask.
Add 5 drops of indicator
3) Using the funnel, fill the burette with HCl. Hold above beaker first and allow a few drops to flow through to remove air bubbles.
4) Using the tap, add the HCl 5ml at a time and swirl to ensure the solution is thoroughly mixed. Continue until the solution turns from pink to colourless and record the volume required.
5) Repeat - rinse equipment using deionised water and continue from step 2. Add acid until approx 5ml from previous end point and slower the rate to identify the exact volume necessary.
6) To reduce anomalies and have an accurate average, repeat the experiment 3 times with acid of different concentrations (0.1, 0.5, 1.0, 1.5 & 2 mol/dm3)
What are the control variables and how will they be controlled?
Volume of alkali (cm3) - use a pipette or measuring cylinder for the same volume each time.
Concentration of alkali (mol/dm3) - use the same alkali solution.
Number of indicator drops - use a pipette and the same no’ of drops each time.
Temperature - use chemicals all at room temperature.
What are the risks involved?
Hazard - risk - control
HCl - irritant to skin and eyes - wear goggles, avoid direct contact, wash if makes contact with skin.
NaOH - irritant to skin and eyes - wear goggles, avoid direct contact, wash if makes contact with skin.
Glass equipment - can break and cut someone if not handled carefully - be careful and clear up anything if it breaks.
Why do we repeat titrations?
In order to gain 3 results which are similar/concordant so that there are no anomalies within our results.
By having 3 results, we are able to calculate a mean which would reduce the impact of random errors (such as adding too much acid/alkali, incorrect burette readings etc).
