Q. Why must you ensure that an experimental procedure is carried out safely?
- To ensure that no risks are posed to the person carrying out the experiment.
- To ensure results are valid. If the experiment is not being carried out safely, results may be affected.
Q. Why might you plan to use a fume cupboard during an experiment?
To remove any harmful gases, vapours, or dust produced during an experiment.
Q. What should be carried out when planning an experiment to ensure that the procedure is as safe as possible?
A risk assessment, this identifies all the potential risks, allowing you to put precautions in place to reduce these risks. Actions that can be taken if the hazard arises should also be noted.
Q. Why is it important that the most efficient experimental procedure is chosen?
To achieve maximum productivity, there would be as little waste and as few processes as possible to make the procedure quicker.
Q. Which is more efficient: producing a product from a reversible reaction or a non-reversible reaction?
The non-reversible because all of the reactants would be converted into products.
Q. How can the reliability of experimental results be increased?
Repeat the experiment to gain more data. Discard any anomalous results. Calculate the mean.
Q. What is a hypothesis?
A prediction made before conducting an experiment based on limited evidence and used as a starting point for further investigation. A hypothesis can be supported by data, but it can never be completely proven to be true. A hypothesis states a relationship between 2 variables.
Q. What are the independent, control and dependent variables?
Independent variable: the factor that is changed during a scientific experiment.
Control variable: the factor which is kept the same throughout the experiment to ensure that the test is fair.
Dependent variable: the factor that depends on/ is changed by the independent variable.
Q. How could the temperature be kept constant?
Place the reaction vessel in a water bath. Water temperature changes much more slowly than air temperature, meaning it is more constant.
Q. What needs to be considered when devising an experimental method?
1. The independent and dependent variables
2. The control variables
3. The apparatus set up
4. The techniques required
5. The range of values you will test
Q. Describe the steps involved in investigating the volume of acid required to neutralise a specific volume of alkali.
1. Use a pipette and pipette filler to measure exactly 25 cm3 of alkali. Place it in a conical flask with a few drops of indicator.
2. Fill the burette with the acid, ensuring there are no air bubbles in the tap. Note the initial volume.
3. Place the conical flask on a white tile under the burette.
4. Do a rough titration to identify the approximate point of neutralisation. Record the final volume in the burette.
5. Carry out further titrations, adding the acid dropwise around the point of neutralisation. Repeat until you get concordant results.
Q. Suggest safety precautions that should be taken when carrying out a titration.
- Clear up any broken glassware or spillages immediately.
- Fill the burette below eye level to prevent chemicals from splashing into your face and eyes.
- Wear gloves and eye protection if using chemicals which are irritants.
Q. Describe the steps involved in measuring the enthalpy change of a neutralisation reaction.
1. Measure the total mass of the acid and alkali.
2. Place the acid in a polystyrene cup. Use a thermometer to measure the initial temperature of the acid.
3. Add the alkali to the polystyrene cup and record the maximum temperature reached by the reaction mixture.
4. Use the equation ΔH = - m x c x ΔT to calculate the enthalpy change (m = mass of acid and alkali, c = specific heat capacity, and ΔT = temperature change)
Q. What apparatus is required to oxidise ethanol to produce a carboxylic acid?
A vertical condenser (for reflux)
Q. Why might a pipette be used instead of a measuring cylinder to measure a volume of solution?
A pipette is much more accurate and precise than a measuring cylinder.
Q. What apparatus can be used to measure the volume of gas produced during an experiment?
Gas syringe or upside-down water-filled measuring cylinder in a water trough.
Q. List the apparatus required for an acid-alkali titration and explain their purpose.
- Burette (to accurately measure the volume of solution added)
- Pipette and pipette filler (to measure the exact volume to be neutralised)
- Clamp and stand (to hold burette)
- Funnel (for pouring a solution into the burette)
- White tile (to make the colour change easier to see)
- Conical flask (to hold reactants, allows swirling)
- Dropping pipette (to add indicator)
Q. What type of flask should be used when oxidising ethanol?
A round-bottomed flask should be used when heating liquids because it allows more uniform heating of the solution.
Q. What precautions should be taken when using a Bunsen burner?
- Tie hair back, and wear safety goggles.
- Make sure the orange safety flame is on when not in use.
- Turn off the gas when the flame is not lit.
- Remove any flammable chemicals from the laboratory.
- Keep the laboratory well ventilated.
Q. Why is it important that glassware is handled carefully?
Glassware is fragile, so careful handling is required to avoid breakage. If glassware breaks during an experiment, hazardous chemicals may be spilt. There must be no small cracks in glassware, as this would allow gas to escape. This may affect the results of an experiment.
Q. What can be used to analyse the potential risk of chemicals used in the reaction?
Hazard symbols on containers of chemicals indicate the risks posed by that chemical.
Q. Give examples of chemical hazards that you may come across in the laboratory.
- Irritant
- Corrosive
- Harmful to the environment
- Flammable
- Health hazard
Q. How can corrosive chemicals be handled safely?
Avoid contact with skin by wearing gloves. Wear safety goggles to avoid the chemical splashing in your eyes. Clear up any spillages immediately.
Q. What degree of precision should results be given to?
The degree of precision should reflect the measuring apparatus used.
Q. What is a control experiment?
All factors are the same as in the experiment, but the value of the independent variable is 0.
Q. Why are control experiments done?
To verify that it is the independent variable affecting the dependent variable.
Q. How can data from an experiment be used to reach a conclusion?
Quantitative data can be plotted on a graph. The trend can be discussed, and a conclusion can be made about whether it supports the original hypothesis.
No comments:
Post a Comment