Experimental Design Flashcards
What is the unit of mass?
g or kg
What is the unit of time?
s
What is the unit of temperature?
degrees celsius
What is the unit of volume?
cm cube
What is the physical quantity of g or kg?
mass
What is the physical quantity of s?
time
What is the physical quantity of degrees celsius?
temperature
What is the physical quantity of cm cube?
volume
What is the other unit for mass?
1 tonne = 1000 kg
1 mg = 10 to the power of -3 g
What is the other unit for time that is used for scientific investigations?
NIL
What is the other unit for temperature?
kelvin, 273.15 K = 0 degrees celsius
What is the other unit for volume?
dm cube, 1 dm cube = 1000 cm cube
A measurement should be recorded according to the __________________________.
A measurement should be recorded to the precision of the apparatus.
Gas volumes may be measured using a _______________.
Gas volumes may be measured using a graduated gas syringe.
Liquid volumes are often measured using a ____________, ___________ or ____________.
Liquid volumes are often measured using a measuring cylinder, burette or pipette.
How do you read a meniscus reading?
For a concave meniscus, the correct volume will be read at the bottom of the curve. For a convex meniscus, the opposite is true and the correct reading will be at the top of the curve.
The precision of the pipette is usually up to _____________ and that of the burette is up to ______________.
The precision of the pipette is usually up to 1 decimal place, and that of the burette is up to 2 decimal places (second d.p. is 0 or 5).
Is it true that measuring cylinders may be of various precisions? Why or why not?
True.
This is because certain smallest division for cylinder are 0.1 ml, 0.5 ml or even 1 ml.
Is a beaker meant to measure the volume of liquids? Why or why not?
A beaker is not to be used to measure volume of liquids. The markings on the side of a beaker are only approximate.
The method of collecting a gas depends on its _________________ and _____________________.
The method of collecting a gas depends on its solubility in water and density relative to air.
What are the three gas collection methods?
Displacement of water, downward delivery and upward delivery.
Displacement of water is not suitable for ______________________________.
Displacement of water is not suitable for gases that dissolve or react with water. e.g. ammonia and sulfur dioxide.
Downward delivery is suitable for __________________________.
Downward delivery is suitable for gases that are denser than air. e.g. chlorine
Upward delivery is suitable for ________________________.
Upward delivery is suitable for gases that are less dense than air. e.g. hydrogen and ammonia.
Often, the gas to be collected is contaminated with _______________. To dry the gas, pass the gas through a ________________. What are some examples?
Often, the gas to be collected is contaminated with water vapour. To dry the gas, pass the gas through a drying agent (also called dessicant).
Some examples are listed below:
- CONCENTRATED sulfuric acid (not suitable for alkaline gases, such as ammonia)— neutralisation will occur
- calcium oxide (not suitable for acidic gases)— e.g. HCl (hydrogen chloride), CO2, SO2
- anhydrous or fused calcium chloride (not suitable for ammonia)
Anhydrous copper (II) sulfate may be used as an indicator for water vapour,
It turns from white to blue in the presence of water.
Hydrogen chloride (gas) vs hydrochloric acid (aqueous solution
What is limestone made up of？
Limestone is a mixture of sand and calcium carbonate, hence separation is needed.
What should be the thought process when doing an experiment?
(Manipulation, measurement and observation) (MMO)
What are the measurements needed?
What are the apparatus needed?
What are the materials needed?
(presentation of data and observations)
- mass to be recorded?
- graph needed?
-mathematical formula needed?
(Analysis, conclusion and evaluation)
- mass needed?
-percentage needed?
Planning
- separation techniques
- solubility
- reaction
What are the steps to weighting out x g of limestone and place it in the beaker provided on an electronic balance?
firstly tare the electronic balance.
place the beaker on the electronic balance and tare the electronic balance.
pour the limestone into the beaker
record down the mass of the limestone based on what is shown on the electronic balance exactly.
What data must you collect to determine the percentage by mass of calcium carbonate in limestone?
The mass of a sample of limestone used in their experiment and the mass of the calcium carbonate in the sample.
ensure that you have the word in the sample.
Some information about silicon dioxide and calcium carbonate are given.
silicon dioxide
- insoluble (solubility in water)
- insoluble (reaction with dilute hydrochloric acid)
calcium carbonate
- insoluble (solubility in water)
- soluble (reaction with dilute hydrochloric acid)
Using this information, what is the next step to be taken in this experiment?
Add excess hydrochloric acid to the mixture.
State your observation when dilute hydrochloric acid was added to the limestone mixture. Using ideas about acids, explain why this was observed.
Effervescence is produced [1m].
The dilute hydrochloric acid reacts with calcium carbonate to form a salt (calcium chloride), water and carbon dioxide, which escapes and forms the effervescence. [1m]
It’s important to mention that the effervescence is due to the formation of carbon dioxide when the hydrochloric acid reacts with calcium carbonate.
Make sure to always link your explanation to the ultimate objective and purpose of the experiment. For e.g. if the question asks, suggest the next step to be take in this experiment and your explain:
Filter the mixture by placing a filer paper at the top of the conical flask. Then slowly pour the mixture onto the filter paper in order to separate the silicon dioxide from the compound that was formed from hydrochloric acid and calcium carbonate. This is because the calcium carbonate reacted with hydrochloric acid and will form a solution, therefore, it will pass through the small pores on the filter paper and become the filtrate while silicon dioxide will not react with hydrchloric acid, therefore it will remain as a solute and will be the residue on the filer paper.
You should talk about______________
Filter to separate the silicon dioxide from the mixture. This allows us to measure the mass of the silicon dioxide in the mixture, and hence, find the mass of calcium carbonate present. (1m)
Feedback on the response shown in the question:
Your response correctly identifies the need to filter the mixture to separate the silicon dioxide, which is a key step in the experiment. However, the explanation provided does not fully align with the answer scheme. The focus should be on measuring the mass of silicon dioxide to find the mass of calcium carbonate, rather than the chemical reactions involved. Remember to include all specified keywords from the answer scheme in your response to ensure full marks.
Suggest how you can tell if the filtration was successful.
The filtration is successful if the filtrate is clear and colourless, showing that all the solids did not pass through the filter paper and are collected as the residue.
The below answer is not perfect: (check the feedback given)
The filtration is successful if after some time, perhaps around 10 mins, nothing is seen dripping through the filter paper from the residue and after pouring distillate on the residue multiple times, this tells me that all the filtrate are already collected at the bottom of the conical flask and thus the filtration was successful.
Your response indicates an understanding of the filtration process, but it does not fully align with the specific criteria outlined in the answer scheme. The key aspect of determining successful filtration is observing that the filtrate is clear and colourless, which shows that all solids have been collected as residue. In your response, you mentioned the absence of dripping and the collection of filtrate, but did not address the clarity and colourlessness of the filtrate. Focusing on these aspects will help improve your response.
After filtering silicon dioxide and a mixture of hydrochloric acid and calcium carbonate, will the residue collected at this point be pure? Why?
No, the residue is likely to contain some acid and dissolved calcium carbonate.
Suggest what can be done to remove the impurities (some acid and dissolved calcium carbonate) in the residue in order to obtain pure silicon dioxide.
The residue can be washed with distilled water to remove any residual acid or salt on the silicon dioxide.
Form a procedure that will allow you to determine the percentage by mass of calcium carbonate in limestone.
- Weigh out x g of limestone and place it in the beaker provided.
- Add excess dilute hydrochloric acid to dissolve all the calcium carbonate.
- Filter the mixture to collect silicon dioxide as the residue.
- Rinse the silicon dioxide with distilled water.
- Air-dry the silicon dioxide/ Oven dry the silicon dioxide in low heat.
- Weight the mass of the dry silicon dioxide (y) using an electronic balance.
- % of calcium carbonate in the= [(x-y)/x] times 100%
What does the term “name” mean in a question?
requires candidates to spell out the word; symbol or formula is not acceptable.
What does the term “calculate” mean in a question?
is used when a numerical answer is required. In general, working should be shown, especially where two or more steps are involved.
