C8 Ai Flashcards
What does purity mean in chemistry?
A pure substance contains only one compound or element throughout and is not mixed with anything else.
In everyday terms, purity may refer to natural states like pure milk or beeswax, but in chemistry, it is more specific.
How can you determine the purity of a substance using its boiling or melting point?
A chemically pure substance will melt or boil at a specific temperature. Impurities lower the melting point and widen the melting range, while they increase the boiling point and may cause a boiling range.
The closer the measured melting or boiling point is to the known value, the purer the sample.
What are formulations?
Formulations are mixtures designed for a particular use, made by following a specific recipe with carefully measured components.
Examples include paints, cleaning products, fuels, and medicines.
What are the components of paint as a formulation?
Paint is made up of:
* Pigment
* Solvent
* Binder
* Additives
Each part serves a specific purpose, such as giving color or altering viscosity.
What is chromatography?
Chromatography is a method used to separate different components in a mixture.
It involves a mobile phase and a stationary phase.
What role does the solvent play in paper chromatography?
The solvent moves up the paper, carrying the substances with it, allowing for the separation of components based on solubility.
The more soluble a chemical is in the solvent, the further it will travel.
True or False: Impurities in a sample can make the melting point more consistent.
False
Impurities typically widen the range of melting points.
Fill in the blank: In everyday life, formulations can be found in _______.
cleaning products, fuels, medicines, cosmetics, fertilisers, metal alloys, food and drink.
These formulations are tailored for specific applications.
What happens to the spots in chromatography if you repeat the experiment?
The spots should remain consistent in position and size, indicating reproducibility of the results.
Variability in results may indicate issues with the sample or technique.
Why is knowing if a product is pure important?
It is crucial for the production of medicines and food to ensure safety and effectiveness.
Chemists utilize various methods to verify the purity of substances.
What is chromatography?
A method used to separate the substances in a mixture
Chromatography can also be used to identify the substances.
What are the two phases of chromatography?
- Mobile phase
- Stationary phase
In paper chromatography, the mobile phase is a solvent, and the stationary phase is the paper.
What is the mobile phase in paper chromatography?
A solvent (e.g. water or ethanol)
The mobile phase allows molecules to move.
What is the stationary phase in paper chromatography?
The paper
The stationary phase does not allow molecules to move.
What does the solvent do in paper chromatography?
Moves up the paper and carries substances in the mixture with it
This movement allows for the separation of different chemicals.
What is ‘distribution’ in chromatography?
The amount of time a chemical spends dissolved in the solvent or stuck on the paper
This affects how far the chemical moves up the paper.
What happens to more soluble chemicals during chromatography?
They spend more time dissolved in the solvent and move further up the paper
This results in a higher position on the chromatogram.
What is a chromatogram?
A visual representation showing the results of chromatography experiments
It displays different spots for different chemicals.
What is the solvent front in chromatography?
The furthest point reached by the solvent during a chromatography experiment
It indicates how far the solvent has traveled.
What does it mean if a chromatogram shows only one spot?
There is only one chemical in the substance, indicating it is pure
This should be consistent across different solvents.
What does it indicate if a substance shows multiple spots on a chromatogram?
The substance contains at least that many different chemicals
For example, three spots indicate at least three chemicals.
What happens if you repeat chromatography with a different solvent?
You will get a different chromatogram
The spots may travel different distances compared to the solvent front.
Fill in the blank: The more soluble a chemical is, the more time it spends _______.
dissolved in the solvent
True or False: You can see the chemicals moving between the two phases in chromatography.
False
The movement occurs but is not visible.
What is the Rf value in chromatography?
The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent.
Rf stands for ‘retention factor’ and is a key measurement in chromatography.
How does the distance a substance moves through the stationary phase relate to its Rf value?
The further a substance moves through the stationary phase, the larger the Rf value.
What is the formula to calculate the Rf value?
Rf = distance moved by substance (B) / distance moved by solvent (A)
Calculate the Rf value if the distance moved by the substance is 29 mm and the distance moved by the solvent is 41 mm.
Rf = 29 mm / 41 mm = 0.70731… = 0.7
Give the answer to the smallest number of significant figures in the calculation.
What happens to the Rf value of a chemical if the solvent is changed?
The Rf value of a chemical will change if you change the solvent.
How can chromatography be used to identify substances in mixtures?
By running a pure sample of a substance next to the mixture and comparing Rf values.
What indicates that a substance is likely present in a mixture when using chromatography?
If the Rf value of the reference compound matches one of the spots in the mixture.
If two substances have the same Rf value in one solvent, what should you do to confirm their identity?
Repeat the experiment with a different solvent.
What is the range of Rf values in chromatography?
Rf values will always be between 0 and 1.
If a spot on a chromatogram moved 6.3 cm from the baseline and the solvent front moved 8.4 cm, what is the Rf value?
Rf = 6.3 cm / 8.4 cm
Calculate this Rf value to determine the retention factor of the substance.
True or False: An Rf value can be greater than 1.
False
What is the Rf value in chromatography?
The ratio between the distance travelled by the dissolved substance and the distance travelled by the solvent.
Rf stands for ‘retention factor’ and is a key measurement in chromatography.
How does the distance a substance moves through the stationary phase relate to its Rf value?
The further a substance moves through the stationary phase, the larger the Rf value.
What is the formula to calculate the Rf value?
Rf = distance moved by substance (B) / distance moved by solvent (A)
Calculate the Rf value if the distance moved by the substance is 29 mm and the distance moved by the solvent is 41 mm.
Rf = 29 mm / 41 mm = 0.70731… = 0.7
Give the answer to the smallest number of significant figures in the calculation.
What happens to the Rf value of a chemical if the solvent is changed?
The Rf value of a chemical will change if you change the solvent.
How can chromatography be used to identify substances in mixtures?
By running a pure sample of a substance next to the mixture and comparing Rf values.
What indicates that a substance is likely present in a mixture when using chromatography?
If the Rf value of the reference compound matches one of the spots in the mixture.
If two substances have the same Rf value in one solvent, what should you do to confirm their identity?
Repeat the experiment with a different solvent.
What is the range of Rf values in chromatography?
Rf values will always be between 0 and 1.
If a spot on a chromatogram moved 6.3 cm from the baseline and the solvent front moved 8.4 cm, what is the Rf value?
Rf = 6.3 cm / 8.4 cm
Calculate this Rf value to determine the retention factor of the substance.
True or False: An Rf value can be greater than 1.
False
What gas bleaches damp litmus paper, turning it white?
Chlorine
Chlorine is a common gas tested in practical experiments.
What happens when a glowing splint is placed in a test tube containing oxygen?
The glowing splint relights
This is a classic test for oxygen.
How can you test for carbon dioxide?
By bubbling it through calcium hydroxide solution
Calcium hydroxide solution is also called limewater.
What is the result when carbon dioxide is bubbled through limewater?
The solution turns cloudy
This indicates the presence of carbon dioxide.
What sound is produced when a lit splint is placed in hydrogen gas?
A ‘squeaky pop’
This is a distinctive test for hydrogen.
Fill in the blank: The solution of calcium hydroxide is also called _______.
limewater
Limewater is commonly used in gas tests.
True or False: Chlorine gas can be tested using litmus paper.
True
Chlorine gas bleaches damp litmus paper.
What is the purpose of bubbling gas through limewater in the context of gas tests?
To check for the presence of carbon dioxide
This reaction produces a cloudy solution if CO2 is present.
What is the chemical formula for hydrogen gas?
H2
Hydrogen gas is tested by its characteristic sound when ignited.
What is the result of a successful test for oxygen?
Glowing splint relights
This is a reliable indicator of oxygen’s presence.
What practical experiment is described for testing gases?
Tests for 4 common gases
The gases include chlorine, oxygen, carbon dioxide, and hydrogen.
