Chapter 1: Experimental Chemistry Flashcards
What is an element?
- The simplest substance that cannot be broken down into sny other substances
- Made up of one atom only
- Diatomic elements are covalent molecules
What is a compound?
- 2 or more elements chemically combined together
- Has their own set of physical properties
- Has a fixed ratio
- Can be separated chemically
What is a mixture?
- Elements and compounds with no fixed ratio
- Does not have its own physical properties
- Properties are same as its constituents
- M.p. and b.p. are not fixed
- Are formed and separated by physical methods
What are the SI units for mass, time, temperature, length, and volume of gas/liquid?
kg, s, K, m^3
How many kgs and gs is 1 tonne?
1000kg, 1 x 10^6g
How many l and cm^3 is 1 dm^3?
1l, 1000cm^3
What is the tool for the measurement of mass and how is it rounded off?
Electronic balance, nearest 0.1g
What is the tool for the measurement of time and how is it rounded off?
Stopwarch, nearest s
What is the tool for the measurement of temperature and how is it rounded off?
Thermometer, nearest 0.5°C
What are the tools for the measurement of volume of liquid in increasing accuracy? Include what they are rounded to.
- Beaker
- Measuring cylinder (1 d.p.)
- Pipette
- Volumetric flask
- Burette (2 d.p.)
What is the tool for the measurement of gas?
Gas syringe
What type of gas does the method downward displacement of water collect?
Gases that are insoluble or slightly soluble in water. (H2, O2, CO2)
What type of gas does the method downward delivery collect?
Gases denser than air. (Cl2, HCl)
What type of gas does the method upward delivery collect?
Gases less dense than air. (Ammonia/NH3)
What are the separation techniques used to separate solid-solid mixtures?
- Magnetic attraction
- Sieving
- Using suitable solvents (e.g. water and salt)
What are the separation techniques used to separate solid-liquid mixtures?
- Filtration
- Evaporation to dryness
- Crystallisation
- Simple distillation
What are the separation techniques used to separate liquid-liquid mixtures?
- Chromatography
- Fractional distillation
What are the two ways to obtain a soluble solid dissolved in water and how to determine which one is suitable to use?
If stable to heat/does not have water of crystallisation (sodium & potassium salts):
Evaporation to dryness
If not stable to heat (decomposes upon heating e.g. sugar)/has water of crystallisation:
Crystallisation
Describe the process of crystallisation.
- Dissolve the impure solid in water/solvent
- Evaporate the excess water/solvent until a saturated solution is obtained
- Cool the hot solution until solid appears as pure crystals
- Wash the crystals with cold water
- Dry the crystals by pressing between sheets of filter paper
What is the separation technique used to obtain a pure sample of liquid from a solution?
Simple distillation
Why are boiling stones put in the flask when heating during simple distillation?
To ensure smooth boiling
Why is the thermometer placed at the mouth of the condenser during simple distillation?
To ensure purity of the liquid (pure: b.p. is fixed)
What is the technique fractional distillation used to separate?
Miscible liquid-liquid mixtures with close boiling points.
How does fractional distillation work?
Repeated condensation and evaporation takes place at the fractionating column and separates liquids with close b.p. effectively. The liquid with the lowest b.p. will be collected first, change the receiver when the temperature on the thermometer increases to the b.p. of another solvent.
