Experimental Techniques

Chemistry is all about experiments. Through these experiments chemists are able to know more about the chemicals present in the world and those that could be made. In order to test their ideas, chemists design the experiments that need to be accurate. For this accuracy Chemists use different tools and methods to come up with the desired/required product. There are some Experimental Techniques that help us do that.

[gap height=”22″]Measurement

For experiments to take place, Measurement is the first and the foremost task.

Measuring Time

stop-watch-aolpapers.comTime is an important measurement regarding experiments. The SI (System International) Unit for time is seconds (S). In Laboratories Stopwatch is used for taking readings. There are two types of stop watch :
  1. Analogue stopwatch : that consists of a knob, secondary dial and a main dial.
  2. Digital stopwatch : This is a much more accurate and rather a required stopwatch in the modern experiments due to more precision in it.

Measuring Mass

Mass is the amount of matter packed in a body.
The SI (System International) Unit is kilogram (kg). Mostly small masses are required to be measured that requires even more efficiency and accurate readings. Two types of instruments are commonly used:- Beam balance & Electronic balance. In the above stated requirements Electronic balance that has an accuracy of 0.01 grams is used for having precise measurements.

Measuring Volume(Liquids)

 measuring volume of liquids
 Scientific experiments often have a liquid component in them. For an accurate experiment everything needs to be perfect that means the volume being measured should be of the same accuracy level or even better. There are different experiments that help us in measuring volumes quickly, efficiently and precisely.

The SI (System International) Unit is cubic meters m3 that is equal to 1000 litres.

 

Collecting and Measuring Volume of Gases

To collect a gas we need to know about its solubility in water and its density compared to air before carrying out an experiment.

Gases solubility and density compared to air

Density of gas = 30 (air density)

  1. NH3                   SOLUBLE                                BASIC                  Lighter
  2. CL2                    SOLUBLE                                ACIDIC                Denser
  3. Hcl                     SLIGHTLY SOLUBLE            ACIDIC                  Denser
  4. S02                    SLIGHTLY SOLUBLE            ACIDIC                  Denser
  5. O2                      SOLUBLE                               NEUTRAL           Slightly Denser
  6. CO2                   INSOLUBLE                           ACIDIC                Denser
  7. H2                     INSOLUBLE                           NEUTRAL           Lighter

Gases insoluble in water are collected through displacement of water.

Gases lighter than air are collected through Upward Delivery.

Gases denser / heavier than air are collected through upward delivery.

Drying Gases

Thermometer aolpapers.com

It is required to dry a gas when it is collected through a solvent. The common drying agents are fused calcium chloride, calcium oxide and concentrated sulfuric acid. The tube of the moist gas should be immersed in the drying agent and the second tube must be out of it.

Measuring  Temperature

The SI (System International) Unit is Kelvin (K), but another unit that is commonly used is degree Celsius (°C).
273 K = 0°C

Criteria of purity

A substance is said to be pure when it is made up of only one substance. This substance should not be mixed neither combined with other.

Methods of purification

To figure out the impurities present in a substances, there are different methods that are given below:

Fixed Melting / Boiling Point

  •  Pure solids have fixed melting points, with impurities a depression in melting point is seen.
  • Pure liquids have fixed boiling points, with impurities an elevation in boiling point is seen.

Chromatography

Definition: A technique / process where a solvent is used to separate a mixture into its components.

Chromatography helps us in separating a sample’s components and identify the number of components in the sample and whether the sample is pure.

Rf Value:

It is a ratio that means it does not have any units.

Distance travelled by the substance / Distance travelled by the substance

Separating a Solid from a Liquid

chemistry revision notes chapter 2

Decanting

This can be called as the simplest technique of separating a substance where water is just poured away.

Filtration

A process where small solid particles are separated from a solvent. The filter papers sieves the solid particles that is called as residue and the water that is passed down is called filtrate.

Crystallization

This separation technique is used when a soluble substance is used to separate from water. To separate it is heated, water is evaporated, This technique is also known as Evaporation to dryness. The end result is the solid product; however, substances decompose in this process as well.

Separating Solids

Magnetism

Substances that are attracted with magnets can be separated from those that are not with help of a magnet only.

Sublimation

Solids sublime to gases. Substances that sublime can be separated from those that cannot.

Separating Liquids

Simple DistillationFractional_distillation_lab_apparatus aolpapers.svg

Process where  a liquid is boiled and vapor is condensed back. The two liquids have different boiling points where one boils off first than the other.

Fractional Distillation

When two liquids are miscible , fractional distillation is the most feasible way to do that. The process is almost same as simple distillation. The process can separate more than two different solvents.

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