Measuring of Quantities

below are different ways in which quantities are measured.

  • Time is measured using a stop watch by determining the period elapsed between the start and ending of an event e.g. time taken for a liquid to reach boiling point.
  • Temperature is recorded by putting a thermometer in a vessel to determine the heat released or absorbed, the melting point or melting point of a liquid.
  • Mass is recorded by putting a substance to be measured on an electronic balance.
  • Volume is measure using measuring cylinder, by pouring the desired liquid into the cylinder and taking the reading

The following are Some of the measuring apparatus

  • Stopwatch or stop clock : for time
  • thermometers : for temperature
  • electronic/beam balances : for mass
  • Burettes, pipettes, volumetric flask, measuring cylinder, and gas syringes : for recording volume.
  • The tube is used for heating and mixing liquids or solids.

Criteria of purity

This refers to all those physical properties which are characteristic of a pure substance.

what is the differences between a pure substance and a mixture ?

A pure substance has a sharp melting point and fixed density while an impure substance has melt or boil over a range of temperatures.

how to determine the purity of a substance:

Put a thermometer into an ice or a liquid and apply heat. For a pure substance the temperature will remain at the at the same at boiling or melting point until complete change of state take place as the liquid change its state to gas or ice change state to liquid at melting or boiling points while a mixture melt or boil at a range of temperature.

The importance of purity of a substance.

purity in substances such as foodstuffs, medicines, drinks is very important because impurities can affect the health of animals e.g. human

In industry, the computer processor chip must be in purest of silicon otherwise it will not work.

Separating Mixture

Separation techniques are methods used to obtain pure substances from their mixtures. Substances usually exist as mixtures and special ways are used to separate them.

Distinguishing between physical and chemical changes

Physical change

  • No new substances formed
  • Is reversible
  • No absorption release of energy

Chemical change

  • New substances are formed
  • Not reversible by simple means
  • Energy is released or absorbed

Terms used in separation techniques

Mixture : A mixture is a substance which consists of two or elements which are physically combined but not chemically combined.

Solution : A solution is a mixture made up of a solvent and a solute.

Solvent : A solvent is a liquid in which a solute dissolves.

Solute : A solute is a substance that dissolves in a solvent. A solute can either be a solid, liquid or gas.

Miscible liquids : Miscible liquids are liquids that can mix completely.

Immiscible liquids : Immiscible liquids are liquids that do not mix completely.

Residue : A residue is a solid that is trapped on the filter paper during filtration.

Filtrate : A filtrate is a clear liquid collected after filtration.

Different methods of separating techniques.

Decantation : If a mixture contains solid particles solid particle that can be seen, and that will settle to the bottom of the container, if left to stand ' it can be separated be decantation. You can. Carefully pour off the all the quid so that the solid substance remains

Filtration : The act or process of filtering, especially the process of passing a liquid or gas, such as air, through a filter in order to remove solid particles, is used to separate soluble and insoluble substances. A mixture of soluble and insoluble substances is dissolved in water and thereafter filtered to remove the insoluble substance. The filtrate can evaporated and crystallized to recover the solute.

Crystallization : is the process used to recover a solute from. A solution is heated to saturate it and is later let to cool down. When a solution becomes saturated, it means that the solvent cannot ‘‘hold’, any more solute in solution at that temperature, so the solute is forced out of the solution in the form of solid crystals.

Simple distillation : is the process used to separate a liquid from a solution by evaporating the mixture and condensing the mixture back to liquid.

Fractional distillation , is the process used to separate mixtures with different boiling point. e.g. pure water, boiling point 100℃ and ethanol with boiling point 73℃ are heated to 100℃ and 73℃ respectively at the temperature is let to at constant until all the ethanol evaporate and the raised to 100℃

Magnetic separation : is used to separate magnetic materials from non-magnetic material. Iron metal can be separated from a mixture of sulphur using a magnet.

Evaporation: is the process used to recover a solvent from a solution. Salt crystals can be recovered from a solution water and salt by evaporating the mixture.

Sublimation : is the change of state from gas to solid or solid to gas directly. It is a technique used to separate substances that undergo sublimation. It works well when a non-sublimating substance has a high melting point.

Separating funnel ; is use to separate liquids that are immiscible, they quickly separate into layers once poured into the funnel. The tap at the bottom of the funnel is opened to pour off the bottom layer, leaving the upper layer or layers. Immiscible Using a separating funnel makes it easier to see exactly where the oil layer starts. Therefore you can turn off the tap just before any oil contaminates the water sample. You can discard a small amount of oil to make sure that all the water particles have been removed from the funnel, before you collect the pure oil in another container.

centrifuge is another method that can separate two or more immiscible liquids. This method uses a piece of apparatus known as a centrifuge, which rotates the container holding the sample liquid around a fixed axis, but at an angle to the vertical. As the centrifuge rotates, the more dense liquids are pushed outwards and towards the bottom of the container, while the less dense liquids are pulled inwards and upwards. The liquid on top can be poured off or using a pipette too remove it. A laboratory centrifuge: As the rotor rotates, the more dense substance collects at the bottom of each container

Chromatography : this is a separating technique in which a mixture is separated as it moves across porous surface, carried by an appropriate developing solvent. Different substance in the mixture will interact differently with both the solvent and the surface, therefore they will separate. The substance that dissolves more readily and is least attracted to the surface, moves the fastest. It therefore travels furthest from the starting line, separating itself from the other substances in the mixture.