Section 1 b) Atoms Flashcards
- 4- describe and explain experiments to investigate the small size of particles and their movement including:
- Dilution of coloured solutions
- Diffusion experiments
Experiment on diffusion-
In a beaker of water, a deeply coloured substance (potassium manganate) is kept. After 10-20 mins, the whole solution turned purple. That’s because Potassium manganate is diffused in the solution. If it is replaced with heavier or bigger particles, it will take longer to diffuse and often it won’t.
1.4- diffusion experiment
http://shawonnotes.ucoz.com/IGCSE_Chemistry/images/clip_image008.jpg
1) When the glass lid is removed, the bromine rises to the top because it is made up of small particles which occupy spaces inside both jars by diffusion.
Experiment 2- http://shawonnotes.ucoz.com/IGCSE_Chemistry/images/clip_image009.jpg
From the cotton wool, which is soaked in Ammonia (aqeous), ammonia gas is then produced. From the cotton wool, which is soaked in hydrochloric acid, hydrogen chloride gas is produced. Both gases will move towards each other inside the glass and meet near the cotton wool which is soaked in hydrochloric acid. The gases forms a white smoke of ammonium chloride.
NH3 (g) + HCl(g) –> NH4Cl(s)
This shows that ammonia gas move faster than hydrogen chloride gas in the same length of time. Because ammonia is lighter than hydrogen chloride gas. So ammonia diffuses faster.
The factors that affects the diffusion process are:-
(i) Molecular Mass(Mr)
(ii) Temperature
The molecules with low molecular mass diffuse faster than the higher molecular masses.
Increase in temperature increases the diffusion rate.
1.5- understand the terms atom and molecule
Atom- the smallest particle of an element is called an atom. They consist of electrons, protons and neutrons. They can take part in chemical reactions directly.
Molecules- the smallest particles of an element or compounds which can exist independent are called molecules. Made up of different types of atom. They cannot take part in chemical reactions without breaking up into its atoms.
1.6- understand the differences between elements, compounds and mixtures
Elements- Pure substance that cannot be split into simpler substances by chemical process or electricity. The smallest part of an element are called atoms. The elements are expressed by using chemical symbols.
Compound- pure substance which contain two or more different types of element, which are chemically combined. The smallest particles of a compound are called molecules. Expressed by using chemical formulas. To make a compound, a chemical reaction needs to take place. Compounds cannot be separated by physical methods of separation. In compounds there must be a fixed proportion of substance. To make a compound, energy changes must take place.
Mixture- gathering of two or more substances without chemical bonding. To make a mixture no chemical reaction needs to take place. They can be separated by physical methods of separation. No fixed proportion of substance in a mixture. To make a mixture no energy change will take place.
1.7 - describe experimental techniques for the separation of mixtures, including simple distillation, fractional distillation, filtration, crystallisation and paper chromatography.
Filtration- Mixture poured into the filter funnel, which has tiny holes to allow the liquid molecules to pass through. But the solid particles get trapped on the filter paper as residue.
Distillation- Solution heated in a round flask. The liquid solvent will evaporate and pass through the condenser. While passing, it condenses and drops of liquid will be poured in a beaker. The collected liquid is called distillate.
Fractional distillation- A tall column is fitted above the mixture, with several condensers coming off at different heights. The column is hot at the bottom and cool at the top. Substances with high boiling points condense at the bottom and substances with low boiling points condense at the top. Like distillation, fractional distillation works because the different substances in the mixture have different boiling points.
Crystallisation- Heat salt solution to make it saturated, test the solution whether it is matured or not by dipping a clean dry cold glass rod into the solution. It is it matured, crystals will form on the end of the glass rod. Then filter the solution to collect the crystals, wash the crystals with cold distilled water to remove any impurities. Then dry them and keep in few sheets of filter paper.
Paper chromatography- Small step of ink placed in the centre of filter paper. when the drop has dried add another in the same spot and allow to dry. Add ethanol (solvent) drop by drop onto this spot. Addition of the ethanol will cause the spot of ink to slowly spread out into different coloured rings.
1.8- explain how information from chromatograms can be used to identify the composition of a mixture.
Chromatography paper is taken. Sample (unknown) is placed along a pencil line. Then known elements are placed side by side of the sample in the same line. The sheet of chromatography is coiled into a cylinder, secured with adhesive. Put in a beaker containing a suitable solvent.. Identical dyes produce spots at the same height in the same colour when the same solvent is used.
