All acids produce hydrogen ions, in aqueous solution. (Hydrogen ions must be present) Hydrogen Ions (H+)
HYDROGEN IONS (H+) MUST BE PRESENT TO BE CALLED AN ACID Thus, for example Hydrochloric acid is not an acid in gaseous form, only in aqueous solution.
Acids have a sour taste.
Acids dissolve in water to form solutions which conduct electricity.
Acid turns blue litmus paper red.
Acids have a pH < 7
Acids react with reactive metals to form hydrogen and a salt. However, there are some acid and metal reactions that do not give hydrogen.
Acids only show the properties of acids when the are dissolved in water. This is because acids dissociate in water to produce hydrogen ions which are responsible for acidic properties.
Bases and Alkalis A base is any metal oxide or hydroxide. We can also define base as a substance that reacts with an acid to give a salt and water only. An alkalis is a bass that is soluble in water (most bases are insoluble in water) Alkalis have a bitter taste and soapy feel. Alkalis turn red litmus paper blue. An alkalis produce hydroxide ions when dissolved in water. All alkalis can react with acids to form a salt and water only. This reaction is called neutralisation. Alkalis heated with ammonium salts give off ammonia gas. Concentration and Strengths The term concentration tells us how much a substance is dissolved in 1 dm3 of the solution. The term strength refers to how easily an acid or an alkali dissociates when dissolved in water. A strong acid dissociates easily in water, while a weak acid does not fully dissociate when dissolved in water.The strength of an acid or alkali cannot be changed. The PH Scale The pH scale is a set of numbers used to indicate whether a solution is acidic, neutral or alkaline. Acids have pH values less than 7, alkalis have pH values greater than 7, and a neutral solution has a pH value of exactly 7. Types of Oxides Many acids and alkalis are formes by dissolving oxides in water. An oxide is a compound of oxygen and another element. Acidic Oxides Non-Metals may form acidic oxides. Most acidic oxides dissolve in water to form an acid. Acid oxides do not react with acids. However, they react with alkalis to form a salt and water. Basic Oxides The oxides of metals are basic oxides. Most basic oxides are insoluble in water. A few oxides, however, dissolve readily in water. They are called alkalis. Amphoteric Oxides Amphoteric Oxides are metallic oxides that react with both acids and bases to form salt and water. Neutral Oxides Some non- metals form oxides that show neither basic nor acidic properties. These oxides are called neutral oxeds and they are insoluble in water.
Diffusion is the movement of particles from a high concentration to a low concentration. Diffusion can be seen as a spreading out of particles resulting in an even distribution of the particles. You can see diffusion when you place a drop of food colouring in water. The colour slowly spreads out through the water. If matter were not made of particles that are constantly moving then we would only see a clump of colour when we put the food colouring in water, as there would be nothing that could move about and mix in with the water. *Diffusion occurs in solids too.
Diffusion is a result of the constant thermal motion of particles. In 1828 Robert Brown observed that pollen grains suspended in water moved about in a rapid, irregular motion. This motion has since become known as Brownian motion. Brownian motion is essentially diffusion of many particles. Brownian motion can also be seen as the random to and fro movement of particles.
The rate of diffusion is dependent on:
1. Temperature
2. Molecular Mass of the particles
3. Concentration gradient
From the kinetic particle Theory, it can be deduced that the rate of diffusion depends on the speed of the particles. The faster the particles move, the higher the rate of diffusion.
Hence, the higher the temperature, the higher the rate of diffusion.
Under the same conditions of temperature and pressure, a substance with a lower relative Molecular Mass diffuses faster than a substance with a higher Molecular Mass. Hence,the lower the Molecular Mass, the higher the rate of diffusion.
The following video will show how temperature and MW affects the rate of diffusion.
Water has an open structure. Thus, when alcohol is added, the molecules of alcohol will fill up the empty spaces in the water's open structure. Therefore, the overall volume of the both will decrease when added together.
The kinetic particle theory states that all matter is made up of tiny particles that are in constant random motion and constantly collide with each other.(Particles is an umbrella term, and atoms are under the category of particles.) The degree to which the particles move is determined by the amount of energy they have and their relationship to other particles. The particles might be atoms, molecules or ions. Use of the general term 'particle' means the precise nature of the particles does not have to be specified. Particle theory helps to explain properties and behaviour of materials by providing a model which enables us to visualise what is happening on a very small scale inside those materials. As a model it is useful because it appears to explain many phenomena but as with all models it does have limitations.
Solids, liquids and gases
In solids the particles
In liquids the particles
In gases the particles
are held tightly and packed fairly close together - they are strongly attracted to each other
o are in fixed positions but they do vibrate
are fairly close together with some attraction between them
are able to move around in all directions but movement is limited by attractions between particles
have little attraction between them
are free to move in all directions and collide with each other and with the walls of a container and are widely spaced out
Fig 1 Particles in solids, liquids and gases
The properties of matter
Solids
Liquids
Gases
have a definite shape
maintain that shape
are difficult to compress as the particles are already packed closely together
are often dense as there are many particles packed closely together
do not have a definite shape
flow and fill the bottom of a container. They maintain the same volume unless the temperature changes
are difficult to compress because there are quite a lot of particles in a small volume
are often dense because there are quite a lot of particles in a small volume
do not have a definite shape
expand to fill any container
are easily compressed because there are only a few particles in a large volume
are often low density as there are not many particles in a large space
Kinetic Particle Theory - how it explains changes of states
For example:
During Melting,
1. When a solid is heated, heat energy is absorbed by the particles.
2. The heat energy is then converted into kinetic energy and the particles begin to vibrate faster.
3. At the melting point, the particles vibrate vigorously enough to overcome their forces of attraction (break away from their fixed positions). Hence melting occurs.
- * During melting, the temperature remains constant at the melting point because the heat absorbed is used to overcome the forces of attraction between the particles.
During Freezing,
1. When a liquid is cooled, the particles lose kinetic energy. They move more and more slowly.
2. At the freezing point the particles can only vibrate about their fixed positions and hence a solid is formed.
Sublimation:
o Some sublimation such as iodine, ammonium chloride, mothball and dry ice(solid carbon dioxide) sublime on gentle heating. The solid changes to a gas without melting.
o Sublimation occurs because the particles at the surface of the solid have enough energy to break away from the solid and escape as a gas.
Evaporation:
o Evaporation is a change from the liquid to the gaseous state that occurs at any temperature below the boiling point.
o Evaporation occurs slowly and takes place only at the surface of the liquid.
o Evaporation occurs because the particles at the surface of the liquid have enough energy to break away from the liquid and escape as a gas.
o During evaporation, the particles left behind have a lower kinetic energy and therefore cause cooling effect.
o Further explaining:
- Water is made up of many molecules that are in constant, random motion.
- These molecules collide with each other to gain or lose kinetic energy from or to other molecules.
- The molecules nearer to the surface of the water and have high enough kinetic energy will be able to change from liquid to gaseous state.
- Since the molecules with higher kinetic energy have moved out of the water, the average kinetic energy of the water drops which in turns means that the temperature of water will drop as well.
A separation technique is where you use a method to separate a substance from another substance, you can use chromotography, distillation, filtering ect.
Solid from liquid
There are four
methods to separate a solid from a liquid. Decanting is used to separate a
dense, insoluble solid from a liquid. Filtration is used to separate a mixture
from a solid and a liquid. Substances that do not decompose on strong
heating can be purified by evaporation to dryness. Crystallisation is used to
purify crystals and substances that decompose on strong heating. A saturated
solution can be produced by evaporation.
Filtration
method can also be used to separate two solids but only if one of them is
soluble in a solvent. A magnet can be used to separate magnetic substances,
such as iron, nickel, cobalt and steel, from non- magnetic ones.
Filtration
Filtration is commonly the mechanical or physical operation which is used for the separation of solids from fluids (liquids or gases) by interposing a filter through which only the fluid can pass.Upon filtration, the solid that remains on the filter paper is called the residue, while the liquid that passes through the filter paper is called the filtrate.
How to set up a filtration (experiment)?
1. Prepare a filter cone:
2. Gravity filtration with a filter cone:
The following video will show the filtration experiment as seen in the above procedures:
Distillation
Simple
distillation is used to obtain a pure solvent from a solution.
The following video shows and explains about simple distillation:
Fractional
distillation is used to separate a mixture of miscible liquids. The liquid with
the lowest boiling point distils over first.
The following video shows fractional distillation:
Crystallisation
Crystallisation is a separation technique that is used to separate a solid that has dissolved in a liquid and made a solution. The solution is warmed in an open container, allowing the solvent to evaporate, leaving a saturated solution. A solution that has much solid dissolved in it as it can possibly contain is called a saturated solution. As the saturated solution is allowed to cool, the solid will come out of the solution and crystals will start to grow. The crystals can then be collected and allowed to dry.
-Making a substance pure
-Solution should be saturated
-Change the state of substance
from aqueous (aq) to solid.
Chromatography
Chromatography is used to separate or analyse the components in a sample. Chromatography is also used to determine the purity of a sample. A pure sample gives only one spot on a chromatogram. Rf value is the distance travelled by the substance divided by the distance travelled by the solvent. A locating agent is used on a chromatogram to help us see the colourless substances.
Chromatography: "A method, often used in laboratories, which enables the easy and efficient separation of mixtures of chemical compounds using the phenomenon of adsorption." The word comes from the Greek chromatos (color) and graphein (to write). So, as one might guess, chromatography involves separating chemicals and identifying them by color.
The process relies on the fact that different molecules will behave in different ways when they are dissolved in a solvent and moved across an absorbent medium. In a very simple example, one could take ink and make a mark on a piece of paper. The paper could be dipped into water, and the capillary action of the water would pull the ink through the paper. As the ink moved, its ingredients would separate out, revealing a distinctive pattern which could be used to determine the components of the ink.
The following video shows the procedure in paper chromatography and how to find the Rf values:
Extra:
In 1910, Tswett first used this method in the separation of leaf pigments, and the technique achieved rapid growth later when it was applied to the separation of carotinoid pigments, among other uses.
The separation method called 'column chromatography' uses a glass column filled with adsorbent though which passes a composite liquid mixture. The technique operates such that each component will form in a different section of the column arranged by color according to the adsorption affinity of each material.
In performing column chromatography, a vertical glass column is filled evenly with the proper amount of adsorbent. Next, a liquid mixture is poured into the column and the liquid passes through the adsorbent. Each compound is absorbed into beds at different heights depending on the component's individual adsorption affinity.
At this stage, the sections into which each of the components have been absorbed are still not completely separated. However, if the appropriate desorbent is poured into the column, the components which have been adsorbed on the adsorbent dissolve into the desorbent and start moving downwards in the column. Each component moves towards the lower part of the column, but the migration rates again differ according to each component's adsorption affinity. The components in the lower layers move faster, and in the end, each components will be clearly separated. This stage of the column chromatography process is called 'development.'
If the material being separated is a mixture of pigments, there will be colored zones at different heights in the column filled with adsorbent. These colored zones are called a chromatogram.
When the development stage is over and the pigments appear, the adsorbent is pushed out of the column, divided into each zone and the absorbates are extracted separately using a desorbent. This stage of the process is called 'elution.' Alternately, without removing the adsorbent from the column, a desorbent may be successively poured in from above, and each zone preferentially eluted by the desorbent will dissolve into it and trickle down the column one at a time. The liquids can then be collected from the bottom of the column as they drip out."
-To separate a mixture
-Find out the number of
components
-Depends on solubility of
compounds/ substances in a solvent
-When the solvent comes into
contact with the ink, the compounds in the ink can “choose” to stay at its
place or get absorbed and follow the water up the chromatography paper. Thus,
the higher the solubility of the compounds, the lesser the distance travelled.
The purity of a
substance can be determined by measuring its melting point or boiling point. A
pure solid melts completely at a fixed temperature. Impurities lower the
melting point and increase the boiling point of a liquid. When pressure
increases, the boiling point of a liquid increases. Likewise, when pressure
decreases, the boiling point of the liquid decreases.
