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Chemistry

Chemistry

DISTINCTION BETWEEN COMPOUNDS AND MIXTURES

DISTINCTION BETWEEN COMPOUNDS AND MIXTURES   The following example of iron, sulphur and iron sulphide will make us understand the difference between mixtures and compounds.   Properties of Iron and Sulphur The following experiment shows the difference in properties between the elements iron and sulphur.   Preparation of a Mixture of Iron and Sulphur Take about 7g of freshly powdered iron, and a little more than 4 g of sulphur. Mix them well. However well it may be mixed, the iron and sulphur particles can be seen separately. Also the above said properties of both iron and sulphur will still be exhibited by this mixture.   Preparation of Iron Sulphide Take this mixture of iron and sulphur in a hard glass test tube. Heat over spirit lamp or burner. The sulphur starts melting. Then the mixture catches fire. Stop heating. The flame spreads throughout the mixture, evolving heat. When it dies… Read More »DISTINCTION BETWEEN COMPOUNDS AND MIXTURES

Chemistry

CONSTITUENTS OF MATTER

CONSTITUENTS OF MATTER   Atoms, Molecules, Elements and Compounds The Atom An atom is the smallest particle of a substance which can have its own characteristic properties. Atoms are built up of even more fundamental sub-atomic particles. These are electrons, protons and neutrons.   The protons and neutrons are in the nucleus (centre) of the atom and the electrons orbit round the outside in shells (energy levels or layers). So you will often see pictures of atoms that look a little like this:   How many protons, neutrons and electrons does an atom have? You can work this out using the periodic table. Every element in the periodic table has two numbers with it: the atomic number and the mass number.   For example for lithium, the numbers are: The atomic number is the number of protons that the atom has. It is also the number of electrons that the atom has. So… Read More »CONSTITUENTS OF MATTER

Chemistry

CONDUCTORS AND INSULATORS

CONDUCTORS AND INSULATORS  The ability to conduct electricity is the major simple distinction between elements that are metals and non-metals.   Electrical Conductors A conductor is a material that conducts electricity but is not chemically changed in the process. They carry an electric current through freely moving electrons when a potential difference is applied across them. They include: All metals (molten or solid) and the non-metal carbon (graphite). This conduction involves the movement of free or delocalized electrons (e- charged particles) and does not involve any chemical change. Any molten or dissolved material in which the liquid contains free moving ions is called the electrolyte. Ions are charged particles eg Na+ sodium ion, or Cl- chloride ion, and their movement or flow constitutes an electric current, because a current is moving charged particles. All metals and graphite are conductors of electricity.   Insulators An insulator is a material that does… Read More »CONDUCTORS AND INSULATORS

Chemistry

CLASSIFICATION OF SUBSTANCES

Pure Substance Pure means that only one substance is present in the material and can be a pure element or compound. A simple physical test for purity, and properties that can help identify a substance, is to measure the boiling point or melting point. Every pure substance melts and boils at a fixed temperature.   If a liquid is pure, it should boil at a constant temperature called the boiling point e.g. water boils at 100oC. An impure liquid will boil at a higher temperature if it contains a dissolved solid impurity e.g. seawater, containing dissolved salts, boils at over 100oC. The boiling then takes place over a range of temperatures. If a solid is pure, it melts sharply at its fixed melting point.   An impure solid melts below its expected melting point and the more impure, the wider the temperature melting range, e.g. a water and salt mixture… Read More »CLASSIFICATION OF SUBSTANCES

Chemistry

CONDUCTORS AND NON-CONDUCTORS

CONDUCTORS AND NON-CONDUCTORS  All metals (copper, iron, lead, magnesium etc) and graphite, a non-metal. Most non-metals (sulphur, iodine, charcoal etc.) Most solid compounds (All gases are non-conductors)   Liquids are classified in three groups as regards their conductivity of electricity: (i) Those that pass an electric current and are not decomposed by if (conductors) (ii) Those that pass an electric current and are decomposed by it (electrolytes) (iii) Those that do not pass an electric current (non-electrolytes).   In summary, the following substances are electrolytes: Molten salts Solutions of salts in water Solutions of acids Solutions of alkalis   Metallic conductivity: Electrons flow(carry charge) It is a property of elements, graphite and alloys It takes place in solids and liquids No chemical change takes place.   Electrolytic conductivity: Ions flow (carry charge) It is a property of ionic compounds Takes place in liquids (molten salts) and solutions but not solids… Read More »CONDUCTORS AND NON-CONDUCTORS

Chemistry

COMPOUNDS AND THEIR PROPORTIONS

COMPOUNDS AND THEIR PROPORTIONS  All elements are represented by a chemical symbol. It is either a single capital letter, or a capital letter followed by a small letter. Examples: Ca = calcium Cu = copper C = carbon N = nitrogen Combinations of symbols represent compounds. These compounds are called chemical formulas.   Example: H20 2 hydrogen atoms 1 oxygen atom If no number is shown beside the symbol, a 1 is understood. If more than 1 atom is present, a small number is shown after the atom to indicate how many atoms are in the compound. NaHCO3 = Sodium Hydrogen Carbonate (baking soda) 1 atom Na = Sodium 1 atom H = Hydrogen 1 atom C = Carbon 3 atoms O = Oxygen     See also SIMPLE MACHINE AIR AND COMBUSTION AN ALKALI BASES AND INDICATORS EVAPORATION AND BOILING

Chemistry

MATTER

MATTER  Matter is: Anything that has mass and occupies space (has volume) Composed of particles (molecules, ions, atoms). These are in constant motion attracting one another with inter-particle forces (or cohesive) Is a solid, liquid or gas depending on interparticle forces of attraction and spaces between particles.   Matter has many properties. It can have physicaL properties like different densities, melting points, boiling points, freezing points, color or smells. There are also chemical properties that define matter. A good example of chemical properties is the way elements combine with each other in reactions. Matter can change in two major ways, physically and chemically.   Physical Changes These are changes that do not result in the production of a new substance. Only the physical state of the material changes. The substance retains exactly the same chemical composition. If you melt a block of ice, you still have water at the end… Read More »MATTER

Chemistry

SIMPLE CLASSIFICATION OF SUBSTANCES

CLASSIFICATION OF SUBSTANCES  Matter Matter can be classified as either a mixture or a pure substance. Mixtures contain at least two substances. If you can see the different parts of the mixture it is called a mixture.E.g. Soil and concrete   Properties of mixtures depend on the proportions of the parts. Have you ever made a cup of coffee and added too much sugar? Pure substances have properties that are always the same. You can identify an unknown substance by testing its properties, e.g. Gold     Activity Which of these substances is/ is not a mixture? What made it possible for you to determine whether or not it was a mechanical mixture? What about the other substances? Is it hard to tell them apart? Of course. It is hard to determine whether they are solutions or pure substances by just looking at them.   You must take into consideration… Read More »SIMPLE CLASSIFICATION OF SUBSTANCES

Chemistry

NAMES OF LABORATORY APPARATUS

Which apparatus? You wouldn’t dream of trying a chicken using a spoon, or of drying your hair in over a stove! In everyday life, we need to use the right tools for the job we are doing. The same is true in the science lab. There are lots of types of different chemical apparatus, all designed to do different jobs. Using the right apparatus makes your practical work safer. The pictures below show some of the apparatus you will be expected to know about and use in a chemistry laboratory.   Burette Made from accurate uniform wall tubing to insure the stipulated capacity tolerances. Features durable, permanent markings; fine, sharp lines and large, easy-to-read numbers. The stopcock is carefully ground and finished to assure a leak-free operation. A burette is used to deliver solution in precisely measured, variable volumes.   To fill a burette, close the stopcock at the bottom… Read More »NAMES OF LABORATORY APPARATUS

Chemistry

SCIENTIFIC METHOD

SCIENTIFIC METHOD  The scientific method is a set of ideas or a procedure that scientists use to investigate things they want to understand. By using the method, you can be sure you’re carrying out your project correctly. The scientific method allows you to investigate an experiment in a step-by-step method.   Problem: What are you going to solve in the lab? The problem or purpose explains exactly what you hope to accomplish in the investigation. Hypothesis: How do you think it is going to turn out? Use the facts you already know to come up with a guess that might really make sense. Materials and Apparatus: List what equipment you will need to complete the experiment. (Include diagrams of set up apparatus if required to do so in this section. Procedure: What you must do to complete the experiment. Write down the steps you need to follow.   Data and Work: Include the tables, observations… Read More »SCIENTIFIC METHOD

Chemistry

CHEMISTRY LABORATORY

Safety rules and regulations Your school science laboratory is set up so that you can perform science experiments in safety provided that you follow the proper procedures and safety precautions listed below. Your teacher will give you specific information about the safety routines used in your school. It is essential for all concerned that certain rules be followed while in the lab.   Read the following carefully and ask questions necessary for clarity. Goggles will be worn at all times. No exceptions. Failure to wear goggles will result in expulsion from laboratory. Full shoes are required. No sandal, flip-flops, etc. are allowed. Lab apron is required when wearing shorts, tank tops, etc. Keep locker drawers closed when not in use. Do not leave flames unattended. Turn burners off when not in use. Remember that most chemicals are flammable, toxic, carcinogenic or all three. Treat them accordingly. Do not ingest chemicals.… Read More »CHEMISTRY LABORATORY

Chemistry

INTRODUCTION TO CHEMISTRY

INTRODUCTION TO CHEMISTRY  Welcome to Chemistry, the Science concerned with the study of matter. In simplest terms, chemistry is the science of matter. Anything that can be touched, tasted, smelled, seen or felt is made of chemicals. Different thing feel, taste, smell and appear differently- like t fresh vegetables.   If you are blindfolded and asked to identify potatoes, onions, carrots or cabbages from a pack, chances are you could, chances are you could- based on interactions with them in your home kitchen. Chemistry will supply you with the knowledge and understanding to engage as informed citizens with science based issues.   You will use contemporary and relevant contexts of interest such as environmental issues to gain greater scientific knowledge. You will study the patterns and properties of the elements and how these combine to produce useful materials, such as air and water among others.   Throughout the course you… Read More »INTRODUCTION TO CHEMISTRY

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