chemistry paper 1

• An element is defined as all of the atoms being the same.
• A compound is formed when atoms of different elements are chemically combined in fixed proportions.
• A mixture contains different elements or compounds but they are not chemically combined.
• A molecule is a collection of atoms, even if they are the same element, that are chemically combined.
• Mixtures can be separated using physical separation techniques such as filtration, distillation, crystallization, or chromatography.
• A molecule is different from a compound in that a molecule has any elements chemically combined, even if they are the same element.
• Molecules include methane, water, and ammonia, which are also compounds because they contain different elements chemically combined.
• Chlorine and oxygen are examples of molecules, as they contain two atoms of the same element chemically combined.
• The periodic table shows all of the different elements, each with a symbol and every symbol starts with a capital letter.
• Some symbols have a second lowercase letter, indicating the chemical formula for the compound.
• A chemical formula tells us the elements in a molecule and the numbers of atoms of each element.
• The chemical formula for hydrogen fluoride is HF.
• The chemical formula for potassium iodide is KI.
• The chemical formula for potassium iodide contains the elements Potassium and iodine, and there are no small numbers to the right of these symbols, indicating that the compound has one atom of each element.
• The chemical formula for calcium sulfate is CaSO4.
• The chemical formula for calcium sulfate contains the elements calcium, sulfur, and oxygen, and there are no small numbers to the right of the oxygen, indicating that the compound has one atom of oxygen.
• In a specific compound, the number of atoms of each element is fixed and cannot be changed, as changing one small number results in a different compound.
• The compound calcium sulfate and the compound calcium sulfite have different chemical formulas but the same number of atoms of each element.
• The compound magnesium hydroxide contains brackets in its formula, which are used by chemists to work out how the atoms bond together.
• In the compound magnesium hydroxide, the number of atoms of each element can be determined by looking at the symbols and noting that there is no small number to the right of the Magnesium, indicating one atom of magnesium.
• Inside the brackets of the compound magnesium hydroxide, there are two atoms of oxygen and two atoms of hydrogen, as indicated by the small two to the right of the brackets.
• The small number to the right of the brackets in a chemical formula multiplies everything inside the brackets, as demonstrated in the compound magnesium hydroxide.
• In the compound magnesium hydroxide, the small two to the right of the brackets multiplies the number of atoms of each element, resulting in two atoms of oxygen and two atoms of hydrogen.
• The compounds copper iodide, iron bromide, zinc carbonate, and aluminum hydroxide have different chemical formulas but the same number of atoms of each element.
• Physical separation techniques can only be used to separate mixtures, not to separate the elements in a compound.
• Filtration is a physical separation technique used to separate an insoluble solid from a liquid.
• Silver chloride is an insoluble solid that can be separated from water using filtration.
• Filtration works by passing the liquid through a filter paper, trapping the solid material at the end.
• Crystallization is a physical separation technique used to separate a soluble solid from a liquid.
• Sodium chloride is a soluble solid that can be separated from water using crystallization.
• Crystallization works by allowing the water to evaporate, leaving behind crystals of solid sodium chloride.
• Certain chemicals will break down if heated, so it's sometimes better to allow the water to evaporate on its own.
• Physical separation technique: Simple distillation.
• In the previous video, crystallization was used to separate a dissolved solid from a liquid.
• In simple distillation, the liquid is evaporated by heating and then condensed back to a liquid by cooling.
• The liquid in a solution in water is called an aqueous Solution.
• Crystallization is a great way of separating a dissolved solid from a liquid.
• Simple distillation is used to separate a dissolved solid from a liquid but keep the liquid.
• Another type of distillation is fractional distillation, which will be looked at in the next video.
• Simple distillation consists of two stages: evaporating the liquid by heating and condensing the vapor back to a liquid by cooling.