Theories of acids and bases. In fact, the reaction between HCl and water is reversible, but only to a very minor extent. In order to generalise, consider an acid HA, and think of the reaction as being reversible. Thinking about the forward reaction: The HA is an acid because it is donating a proton (hydrogen ion) to the water. The water is a base because it is accepting a proton from the HA. But there is also a back reaction between the hydroxonium ion and the A- ion: The H3O+ is an acid because it is donating a proton (hydrogen ion) to the A- ion. The reversible reaction contains two acids and two bases. When the acid, HA, loses a proton it forms a base, A-. Members of a conjugate pair differ from each other by the presence or absence of the transferable hydrogen ion.
If you are thinking about HA as the acid, then A- is its conjugate base. If you are thinking about A- as the base, then HA is its conjugate acid. The water and the hydroxonium ion are also a conjugate pair. A second example of conjugate pairs. Strong and weak acids. When an acid dissolves in water, a proton (hydrogen ion) is transferred to a water molecule to produce a hydroxonium ion and a negative ion depending on what acid you are starting from. In the general case . . . These reactions are all reversible, but in some cases, the acid is so good at giving away hydrogen ions that we can think of the reaction as being one-way. The acid is virtually 100% ionised. For example, when hydrogen chloride dissolves in water to make hydrochloric acid, so little of the reverse reaction happens that we can write: At any one time, virtually 100% of the hydrogen chloride will have reacted to produce hydroxonium ions and chloride ions.
Hydrogen chloride is described as a strong acid. A strong acid is one which is virtually 100% ionised in solution. Other common strong acids include sulphuric acid and nitric acid. You may find the equation for the ionisation written in a simplified form: This version is often used in this work just to make things look easier.
Calculating molarity, molar concentration of solutions how to determine solubility practice questions gcse chemistry Calculations 11. igcse KS4 science A level GCE AS A2 O Level practice questions exercises. 11. Molarity, volumes and the concentration of solutions Appendix on How to make up a standard solution is on a separate page See also 14.3 dilution of solutions calculations Revise section 7. moles and mass before proceeding in this section 11 and eventually you may need to be familiar with the use of the apparatus illustrated above, some of which give great accuracy when dealing with solutions and some do not.
It is very useful to be know exactly how much of a dissolved substance is present in a solution of particular concentration or volume of a solution. There are more questions involving molarity in section 12. on titrations and section 14.3 on dilution calculations and APPENDIX on SOLUBILITY How do you find out how soluble a substance is in water? Reminder: solute + solvent ==> solution i.e. the solute is what dissolves, the solvent is what dissolves it and the resulting homogeneous mixture is the solution. (3) Next, an evaporating dish (basin) is accurately weighed. . (7) Calculations. Understanding the names of organic compounds. If you had to name this yourself: How do you know what order to write the different alkyl groups at the beginning of the name? The convention is that you write them in alphabetical order - hence ethyl comes before methyl which in turn comes before propyl.
The cycloalkanes In a cycloalkane the carbon atoms are joined up in a ring - hence cyclo. Example: Write the structural formula for cyclohexane. hexan shows 6 carbons with no carbon-carbon double bonds. cyclo shows that they are in a ring. The alkenes Example 1: Write the structural formula for propene. prop counts 3 carbon atoms in the longest chain. en tells you that there is a carbon-carbon double bond. Putting in the hydrogens gives you: Example 2: Write the structural formula for but-1-ene. but counts 4 carbon atoms in the longest chain and en tells you that there is a carbon-carbon double bond. No number was necessary in the propene example above because the double bond has to start on one of the end carbon atoms. The carbon skeleton is: Alkanes and cycloalkanes with chlorine or bromine. The reaction between alkanes and fluorine This reaction is explosive even in the cold and dark, and you tend to get carbon and hydrogen fluoride produced.
It is of no particular interest. For example: The reaction between alkanes and iodine Iodine doesn't react with the alkanes to any extent - at least, under normal lab conditions. The reactions between alkanes and chlorine or bromine There is no reaction in the dark. In the presence of a flame, the reactions are rather like the fluorine one - producing a mixture of carbon and the hydrogen halide. The interesting reactions happen in the presence of ultra-violet light (sunlight will do). We'll look at the reactions with chlorine. Methane and chlorine Substitution reactions happen in which hydrogen atoms in the methane are replaced one at a time by chlorine atoms. Balancing Chemical Equations.
Balancing Chemical Equations Balancing Chemical Equations: Problems #1 - 10 Balancing Chemical Equations: Problems #11 - 25 Balancing Chemical Equations: Problems #26 - 45 Balancing Chemical Equations: Problem List only The meaning of a modern chemical equation Return to Equations Menu Chemical equations usually do not come already balanced. All chemical calculations you will see in other units must be done with a balanced equation. IMPORTANT DEFINITION: A balanced equation has equal numbers of each type of atom on each side of the equation. The Law of Conservation of Mass is the rationale for balancing a chemical equation. "We may lay it down as an incontestible axiom, that, in all the operations of art and nature, nothing is created; an equal quantity of matter exists both before and after the experiment; the quality and quantity of the elements remain precisely the same; and nothing takes place beyond changes and modifications in the combination of these elements.
" Answer: 18. And it's done. Introduction to Time-of-Flight Mass Spectrometry. Mass spectrometry A mass spectrometer is simply a device designed to determine the mass of individual atoms or molecules. Atoms of different elements have different masses and thus a knowledge of the molecular mass can very often be translated into a knowledge of the chemical species involved. There are many strategies for measuring the atomic/molecular mass, but nearly all of them require that the molecule carry some charge. When charged the atom/molecule is called an ion and it may be manipulated with electric and magnetic fields. This manipulation usually takes place in a vacuum so that the flight paths are not dominated by scattering events. The material to be analysed may start as a solid, liquid or gas, but one way or the other the molecules must be separated from each other first i.e. they must be in the gas phase.
Often this can be as simple as applying some heat, but there are of course various other strategies specific to particular applications. Time of flight mass measurement. Redox Reactions: Crash Course Chemistry #10. Rules for Assigning Oxidation Numbers to Elements - dummies. Oxidation numbers are bookkeeping numbers.
They allow chemists to do things such as balance redox (reduction/oxidation) equations. Oxidation numbers are positive or negative numbers, but don’t confuse them with positive or negative charges on ions or valences. Oxidation numbers are assigned to elements using these rules: Rule 1: The oxidation number of an element in its free (uncombined) state is zero — for example, Al(s) or Zn(s). These rules give you another way to define oxidation and reduction — in terms of oxidation numbers. For example, consider this reaction, which shows oxidation by the loss of electrons: Notice that the zinc metal (the reactant) has an oxidation number of zero (rule 1), and the zinc cation (the product) has an oxidation number of +2 (rule 2).
Reduction works the same way. The copper is going from an oxidation number of +2 to zero. Electronic structures of ions. Working out the electronic structures of ions Ions are atoms (or groups of atoms) which carry an electric charge because they have either gained or lost one or more electrons. If an atom gains electrons it acquires a negative charge. If it loses electrons, it becomes positively charged. The electronic structure of s- and p-block ions Write the electronic structure for the neutral atom, and then add (for a negative ion) or subtract electrons (for a positive ion). To write the electronic structure for Cl -: To write the electronic structure for O2-: To write the electronic structure for Na+: To write the electronic structure for Ca2+: The electronic structure of d-block ions Here you are faced with one of the most irritating facts in chemistry at this level!
That means that you work on the assumption that the 3d electrons are added after the 4s ones. However, in all the chemistry of the transition elements, the 4s orbital behaves as the outermost, highest energy orbital. You must remember this: Electronic structures of atoms. You can see that it is going to get progressively tedious to write the full electronic structures of atoms as the number of electrons increases. There are two ways around this, and you must be familiar with both. Shortcut 1: All the various p electrons can be lumped together. For example, fluorine could be written as 1s22s22p5, and neon as 1s22s22p6. This is what is normally done if the electrons are in an inner layer. If the electrons are in the bonding level (those on the outside of the atom), they are sometimes written in shorthand, sometimes in full.
Don't worry about this. For example, although we haven't yet met the electronic structure of chlorine, you could write it as 1s22s22p63s23px23py23pz1. Notice that the 2p electrons are all lumped together whereas the 3p ones are shown in full. Shortcut 2: You can lump all the inner electrons together using, for example, the symbol [Ne]. On this basis the structure of chlorine would be written [Ne]3s23px23py23pz1.
The third period. Atomic orbitals. A 1s orbital holding 2 electrons would be drawn as shown on the right, but it can be written even more quickly as 1s2. This is read as "one s two" - not as "one s squared". You mustn't confuse the two numbers in this notation: The order of filling orbitals - the Aufbau Principle Aufbau is a German word meaning building up or construction. We imagine that as you go from one atom to the next in the Periodic Table, you can work out the electronic structure of the next atom by fitting an extra electron into the next available orbital. Electrons fill low energy orbitals (closer to the nucleus) before they fill higher energy ones.
Where there is a choice between orbitals of equal energy, they fill the orbitals singly as far as possible. This filling of orbitals singly where possible is known as Hund's rule. The diagram (not to scale) summarises the energies of the orbitals up to the 4p level that you will need to know when you are using the Aufbau Principle. Orbitals: Crash Course Chemistry #25.