Chapter 4
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What are acids?
• Species that release H+ ions in aqueous solutions
What are bases? Give 3 types.
• Substances that readily accept H+ ions (from acids) • Metal oxides, carbonates and alkalis
What are alkalis?
• Species that release hydroxide ions in aqueous solutions
What are strong acids?
• Acids that dissociate completely in solution
What are weak acids?
• Acids that only dissociate partially in solution
Which types of acids tend to be weak acids? Give an example.
• Organic acids • Ethanoic acid (CH3COOH)
How are the salts formed from carboxylic acids named?
• After their stem (e.g. meth, eth, etc.) add ‘anoate’ • E.g. sodium ethanoate
What is neutralisation?
• A reaction of: • H+ and OH- to form water • acids and bases
How do acids and metal oxides react together?
• Acids + metal oxides -> salt + water
How do acids and metal hydroxides react together?
• Acids + metal hydroxides -> salt + water
How do acids and metal carbonates react together?
• Acids + metal carbonate -> salt + water + carbon dioxide
What 3 things can titrations be used for?
• Finding the concentration of a solution • Identifying unknown chemicals • Finding the purity of a substance
What is a standard solution?
• A solution of known concentration
How do you prepare a standard solution?
• The solid is weighed accurately. • It is dissolved in a beaker using less distilled water than needed to fill the volumetric flask to the graduation line. • The solution is transferred to a 250cm^3 volumetric flask. The last traces of the solution are rinsed into the flask with distilled water. • The flask is filled to the graduation line using distilled water a drop at a time, until the bottom of the meniscus lines up exactly with the mark when viewed at eye level from the mark. • A stopper is put on the volumetric flask, and it is then inverted several times to mix the solution thoroughly.
What are 2 common errors when creating a standard solution, and what impact do they have?
• Too much water is added; the solution is too dilute • The flask is not inverted; the concentration is not consistent, so neither will the titration results be
What are concordant results? How are they used, and why?
• Results within 0.1cm^3 of each other • Titrations are repeated until you obtain concordant results, which are then used to calculate the mean titre, to prevent accuracy from being lost
What is an oxidation number?
• A measure of the number of electrons that an atom uses to bond with atoms of another element
What is an oxidation state?
• The oxidation number
What is the oxidation number of an element, and which situations does this apply to?
• 0 • This includes if it exists as a molecule (such as oxygen)
What is the oxidation number of an ion?
• It is the same as its ionic charge • However, the sign comes before the number
How do you find the oxidation number of elements in a compound?
• The individual charges added up equal the total charge of the compound
Give an example of an exception when it comes to the oxidation numbers of elements in compounds.
• When a compound contains both Cl and O, Cl may not have the oxidation number -1
What are Roman numerals used for in the name of compounds?
• They show the oxidation state of an element • They don’t show the sign, but that is clear from the context
What are the 3 different ways of defining oxidation?
• The addition of oxygen • The loss of electrons • An increase in oxidation number