chemical changes

• What is Ph?

  a measure of how acidic or alkaline a solution is
• what is a neutral ph?

  7
• acid ph scale

  0-6
• alkali ph scale

  8-14
• how can we measure ph?

  indicators, ph probe connected to a meter
• what is an advantage of a ph probe ?

  more accurate
• an acid

  any substance with a ph less than 7
• what is an alkali?

  ph greater than 7
• what makes a solution alkaline?

  hydroxide ions
• acid and a base ( neutralisation reaction)

  salt + water
• what does each increase of one on the ph scale mean?

  the hydrogen ions are increasing by x10
• what makes a solution acidic?

  hydrogen ions
• ionsise

  When acid molecules are added to water and split apart, we say that they 'ionise' or 'dissociate'.
• what is the difference between strong acids and weak ones?

  Strong acids ionise completely, whereas weak acids only partially ionise.
• Name three strong acids?

  hydrochloric acid, nitric acid, sulfuric acid
• where does the equilibrium lie in a weak acid?

  left
• Name 3 weak acids

  citric,carbonic,ethanoic
• Strength of an acid

  The proportion of acid molecules which dissociate into hydrogen ions
• As the concentration of hydrogen ions in a solution increases, what happens to the pH?

  decreases
• Which products are formed when an acid reacts with a metal oxide?

  Acid + metal oxide ➔ salt + water
• What type of reaction is it when an acid and a base react together?

  Neutralisation reaction
• what happens during a neutralisation reaction?

  During a neutralisation reaction, the positive hydrogen ions from the acid react with the negative hydroxide ions from the alkali to form molecules of water.
• Which products are formed when an acid reacts with a metal hydroxide?

  Acid + metal hydroxide ➔ salt + water
• how do we work out a salts formula?

  To work out the formula of the salt, take the positive ion from the base, such as sodium from sodium oxide (Na2O), and the negative ion from the acid, such as chloride from hydrochloric acid (HCl), and combine them together.
• Which products are formed when an acid reacts with a metal carbonate?

  Acid + metal carbonate ➔ salt + water + carbon dioxide
• When a soluble salt is formed from an acid and an insoluble base, how do you know when an excess of base has been added?

  Some of the reactant will be left unreacted
• Which factor determines the reactivity of a metal?

  How easily the atoms of that element lose their outer electrons
• When metals react, do the atoms become positive or negative ions?

  positive
• Do metals react more violently with water or acid?

  acid
• Reaction of metal with acid

  metal + acid = salt + hydrogen
• Displacement

  A more reactive metal displaces a less reactive metal
• Oxidation


  Loss of electrons, gain of oxygen
• reduction


  gain of electrons, loss of oxygen
• how do we use carbon to extract metals?

  Pure metals can be extracted from metal oxides using the element carbon.

  The carbon causes the metal to lose its oxygen, so the metal becomes reduced.

  This produces CO2, and can only work for metals less reactive than carbon.
• Why do we find pure gold in the ground, but not pure iron?

  Gold is unreactive, so doesn't react with any other elements

  Iron is reactive enough to react with oxygen so is oxidised to iron oxide
• What is a redox reaction?

  an oxidation reaction paired with a reduction reaction