Chemical Changes

Explain what happens to the pH of an acid as the acid is diluted with water (2)

• pH increases

• the concentration of hydrogen ions decreases

• use a pipette to add the alkali

• any two from:

  • into a conical flask

  • add an indicator (to the alkali)

  • takt the initial burette reading

  • use a white tile

The student adds zinc oxide to hydrochloric acid until the zinc oxide is in excess.

Give one observation that the student could make to show that the zinc oxide is in excess (1)

solid remaining

Describe how a student should obtain crystals of zinc chloride from a solution of zinc chloride (2)

• heat the solution until point of crystallisation

• leave the solution (to cool/crystallise)

Magnesium can reduce silicon dioxide

Give one reason why the products are difficult to separate if magnesium is used to reduce silicon dioxide (1)

both products are solid

Which indicators can be used for titration and what are the colour changes?

• phenolphthalein: colourless to pink

• methyl orange: yellow to red/orange/pink

• Litmus: blue to red