Check this out..acid and base

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[Teoh Kai Yuan]

6.   Magnesium hydroxide is one of the ingredients found in the toothpaste. Magnesium hydroxide is an alkali
(a) How is an alkali different from a alkali
(b) We use toothpaste when brushing our teeth. Explain briefly how the use of toothpaste
     can help to prevent tooth decay
(c) The pH value of 1.0 mol dm-3  magnesium hydroxide is higher than that of ammonia,
     suggest one test which can be used to distinguish magnesium hydroxide from ammonia
     (without using indicator). State the expected observation
(d) Explain why a solid magnesium hydroxide does not conduct electric current, whereas a
      solution of magnesium hydroxide in water conducts electric current
(e) Apart from using indicator, describe another chemical test that can be used to show the
     alkalinity properties. You should include the reagents used, observation and a chemical
     equation

This is my answer..
(a) An alkali is a soluble salt that forms solution when dissolved in water
(b) Toothpaste contains magnesium hydroxide which acts as a base to neutralize the acids
     released by the bacteria
(c) By measuring the electrical conductivity of both alkaline. Ammonia which is a weak acid
     has lower electrical conductivity than magnesium hydroxide and therefore, would give a
     smaller current measurement
(d) Solid magnesium hydroxide do not conduct electricity because the ions are held in a lattice
     and do not move freely. However, when the magnesium hydroxide dissolved in water, they
     can conduct electricity because magnesium hydroxide ionizes to magnesium ions and
     hydroxide ions, and thereby conducts electricity
(e) Add ammonium salts to the alkali and heat the compound. Effervescence is seen.
     Ammonia gas is liberated
    Mg(OH)2 + 2 NH4Cl → MgCl2 + 2 H2O + 2 NH3

This is only my answer..can anyone help me to check..i scare teach wrong information to the student

[Jong Kah Yin]

Hi,
A slight modification to your answers :
(a) alkali are bases (Metal oxides/hydroxides) that are soluble in water, producing hydroxide ions.
(e) For a chemical test, include method/actions taken, materials used and observation
     - in your answer, it should include the observation, that is, a dense white fume is produced     
    when a glass rod immersed in concentrated HCl is brought near the mouth of the test tube

The rest of your answers are good. Keep it up!

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