Tag: distinguish between black copper oxide and black manganese dioxide

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Multiple choice distinguish between black copper oxide and black manganese dioxide practical work chemistry

$CuO$ reacts with $HCl$ but $Cu$ does not, why?

  1. Copper has a higher reduction potential than hydrogen, it does not react with non-oxidising acids like $HCl$
  2. Copper has a lower reduction potential than hydrogen, it does not react with non-oxidising acids like $HCl$

  3. Copper is a least reactive metal hence does not react with any acid
  4. Both $Cu$ and $CuO$ does not react with $HCl$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Copper does not react with $HCl$ acid, but copper oxide does react. Copper has a higher reduction potential than hydrogen, hence it does not react with non-oxidising acids like $HCl$ or dil.$H _2SO _4$.
But metal oxides are basic substances, and so they generally react with acids forming respective salt and water. 

Multiple choice distinguish between black copper oxide and black manganese dioxide practical work chemistry

Why should the reaction between manganese dioxide and hydrochloric acid carried out in a fume cupboard?

  1. Manganese causes skin irritations

  2. Both reactants and products causes itching

  3. Chlorine gas is poisonous

  4. None of above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

When manganese dioxide is treated with hydrochloric acid, chlorine gas is released as a product which can be poisonous. Hence, the procedure should take place in a fume cupboard to prevent any harmful effects.

Multiple choice distinguish between black copper oxide and black manganese dioxide practical work chemistry

When manganese dioxide is treated with HCl, the oxidising agent in the reaction is__________.

  1. $MnO _2$
  2. $HCl$
  3. $H _2O$

  4. The reaction is not a redox reaction
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When Manganese dioxide reacts with $HCl$, it gives chlorine gas, water and $MnCl _2$. $MnO _2$ is the oxidising agent as it oxidises $HCl$ to $Cl _2$ which loses the hydrogen atom.

Multiple choice distinguish between black copper oxide and black manganese dioxide practical work chemistry

On reacting $MnO _2$ with $HCl$,
1. $Mn^{4+}$ is reduced to      
2. $Cl^{-}$ is oxidised to

  1. $Mn^{3+}, Cl^{4+}$
  2. $Mn^{2+}, Cl$
  3. $Mn, Cl$
  4. $Mn$ is not reduced nor $Cl$ is oxidised
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Manganese dioxide on reacting with hydrochloric acid, undergoes redox reaction. $MnO _2$ is the oxidising agent while $HCl$ is the reducing agent. $Mn^{4+}$ is thus reduced to $Mn^{2+}$ whereas, $Cl^{-}$ is oxidised to $Cl$.