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March 24, 2017

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1) Metals that are above hydrogen in the reactivity series react with dilute hydrochloric acid to produce hydrogen gas. Lead is just above hydrogen in the reactivity series.I read a book that says no reaction occurs between lead & dilute acid. Why? Is it because the reaction is too slow?

2) Magnesium + Iron (II) Chloride gives Magnesium chloride + iron. What colour is the iron solid? Black?

3)When reacting a metal with steam, the delivery tube must be removed from the water in the trough before turning off the Bunsen flame. This is to prevent water from being sucked back into the hot test tube. Why will water be sucked back into the hot test tube?

Thank you!

  • Chemistry-please help - ,

    1) Metals that are above hydrogen in the reactivity series react with dilute hydrochloric acid to produce hydrogen gas. Lead is just above hydrogen in the reactivity series.I read a book that says no reaction occurs between lead & dilute acid. Why? Is it because the reaction is too slow?
    It is slow but one of the reasons why it is so slow (and some may say actually doesn't react) is because the surface atoms of Pb react with the HCl to form PbCl2. It just happens that PbCl2 is not soluble in water and even less soluble in HCl. Therefore, the first layer of Pb atoms do react, forming a coating of PbCl2, and that hinders further reaction.

    2) Magnesium + Iron (II) Chloride gives Magnesium chloride + iron. What colour is the iron solid? Black?
    Yes, finely divided iron is black.
    3)When reacting a metal with steam, the delivery tube must be removed from the water in the trough before turning off the Bunsen flame. This is to prevent water from being sucked back into the hot test tube. Why will water be sucked back into the hot test tube?
    Remember Charles' Law (volume vs temperature). When the gases in the heated tube cool, the volume contracts, that causes the pressure to drop and that causes the liquid to be sucked into the heated tube. Actually, you can skip the volume part and just remember that pressure decreases with decreasing temperature. When the temperature of the heated tube cools, the pressure is decreased, and the water is sucked in to equalize the pressure.

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