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匿名 發問於 科學及數學化學 · 7 年前

S3 Chem (20點)

1) Being very light, helium can be used to fill balloons and airships. Predict whether xenon can also be used. Explain your answer.

2)Name the products formed for each of the following chemical changes

-->Magnesium is burnt in air

-->Calcium is put into water

3)Describe what would be observed when a piece of strontium is put into dilute

hydrochloric acid.

4) Give 2 pieces of evidence that strontium is more reactive than magnesium.

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3 個解答

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  • 7 年前
    最愛解答

    1. It cannot be used to fill balloons and airships because the molar mass of He is 4.0 and the molar mass of air is about 15. By Avogadro's law, the volume of all gas is same if the amount of molecules are equal,therefore the density oftwo gases can be compared, regardless of the volume. As the mass of He is smaller than air, balloons and airships can float on air when they are filled with He. However, the molar mass of Xe is131.3 which is much larger than He and air. It cannot float on air.

    2.

    Mg will react with the O2 in air when it is burnt ,with the equation

    2Mg+O2----->2MgO

    Ca will react with H2O when it is put into water, with the equation

    Ca+2H2O----->Ca(OH)2+H2

    3. It will give a large amount of colourless gas bubbles due to these reactions

    Sr+2HCl----->SrCl2+H2

    Sr+2H2O----->Sr(OH)2+H2

    4.Sr can react water in room temperature and pressure but Mg cannot.

    Sr has a higher position in ECS than Mg which shows that it loses electrons more easily than Mg

    資料來源: me
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  • 7 年前

    1. Xenon is less light than helium but i'm not sure whether it can make them float

    2.Magnesium is burnt in air--> Magnesium oxide

    Calcium is put into water--> Calcium hydroxide

    3. colourless bubbles give out

    4. It gives out more bubbles when put into dilute acid (hydrogen)

    The reaction between strontium with water has a higher rate than that of magnesium with water

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  • 匿名
    7 年前

    u can find the answer in the hk a-level pastpaper (topic:inorganic chem)

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