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15 September, 22:15

Element X reacts with hydrogen gas at 200°C to form compound Y. When Y is heated to a higher temperature, it decomposes to the element X and hydrogen gas in the ratio of 559 mL of H2 (measured at standard temperature and pressure) for 1.00 g of X reacted. X also combines with chlorine to form a compound Z, which contains 63.89 percent by mass of chlorine. Deduce the identity of X. The symbol of element X is

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  1. 15 September, 23:44
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    X is calcium with the symbol Ca

    Explanation:

    From the first statement:

    X reacted with H2 to produce Z i. e

    X + H2 - > Y

    Y is heated to form X and H2 i. e

    Y - > X + H2

    Let us obtain moles of H2 produced. This is illustrated below:

    Volume of H2 produced = 559 mL = 0.559 L.

    I mole of H2 occupy 22.4L at stp

    Therefore, b mol of H2 will occupy 0.559 L at stp i. e

    b mol of H2 = 0.559/22.4

    b mol of H2 = 0.025 mole

    Next 0.025 mole of H2 to gram ...

    Molar Mass of H2 = 2x1 = 2g/mol

    Mole of H2 = 0.025 mole

    Mass = number of mole x molar Mass

    Mass of H2 = 0.025 x 2

    Mass of H2 = 0.05g

    From the question given, we were told that 1g of X reacted. This means that 1g of X reacted with 0.05g of H2. Now let us determine the mass of X that will react with 1 mol (i. e 2g) of H2. This is illustrated below:

    From the reaction,

    It was discovered that 1g of X reacted with 0.05g of H2.

    Therefore, P g of X will react with 2g of H2 i. e

    P g of X = 2/0.05 = 40g/mol

    The molar mass of X is 40g/mol.

    Now let us consider the second statement to see if we'll obtained the same result as 40g/mol of X

    From the second statement:

    X also combines with chlorine to form a compound Z, which contains 63.89 percent by mass of chlorine i. e

    X + Cl2 - > Z

    Molar Mass of Z (X + 2Cl) = X + (35.5 x 2) = X + 71.

    Z contains 63.89% by mass of Cl2.

    We can obtain the molar mass of X as follow:

    Percentage by mass of Cl2 in the compound Z is given by:

    Mass of Cl2/Molar Mass x100

    63.89/100 = 71 / (X + 71)

    Cross multiply to express in linear form

    63.89 (X + 71) = 100 x 71

    Clear the bracket

    63.89X + 4536.19 = 7100

    Collect like terms

    63.89X = 7100 - 4536.19

    63.89X = 2563.81

    Divide both side by 63.89

    X = 2563.81/63.89

    X = 40g/mol

    Now we can see that in both experiments, the molar mass of X is 40g/mol.

    Comparing the value of X i. e 40g/mol with that from the periodic table, X is calcium with the symbol Ca
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