Chemistry

1)Suppose a piece of lead with a mass of 14.9 g at a temperature of 92.5 degrees is dropped into an insulated container of water. The mass of water is 165 g and its temperature before adding the lead is 20.0 degrees. What is the final temperature of the system?

2)What are the proportions by mass of the elements in the compound sodium sulfate, Na2SO4?

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  1. 1.
    heat lost piece of lead + heat gained by wter = 0
    heat lost by lead = mass x specific heat lead x (Tf-Ti) where Tf is final T (in this case the unknown) and Ti is the initial T of the lead.

    heat gained by wter = mass x specific heat water x (Tf - Ti).

    Solve for Tf. Post your work if you get stuck.

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  2. 2.
    molar mass Na2SO4 is approximately,
    (2 x 23) + 32 + (4 x 16) = 142. You should confirm this by looking up the atomic masses in the periodic table and adding them.
    Then
    %Na = [(2 x 23)/142]*100
    %S = (32/142)*100
    %O = [(4 x 16)/142]*100

    I have rounded here and there so you need to look these numbers up from the periodic table and recalculate to the number of significant figures your teacher wants.

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