Question

7. For each of the following experimental or calculation errors, tell if the calculated value of R, in question 4, would be too high, too low or unchanged. Explain your answers. a. The temperature of the water was recorded too low. b. The mass of the magnesium was recorded too high. c. The magnesium was coated with magnesium oxide. d. Some air bubbles were introduced when the eudiometer was inverted. Some of the hydrogen gas dissolved in the water. (Hint: If it is dissolved, it won't be a bubble!) e.

Answer 1

Answer 4) First of all, in answer 4, the pressure computed is wrong. 30.25 inch of Hg = 768.35 mm Hg not 30.25 mm Hg.

Therefore, R will be = PV/nT = 1.01098699 x 0.0562/0.00202469136x 298.15 = 0.0941213698.

And the percent error is - 14.64%

One possible source for this error could be n or T reported low. (Any option from 7a, d, and e)

Now, to answer 7th,

a) If the Temp was recorded too low, the R value will be too high ( T low in denominator)

b) If mass of Mg is too high, moles of Mg will be too high and therefore, moles of H2 will be too high, that is, R will be too low(n in the denominator is too high)

c) If the Magnesium were coated with MgO, we will wrongly report the mass as high(extra mass of oxugen evaluated), and therefore moles of Mg will be high and moles of H2 will be high, R will again be low(n in the denominator too high).

d) If some air bubbles are introduced, that is, pressure of H2 gas will be wrongly recorded as high due to the pressure of air bubbles in the gas. Hence, R will be high. (P high in the numerator)

e) If some of the hydrogen is dissolved in a water, no of moles in its gas phase will decrease, decrease of n leads to increase in reported R(n in denominator) hence, R will be more.