A student carries out an experiment to identify an unknown metal Use the experim

Question

A student carries out an experiment to identify an unknown metal Use the experimental results and observations from the netbook (below) to identify the metal, assuming a + 2 charge on the metal ion in solution. See Figure on page 1 of the exam. Balanced equation: M (s) + 2 HCI (aq) rightarrow H_2 (g) + MC1_2 (aq) Calculate the atomic weigh: of the unknown metal based on the data. b. Identify the unknown metal and clearly explain how you determined your claim. c. A possible source of error is that there was no: sufficient HCI added for the reaction i. Is this source of error consistent with the direction of the error observed in this experiment? Explain your answer ii. Use limiting reagent calculations with the information giver, to prove HCI was not the limiting reactant iii. Use the experimental observations above to give two reasons that prove HCI was not the limiting reactant

Explanation / Answer

a)

MW = mass of metal / mol of metal

mass = 0.2446 g

mo of gas = from ideal gas law

PV = nRT

n = PV/(RT) = (763.51 - 23) (94.56/1000)/(62.32*(23+273)) = 0.0037959 mol

then

rati is:

1 mol of gas = 1 mol of metal

so

mol of metal = 0.0037959

MW = masS7mol = 0.2446/0.0037959 = 64.44 g/mol

b)

The nearest metal is Copper/Zinc, since this is silvery, this is most likely Zinc

c)

i)

if not enugh acid is added, then the ratios are incorrect,

this can be observed if we add excess HCl in order to see a 100% cnversion of the metal

ii)

mol of HCl = MV = 12*16 = 192 mmol = 0.192 mol

Clearly, there is much more HCl than the metal 1:2 ratio, so this is in excess

iii)

- There is no more "silvery colored solid"

- No more bubbles are formed, implies no more reaction

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