Briefly discuss whether each of the following \"mistakes\" would produce a high
ID: 960744 • Letter: B
Question
Briefly discuss whether each of the following "mistakes" would produce a high result, a low result, or make no difference in the value obtained for the gas constant, R. The water level in the flask dropped below the tip of tube C. Loss of some potassium chlorate from the test tube. Incomplete decomposition of the potassium chlorate. The correction for the vapor pressure of water was omitted in the calculation. Failure to use the MnO_2 catalyst. Why is it necessary to equalize the pressure of the receiving beaker and the flask before measuring the delivered volume of water?Explanation / Answer
i) The water level in the flask dropped below the tip of tube C
Tube C is the gas inlet tubing. It passes the gas from tube to flask. Which will create a pressure in flask and water will be transferred to beaker. It does not matter if tip is immersed in water or not as flask is gas tight. And gas cannot pass to beaker as that tip is immersed in water to create a siphon.
It will make no difference.
ii) Loss of some potassium chlorate from the test tube.
Loss of potassium chlorate will affect the weight, which in turn will increase the value of oxygen produced. And so will increase n(number of moles). Which will decrease R value.
R= PV/nT (n is in denominator, higher the n, lower the R)
It will give a low result.
iii) Incomplete decomposition of potassium chlorate.
Incomplete decomposition will produce less oxygen and weight of oxygen will be less.
It will result in higher value of R.
It will give a high result.
iv) The correction for the vapor pressure of water was omitted in the calculation.
The vapor pressure of water is reasonably high at ambient temperature; it makes a significant contribution to the total pressure.
Vapor pressure needs to be subtracted from total pressure. Else, it will give high pressure which will result in higher value of R.
It will give a high result.
v) Failure to use the MnO2 catalyst.
MnO2 reacts with potassium chlorate to produce O2.
If not added O2 will not be produced. Result in decrease in pressure.
Give higher value of R.
It will give a high result.
4. Equalizing the water levels equalizes the pressures and ensures that the total pressure in the flask is atmospheric and does not contain a contribution from the pressure due to the height of the water column.
If the pressure in the bottle is greater than that of the atmosphere, water will flow from the bottle into the beaker. If the internal pressure is lower, water will be forced into the bottle by the atmosphere.
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