G Currell & A A Dowman, Wiley-Blackwell, 2009

- The reading,
*W*', on an electronic balance is related to the mass,*W*, on the pan by the equation:*W*' =*m*×*W*+*c*

and for direct measurements the value of*m*=1 and*c*= 0.

The 'Tare' facility on the balance allows the mass of a container to be 'taken off' the total mass, so that it records just the mass of the contents.

Which of the following statements is true?- Adjusting the 'Tare' control changes the value of '
*m*' in the equation. - Adjusting the 'Tare' control changes the value of '
*c*' in the equation. - Adjusting the 'Tare' control changes the values of both '
*m*' and '*c*' in the equation simultaneously. - None of the above

- Adjusting the 'Tare' control changes the value of '
- The voltage output,
*E*(in mV), from a combination pH electrode is given by the equation:*E*=*E*_{o}- (2.3*RT/F*)×(pH - 7.0)

where*T*is the absolute temperature,*R*and*F*are constants and*E*_{o}is a constant offset voltage.

The solid line on the graph below shows the output,*E*, at a temperature of 25^{o}*C*.

If the temperature,*T*, is**increased**, which line will show the new relationship?- Line A
- Line B
- Line C
- Line D

- In an atomic absorption spectrophotometer, a solution containing copper records an absorbance,
*A*= 0.217.

A known amount of copper is added to the solution,**increasing**the concentration by 5.0 ppm, and the new solution records an absorbance of*A*= 0.532.

Calculate the concentration (to 2 sf) of the copper in the original solution, assuming that the response of the instrument is linear over this range of concentrations.- 0.29 ppm
- 1.6 ppm
- 3.4 ppm
- 8.4 ppm

- The linear range of a thermal conductivity detector for gas chromatography has a sensitivity of 8.0 µV/ppm for methane, and an offset voltage output at zero concentration equal to 40 µV.

Calculate the concentration of methane which would give an output voltage of 120 µV.- 20 ppm
- 10 ppm
- 11 ppm
- 15 ppm

- The three plots below show the residual values produced in linear x-y regression calculations of experimental data (from x = 0 upwards):

which one of the following statements is most likely to be correct?- R1 shows random variations around a linear relationship passing through the origin
- R2 shows a linear relationship that becomes curved at lower x-values
- R3 shows random variations around a constant y-value equal to zero.
- None of the above