Question

the absorbance scale of a spectrophotometer was tested at 254 nm wavelength with a standard solution that had a known absorbance value of 0.470. Eight replicate measurements of the absorbance with the spectrometry gave the following results: Mean = 0.465; standard deviation = 0.005. The 95% confidence interval of these measurements will have this value as its upper confidence limit

Answer 1

mean=0.465

sample size=8 measurements

sd=0.005

confidence level for 95%

then from above data we can find out the upper confidence level as,

we will convert percentage to a decimal, 0.95/2=0.475.

now we will put the value of z form the z table which is =1.96.

now,we will calculate the standard error from standard deviation,

=sd/sqrt of sample size

=.005/sqrt of 8

=0.005/2.828

=0.00176

then we can multiply Confidece Ievel*Standard error

=1.96*0.00176

=0.00344 (margin of error)

now we can calculate the upper confidence limit(interval) from above information.

=mean(+) margin of error (for lower confidence level mean-margin of error)

=0.465+.0034

upper confidence limit=0.4684