Colorimetry

We can use a standard solution of known concentration to determine the concentration of an unknown sample by measuring the _____ of our known and unknown samples using a _____ and then creating a _____.

Absorbance; spectrophotometer; standard curve

When using a spectrophotometer, transmittance refers to the _____.

Amount of light that passes completely through the sample and strikes the detector

When using a spectrophotometer, absorbance refers to the _____.

Amount of light that is absorbed by the sample

When using a spectrophotometer, an increase in concentration will result in a _____ in absorbance and _____ in transmittance, as these two variables have an _____ relationship.

Increase; decrease; inverse

If a solution is colored, the intensity of the color will depend on the _____ of the solution. The more intense the color, the _____ the absorbance.

Concentration; higher

Colorimetry is a scientific technique used to determine the concentration of _____ compounds in solutions where the concentration of a solute is proportional to the _____.

Colored; absorbance

To create a standard curve using a spectrophotometer, you measure the _____ of various samples with _____ concentration, which can then be used to determine the concentration of an _____ solution.

Absorbance; known; unknown

To create a standard curve using a spectrophotometer, graph the _____ on the x-axis and the _____ on the y-axis for all data points, including _____ and _____ on your graph. Make sure your graph is formatted as a _____ with a _____. Excel will give you the _____ and _____, and you can plug in _____ to solve for _____.

Concentration; absorbance; labels; units; scatterplot; trend line; slope; y-intercept; absorbance; unknown concentration

Blank solutions consist of _____. In this solution, our blank solution consisted of _____ and _____, but not _____.

Everything except the compound of interest; iodine; water; starch

Blank solutions must be used in order to calibrate _____.

Absorbance

Because this experiment involved the use of iodine, everyone should be wearing _____, _____, and _____. Iodine should be disposed of in a _____, not the _____.

Gloves; glasses; closed-toe shoes; marked chemical waste container; sink

Using the equation _____, given Tube 1 had an initial starch concentration of 0.5 g/L, Tube 2 had an initial starch concentration of _____, Tube 3 had an initial starch concentration of _____, and Tube 4 had an initial starch concentration of _____.

C₁V₁ = C₂V₂; 0.25 g/L; 0.125 g/L; 0.0625 g/L

After water was added to each tube, Tube 1 had a starch concentration of _____, Tube 2 had a starch concentration of _____, Tube 3 had a starch concentration of _____, and Tube 4 had a starch concentration of _____.

0.05 g/L; 0.025 g/L; 0.0125 g/L; 0.00625 g/L

Before adding iodine to the test tubes, there (was/was no) difference in color because _____.

Was no; iodine is the color-changing agent and was not yet added

Water was added to the tubes before placing them in the spectrophotometer in order to _____ the solutions and ensure that there was a _____ and therefore _____. this step was skipped, then all of the tubes would be relatively _____ and have a _____ absorbance, affecting the accuracy of our results.

Dilute; visible difference in their color/concentration; absorbance; dark; similar

The preparation of _____ in this experiment has the greatest potential to introduce error because _____.

Tube 2; the accuracy of Tube 3 and Tube 4 are dependent on that of Tube 2

Serial dilution is preferred over directly preparing 0.0625 g/L from stock because it is possible to create a _____ in concentration, which helps protect against errors in _____. It is also likely to result in more accurate results because the desired final concentration is very _____, so even small errors in preparation can drastically change the results.

Trend; individual data points; low

Always check that your cuvette does not have any _____ nor _____ before obtaining a reading from the spectrophotometer.

Bubbles; fingerprints

The blank has an absorbance of 0 in order to account for the absorbance that may be due to the _____ and _____, allowing us to focus on the absorbance created by the _____.

Iodine; water; starch

_____ showed the greatest variability in absorbance.

Tube 1

Lower concentrations might show greater relative error because that quantities are so _____ that even small errors can result in a drastic skewing of the results. Additionally, errors made _____ in the experiment can _____ at lower concentrations.

Small; earlier; compound

Variability in the experiment performed during this lab may have affected the accuracy of our _____, which may mean that it cannot accurately calculate the _____.

Trend line equation; unknown concentration of starch

The R² value for our data should be very close to _____, indicating that there is a _____, _____ correlation between the _____ and _____. This indicates that _____, and therefore our data should be reliable enough to _____ next lab.

1; strong; positive; starch concentration; absorbance; starch concentration is a good predictor of absorbance; determine an unknown concentration

If a bubble was present in the cuvette, absorbance would _____ because the bubble would _____.

Increase; prevent light from passing through the solution

If the cuvette had fingerprints on the outside, absorbance would _____ because the fingerprints would _____.

Increase; create an additional film on the outside of the cuvette that could absorb light

If the blank was prepared without iodine, the absorbance of the later solutions would _____ because the absorbance would _____.

Increase; take into account the effect of both the iodine and starch, rather than just the starch

If Tube 3 was not mixed thoroughly before measurement, the absorbance could either increase or decrease depending on the portion of the tube that was ultimately pipetted into the cuvette. If a less concentrated of Tube 3 was pipetted into the cuvette, then absorbance would _____ because _____. If a more concentrated area of Tube 3 was pipetted into the cuvette, then absorbance would _____ because _____.

Decrease; there is less starch available to absorb light; increase; there is more starch available to absorb light

In this experiment, _____ error would be most likely because _____. For example, although there were _____ for the starch, iodine, and water, each _____ required _____ for measurement.

Human; there were many measurements that had to be done by hand rather than using a tool with consistent results; dispensers; transfer; a group member