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## Another Problem 1

In an experiment, a chemist allows a red solution to flow at a rate of 0.1 mL per second for 14 seconds into a beaker containing a blue solution. The red solution has a density of 1.10 g/mL, and the blue solution has a density of 0.98 g/mL. Rounding each answer to the correct number of significant figures, if there are initially 20. mL of blue solution in the beaker:

(a)
How many grams of blue solution are in the beaker?
(b)
How many milliliters of red solution have been added after 14 seconds?
(c)
How many grams of red solution have been added after 14 seconds?
(d)
Recalculate the answers for (b) and (c) for a red flow rate of 0.10 mL per second.

### Solutions: `(a) 20 g (b) 1 mL (c) 2 g (d) 1.4 mL, 1.5 g` Sketch:

This is largely a problem of unit conversions and keeping track of significant figures. For a flow rate of 0.1 ml per second, there is only 1 significant figure for this measurement, so the answers that use this quantity are only good to 1 significant figure.

(a)
20. mL x .98 g/mL = 19.6 g, but to 2 sig figs, this is rounded to 20. g.
(b)
0.1 mL/s x 14 s = 1.4 mL, so to 1 sig fig this is rounded down to 1 mL.
(c)
0.1 mL/s x 14 s x 1.10 g/mL = 1.54 g, so to 1 sig fig this is rounded up to 2 g.
(d)
0.10 mL/s x 14 s = 1.4 mL, so to 2 sig fig this is 1.4 mL
0.10 mL/s x 14 s x 1.10 g/mL = 1.54 g, so to 2 sig fig this is rounded down to 1.5 g.

Next Try It Out Problem.

Developed by
Shodor
in cooperation with the Department of Chemistry,
The University of North Carolina at Chapel Hill