Question

4. How would you report the value from the measurement of 25 mL using a 25 mL buret that has an uncertainty of +/-0.05 mL? 25.00 ± 0.05 mL 5. What is the correct answer to the following mathematical operation: 42.620 g/10.0 mL 10:0 42.620 = 4. 29 mL notation? 6. What is the value of the exponent when expressing 0.000.000 000 000 000 000 204 in scientific 2.04 x 1019 7. If air is 20.9% oxygen by volume, what is the volume of air that contains 225 mL of oxygen? 225mL x 20.9 mLO

Answer 1

Answer 4

Uncertainty is 0.05 mL

So, answer to be reported = 25 $\pm$ 0.05 mL.

Answer 5

Mass has 5 significant figures

Volume has 3 significant figures

The operation is dividing mass by volume

So, answer is 42.620/10.0 = 4.2620 g/mL

Now, the answer must be reported in minimum number of significant figures (which is 3 in present case), so final answer is 4.26 g/mL

Answer 6

In scientific notation, there should be only one digit before decimal.

So, the given number is written as 2.04 x 10^-19.

Value of exponent is (-19).

Answer 7

20.9% by volume of oxygen means 20.9 mL of oxygen is contained in 100 mL of air.

225 ml oxygen will be present in = (100/20.9)*225

= 1076.55 mL of air.

Answer should be reported in 3 significant figures in scientific notation.

For that third digit i.e. 7 must be rounded up as the fourth digit ,6, is greater than 5.

So, volume of air that contains 225 mL of oxygen is

1.08 x 10³ mL.