Laboratory Worksheet Name: Selena Lopez How many sig figs are in the number 0.00

Question

Laboratory Worksheet Name: Selena Lopez How many sig figs are in the number 0.00620? d.5 1. a. 2 C.4 2. Convert 2855 mg to kg. a. 2.855 x 10 3kg b. 2.855 kg c. 0.02855 kg d. 3.503 x 104 kg 3. W hat is the edge length of a 155 g iron cube? The density of iron is 7.86 and the volume of a cube is equal to the edge length cubed. a. 0.0197 cm b. 19.7 cm c. 1218 cm d. 2.70 cm 4. How much heat must be absorbed by 125 g of ethanol to change its temperature from 21.5 to 34.8 ? Cethanol-2.421/g°C a. 6.95 k b. 4.02 x 103 kJ c. 86.6 kJ d. 4.02 k 5. A European doctor reports that you have a fever of 39.2 °C. What is your fever in degrees Fahrenheit? a. 102.6 OF b. 128.26 oF c. 71.2°F d. 4 °F 6. How many neutrons does the Fe-56 isotope contain? a. 26 b. 30 c. 56 d. 112

Explanation / Answer

Q1

Significant figures rules

Perform operations as usual... then

account for the significant figures of each number.

Recall:

- ZEROS to the left do NOT matter ; 0.02 and 0.2 will have 1 sig. fig (digit = 2)

- ZEROS between numbers, DO matter 0.0202 and 0.202  will have 3 sig fig (digits 2, 0 and 2)

- ZEROS to the right, DO matter, since those show precise data i.e. 2.0 vs. 2.00 exists (2 sig fig. vs 3 sig. fig)

Then... apply rule, round as required

* Addition / Subscraction --> round answer to the LEAST sig. fig of the operation ( i.e. 2 sig fig vs. 3 sig fig --> round to 2 sig. fig)

* Multiplication/Division --> round answer to the LEAST sig. fig of the operation ( i.e. 2 sig fig vs. 3 sig fig --> round to 2 sig. fig)

then

0.00620 has only 3 sig fig

Q2

2855 mg --> 2855*10^-6 kg = 0.002855 kg

Q3

D = mass/V

V = mass/D= 155/7.86 = 19.72 cm3

E = (19.72 )^(1/3) = 2.701

E = 2.70 cm

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