Mid-term: Units, Calculations, Atomic Structure, Periodic table

Question 1

Volume of a cube of side 0.563 nm in nm cube and mm cube.

Answer 1

0. 178 nm^3
1. 78 x 10^(-22) cm^3

Question 2

Density of a gemstone is 3.26 g/cm^3. Density: kg/m^3 ? Volume of a 2 g sample?

Answer 2

3260 kg/ m^3

0.6 cm^3

Question 3

Titanium ball has mass 16.19 g; diameter 19.0 mm.

Algorithm for changing units?

What is the density in g/cm^3? (Pi ~ 3.142) and what is the volume?

Answer 3

Write down the steps.

V = 3.59 g/cm^3

D= 4.51 g/cm^3

Question 4

Convert 20 km/s^2 to pm/h^2.

What is the algorithm?

Answer 4

3 x 10^23 pm/h^2

(20 km/(1 s^2)) * ( (10^15 pm)/(1 km)) * ((3600 s)/(1 h))^2

Question 5

Three melting points: 66.5, 65.3 and 65.2 degrees C. Reference value is 301.5 K.

What is the algorithm?

What is the % error?

Was their data precise, accurate, both or neither?

Answer 5

133%

1. Experimental = Calculate average
2. Theoretical = Convert from K to C.
3. percent_error = (experimental - theoretical)/theoretical * 100

Question 6

Abundance of Mg-24 in seawater is 78.70%; AMU: 23.985

Mg-25 has AMU: 24.986

Mg-26 has AMU:25.983

Calculate the relative abundance of Mg-25 and Mg-26.

What is the algorithm?

Answer 6

Mg-25: 10.59%

Mg-24: 10.71%

Look up the Average atomic mass of Mg in the periodic table: 24.31 AMU.

x+y = 1 - 0.787

23.985*0.7870 + 24.986x + 25.983y = 24.31

Solve.

Question 7

Joules needed to take 1 pound of lead from room temp (25 degrees Celsius) to melting point (327 Celsius) ? Number of joules to melt it?

1 lb = 0.4536 kg

Sp heat lead = 0.159 J/g/C

Heat of fusion of lead =0.0247 kJ/g

What is the algorithm?

Answer 7

3. 30 x 10^4 J
4. Draw the diagram.
5. Convert 1 pound to grams
6. Calculate Qa
7. Calculate Qb, converting units.
8. Answer is Qa + Qb

Question 8

A 120.0 g spoon at 4.4 deg C is plunged into a cup of hot chocolate (120.0 g). Temperature drops from 90.0 C to 75.0 C. What is the specific heat of the hot chocolate? Sp heat aluminum is 0.902 J/g deg C?

What is the algorithm?

Answer 8

Cp = 4.24 J/g deg C.

Q_lost = Q_gained

m1 * Cp1 * (t2 - t1) = m2 * Cp2 * (t2-t1)

Question 9

What is the algorithm for estimating age of a sample given C-14 measurement?

Estimate Age of sample and the year it was made: C-14 activity of 11.2 disintegrations per minute per gram.

Half life C-14 is 5730 years.

C-14 activity in living material: 14

Answer 9

ln (A_0/A_t) = n * ln 2

t = n* t_half

ln(14/11.2) = n*ln 2

n = 0.322

t = n*t_half = 1844.65 years

Question 10

I-131 half life is 8.05 days

If you ingest a sample of NaI containing I-131 how much time before it decays to 6.25% of original activity?

Answer 10

A_t/A_0 = (1/2)^n

t = t_half * n.